libpng-1.6.54-apng.patch

diff -Naru libpng-1.6.54.org/png.h libpng-1.6.54/png.h
--- libpng-1.6.54.org/png.h	2026-01-15 09:54:33.410881877 +0900
+++ libpng-1.6.54/png.h	2026-01-15 14:49:49.345302877 +0900
@@ -328,6 +328,10 @@
 #   include "pnglibconf.h"
 #endif
 
+#define PNG_APNG_SUPPORTED
+#define PNG_READ_APNG_SUPPORTED
+#define PNG_WRITE_APNG_SUPPORTED
+
 #ifndef PNG_VERSION_INFO_ONLY
 /* Machine specific configuration. */
 #  include "pngconf.h"
@@ -423,6 +427,17 @@
  * See pngconf.h for base types that vary by machine/system
  */
 
+#ifdef PNG_APNG_SUPPORTED
+/* dispose_op flags from inside fcTL */
+#define PNG_DISPOSE_OP_NONE        0x00U
+#define PNG_DISPOSE_OP_BACKGROUND  0x01U
+#define PNG_DISPOSE_OP_PREVIOUS    0x02U
+
+/* blend_op flags from inside fcTL */
+#define PNG_BLEND_OP_SOURCE        0x00U
+#define PNG_BLEND_OP_OVER          0x01U
+#endif /* PNG_APNG_SUPPORTED */
+
 /* This triggers a compiler error in png.c, if png.c and png.h
  * do not agree upon the version number.
  */
@@ -801,6 +816,10 @@
    (png_structp, png_infop));
 typedef PNG_CALLBACK(void, *png_progressive_end_ptr,
    (png_structp, png_infop));
+#ifdef PNG_APNG_SUPPORTED
+typedef PNG_CALLBACK(void, *png_progressive_frame_ptr,
+   (png_structp, png_uint_32));
+#endif
 
 /* The following callback receives png_uint_32 row_number, int pass for the
  * png_bytep data of the row.  When transforming an interlaced image the
@@ -3506,6 +3525,80 @@
  *  END OF HARDWARE AND SOFTWARE OPTIONS
  ******************************************************************************/
 
+#ifdef PNG_APNG_SUPPORTED
+PNG_EXPORT(260, png_uint_32, png_get_acTL,
+   (png_structp png_ptr, png_infop info_ptr,
+    png_uint_32 *num_frames, png_uint_32 *num_plays));
+
+PNG_EXPORT(261, png_uint_32, png_set_acTL,
+   (png_structp png_ptr, png_infop info_ptr,
+    png_uint_32 num_frames, png_uint_32 num_plays));
+
+PNG_EXPORT(262, png_uint_32, png_get_num_frames,
+   (png_structp png_ptr, png_infop info_ptr));
+
+PNG_EXPORT(263, png_uint_32, png_get_num_plays,
+   (png_structp png_ptr, png_infop info_ptr));
+
+PNG_EXPORT(264, png_uint_32, png_get_next_frame_fcTL,
+   (png_structp png_ptr, png_infop info_ptr,
+    png_uint_32 *width, png_uint_32 *height,
+    png_uint_32 *x_offset, png_uint_32 *y_offset,
+    png_uint_16 *delay_num, png_uint_16 *delay_den,
+    png_byte *dispose_op, png_byte *blend_op));
+
+PNG_EXPORT(265, png_uint_32, png_set_next_frame_fcTL,
+   (png_structp png_ptr, png_infop info_ptr,
+    png_uint_32 width, png_uint_32 height,
+    png_uint_32 x_offset, png_uint_32 y_offset,
+    png_uint_16 delay_num, png_uint_16 delay_den,
+    png_byte dispose_op, png_byte blend_op));
+
+PNG_EXPORT(266, png_uint_32, png_get_next_frame_width,
+   (png_structp png_ptr, png_infop info_ptr));
+PNG_EXPORT(267, png_uint_32, png_get_next_frame_height,
+   (png_structp png_ptr, png_infop info_ptr));
+PNG_EXPORT(268, png_uint_32, png_get_next_frame_x_offset,
+   (png_structp png_ptr, png_infop info_ptr));
+PNG_EXPORT(269, png_uint_32, png_get_next_frame_y_offset,
+   (png_structp png_ptr, png_infop info_ptr));
+PNG_EXPORT(270, png_uint_16, png_get_next_frame_delay_num,
+   (png_structp png_ptr, png_infop info_ptr));
+PNG_EXPORT(271, png_uint_16, png_get_next_frame_delay_den,
+   (png_structp png_ptr, png_infop info_ptr));
+PNG_EXPORT(272, png_byte, png_get_next_frame_dispose_op,
+   (png_structp png_ptr, png_infop info_ptr));
+PNG_EXPORT(273, png_byte, png_get_next_frame_blend_op,
+   (png_structp png_ptr, png_infop info_ptr));
+PNG_EXPORT(274, png_byte, png_get_first_frame_is_hidden,
+   (png_structp png_ptr, png_infop info_ptr));
+PNG_EXPORT(275, png_uint_32, png_set_first_frame_is_hidden,
+   (png_structp png_ptr, png_infop info_ptr, png_byte is_hidden));
+
+#ifdef PNG_READ_APNG_SUPPORTED
+PNG_EXPORT(276, void, png_read_frame_head,
+   (png_structp png_ptr, png_infop info_ptr));
+#ifdef PNG_PROGRESSIVE_READ_SUPPORTED
+PNG_EXPORT(277, void, png_set_progressive_frame_fn,
+   (png_structp png_ptr,
+    png_progressive_frame_ptr frame_info_fn,
+    png_progressive_frame_ptr frame_end_fn));
+#endif /* PNG_PROGRESSIVE_READ_SUPPORTED */
+#endif /* PNG_READ_APNG_SUPPORTED */
+
+#ifdef PNG_WRITE_APNG_SUPPORTED
+PNG_EXPORT(278, void, png_write_frame_head,
+   (png_structp png_ptr, png_infop info_ptr,
+    png_uint_32 width, png_uint_32 height,
+    png_uint_32 x_offset, png_uint_32 y_offset,
+    png_uint_16 delay_num, png_uint_16 delay_den,
+    png_byte dispose_op, png_byte blend_op));
+
+PNG_EXPORT(279, void, png_write_frame_tail,
+   (png_structp png_ptr, png_infop info_ptr));
+#endif /* PNG_WRITE_APNG_SUPPORTED */
+#endif /* PNG_APNG_SUPPORTED */
+
 /* Maintainer: Put new public prototypes here ^, in libpng.3, in project
  * defs, and in scripts/symbols.def.
  */
@@ -3514,7 +3608,11 @@
  * one to use is one more than this.)
  */
 #ifdef PNG_EXPORT_LAST_ORDINAL
+#ifdef PNG_APNG_SUPPORTED
+   PNG_EXPORT_LAST_ORDINAL(279);
+#else
    PNG_EXPORT_LAST_ORDINAL(259);
+#endif /* PNG_APNG_SUPPORTED */
 #endif
 
 #ifdef __cplusplus
diff -Naru libpng-1.6.54.org/pngget.c libpng-1.6.54/pngget.c
--- libpng-1.6.54.org/pngget.c	2026-01-15 09:54:33.410881877 +0900
+++ libpng-1.6.54/pngget.c	2026-01-16 15:37:23.199617980 +0900
@@ -1366,4 +1366,166 @@
 #  endif
 #endif
 
