Fix depth clamping during 'very' early depth test.

We perform depth testing before computing scanline invariants, as an
optimization. But it was not taking into account that the
fixed-function depth value may require clamping due to the depth bias.

Bug swiftshader:82

Change-Id: I6f8953f9d060c73b5fe209b8cbad70e7cb7588b4
Reviewed-on: https://swiftshader-review.googlesource.com/13088
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>

src/Renderer/QuadRasterizer.cpp

diff --git a/src/Renderer/QuadRasterizer.cpp b/src/Renderer/QuadRasterizer.cpp
index 2855e16..795e1ee 100644
--- a/src/Renderer/QuadRasterizer.cpp
+++ b/src/Renderer/QuadRasterizer.cpp
@@ -180,7 +180,7 @@
 
 					For(Int x = x0, x < x1, x += 2)
 					{
-						Float4 z = interpolate(xxxx, Dz[0], z, primitive + OFFSET(Primitive,z), false, false);
+						Float4 z = interpolate(xxxx, Dz[0], z, primitive + OFFSET(Primitive,z), false, false, state.depthClamp);
 
 						Float4 zValue;
 
@@ -316,7 +316,7 @@
 		Until(y >= yMax)
 	}
 
-	Float4 QuadRasterizer::interpolate(Float4 &x, Float4 &D, Float4 &rhw, Pointer<Byte> planeEquation, bool flat, bool perspective)
+	Float4 QuadRasterizer::interpolate(Float4 &x, Float4 &D, Float4 &rhw, Pointer<Byte> planeEquation, bool flat, bool perspective, bool clamp)
 	{
 		Float4 interpolant = D;
 
@@ -330,6 +330,11 @@
 			}
 		}
 
+		if(clamp)
+		{
+			interpolant = Min(Max(interpolant, Float4(0.0f)), Float4(1.0f));
+		}
+
 		return interpolant;
 	}
 

src/Renderer/QuadRasterizer.hpp

diff --git a/src/Renderer/QuadRasterizer.hpp b/src/Renderer/QuadRasterizer.hpp
index 5616112..4dfe527 100644
--- a/src/Renderer/QuadRasterizer.hpp
+++ b/src/Renderer/QuadRasterizer.hpp
@@ -49,7 +49,7 @@
 
 		bool interpolateZ() const;
 		bool interpolateW() const;
-		Float4 interpolate(Float4 &x, Float4 &D, Float4 &rhw, Pointer<Byte> planeEquation, bool flat, bool perspective);
+		Float4 interpolate(Float4 &x, Float4 &D, Float4 &rhw, Pointer<Byte> planeEquation, bool flat, bool perspective, bool clamp);
 
 		const PixelProcessor::State &state;
 		const PixelShader *const shader;

src/Shader/PixelRoutine.cpp

diff --git a/src/Shader/PixelRoutine.cpp b/src/Shader/PixelRoutine.cpp
index 90e2073..e681fb4 100644
--- a/src/Shader/PixelRoutine.cpp
+++ b/src/Shader/PixelRoutine.cpp
@@ -94,12 +94,7 @@
 					x -= *Pointer<Float4>(constants + OFFSET(Constants,X) + q * sizeof(float4));
 				}
 
-				z[q] = interpolate(x, Dz[q], z[q], primitive + OFFSET(Primitive,z), false, false);
-
-				if(state.depthClamp)
-				{
-					z[q] = Min(Max(z[q], Float4(0.0f)), Float4(1.0f));
-				}
+				z[q] = interpolate(x, Dz[q], z[q], primitive + OFFSET(Primitive,z), false, false, state.depthClamp);
 			}
 		}
 
@@ -146,7 +141,7 @@
 
 			if(interpolateW())
 			{
-				w = interpolate(xxxx, Dw, rhw, primitive + OFFSET(Primitive,w), false, false);
+				w = interpolate(xxxx, Dw, rhw, primitive + OFFSET(Primitive,w), false, false, false);
 				rhw = reciprocal(w, false, false, true);
 
 				if(state.centroid)
@@ -163,7 +158,7 @@
 					{
 						if(!state.interpolant[interpolant].centroid)
 						{
-							v[interpolant][component] = interpolate(xxxx, Dv[interpolant][component], rhw, primitive + OFFSET(Primitive, V[interpolant][component]), (state.interpolant[interpolant].flat & (1 << component)) != 0, state.perspective);
+							v[interpolant][component] = interpolate(xxxx, Dv[interpolant][component], rhw, primitive + OFFSET(Primitive, V[interpolant][component]), (state.interpolant[interpolant].flat & (1 << component)) != 0, state.perspective, false);
 						}
 						else
 						{
@@ -198,7 +193,7 @@
 
 			if(state.fog.component)
 			{
-				f = interpolate(xxxx, Df, rhw, primitive + OFFSET(Primitive,f), state.fog.flat & 0x01, state.perspective);
+				f = interpolate(xxxx, Df, rhw, primitive + OFFSET(Primitive,f), state.fog.flat & 0x01, state.perspective, false);
 			}
 
 			setBuiltins(x, y, z, w);