Clipper.cpp

// Copyright (c) 2013- PPSSPP Project.

// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, version 2.0 or later versions.

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License 2.0 for more details.

// A copy of the GPL 2.0 should have been included with the program.
// If not, see http://www.gnu.org/licenses/

// Official git repository and contact information can be found at
// https://github.com/hrydgard/ppsspp and http://www.ppsspp.org/.

#include <algorithm>

#include "GPU/GPUState.h"

#include "GPU/Software/BinManager.h"
#include "GPU/Software/Clipper.h"
#include "GPU/Software/Rasterizer.h"
#include "GPU/Software/RasterizerRectangle.h"
#include "GPU/Software/TransformUnit.h"

#include "Common/Profiler/Profiler.h"

namespace Clipper {

enum {
	SKIP_FLAG = -1,
	CLIP_NEG_Z_BIT = 0x20,
};

static inline int CalcClipMask(const ClipCoords &v) {
	// This checks `x / w` compared to 1 or -1, skipping the division.
	if (v.z < -v.w)
		return -1;
	return 0;
}

inline bool different_signs(float x, float y) {
	return ((x <= 0 && y > 0) || (x > 0 && y <= 0));
}

inline float clip_dotprod(const ClipVertexData &vert, float A, float B, float C, float D) {
	return (vert.clippos.x * A + vert.clippos.y * B + vert.clippos.z * C + vert.clippos.w * D);
}

inline void clip_interpolate(ClipVertexData &dest, float t, const ClipVertexData &a, const ClipVertexData &b) {
	bool outsideRange = false;
	dest.Lerp(t, a, b);
	dest.v.screenpos = TransformUnit::ClipToScreen(dest.clippos, &outsideRange);
	dest.v.clipw = dest.clippos.w;

	// If the clipped coordinate is outside range, then we throw it away.
	// This prevents a lot of inversions that shouldn't be drawn.
	if (outsideRange)
		dest.v.screenpos.x = 0x7FFFFFFF;
}

#define CLIP_POLY( PLANE_BIT, A, B, C, D )							\
{																	\
	if (mask & PLANE_BIT) {											\
		int idxPrev = inlist[0];									\
		float dpPrev = clip_dotprod(*Vertices[idxPrev], A, B, C, D );\
		int outcount = 0;											\
																	\
		inlist[n] = inlist[0];										\
		for (int j = 1; j <= n; j++) { 								\
			int idx = inlist[j];									\
			float dp = clip_dotprod(*Vertices[idx], A, B, C, D );	\
			if (dpPrev >= 0) {										\
				outlist[outcount++] = idxPrev;						\
			}														\
																	\
			/* Skipping w sign mismatches avoids inversions, but is incorrect.  See #16131. */ \
			/* For now, it's better to avoid inversions as they usually are undesired. */ \
			if (different_signs(dp, dpPrev)) { \
				auto &vert = Vertices[numVertices++];				\
				if (dp < 0) {										\
					float t = dp / (dp - dpPrev);					\
					clip_interpolate(*vert, t, *Vertices[idx], *Vertices[idxPrev]);		\
				} else {											\
					float t = dpPrev / (dpPrev - dp);				\
					clip_interpolate(*vert, t, *Vertices[idxPrev], *Vertices[idx]);		\
				}													\
				outlist[outcount++] = numVertices - 1;				\
			}														\
																	\
			idxPrev = idx;											\
			dpPrev = dp;											\
		}															\
																	\
		if (outcount < 3)											\
			continue;												\
																	\
		{															\
			int *tmp = inlist;										\
			inlist = outlist;										\
			outlist = tmp;											\
			n = outcount;											\
		}															\
	}																\
}

#define CLIP_LINE(PLANE_BIT, A, B, C, D)						\
{																\
	if (mask & PLANE_BIT) {										\
		float dp0 = clip_dotprod(*Vertices[0], A, B, C, D );	\
		float dp1 = clip_dotprod(*Vertices[1], A, B, C, D );	\
																\
		if (mask0 & PLANE_BIT) {								\
			if (dp0 < 0) {										\
				float t = dp1 / (dp1 - dp0);					\
				clip_interpolate(*Vertices[0], t, *Vertices[1], *Vertices[0]); \
			}													\
		}														\
		dp0 = clip_dotprod(*Vertices[0], A, B, C, D );			\
																\
		if (mask1 & PLANE_BIT) {								\
			if (dp1 < 0) {										\
				float t = dp1 / (dp1- dp0);						\
				clip_interpolate(*Vertices[1], t, *Vertices[1], *Vertices[0]); \
			}													\
		}														\
	}															\
}