+#ifdef PNG_APNG_SUPPORTED
+png_uint_32 PNGAPI
+png_get_acTL(png_structp png_ptr, png_infop info_ptr,
+             png_uint_32 *num_frames, png_uint_32 *num_plays)
+{
+   png_debug1(1, "in %s retrieval function", "acTL");
+
+   if (png_ptr != NULL && info_ptr != NULL &&
+       (info_ptr->valid & PNG_INFO_acTL) &&
+       num_frames != NULL && num_plays != NULL)
+   {
+      *num_frames = info_ptr->num_frames;
+      *num_plays = info_ptr->num_plays;
+      return 1;
+   }
+
+   return 0;
+}
+
+png_uint_32 PNGAPI
+png_get_num_frames(png_structp png_ptr, png_infop info_ptr)
+{
+   png_debug(1, "in png_get_num_frames");
+
+   if (png_ptr != NULL && info_ptr != NULL)
+      return info_ptr->num_frames;
+   return 0;
+}
+
+png_uint_32 PNGAPI
+png_get_num_plays(png_structp png_ptr, png_infop info_ptr)
+{
+   png_debug(1, "in png_get_num_plays");
+
+   if (png_ptr != NULL && info_ptr != NULL)
+      return info_ptr->num_plays;
+   return 0;
+}
+
+png_uint_32 PNGAPI
+png_get_next_frame_fcTL(png_structp png_ptr, png_infop info_ptr,
+                        png_uint_32 *width, png_uint_32 *height,
+                        png_uint_32 *x_offset, png_uint_32 *y_offset,
+                        png_uint_16 *delay_num, png_uint_16 *delay_den,
+                        png_byte *dispose_op, png_byte *blend_op)
+{
+   png_debug1(1, "in %s retrieval function", "fcTL");
+
+   if (png_ptr != NULL && info_ptr != NULL &&
+       (info_ptr->valid & PNG_INFO_fcTL) &&
+       width != NULL && height != NULL &&
+       x_offset != NULL && y_offset != NULL &&
+       delay_num != NULL && delay_den != NULL &&
+       dispose_op != NULL && blend_op != NULL)
+   {
+      *width = info_ptr->next_frame_width;
+      *height = info_ptr->next_frame_height;
+      *x_offset = info_ptr->next_frame_x_offset;
+      *y_offset = info_ptr->next_frame_y_offset;
+      *delay_num = info_ptr->next_frame_delay_num;
+      *delay_den = info_ptr->next_frame_delay_den;
+      *dispose_op = info_ptr->next_frame_dispose_op;
+      *blend_op = info_ptr->next_frame_blend_op;
+      return 1;
+   }
+
+   return 0;
+}
+
+png_uint_32 PNGAPI
+png_get_next_frame_width(png_structp png_ptr, png_infop info_ptr)
+{
+   png_debug(1, "in png_get_next_frame_width");
+
+   if (png_ptr != NULL && info_ptr != NULL)
+      return info_ptr->next_frame_width;
+   return 0;
+}
+
+png_uint_32 PNGAPI
+png_get_next_frame_height(png_structp png_ptr, png_infop info_ptr)
+{
+   png_debug(1, "in png_get_next_frame_height");
+
+   if (png_ptr != NULL && info_ptr != NULL)
+      return info_ptr->next_frame_height;
+   return 0;
+}
+
+png_uint_32 PNGAPI
+png_get_next_frame_x_offset(png_structp png_ptr, png_infop info_ptr)
+{
+   png_debug(1, "in png_get_next_frame_x_offset");
+
+   if (png_ptr != NULL && info_ptr != NULL)
+      return info_ptr->next_frame_x_offset;
+   return 0;
+}
+
+png_uint_32 PNGAPI
+png_get_next_frame_y_offset(png_structp png_ptr, png_infop info_ptr)
+{
+   png_debug(1, "in png_get_next_frame_y_offset");
+
+   if (png_ptr != NULL && info_ptr != NULL)
+      return info_ptr->next_frame_y_offset;
+   return 0;
+}
+
+png_uint_16 PNGAPI
+png_get_next_frame_delay_num(png_structp png_ptr, png_infop info_ptr)
+{
+   png_debug(1, "in png_get_next_frame_delay_num");
+
+   if (png_ptr != NULL && info_ptr != NULL)
+      return info_ptr->next_frame_delay_num;
+   return 0;
+}
+
+png_uint_16 PNGAPI
+png_get_next_frame_delay_den(png_structp png_ptr, png_infop info_ptr)
+{
+   png_debug(1, "in png_get_next_frame_delay_den");
+
+   if (png_ptr != NULL && info_ptr != NULL)
+      return info_ptr->next_frame_delay_den;
+   return 0;
+}
+
+png_byte PNGAPI
+png_get_next_frame_dispose_op(png_structp png_ptr, png_infop info_ptr)
+{
+   png_debug(1, "in png_get_next_frame_dispose_op");
+
+   if (png_ptr != NULL && info_ptr != NULL)
+      return info_ptr->next_frame_dispose_op;
+   return 0;
+}
+
+png_byte PNGAPI
+png_get_next_frame_blend_op(png_structp png_ptr, png_infop info_ptr)
+{
+   png_debug(1, "in png_get_next_frame_blend_op");
+
+   if (png_ptr != NULL && info_ptr != NULL)
+      return info_ptr->next_frame_blend_op;
+   return 0;
+}
+
+png_byte PNGAPI
+png_get_first_frame_is_hidden(png_structp png_ptr, png_infop info_ptr)
+{
+   png_debug(1, "in png_first_frame_is_hidden");
+
+   if (png_ptr != NULL)
+      return (png_byte)(png_ptr->apng_flags & PNG_FIRST_FRAME_HIDDEN);
+
+   PNG_UNUSED(info_ptr)
+
+   return 0;
+}
+#endif /* PNG_APNG_SUPPORTED */
 #endif /* READ || WRITE */
diff -Naru libpng-1.6.54.org/pnginfo.h libpng-1.6.54/pnginfo.h
--- libpng-1.6.54.org/pnginfo.h	2025-05-11 18:44:02.085040902 +0900
+++ libpng-1.6.54/pnginfo.h	2026-01-15 13:50:32.228564907 +0900
@@ -259,5 +259,18 @@
 #ifdef PNG_sRGB_SUPPORTED
    int rendering_intent;
 #endif
+
+#ifdef PNG_APNG_SUPPORTED
+   png_uint_32 num_frames; /* including default image */
+   png_uint_32 num_plays;
+   png_uint_32 next_frame_width;
+   png_uint_32 next_frame_height;
+   png_uint_32 next_frame_x_offset;
+   png_uint_32 next_frame_y_offset;
+   png_uint_16 next_frame_delay_num;
+   png_uint_16 next_frame_delay_den;
+   png_byte next_frame_dispose_op;
+   png_byte next_frame_blend_op;
+#endif
 };
 #endif /* PNGINFO_H */
diff -Naru libpng-1.6.54.org/pngpread.c libpng-1.6.54/pngpread.c
--- libpng-1.6.54.org/pngpread.c	2025-07-06 11:06:43.933735454 +0900
+++ libpng-1.6.54/pngpread.c	2026-01-16 16:44:17.565675229 +0900
@@ -200,6 +200,105 @@
 
    chunk_name = png_ptr->chunk_name;
 
+#ifdef PNG_READ_APNG_SUPPORTED
+   if (png_ptr->num_frames_read > 0 &&
+       png_ptr->num_frames_read < info_ptr->num_frames)
+   {
+      if (chunk_name == png_IDAT)
+      {
+         /* Discard trailing IDATs for the first frame. */
+         if (png_ptr->mode & PNG_HAVE_fcTL || png_ptr->num_frames_read > 1)
+            png_error(png_ptr, "Misplaced IDAT in APNG stream");
+
+         if (png_ptr->push_length + 4 > png_ptr->buffer_size)
+         {
+            png_push_save_buffer(png_ptr);
+            return;
+         }
+
+         png_ptr->mode &= ~PNG_HAVE_CHUNK_HEADER;
+         return;
+      }
+      else if (chunk_name == png_fdAT)
+      {
+         if (png_ptr->buffer_size < 4)
+         {
+            png_push_save_buffer(png_ptr);
+            return;
+         }
+
+         png_ensure_sequence_number(png_ptr, 4);
+
+         if (!(png_ptr->mode & PNG_HAVE_fcTL))
+         {
+            /* Discard trailing fdATs for frames other than the first. */
+            if (png_ptr->num_frames_read < 2)
+               png_error(png_ptr, "Misplaced fdAT in APNG stream");
+
+            if (png_ptr->push_length + 4 > png_ptr->buffer_size)
+            {
+               png_push_save_buffer(png_ptr);
+               return;
+            }
+
+            png_ptr->mode &= ~PNG_HAVE_CHUNK_HEADER;
+            return;
+         }
+
+         else
+         {
+            /* Frame data follows. */
+            png_ptr->idat_size = png_ptr->push_length - 4;
+            png_ptr->mode |= PNG_HAVE_IDAT;
+            png_ptr->process_mode = PNG_READ_IDAT_MODE;
+
+            return;
+         }
+      }
+
+      else if (chunk_name == png_fcTL)
+      {
+         if (png_ptr->push_length + 4 > png_ptr->buffer_size)
+         {
+            png_push_save_buffer(png_ptr);
+            return;
+         }
+
+         png_read_reset(png_ptr);
+         png_ptr->mode &= ~PNG_HAVE_fcTL;
+
+         png_handle_fcTL(png_ptr, info_ptr, png_ptr->push_length);
+
+         if (!(png_ptr->mode & PNG_HAVE_fcTL))
+            png_error(png_ptr, "Missing required fcTL chunk in APNG stream");
+
+         png_read_reinit(png_ptr, info_ptr);
+         png_progressive_read_reset(png_ptr);
+
+         if (png_ptr->frame_info_fn != NULL)
+            (*(png_ptr->frame_info_fn))(png_ptr, png_ptr->num_frames_read);
+
+         png_ptr->mode &= ~PNG_HAVE_CHUNK_HEADER;
+
+         return;
+      }
+
+      else
+      {
+         if (png_ptr->push_length + 4 > png_ptr->buffer_size)
+         {
+            png_push_save_buffer(png_ptr);
+            return;
+         }
+         png_warning(png_ptr, "Ignoring unexpected chunk in APNG sequence");
+         png_ptr->mode &= ~PNG_HAVE_CHUNK_HEADER;
+         return;
+      }
+
+      return;
+   }
+#endif /* PNG_READ_APNG_SUPPORTED */
+
    if (chunk_name == png_IDAT)
    {
       if ((png_ptr->mode & PNG_AFTER_IDAT) != 0)
@@ -268,6 +367,9 @@
 
    else if (chunk_name == png_IDAT)
    {
+#ifdef PNG_READ_APNG_SUPPORTED
+      png_have_info(png_ptr, info_ptr);
+#endif
       png_ptr->idat_size = png_ptr->push_length;
       png_ptr->process_mode = PNG_READ_IDAT_MODE;
       png_push_have_info(png_ptr, info_ptr);
@@ -278,6 +380,31 @@
       return;
    }
 
