1 files changed, 40 insertions, 0 deletions
diff --git a/Source/Core/VideoCommon/VertexManagerBase.cpp b/Source/Core/VideoCommon/VertexManagerBase.cpp
index 38cfd19630..80ea3b5bb9 100644
--- a/Source/Core/VideoCommon/VertexManagerBase.cpp
+++ b/Source/Core/VideoCommon/VertexManagerBase.cpp
@@ -241,3 +241,43 @@ void VertexManager::DoState(PointerWrap& p)
 {
 	g_vertex_manager->vDoState(p);
 }
+
+void VertexManager::CalculateZSlope(u32 stride)
+{
+	float vtx[9];
+	float out[12];
+
+	// Lookup vertices of the last rendered triangle and software-transform them
+	// This allows us to determine the depth slope, which will be used if zfreeze
+	// is enabled in the following flush.
+	for (unsigned int i = 0; i < 3; ++i)
+	{
+		u8* vtx_ptr = s_pCurBufferPointer - stride * (3 - i);
+		vtx[0 + i * 3] = ((float*)vtx_ptr)[0];
+		vtx[1 + i * 3] = ((float*)vtx_ptr)[1];
+		vtx[2 + i * 3] = ((float*)vtx_ptr)[2];
+
+		VertexShaderManager::TransformToClipSpace(&vtx[i * 3], &out[i * 4]);
+
+		// viewport offset ignored because we only look at coordinate differences.
+		out[0 + i * 4] = out[0 + i * 4] / out[3 + i * 4] * xfmem.viewport.wd;
+		out[1 + i * 4] = out[1 + i * 4] / out[3 + i * 4] * xfmem.viewport.ht;
+		out[2 + i * 4] = out[2 + i * 4] / out[3 + i * 4] * xfmem.viewport.zRange + xfmem.viewport.farZ;
+	}
+	float dx31 = out[8] - out[0];
+	float dx12 = out[0] - out[4];
+	float dy12 = out[1] - out[5];
+	float dy31 = out[9] - out[1];
+
+	float DF31 = out[10] - out[2];
+	float DF21 = out[6] - out[2];
+	float a = DF31 * -dy12 - DF21 * dy31;
+	float b = dx31 * DF21 + dx12 * DF31;
+	float c = -dx12 * dy31 - dx31 * -dy12;
+
+	float slope_dfdx = -a / c;
+	float slope_dfdy = -b / c;
+	float slope_f0 = out[2];
+
+	PixelShaderManager::SetZSlope(slope_dfdx, slope_dfdy, slope_f0);
+}