static inline bool CheckOutsideZ(ClipCoords p, int &pos, int &neg) {
	constexpr float outsideValue = 1.000030517578125f;
	float z = p.z / p.w;
	if (z >= outsideValue) {
		pos++;
		return true;
	}
	if (-z >= outsideValue) {
		neg++;
		return true;
	}
	return false;
}

static void RotateUV(const VertexData &tl, const VertexData &br, VertexData &tr, VertexData &bl) {
	const int x1 = tl.screenpos.x;
	const int x2 = br.screenpos.x;
	const int y1 = tl.screenpos.y;
	const int y2 = br.screenpos.y;

	if ((x1 < x2 && y1 > y2) || (x1 > x2 && y1 < y2)) {
		std::swap(bl.texturecoords, tr.texturecoords);
	}
}

// This is used for rectangle texture projection, which is very uncommon.
// To avoid complicating the common rectangle path, this just uses triangles.
static void AddTriangleRect(const VertexData &v0, const VertexData &v1, BinManager &binner) {
	VertexData buf[4];
	buf[0] = v1;
	buf[0].screenpos = ScreenCoords(v0.screenpos.x, v0.screenpos.y, v1.screenpos.z);
	buf[0].texturecoords = v0.texturecoords;

	buf[1] = v1;
	buf[1].screenpos = ScreenCoords(v0.screenpos.x, v1.screenpos.y, v1.screenpos.z);
	buf[1].texturecoords = Vec3Packed<float>(v0.texturecoords.x, v1.texturecoords.y, v0.texturecoords.z);

	buf[2] = v1;
	buf[2].screenpos = ScreenCoords(v1.screenpos.x, v0.screenpos.y, v1.screenpos.z);
	buf[2].texturecoords = Vec3Packed<float>(v1.texturecoords.x, v0.texturecoords.y, v1.texturecoords.z);

	buf[3] = v1;

	VertexData *topleft = &buf[0];
	VertexData *topright = &buf[1];
	VertexData *bottomleft = &buf[2];
	VertexData *bottomright = &buf[3];

	// DrawTriangle always culls, so sort out the drawing order.
	for (int i = 0; i < 4; ++i) {
		if (buf[i].screenpos.x < topleft->screenpos.x && buf[i].screenpos.y < topleft->screenpos.y)
			topleft = &buf[i];
		if (buf[i].screenpos.x > topright->screenpos.x && buf[i].screenpos.y < topright->screenpos.y)
			topright = &buf[i];
		if (buf[i].screenpos.x < bottomleft->screenpos.x && buf[i].screenpos.y > bottomleft->screenpos.y)
			bottomleft = &buf[i];
		if (buf[i].screenpos.x > bottomright->screenpos.x && buf[i].screenpos.y > bottomright->screenpos.y)
			bottomright = &buf[i];
	}

	RotateUV(v0, v1, *topright, *bottomleft);

	binner.AddTriangle(*topleft, *topright, *bottomleft);
	binner.AddTriangle(*bottomleft, *topright, *topleft);
	binner.AddTriangle(*topright, *bottomright, *bottomleft);
	binner.AddTriangle(*bottomleft, *bottomright, *topright);
}

void ProcessRect(const ClipVertexData &v0, const ClipVertexData &v1, BinManager &binner) {
	if (!binner.State().throughMode) {
		// If any verts were outside range, throw the entire prim away.
		if (v0.OutsideRange() || v1.OutsideRange())
			return;

		// We may discard the entire rect based on depth values.
		int outsidePos = 0, outsideNeg = 0;
		CheckOutsideZ(v0.clippos, outsidePos, outsideNeg);
		CheckOutsideZ(v1.clippos, outsidePos, outsideNeg);