+#ifdef PNG_READ_APNG_SUPPORTED
+   else if (chunk_name == png_acTL)
+   {
+      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
+      {
+         png_push_save_buffer(png_ptr);
+         return;
+      }
+
+      png_handle_acTL(png_ptr, info_ptr, png_ptr->push_length);
+   }
+
+   else if (chunk_name == png_fcTL)
+   {
+      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
+      {
+         png_push_save_buffer(png_ptr);
+         return;
+      }
+
+      png_handle_fcTL(png_ptr, info_ptr, png_ptr->push_length);
+   }
+
+#endif /* PNG_READ_APNG_SUPPORTED */
+
    else
    {
       PNG_PUSH_SAVE_BUFFER_IF_FULL
@@ -409,7 +536,11 @@
       png_byte chunk_tag[4];
 
       /* TODO: this code can be commoned up with the same code in push_read */
+#ifdef PNG_READ_APNG_SUPPORTED
+      PNG_PUSH_SAVE_BUFFER_IF_LT(12)
+#else
       PNG_PUSH_SAVE_BUFFER_IF_LT(8)
+#endif
       png_push_fill_buffer(png_ptr, chunk_length, 4);
       png_ptr->push_length = png_get_uint_31(png_ptr, chunk_length);
       png_reset_crc(png_ptr);
@@ -417,17 +548,63 @@
       png_ptr->chunk_name = PNG_CHUNK_FROM_STRING(chunk_tag);
       png_ptr->mode |= PNG_HAVE_CHUNK_HEADER;
 
+#ifdef PNG_READ_APNG_SUPPORTED
+      if (png_ptr->chunk_name != png_fdAT && png_ptr->num_frames_read > 0)
+      {
+         if (png_ptr->flags & PNG_FLAG_ZSTREAM_ENDED)
+         {
+            png_ptr->process_mode = PNG_READ_CHUNK_MODE;
+            if (png_ptr->frame_end_fn != NULL)
+               (*(png_ptr->frame_end_fn))(png_ptr, png_ptr->num_frames_read);
+            png_ptr->num_frames_read++;
+            return;
+         }
+         else
+         {
+            if (png_ptr->chunk_name == png_IEND)
+               png_error(png_ptr, "Not enough image data");
+            if (png_ptr->push_length + 4 > png_ptr->buffer_size)
+            {
+               png_push_save_buffer(png_ptr);
+               return;
+            }
+            png_warning(png_ptr, "Ignoring unexpected chunk in APNG sequence");
+            png_crc_finish(png_ptr, png_ptr->push_length);
+            png_ptr->mode &= ~PNG_HAVE_CHUNK_HEADER;
+            return;
+         }
+      }
+      else
+#endif
+#ifdef PNG_READ_APNG_SUPPORTED
+      if (png_ptr->chunk_name != png_IDAT && png_ptr->num_frames_read == 0)
+#else
       if (png_ptr->chunk_name != png_IDAT)
+#endif
       {
          png_ptr->process_mode = PNG_READ_CHUNK_MODE;
 
          if ((png_ptr->flags & PNG_FLAG_ZSTREAM_ENDED) == 0)
             png_error(png_ptr, "Not enough compressed data");
 
+#ifdef PNG_READ_APNG_SUPPORTED
+         if (png_ptr->frame_end_fn != NULL)
+            (*(png_ptr->frame_end_fn))(png_ptr, png_ptr->num_frames_read);
+         png_ptr->num_frames_read++;
+#endif
+
          return;
       }
 
       png_ptr->idat_size = png_ptr->push_length;
+
+#ifdef PNG_READ_APNG_SUPPORTED
+      if (png_ptr->num_frames_read > 0)
+      {
+         png_ensure_sequence_number(png_ptr, 4);
+         png_ptr->idat_size -= 4;
+      }
+#endif
    }
 
    if (png_ptr->idat_size != 0 && png_ptr->save_buffer_size != 0)
@@ -501,6 +678,15 @@
    if (!(buffer_length > 0) || buffer == NULL)
       png_error(png_ptr, "No IDAT data (internal error)");
 
+#ifdef PNG_READ_APNG_SUPPORTED
+   /* If the app is not APNG-aware, decode only the first frame. */
+   if (!(png_ptr->apng_flags & PNG_APNG_APP) && png_ptr->num_frames_read > 0)
+   {
+      png_ptr->flags |= PNG_FLAG_ZSTREAM_ENDED;
+      return;
+   }
+#endif
+
    /* This routine must process all the data it has been given
     * before returning, calling the row callback as required to
     * handle the uncompressed results.
@@ -934,6 +1120,18 @@
    png_set_read_fn(png_ptr, progressive_ptr, png_push_fill_buffer);
 }
 
+#ifdef PNG_READ_APNG_SUPPORTED
+void PNGAPI
+png_set_progressive_frame_fn(png_structp png_ptr,
+                             png_progressive_frame_ptr frame_info_fn,
+                             png_progressive_frame_ptr frame_end_fn)
+{
+   png_ptr->frame_info_fn = frame_info_fn;
+   png_ptr->frame_end_fn = frame_end_fn;
+   png_ptr->apng_flags |= PNG_APNG_APP;
+}
+#endif
+
 png_voidp PNGAPI
 png_get_progressive_ptr(png_const_structrp png_ptr)
 {
diff -Naru libpng-1.6.54.org/pngpriv.h libpng-1.6.54/pngpriv.h
--- libpng-1.6.54.org/pngpriv.h	2026-01-15 09:54:33.411881875 +0900
+++ libpng-1.6.54/pngpriv.h	2026-01-16 15:15:06.727223750 +0900
@@ -653,6 +653,10 @@
 #define PNG_HAVE_CHUNK_AFTER_IDAT 0x2000U /* Have another chunk after IDAT */
 #define PNG_WROTE_eXIf            0x4000U
 #define PNG_IS_READ_STRUCT        0x8000U /* Else is a write struct */
+#ifdef PNG_APNG_SUPPORTED
+#define PNG_HAVE_acTL            0x10000U
+#define PNG_HAVE_fcTL            0x20000U
+#endif
 
 /* Flags for the transformations the PNG library does on the image data */
 #define PNG_BGR                 0x0001U
@@ -917,6 +921,13 @@
 #define png_tRNS PNG_U32(116,  82,  78,  83)
 #define png_zTXt PNG_U32(122,  84,  88, 116)
 
+#ifdef PNG_APNG_SUPPORTED
+
+/* For png_struct.apng_flags: */
+#define PNG_FIRST_FRAME_HIDDEN       0x0001U
+#define PNG_APNG_APP                 0x0002U
+#endif
+
 /* The following will work on (signed char*) strings, whereas the get_uint_32
  * macro will fail on top-bit-set values because of the sign extension.
  */
@@ -1880,6 +1891,68 @@
    PNG_EMPTY);
 #endif /* PROGRESSIVE_READ */
 
+#ifdef PNG_APNG_SUPPORTED
+PNG_INTERNAL_FUNCTION(void, png_ensure_fcTL_is_valid,
+   (png_structp png_ptr,
+    png_uint_32 width, png_uint_32 height,
+    png_uint_32 x_offset, png_uint_32 y_offset,
+    png_uint_16 delay_num, png_uint_16 delay_den,
+    png_byte dispose_op, png_byte blend_op),
+   PNG_EMPTY);
+
+#ifdef PNG_READ_APNG_SUPPORTED
+PNG_INTERNAL_FUNCTION(void, png_handle_acTL,
+   (png_structp png_ptr, png_infop info_ptr, png_uint_32 length),
+   PNG_EMPTY);
+PNG_INTERNAL_FUNCTION(void, png_handle_fcTL,
+   (png_structp png_ptr, png_infop info_ptr, png_uint_32 length),
+   PNG_EMPTY);
+PNG_INTERNAL_FUNCTION(void, png_handle_fdAT,
+   (png_structp png_ptr, png_infop info_ptr, png_uint_32 length),
+   PNG_EMPTY);
+PNG_INTERNAL_FUNCTION(void, png_have_info,
+   (png_structp png_ptr, png_infop info_ptr),
+   PNG_EMPTY);
+PNG_INTERNAL_FUNCTION(void, png_ensure_sequence_number,
+   (png_structp png_ptr, png_uint_32 length),
+   PNG_EMPTY);
+PNG_INTERNAL_FUNCTION(void, png_read_reset,
+   (png_structp png_ptr),
+   PNG_EMPTY);
+PNG_INTERNAL_FUNCTION(void, png_read_reinit,
+   (png_structp png_ptr, png_infop info_ptr),
+   PNG_EMPTY);
+#ifdef PNG_PROGRESSIVE_READ_SUPPORTED
+PNG_INTERNAL_FUNCTION(void, png_progressive_read_reset,
+   (png_structp png_ptr),
+   PNG_EMPTY);
+#endif /* PNG_PROGRESSIVE_READ_SUPPORTED */
+#endif /* PNG_READ_APNG_SUPPORTED */
+
+#ifdef PNG_WRITE_APNG_SUPPORTED
+PNG_INTERNAL_FUNCTION(void, png_write_acTL,
+   (png_structp png_ptr, png_uint_32 num_frames, png_uint_32 num_plays),
+   PNG_EMPTY);
+PNG_INTERNAL_FUNCTION(void, png_write_fcTL,
+   (png_structp png_ptr,
+    png_uint_32 width, png_uint_32 height,
+    png_uint_32 x_offset, png_uint_32 y_offset,
+    png_uint_16 delay_num, png_uint_16 delay_den,
+    png_byte dispose_op, png_byte blend_op),
+   PNG_EMPTY);
+PNG_INTERNAL_FUNCTION(void, png_write_fdAT,
+   (png_structp png_ptr, png_const_bytep data, png_size_t length),
+   PNG_EMPTY);
+PNG_INTERNAL_FUNCTION(void, png_write_reset,
+   (png_structp png_ptr),
+   PNG_EMPTY);
+PNG_INTERNAL_FUNCTION(void, png_write_reinit,
+   (png_structp png_ptr, png_infop info_ptr,
+    png_uint_32 width, png_uint_32 height),
+   PNG_EMPTY);
+#endif /* PNG_WRITE_APNG_SUPPORTED */
+#endif /* PNG_APNG_SUPPORTED */
+
 #ifdef PNG_iCCP_SUPPORTED
 /* Routines for checking parts of an ICC profile. */
 #ifdef PNG_READ_iCCP_SUPPORTED
diff -Naru libpng-1.6.54.org/pngread.c libpng-1.6.54/pngread.c
--- libpng-1.6.54.org/pngread.c	2026-01-15 09:54:33.412881873 +0900
+++ libpng-1.6.54/pngread.c	2026-01-16 19:10:26.174024695 +0900
@@ -157,16 +157,95 @@
 
       else if (chunk_name == png_IDAT)
       {
+#ifdef PNG_READ_APNG_SUPPORTED
+         png_have_info(png_ptr, info_ptr);
+#endif
          png_ptr->idat_size = length;
          break;
       }
 
+#ifdef PNG_READ_APNG_SUPPORTED
+      else if (chunk_name == png_acTL)
+         png_handle_acTL(png_ptr, info_ptr, length);
+
+      else if (chunk_name == png_fcTL)
+         png_handle_fcTL(png_ptr, info_ptr, length);
+
+      else if (chunk_name == png_fdAT)
+         png_handle_fdAT(png_ptr, info_ptr, length);
+#endif
+
       else
          png_handle_chunk(png_ptr, info_ptr, length);
    }
 }
 #endif /* SEQUENTIAL_READ */
 
+#ifdef PNG_READ_APNG_SUPPORTED
+void PNGAPI
+png_read_frame_head(png_structp png_ptr, png_infop info_ptr)
+{
+   png_byte have_chunk_after_DAT; /* after IDAT or after fdAT */
+
+   png_debug(1, "Reading frame head");
+
+   if (!(png_ptr->mode & PNG_HAVE_acTL))
+      png_error(png_ptr, "Cannot read APNG frame: missing acTL");
+
+   /* Do nothing for the main IDAT. */
+   if (png_ptr->num_frames_read == 0)
+      return;
+
+   png_read_reset(png_ptr);
+   png_ptr->flags &= ~PNG_FLAG_ROW_INIT;
+   png_ptr->mode &= ~PNG_HAVE_fcTL;
+
+   have_chunk_after_DAT = 0;
+   for (;;)
+   {
+      png_uint_32 length = png_read_chunk_header(png_ptr);
+
+      if (png_ptr->chunk_name == png_IDAT)
+      {
+         /* Discard trailing IDATs for the first frame. */
+         if (have_chunk_after_DAT || png_ptr->num_frames_read > 1)
+            png_error(png_ptr, "Misplaced IDAT in APNG stream");
+         png_crc_finish(png_ptr, length);
+      }
+      else if (png_ptr->chunk_name == png_fcTL)
+      {
+         png_handle_fcTL(png_ptr, info_ptr, length);
+         have_chunk_after_DAT = 1;
+      }
+      else if (png_ptr->chunk_name == png_fdAT)
+      {
+         png_ensure_sequence_number(png_ptr, length);
+
+         /* Discard trailing fdATs for all frames except the first. */
+         if (!have_chunk_after_DAT && png_ptr->num_frames_read > 1)
+         {
+            png_crc_finish(png_ptr, length - 4);
+         }
+         else if (png_ptr->mode & PNG_HAVE_fcTL)
+         {
+            png_ptr->idat_size = length - 4;
+            png_ptr->mode |= PNG_HAVE_IDAT;
+            break;
+         }
+         else
+         {
+            png_error(png_ptr, "Misplaced fdAT in APNG stream");
+         }
+      }
+      else
+      {
+         png_warning(png_ptr, "Ignoring unexpected chunk in APNG sequence");
+         png_crc_finish(png_ptr, length);
+      }
+   }
+}
+#endif /* PNG_READ_APNG_SUPPORTED */
+
 /* Optional call to update the users info_ptr structure */
 void PNGAPI
 png_read_update_info(png_structrp png_ptr, png_inforp info_ptr)
diff -Naru libpng-1.6.54.org/pngrutil.c libpng-1.6.54/pngrutil.c
--- libpng-1.6.54.org/pngrutil.c	2026-01-15 09:54:33.413881871 +0900
+++ libpng-1.6.54/pngrutil.c	2026-01-17 10:41:44.972759729 +0900
@@ -922,6 +922,11 @@
    filter_type = buf[11];
    interlace_type = buf[12];
 
+#ifdef PNG_READ_APNG_SUPPORTED
+   png_ptr->first_frame_width = width;
+   png_ptr->first_frame_height = height;
+#endif
+
    /* Set internal variables */
    png_ptr->width = width;
    png_ptr->height = height;
@@ -2718,6 +2723,184 @@
 #  define png_handle_iTXt NULL
 #endif
 