		// With depth clamp off, we discard the rectangle if even one vert is outside.
		if (outsidePos + outsideNeg > 0 && !gstate.isDepthClampEnabled())
			return;
		// With it on, both must be outside in the same direction.
		else if (outsidePos >= 2 || outsideNeg >= 2)
			return;

		bool splitFog = v0.v.fogdepth != v1.v.fogdepth;
		if (splitFog) {
			// If they match the same 1/255, we can consider the fog flat.  Seen in Resistance.
			// More efficient if we can avoid splitting.
			static constexpr float foghalfstep = 0.5f / 255.0f;
			if (v1.v.fogdepth - foghalfstep <= v0.v.fogdepth && v1.v.fogdepth + foghalfstep >= v0.v.fogdepth)
				splitFog = false;
		}
		if (splitFog) {
			// Rectangles seem to always use nearest along X for fog depth, but reversed.
			// TODO: Check exactness of middle.
			VertexData vhalf0 = v1.v;
			vhalf0.screenpos.x = v0.v.screenpos.x + (v1.v.screenpos.x - v0.v.screenpos.x) / 2;
			vhalf0.texturecoords.x = v0.v.texturecoords.x + (v1.v.texturecoords.x - v0.v.texturecoords.x) / 2;

			VertexData vhalf1 = v1.v;
			vhalf1.screenpos.x = v0.v.screenpos.x + (v1.v.screenpos.x - v0.v.screenpos.x) / 2;
			vhalf1.screenpos.y = v0.v.screenpos.y;
			vhalf1.texturecoords.x = v0.v.texturecoords.x + (v1.v.texturecoords.x - v0.v.texturecoords.x) / 2;
			vhalf1.texturecoords.y = v0.v.texturecoords.y;

			VertexData vrev1 = v1.v;
			vrev1.fogdepth = v0.v.fogdepth;

			if (binner.State().textureProj) {
				AddTriangleRect(v0.v, vhalf0, binner);
				AddTriangleRect(vhalf1, vrev1, binner);
			} else {
				binner.AddRect(v0.v, vhalf0);
				binner.AddRect(vhalf1, vrev1);
			}
		} else if (binner.State().textureProj) {
			AddTriangleRect(v0.v, v1.v, binner);
		} else {
			binner.AddRect(v0.v, v1.v);
		}
	} else {
		// through mode handling
		if (Rasterizer::RectangleFastPath(v0.v, v1.v, binner)) {
			return;
		} else if (gstate.isModeClear() && !gstate.isDitherEnabled()) {
			binner.AddClearRect(v0.v, v1.v);
		} else {
			binner.AddRect(v0.v, v1.v);
		}
	}
}

void ProcessPoint(const ClipVertexData &v0, BinManager &binner) {
	// If any verts were outside range, throw the entire prim away.
	if (!binner.State().throughMode) {
		if (v0.OutsideRange())
			return;
	}

	// Points need no clipping. Will be bounds checked in the rasterizer (which seems backwards?)
	binner.AddPoint(v0.v);
}

void ProcessLine(const ClipVertexData &v0, const ClipVertexData &v1, BinManager &binner) {
	if (binner.State().throughMode) {
		// Actually, should clip this one too so we don't need to do bounds checks in the rasterizer.
		binner.AddLine(v0.v, v1.v);
		return;
	}

	// If any verts were outside range, throw the entire prim away.
	if (v0.OutsideRange() || v1.OutsideRange())
		return;

	int outsidePos = 0, outsideNeg = 0;
	CheckOutsideZ(v0.clippos, outsidePos, outsideNeg);
	CheckOutsideZ(v1.clippos, outsidePos, outsideNeg);

	// With depth clamp off, we discard the line if even one vert is outside.
	if (outsidePos + outsideNeg > 0 && !gstate.isDepthClampEnabled())
		return;
	// With it on, both must be outside in the same direction.
	else if (outsidePos >= 2 || outsideNeg >= 2)
		return;

	int mask0 = CalcClipMask(v0.clippos);
	int mask1 = CalcClipMask(v1.clippos);
	int mask = mask0 | mask1;
	if ((mask & CLIP_NEG_Z_BIT) == 0) {
		binner.AddLine(v0.v, v1.v);
		return;
	}

	ClipVertexData ClippedVertices[2] = { v0, v1 };
	ClipVertexData *Vertices[2] = { &ClippedVertices[0], &ClippedVertices[1] };
	CLIP_LINE(CLIP_NEG_Z_BIT,  0,  0,  1, 1);