+#ifdef PNG_READ_APNG_SUPPORTED
+void /* PRIVATE */
+png_handle_acTL(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
+{
+   png_byte data[8];
+   png_uint_32 num_frames;
+   png_uint_32 num_plays;
+
+   png_debug(1, "in png_handle_acTL");
+
+   if (!(png_ptr->mode & PNG_HAVE_IHDR))
+   {
+      png_error(png_ptr, "Missing IHDR before acTL");
+   }
+   else if (png_ptr->mode & PNG_HAVE_IDAT)
+   {
+      png_warning(png_ptr, "Ignoring misplaced acTL after IDAT");
+      png_crc_finish(png_ptr, length);
+      return;
+   }
+   else if (png_ptr->mode & PNG_HAVE_acTL)
+   {
+      png_warning(png_ptr, "Ignoring duplicate acTL");
+      png_crc_finish(png_ptr, length);
+      return;
+   }
+   else if (length != 8)
+   {
+      png_warning(png_ptr, "Ignoring acTL with incorrect length");
+      png_crc_finish(png_ptr, length);
+      return;
+   }
+
+   png_crc_read(png_ptr, data, 8);
+   png_crc_finish(png_ptr, 0);
+
+   num_frames = png_get_uint_31(png_ptr, data);
+   num_plays = png_get_uint_31(png_ptr, data + 4);
+
+   /* The set function will do error checking on num_frames. */
+   if (png_set_acTL(png_ptr, info_ptr, num_frames, num_plays))
+      png_ptr->mode |= PNG_HAVE_acTL;
+}
+
+void /* PRIVATE */
+png_handle_fcTL(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
+{
+   png_byte data[22];
+   png_uint_32 width;
+   png_uint_32 height;
+   png_uint_32 x_offset;
+   png_uint_32 y_offset;
+   png_uint_16 delay_num;
+   png_uint_16 delay_den;
+   png_byte dispose_op;
+   png_byte blend_op;
+
+   png_debug(1, "in png_handle_fcTL");
+
+   png_ensure_sequence_number(png_ptr, length);
+
+   if (!(png_ptr->mode & PNG_HAVE_IHDR))
+   {
+      png_error(png_ptr, "Missing IHDR before fcTL");
+   }
+   else if (png_ptr->mode & PNG_HAVE_IDAT)
+   {
+      /* For any frames other then the first this message may be misleading,
+       * but correct. PNG_HAVE_IDAT is unset before the frame head is read.
+       * I can't think of a better message.
+       */
+      png_warning(png_ptr, "Ignoring invalid fcTL after IDAT");
+      png_crc_finish(png_ptr, length-4);
+      return;
+   }
+   else if (png_ptr->mode & PNG_HAVE_fcTL)
+   {
+      png_warning(png_ptr, "Ignoring duplicate fcTL within one frame");
+      png_crc_finish(png_ptr, length-4);
+      return;
+   }
+   else if (length != 26)
+   {
+      png_warning(png_ptr, "Ignoring fcTL with incorrect length");
+      png_crc_finish(png_ptr, length-4);
+      return;
+   }
+
+   png_crc_read(png_ptr, data, 22);
+   png_crc_finish(png_ptr, 0);
+
+   width = png_get_uint_31(png_ptr, data);
+   height = png_get_uint_31(png_ptr, data + 4);
+   x_offset = png_get_uint_31(png_ptr, data + 8);
+   y_offset = png_get_uint_31(png_ptr, data + 12);
+   delay_num = png_get_uint_16(data + 16);
+   delay_den = png_get_uint_16(data + 18);
+   dispose_op = data[20];
+   blend_op = data[21];
+
+   if (png_ptr->num_frames_read == 0 && (x_offset != 0 || y_offset != 0))
+   {
+      png_warning(png_ptr, "Ignoring leading fcTL with non-zero frame offset");
+      return;
+   }
+
+   if (info_ptr != NULL)
+   {
+      if (png_ptr->num_frames_read == 0 &&
+          (width != info_ptr->width || height != info_ptr->height))
+      {
+         png_warning(png_ptr,
+                     "Ignoring leading fcTL with incorrect frame size");
+         return;
+      }
+
+      /* The set function will do more error checking. */
+      png_set_next_frame_fcTL(png_ptr, info_ptr, width, height,
+                              x_offset, y_offset, delay_num, delay_den,
+                              dispose_op, blend_op);
+
+      png_read_reinit(png_ptr, info_ptr);
+
+      png_ptr->mode |= PNG_HAVE_fcTL;
+   }
+}
+
+void /* PRIVATE */
+png_have_info(png_structp png_ptr, png_infop info_ptr)
+{
+   if ((info_ptr->valid & PNG_INFO_acTL) && !(info_ptr->valid & PNG_INFO_fcTL))
+   {
+      png_ptr->apng_flags |= PNG_FIRST_FRAME_HIDDEN;
+      info_ptr->num_frames++;
+   }
+}
+
+void /* PRIVATE */
+png_handle_fdAT(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
+{
+   png_ensure_sequence_number(png_ptr, length);
+
+   /* This function is called only from png_read_end(), png_read_info(),
+    * and png_push_read_chunk(). This means one of the following:
+    * - The user doesn't want to read this frame.
+    * - This is an out-of-place fdAT.
+    * In either case, it is safe to ignore the chunk with a warning.
+    */
+   png_warning(png_ptr, "Ignoring fdAT chunk");
+   png_crc_finish(png_ptr, length - 4);
+   PNG_UNUSED(info_ptr)
+}
+
+void /* PRIVATE */
+png_ensure_sequence_number(png_structp png_ptr, png_uint_32 length)
+{
+   png_byte data[4];
+   png_uint_32 sequence_number;
+
+   if (length < 4)
+   {
+      /* TODO: Write a more precise message. */
+      png_error(png_ptr, "Invalid fcTL or fdAT chunk");
+   }
+
+   png_crc_read(png_ptr, data, 4);
+   sequence_number = png_get_uint_31(png_ptr, data);
+
+   if (sequence_number != png_ptr->next_seq_num)
+   {
+      /* TODO: Write a more precise message. */
+      png_error(png_ptr, "Out-of-order sequence number in fcTL or fdAT");
+   }
+
+   png_ptr->next_seq_num++;
+}
+#endif /* PNG_READ_APNG_SUPPORTED */
+
 #ifdef PNG_READ_UNKNOWN_CHUNKS_SUPPORTED
 /* Utility function for png_handle_unknown; set up png_ptr::unknown_chunk */
 static int
@@ -4200,7 +4383,38 @@
       {
          uInt avail_in;
          png_bytep buffer;
+#ifdef PNG_READ_APNG_SUPPORTED
+         png_uint_32 bytes_to_skip = 0;
+
+         while (png_ptr->idat_size == 0 || bytes_to_skip != 0)
+         {
+            png_crc_finish(png_ptr, bytes_to_skip);
+            bytes_to_skip = 0;
+
+            png_ptr->idat_size = png_read_chunk_header(png_ptr);
+            if (png_ptr->num_frames_read == 0)
+            {
+               if (png_ptr->chunk_name != png_IDAT)
+                  png_error(png_ptr, "Not enough image data");
+            }
+            else
+            {
+               if (png_ptr->chunk_name == png_IEND)
+                  png_error(png_ptr, "Not enough image data");
+               if (png_ptr->chunk_name != png_fdAT)
+               {
+                  png_warning(png_ptr,
+                              "Ignoring unexpected chunk in APNG sequence");
+                  bytes_to_skip = png_ptr->idat_size;
+                  continue;
+               }
+
+               png_ensure_sequence_number(png_ptr, png_ptr->idat_size);
 
+               png_ptr->idat_size -= 4;
+            }
+         }
+#else
          while (png_ptr->idat_size == 0)
          {
             png_crc_finish(png_ptr, 0);
@@ -4212,7 +4426,7 @@
             if (png_ptr->chunk_name != png_IDAT)
                png_error(png_ptr, "Not enough image data");
          }
-
+#endif /* PNG_READ_APNG_SUPPORTED */
          avail_in = png_ptr->IDAT_read_size;
 
          if (avail_in > png_chunk_max(png_ptr))
@@ -4283,6 +4497,9 @@
 
          png_ptr->mode |= PNG_AFTER_IDAT;
          png_ptr->flags |= PNG_FLAG_ZSTREAM_ENDED;
+#ifdef PNG_READ_APNG_SUPPORTED
+         png_ptr->num_frames_read++;
+#endif
 
          if (png_ptr->zstream.avail_in > 0 || png_ptr->idat_size > 0)
             png_chunk_benign_error(png_ptr, "Extra compressed data");
@@ -4692,4 +4909,82 @@
 
    png_ptr->flags |= PNG_FLAG_ROW_INIT;
 }
+
+#ifdef PNG_READ_APNG_SUPPORTED
+/* This function should be called after the main IDAT sequence has been read
+ * and before a new fdAT is about to be read. It resets some parts of png_ptr
+ * to make them usable by the read functions again.
+ */
+void /* PRIVATE */
+png_read_reset(png_structp png_ptr)
+{
+   png_ptr->mode &= ~PNG_HAVE_IDAT;
+   png_ptr->mode &= ~PNG_AFTER_IDAT;
+   png_ptr->row_number = 0;
+   png_ptr->pass = 0;
+}
+
+void /* PRIVATE */
+png_read_reinit(png_structp png_ptr, png_infop info_ptr)
+{
+   png_ptr->width = info_ptr->next_frame_width;
+   png_ptr->height = info_ptr->next_frame_height;
+   png_ptr->rowbytes = PNG_ROWBYTES(png_ptr->pixel_depth,png_ptr->width);
+   png_ptr->info_rowbytes = PNG_ROWBYTES(info_ptr->pixel_depth,
+        png_ptr->width);
+   if (png_ptr->prev_row)
+      memset(png_ptr->prev_row, 0, png_ptr->rowbytes + 1);
+}
+
+#ifdef PNG_PROGRESSIVE_READ_SUPPORTED
+/* Same as png_read_reset(), but for the progressive reader. */
+void /* PRIVATE */
+png_progressive_read_reset(png_structp png_ptr)
+{
+#ifdef PNG_READ_INTERLACING_SUPPORTED
+   /* Arrays to facilitate easy interlacing - use pass (0 - 6) as index */
+
+   /* Start of interlace block */
+   const int png_pass_start[] = {0, 4, 0, 2, 0, 1, 0};
+
+   /* Offset to next interlace block */
+   const int png_pass_inc[] = {8, 8, 4, 4, 2, 2, 1};
+
+   /* Start of interlace block in the y direction */
+   const int png_pass_ystart[] = {0, 0, 4, 0, 2, 0, 1};
+
+   /* Offset to next interlace block in the y direction */
+   const int png_pass_yinc[] = {8, 8, 8, 4, 4, 2, 2};
+
+   if (png_ptr->interlaced)
+   {
+      if (!(png_ptr->transformations & PNG_INTERLACE))
+         png_ptr->num_rows = (png_ptr->height + png_pass_yinc[0] - 1 -
+                              png_pass_ystart[0]) /
+                             png_pass_yinc[0];
+      else
+         png_ptr->num_rows = png_ptr->height;
+
+      png_ptr->iwidth = (png_ptr->width +
+                         png_pass_inc[png_ptr->pass] - 1 -
+                         png_pass_start[png_ptr->pass]) /
+                        png_pass_inc[png_ptr->pass];
+   }
+   else
+#endif /* PNG_READ_INTERLACING_SUPPORTED */
+   {
+      png_ptr->num_rows = png_ptr->height;
+      png_ptr->iwidth = png_ptr->width;
+   }
+   png_ptr->flags &= ~PNG_FLAG_ZSTREAM_ENDED;
+   if (inflateReset(&(png_ptr->zstream)) != Z_OK)
+      png_error(png_ptr, "inflateReset failed");
+   png_ptr->zstream.avail_in = 0;
+   png_ptr->zstream.next_in = 0;
+   png_ptr->zstream.next_out = png_ptr->row_buf;
+   png_ptr->zstream.avail_out =
+      (uInt)PNG_ROWBYTES(png_ptr->pixel_depth, png_ptr->iwidth) + 1;
+}
+#endif /* PNG_PROGRESSIVE_READ_SUPPORTED */
+#endif /* PNG_READ_APNG_SUPPORTED */
 #endif /* READ */
diff -Naru libpng-1.6.54.org/pngset.c libpng-1.6.54/pngset.c
--- libpng-1.6.54.org/pngset.c	2025-05-11 18:44:02.087040907 +0900
+++ libpng-1.6.54/pngset.c	2026-01-16 19:22:09.948006831 +0900
@@ -460,6 +460,13 @@
    info_ptr->pixel_depth = (png_byte)(info_ptr->channels * info_ptr->bit_depth);
 
    info_ptr->rowbytes = PNG_ROWBYTES(info_ptr->pixel_depth, width);
+
+#ifdef PNG_APNG_SUPPORTED
+   /* Assume a non-animated PNG in the beginning. This may be overridden after
+    * seeing an acTL chunk later.
+    */
+   info_ptr->num_frames = 1;
+#endif
 }
 
 #ifdef PNG_oFFs_SUPPORTED
@@ -1315,6 +1322,145 @@
 }
 #endif /* sPLT */
 
+#ifdef PNG_APNG_SUPPORTED
+png_uint_32 PNGAPI
+png_set_acTL(png_structp png_ptr, png_infop info_ptr,
+             png_uint_32 num_frames, png_uint_32 num_plays)
+{
+   png_debug1(1, "in %s storage function", "acTL");
+
+   if (png_ptr == NULL || info_ptr == NULL)
+   {
+      png_warning(png_ptr,
+                  "Ignoring call to png_set_acTL with NULL libpng object args");
+      return 0;
+   }
+   if (num_frames == 0)
+   {
+      png_warning(png_ptr,
+                  "Ignoring attempt to set acTL with num_frames zero");
+      return 0;
+   }
+   if (num_frames > PNG_UINT_31_MAX)
+   {
+      png_warning(png_ptr,
+                  "Ignoring attempt to set acTL with num_frames > 2^31-1");
+      return 0;
+   }
+   if (num_plays > PNG_UINT_31_MAX)
+   {
+      png_warning(png_ptr,
+                  "Ignoring attempt to set acTL with num_plays > 2^31-1");
+      return 0;
+   }
+
+   info_ptr->num_frames = num_frames;
+   info_ptr->num_plays = num_plays;
+
+   info_ptr->valid |= PNG_INFO_acTL;
+
+   return 1;
+}
+
+/* delay_num and delay_den can hold any 16-bit values including zero */
+png_uint_32 PNGAPI
+png_set_next_frame_fcTL(png_structp png_ptr, png_infop info_ptr,
+                        png_uint_32 width, png_uint_32 height,
+                        png_uint_32 x_offset, png_uint_32 y_offset,
+                        png_uint_16 delay_num, png_uint_16 delay_den,
+                        png_byte dispose_op, png_byte blend_op)
+{
+   png_debug1(1, "in %s storage function", "fcTL");
+
+   if (png_ptr == NULL || info_ptr == NULL)
+   {
+      png_warning(png_ptr,
+                  "Ignoring call to png_set_fcTL with NULL libpng object args");
+      return 0;
+   }
+
+   png_ensure_fcTL_is_valid(png_ptr, width, height, x_offset, y_offset,
+                            delay_num, delay_den, dispose_op, blend_op);
+
+   /* No checking is required for delay_num and delay_den.
+    * They can hold any 16-bit value, including zero.
+    */
+
+   if (blend_op == PNG_BLEND_OP_OVER)
+   {
+      if (!(png_ptr->color_type & PNG_COLOR_MASK_ALPHA) &&
+          !(png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS)))
+      {
+         png_warning(png_ptr,
+                     "Ignoring wasteful fcTL BLEND_OP_OVER in opaque images");
+         blend_op = PNG_BLEND_OP_SOURCE;
+      }
+   }
+
+   info_ptr->next_frame_width = width;
+   info_ptr->next_frame_height = height;
+   info_ptr->next_frame_x_offset = x_offset;
+   info_ptr->next_frame_y_offset = y_offset;
+   info_ptr->next_frame_delay_num = delay_num;
+   info_ptr->next_frame_delay_den = delay_den;
+   info_ptr->next_frame_dispose_op = dispose_op;
+   info_ptr->next_frame_blend_op = blend_op;
+
+   info_ptr->valid |= PNG_INFO_fcTL;
+
+   return 1;
+}
+
+void /* PRIVATE */
+png_ensure_fcTL_is_valid(png_structp png_ptr,
+                         png_uint_32 width, png_uint_32 height,
+                         png_uint_32 x_offset, png_uint_32 y_offset,
+                         png_uint_16 delay_num, png_uint_16 delay_den,
+                         png_byte dispose_op, png_byte blend_op)
+{
+   if (width == 0 || width > PNG_UINT_31_MAX)
+      png_error(png_ptr, "Invalid frame width in fcTL");
+   if (height == 0 || height > PNG_UINT_31_MAX)
+      png_error(png_ptr, "Invalid frame height in fcTL");
+   if (x_offset > PNG_UINT_31_MAX || y_offset > PNG_UINT_31_MAX)
+      png_error(png_ptr, "Invalid frame offset in fcTL");
+   if (width + x_offset > png_ptr->first_frame_width ||
+       height + y_offset > png_ptr->first_frame_height)
+      png_error(png_ptr, "Oversized frame in fcTL");
+
+   if (dispose_op != PNG_DISPOSE_OP_NONE &&
+       dispose_op != PNG_DISPOSE_OP_BACKGROUND &&
+       dispose_op != PNG_DISPOSE_OP_PREVIOUS)
+      png_error(png_ptr, "Invalid dispose_op in fcTL");
+
+   if (blend_op != PNG_BLEND_OP_SOURCE &&
+       blend_op != PNG_BLEND_OP_OVER)
+      png_error(png_ptr, "Invalid blend_op in fcTL");
+
+   PNG_UNUSED(delay_num)
+   PNG_UNUSED(delay_den)
+}
+
+png_uint_32 PNGAPI
+png_set_first_frame_is_hidden(png_structp png_ptr, png_infop info_ptr,
+                              png_byte is_hidden)
+{
+   png_debug(1, "in png_first_frame_is_hidden");
+
+   if (png_ptr == NULL)
+      return 0;
+
+   if (is_hidden)
+      png_ptr->apng_flags |= PNG_FIRST_FRAME_HIDDEN;
+   else
+      png_ptr->apng_flags &= ~PNG_FIRST_FRAME_HIDDEN;
+
+   PNG_UNUSED(info_ptr)
+
+   return 1;
+}
+#endif /* PNG_APNG_SUPPORTED */
+
 #ifdef PNG_STORE_UNKNOWN_CHUNKS_SUPPORTED
 static png_byte
 check_location(png_const_structrp png_ptr, int location)
diff -Naru libpng-1.6.54.org/pngstruct.h libpng-1.6.54/pngstruct.h
--- libpng-1.6.54.org/pngstruct.h	2025-12-06 20:00:54.866030732 +0900
+++ libpng-1.6.54/pngstruct.h	2026-01-15 13:50:32.229564906 +0900
@@ -391,6 +391,27 @@
    png_byte filter_type;
 #endif
 