	ClipVertexData data[2] = { *Vertices[0], *Vertices[1] };
	if (!data[0].OutsideRange() && !data[1].OutsideRange())
		binner.AddLine(data[0].v, data[1].v);
}

void ProcessTriangle(const ClipVertexData &v0, const ClipVertexData &v1, const ClipVertexData &v2, const ClipVertexData &provoking, BinManager &binner) {
	int mask = 0;
	if (!binner.State().throughMode) {
		// If any verts were outside range, throw the entire prim away.
		if (v0.OutsideRange() || v1.OutsideRange() || v2.OutsideRange())
			return;
		// If all verts have negative W, we also cull.
		if (v0.clippos.w < 0.0f && v1.clippos.w < 0.0f && v2.clippos.w < 0.0f)
			return;

		mask |= CalcClipMask(v0.clippos);
		mask |= CalcClipMask(v1.clippos);
		mask |= CalcClipMask(v2.clippos);

		// We may discard the entire triangle based on depth values.  First check what's outside.
		int outsidePos = 0, outsideNeg = 0;
		CheckOutsideZ(v0.clippos, outsidePos, outsideNeg);
		CheckOutsideZ(v1.clippos, outsidePos, outsideNeg);
		CheckOutsideZ(v2.clippos, outsidePos, outsideNeg);

		// With depth clamp off, we discard the triangle if even one vert is outside.
		if (outsidePos + outsideNeg > 0 && !gstate.isDepthClampEnabled())
			return;
		// With it on, all three must be outside in the same direction.
		else if (outsidePos >= 3 || outsideNeg >= 3)
			return;
	}

	// No clipping is common, let's skip processing if we can.
	if ((mask & CLIP_NEG_Z_BIT) == 0) {
		if (gstate.getShadeMode() == GE_SHADE_FLAT) {
			// So that the order of clipping doesn't matter...
			VertexData corrected2 = v2.v;
			corrected2.color0 = provoking.v.color0;
			corrected2.color1 = provoking.v.color1;
			binner.AddTriangle(v0.v, v1.v, corrected2);
		} else {
			binner.AddTriangle(v0.v, v1.v, v2.v);
		}
		return;
	}

	enum { NUM_CLIPPED_VERTICES = 3, NUM_INDICES = NUM_CLIPPED_VERTICES + 3 };

	ClipVertexData* Vertices[NUM_INDICES];
	ClipVertexData ClippedVertices[NUM_INDICES];
	for (int i = 0; i < NUM_INDICES; ++i)
		Vertices[i] = &ClippedVertices[i];

	// TODO: Change logic when it's a backface (why? In what way?)
	ClippedVertices[0] = v0;
	ClippedVertices[1] = v1;
	ClippedVertices[2] = v2;

	int indices[NUM_INDICES] = { 0, 1, 2, SKIP_FLAG, SKIP_FLAG, SKIP_FLAG };
	int numIndices = 3;

	for (int i = 0; i < 3; i += 3) {
		int vlist[2][2*6+1];
		int *inlist = vlist[0], *outlist = vlist[1];
		int n = 3;
		int numVertices = 3;

		inlist[0] = 0;
		inlist[1] = 1;
		inlist[2] = 2;

		// mark this triangle as unused in case it should be completely clipped
		indices[0] = SKIP_FLAG;
		indices[1] = SKIP_FLAG;
		indices[2] = SKIP_FLAG;

		// The PSP only clips on negative Z (importantly, regardless of viewport.)
		CLIP_POLY(CLIP_NEG_Z_BIT, 0, 0, 1, 1);

		// transform the poly in inlist into triangles
		indices[0] = inlist[0];
		indices[1] = inlist[1];
		indices[2] = inlist[2];
		for (int j = 3; j < n; ++j) {
			indices[numIndices++] = inlist[0];
			indices[numIndices++] = inlist[j - 1];
			indices[numIndices++] = inlist[j];
		}
	}

	for (int i = 0; i + 3 <= numIndices; i += 3) {
		if (indices[i] != SKIP_FLAG) {
			ClipVertexData &subv0 = *Vertices[indices[i + 0]];
			ClipVertexData &subv1 = *Vertices[indices[i + 1]];
			ClipVertexData &subv2 = *Vertices[indices[i + 2]];

			if (subv0.OutsideRange() || subv1.OutsideRange() || subv2.OutsideRange())
				continue;

			if (gstate.getShadeMode() == GE_SHADE_FLAT) {
				// So that the order of clipping doesn't matter...
				subv2.v.color0 = provoking.v.color0;
				subv2.v.color1 = provoking.v.color1;
			}

			binner.AddTriangle(subv0.v, subv1.v, subv2.v);
		}
	}
}

} // namespace