+#ifdef PNG_APNG_SUPPORTED
+   png_uint_32 apng_flags;
+   png_uint_32 next_seq_num;         /* next fcTL/fdAT chunk sequence number */
+   png_uint_32 first_frame_width;
+   png_uint_32 first_frame_height;
+
+#ifdef PNG_READ_APNG_SUPPORTED
+   png_uint_32 num_frames_read;      /* incremented after all image data of */
+                                     /* a frame is read */
+#ifdef PNG_PROGRESSIVE_READ_SUPPORTED
+   png_progressive_frame_ptr frame_info_fn; /* frame info read callback */
+   png_progressive_frame_ptr frame_end_fn;  /* frame data read callback */
+#endif
+#endif
+
+#ifdef PNG_WRITE_APNG_SUPPORTED
+   png_uint_32 num_frames_to_write;
+   png_uint_32 num_frames_written;
+#endif
+#endif /* PNG_APNG_SUPPORTED */
+
 /* New members added in libpng-1.2.0 */
 
 /* New members added in libpng-1.0.2 but first enabled by default in 1.2.0 */
diff -Naru libpng-1.6.54.org/pngtest.c libpng-1.6.54/pngtest.c
--- libpng-1.6.54.org/pngtest.c	2026-01-15 09:54:33.413881871 +0900
+++ libpng-1.6.54/pngtest.c	2026-01-16 15:31:15.016058178 +0900
@@ -877,6 +877,10 @@
    int bit_depth, color_type;
    user_chunk_info my_user_chunk_data;
    int pass, num_passes;
+#ifdef PNG_APNG_SUPPORTED
+   png_uint_32 num_frames;
+   png_uint_32 num_plays;
+#endif
 
    row_buf = NULL;
    error_parameters.file_name = inname;
@@ -1437,6 +1441,22 @@
       }
    }
 #endif
+
+#ifdef PNG_APNG_SUPPORTED
+   if (png_get_valid(read_ptr, read_info_ptr, PNG_INFO_acTL))
+   {
+      if (png_get_acTL(read_ptr, read_info_ptr, &num_frames, &num_plays))
+      {
+         png_byte is_hidden;
+         pngtest_debug2("Handling acTL chunks (frames %ld, plays %ld)",
+                        num_frames, num_plays);
+         png_set_acTL(write_ptr, write_info_ptr, num_frames, num_plays);
+         is_hidden = png_get_first_frame_is_hidden(read_ptr, read_info_ptr);
+         png_set_first_frame_is_hidden(write_ptr, write_info_ptr, is_hidden);
+      }
+   }
+#endif
+
 #ifdef PNG_WRITE_UNKNOWN_CHUNKS_SUPPORTED
    {
       png_unknown_chunkp unknowns;
@@ -1496,6 +1516,111 @@
    t_misc += (t_stop - t_start);
    t_start = t_stop;
 #endif
+#ifdef PNG_APNG_SUPPORTED
+   if (png_get_valid(read_ptr, read_info_ptr, PNG_INFO_acTL))
+   {
+      png_uint_32 frame;
+      for (frame = 0; frame < num_frames; frame++)
+      {
+         png_uint_32 frame_width;
+         png_uint_32 frame_height;
+         png_uint_32 x_offset;
+         png_uint_32 y_offset;
+         png_uint_16 delay_num;
+         png_uint_16 delay_den;
+         png_byte dispose_op;
+         png_byte blend_op;
+         png_read_frame_head(read_ptr, read_info_ptr);
+         if (png_get_valid(read_ptr, read_info_ptr, PNG_INFO_fcTL))
+         {
+            png_get_next_frame_fcTL(read_ptr, read_info_ptr,
+                                    &frame_width, &frame_height,
+                                    &x_offset, &y_offset,
+                                    &delay_num, &delay_den,
+                                    &dispose_op, &blend_op);
+         }
+         else
+         {
+            frame_width = width;
+            frame_height = height;
+            x_offset = 0;
+            y_offset = 0;
+            delay_num = 1;
+            delay_den = 1;
+            dispose_op = PNG_DISPOSE_OP_NONE;
+            blend_op = PNG_BLEND_OP_SOURCE;
+         }
+#ifdef PNG_WRITE_APNG_SUPPORTED
+         png_write_frame_head(write_ptr, write_info_ptr,
+                              frame_width, frame_height,
+                              x_offset, y_offset,
+                              delay_num, delay_den,
+                              dispose_op, blend_op);
+#endif
+         for (pass = 0; pass < num_passes; pass++)
+         {
+#           ifdef calc_pass_height
+               png_uint_32 pass_height;
+
+               if (num_passes == 7) /* interlaced */
+               {
+                  if (PNG_PASS_COLS(frame_width, pass) > 0)
+                     pass_height = PNG_PASS_ROWS(frame_height, pass);
+
+                  else
+                     pass_height = 0;
+               }
+
+               else /* not interlaced */
+                  pass_height = frame_height;
+#           else
+#              define pass_height frame_height
+#           endif
+
+            pngtest_debug1("Writing row data for pass %d", pass);
+            for (y = 0; y < pass_height; y++)
+            {
+#ifndef SINGLE_ROWBUF_ALLOC
+               pngtest_debug2("Allocating row buffer (pass %d, y = %u)...",
+                              pass, y);
+
+               row_buf = (png_bytep)png_malloc(read_ptr,
+                  png_get_rowbytes(read_ptr, read_info_ptr));
+
+               pngtest_debug2("\t0x%08lx (%lu bytes)", (unsigned long)row_buf,
+                  (unsigned long)png_get_rowbytes(read_ptr, read_info_ptr));
+
+#endif /* !SINGLE_ROWBUF_ALLOC */
+               png_read_rows(read_ptr, (png_bytepp)&row_buf, NULL, 1);
+
+#ifdef PNG_WRITE_SUPPORTED
+#ifdef PNGTEST_TIMING
+               t_stop = (float)clock();
+               t_decode += (t_stop - t_start);
+               t_start = t_stop;
+#endif
+               png_write_rows(write_ptr, (png_bytepp)&row_buf, 1);
+#ifdef PNGTEST_TIMING
+               t_stop = (float)clock();
+               t_encode += (t_stop - t_start);
+               t_start = t_stop;
+#endif
+#endif /* PNG_WRITE_SUPPORTED */
+
+#ifndef SINGLE_ROWBUF_ALLOC
+               pngtest_debug2("Freeing row buffer (pass %d, y = %u)", pass, y);
+               png_free(read_ptr, row_buf);
+               row_buf = NULL;
+#endif /* !SINGLE_ROWBUF_ALLOC */
+            }
+         }
+#ifdef PNG_WRITE_APNG_SUPPORTED
+         png_write_frame_tail(write_ptr, write_info_ptr);
+#endif
+      }
+   }
+   else
+#endif
    for (pass = 0; pass < num_passes; pass++)
    {
 #     ifdef calc_pass_height
diff -Naru libpng-1.6.54.org/pngwrite.c libpng-1.6.54/pngwrite.c
--- libpng-1.6.54.org/pngwrite.c	2026-01-15 09:54:33.413881871 +0900
+++ libpng-1.6.54/pngwrite.c	2026-01-16 16:49:59.704764231 +0900
@@ -127,6 +127,11 @@
        * the application continues writing the PNG.  So check the 'invalid'
        * flag here too.
        */
+#ifdef PNG_WRITE_APNG_SUPPORTED
+         if ((info_ptr->valid & PNG_INFO_acTL) != 0)
+            png_write_acTL(png_ptr, info_ptr->num_frames, info_ptr->num_plays);
+#endif
+
 #ifdef PNG_WRITE_UNKNOWN_CHUNKS_SUPPORTED
          /* Write unknown chunks first; PNG v3 establishes a precedence order
           * for colourspace chunks.  It is certain therefore that new
@@ -405,6 +410,11 @@
       png_benign_error(png_ptr, "Wrote palette index exceeding num_palette");
 #endif
 
+#ifdef PNG_WRITE_APNG_SUPPORTED
+   if (png_ptr->num_frames_written != png_ptr->num_frames_to_write)
+      png_error(png_ptr, "Not enough frames written");
+#endif
+
    /* See if user wants us to write information chunks */
    if (info_ptr != NULL)
    {
@@ -1517,6 +1527,42 @@
 }
 #endif
 
+#ifdef PNG_WRITE_APNG_SUPPORTED
+void PNGAPI
+png_write_frame_head(png_structp png_ptr, png_infop info_ptr,
+                     png_uint_32 width, png_uint_32 height,
+                     png_uint_32 x_offset, png_uint_32 y_offset,
+                     png_uint_16 delay_num, png_uint_16 delay_den,
+                     png_byte dispose_op, png_byte blend_op)
+{
+   png_debug(1, "in png_write_frame_head");
+
+   /* There is a chance this has been set after png_write_info was called,
+    * so it would be set but not written. Is there a way to be sure?
+    */
+   if (!(info_ptr->valid & PNG_INFO_acTL))
+      png_error(png_ptr, "Cannot write APNG frame: missing acTL");
+
+   png_write_reset(png_ptr);
+
+   png_write_reinit(png_ptr, info_ptr, width, height);
+
+   if (!(png_ptr->num_frames_written == 0 &&
+         (png_ptr->apng_flags & PNG_FIRST_FRAME_HIDDEN)))
+      png_write_fcTL(png_ptr, width, height, x_offset, y_offset,
+                     delay_num, delay_den, dispose_op, blend_op);
+}
+
+void PNGAPI
+png_write_frame_tail(png_structp png_ptr, png_infop info_ptr)
+{
+   png_debug(1, "in png_write_frame_tail");
+
+   png_ptr->num_frames_written++;
+
+   PNG_UNUSED(info_ptr)
+}
+#endif /* PNG_WRITE_APNG_SUPPORTED */
 
 #ifdef PNG_SIMPLIFIED_WRITE_SUPPORTED
 /* Initialize the write structure - general purpose utility. */
diff -Naru libpng-1.6.54.org/pngwutil.c libpng-1.6.54/pngwutil.c
--- libpng-1.6.54.org/pngwutil.c	2026-01-15 09:54:33.414881869 +0900
+++ libpng-1.6.54/pngwutil.c	2026-01-16 21:11:48.539248758 +0900
@@ -838,6 +838,11 @@
    /* Write the chunk */
    png_write_complete_chunk(png_ptr, png_IHDR, buf, 13);
 
+#ifdef PNG_WRITE_APNG_SUPPORTED
+   png_ptr->first_frame_width = width;
+   png_ptr->first_frame_height = height;
+#endif
+
    if ((png_ptr->do_filter) == PNG_NO_FILTERS)
    {
       if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE ||
@@ -1020,7 +1025,17 @@
 #endif
 
          if (size > 0)
+         {
+#ifdef PNG_WRITE_APNG_SUPPORTED
+            if (png_ptr->num_frames_written == 0)
+               png_write_complete_chunk(png_ptr, png_IDAT, data, size);
+            else
+               png_write_fdAT(png_ptr, data, size);
+#else
             png_write_complete_chunk(png_ptr, png_IDAT, data, size);
+#endif /* PNG_WRITE_APNG_SUPPORTED */
+         }
+
          png_ptr->mode |= PNG_HAVE_IDAT;
 
          png_ptr->zstream.next_out = data;
@@ -1067,7 +1082,17 @@
 #endif
 
          if (size > 0)
+         {
+#ifdef PNG_WRITE_APNG_SUPPORTED
+            if (png_ptr->num_frames_written == 0)
+               png_write_complete_chunk(png_ptr, png_IDAT, data, size);
+            else
+               png_write_fdAT(png_ptr, data, size);
+#else
             png_write_complete_chunk(png_ptr, png_IDAT, data, size);
+#endif /* PNG_WRITE_APNG_SUPPORTED */
+         }
+
          png_ptr->zstream.avail_out = 0;
          png_ptr->zstream.next_out = NULL;
          png_ptr->mode |= PNG_HAVE_IDAT | PNG_AFTER_IDAT;
@@ -1969,6 +1994,82 @@
 }
 #endif
 
+#ifdef PNG_WRITE_APNG_SUPPORTED
+void /* PRIVATE */
+png_write_acTL(png_structp png_ptr,
+               png_uint_32 num_frames, png_uint_32 num_plays)
+{
+   png_byte buf[8];
+
+   png_debug(1, "in png_write_acTL");
+
+   png_ptr->num_frames_to_write = num_frames;
+
+   if (png_ptr->apng_flags & PNG_FIRST_FRAME_HIDDEN)
+      num_frames--;
+
+   png_save_uint_32(buf, num_frames);
+   png_save_uint_32(buf + 4, num_plays);
+
+   png_write_complete_chunk(png_ptr, png_acTL, buf, (png_size_t)8);
+}
+
+void /* PRIVATE */
+png_write_fcTL(png_structp png_ptr,
+               png_uint_32 width, png_uint_32 height,
+               png_uint_32 x_offset, png_uint_32 y_offset,
+               png_uint_16 delay_num, png_uint_16 delay_den,
+               png_byte dispose_op, png_byte blend_op)
+{
+   png_byte buf[26];
+
+   png_debug(1, "in png_write_fcTL");
+
+   if (png_ptr->num_frames_written == 0 && (x_offset != 0 || y_offset != 0))
+      png_error(png_ptr, "Non-zero frame offset in leading fcTL");
+   if (png_ptr->num_frames_written == 0 &&
+       (width != png_ptr->first_frame_width ||
+        height != png_ptr->first_frame_height))
+      png_error(png_ptr, "Incorrect frame size in leading fcTL");
+
+   /* More error checking. */
+   png_ensure_fcTL_is_valid(png_ptr, width, height, x_offset, y_offset,
+                            delay_num, delay_den, dispose_op, blend_op);
+
+   png_save_uint_32(buf, png_ptr->next_seq_num);
+   png_save_uint_32(buf + 4, width);
+   png_save_uint_32(buf + 8, height);
+   png_save_uint_32(buf + 12, x_offset);
+   png_save_uint_32(buf + 16, y_offset);
+   png_save_uint_16(buf + 20, delay_num);
+   png_save_uint_16(buf + 22, delay_den);
+   buf[24] = dispose_op;
+   buf[25] = blend_op;
+
+   png_write_complete_chunk(png_ptr, png_fcTL, buf, (png_size_t)26);
+
+   png_ptr->next_seq_num++;
+}
+
+void /* PRIVATE */
+png_write_fdAT(png_structp png_ptr,
+               png_const_bytep data, png_size_t length)
+{
+   png_byte buf[4];
+
+   png_write_chunk_header(png_ptr, png_fdAT, (png_uint_32)(4 + length));
+
+   png_save_uint_32(buf, png_ptr->next_seq_num);
+   png_write_chunk_data(png_ptr, buf, 4);
+
+   png_write_chunk_data(png_ptr, data, length);
+
+   png_write_chunk_end(png_ptr);
+
+   png_ptr->next_seq_num++;
+}
+#endif /* PNG_WRITE_APNG_SUPPORTED */
+
 /* Initializes the row writing capability of libpng */
 void /* PRIVATE */
 png_write_start_row(png_structrp png_ptr)
@@ -2822,4 +2923,37 @@
    }
 #endif /* WRITE_FLUSH */
 }
+
+#ifdef PNG_WRITE_APNG_SUPPORTED
+void /* PRIVATE */
+png_write_reset(png_structp png_ptr)
+{
+   png_ptr->row_number = 0;
+   png_ptr->pass = 0;
+   png_ptr->mode &= ~PNG_HAVE_IDAT;
+}
+
+void /* PRIVATE */
+png_write_reinit(png_structp png_ptr, png_infop info_ptr,
+                 png_uint_32 width, png_uint_32 height)
+{
+   if (png_ptr->num_frames_written == 0 &&
+       (width != png_ptr->first_frame_width ||
+        height != png_ptr->first_frame_height))
+      png_error(png_ptr, "Incorrect frame size in leading fcTL");
+   if (width > png_ptr->first_frame_width ||
+       height > png_ptr->first_frame_height)
+      png_error(png_ptr, "Oversized frame in fcTL");
+
+   png_set_IHDR(png_ptr, info_ptr, width, height,
+                info_ptr->bit_depth, info_ptr->color_type,
+                info_ptr->interlace_type, info_ptr->compression_type,
+                info_ptr->filter_type);
+
+   png_ptr->width = width;
+   png_ptr->height = height;
+   png_ptr->rowbytes = PNG_ROWBYTES(png_ptr->pixel_depth, width);
+   png_ptr->usr_width = png_ptr->width;
+}
+#endif /* PNG_WRITE_APNG_SUPPORTED */
 #endif /* WRITE */
diff -Naru libpng-1.6.54.org/scripts/symbols.def libpng-1.6.54/scripts/symbols.def
--- libpng-1.6.54.org/scripts/symbols.def	2025-01-26 08:07:01.594606745 +0900
+++ libpng-1.6.54/scripts/symbols.def	2026-01-15 13:50:32.230564905 +0900
@@ -263,3 +263,23 @@
  png_get_mDCV_fixed @257
  png_set_mDCV @258
  png_set_mDCV_fixed @259
+ png_get_acTL @260
+ png_set_acTL @261
+ png_get_num_frames @262
+ png_get_num_plays @263
+ png_get_next_frame_fcTL @264
+ png_set_next_frame_fcTL @265
+ png_get_next_frame_width @266
+ png_get_next_frame_height @267
+ png_get_next_frame_x_offset @268
+ png_get_next_frame_y_offset @269
+ png_get_next_frame_delay_num @270
+ png_get_next_frame_delay_den @271
+ png_get_next_frame_dispose_op @272
+ png_get_next_frame_blend_op @273
+ png_get_first_frame_is_hidden @274
+ png_set_first_frame_is_hidden @275
+ png_read_frame_head @276
+ png_set_progressive_frame_fn @277
+ png_write_frame_head @278
+ png_write_frame_tail @279