Fix polygon offset depth clamp and units resolution.

OpenGL requires depth values to be clamped to the [0, 1] range. Due to
frustum clipping already limiting the range, this can only happen when
non-zero polygon offset parameters are active.

Also fix the 'minimum resolvable difference' for the 32-bit floating-
point internal depth format that we use.

Bug swiftshader:82

Change-Id: Ic9ebcac182a2bc81ab51d79cfe0bb451d340bd1e
Reviewed-on: https://swiftshader-review.googlesource.com/12108
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>

src/Renderer/Context.cpp

diff --git a/src/Renderer/Context.cpp b/src/Renderer/Context.cpp
index e5ee4dc..45ad436 100644
--- a/src/Renderer/Context.cpp
+++ b/src/Renderer/Context.cpp
@@ -276,6 +276,9 @@
 		cullMode = CULL_CLOCKWISE;
 		alphaReference = 0.0f;
 
+		depthBias = 0.0f;
+		slopeDepthBias = 0.0f;
+
 		for(int i = 0; i < RENDERTARGETS; i++)
 		{
 			colorWriteMask[i] = 0x0000000F;

src/Renderer/Context.hpp

diff --git a/src/Renderer/Context.hpp b/src/Renderer/Context.hpp
index 640ec4e..6116794 100644
--- a/src/Renderer/Context.hpp
+++ b/src/Renderer/Context.hpp
@@ -434,6 +434,9 @@
 		CullMode cullMode;
 		float alphaReference;
 
+		float depthBias;
+		float slopeDepthBias;
+
 		TextureStage textureStage[8];
 		Sampler sampler[TOTAL_IMAGE_UNITS];
 

src/Renderer/PixelProcessor.cpp

diff --git a/src/Renderer/PixelProcessor.cpp b/src/Renderer/PixelProcessor.cpp
index db11aed..abf6593 100644
--- a/src/Renderer/PixelProcessor.cpp
+++ b/src/Renderer/PixelProcessor.cpp
@@ -990,6 +990,7 @@
 		state.pixelFogMode = context->pixelFogActive();
 		state.wBasedFog = context->wBasedFog && context->pixelFogActive() != FOG_NONE;
 		state.perspective = context->perspectiveActive();
+		state.depthClamp = (context->depthBias != 0.0f) || (context->slopeDepthBias != 0.0f);
 
 		if(context->alphaBlendActive())
 		{

src/Renderer/PixelProcessor.hpp

diff --git a/src/Renderer/PixelProcessor.hpp b/src/Renderer/PixelProcessor.hpp
index 65f6b92..d3b0602 100644
--- a/src/Renderer/PixelProcessor.hpp
+++ b/src/Renderer/PixelProcessor.hpp
@@ -66,6 +66,7 @@
 			bool occlusionEnabled                     : 1;
 			bool wBasedFog                            : 1;
 			bool perspective                          : 1;
+			bool depthClamp                           : 1;
 
 			bool alphaBlendActive                     : 1;
 			BlendFactor sourceBlendFactor             : BITS(BLEND_LAST);

src/Renderer/Renderer.cpp

diff --git a/src/Renderer/Renderer.cpp b/src/Renderer/Renderer.cpp
index 32e2027..0869697 100644
--- a/src/Renderer/Renderer.cpp
+++ b/src/Renderer/Renderer.cpp
@@ -545,7 +545,7 @@
 
 				if(context->isDrawTriangle(false))
 				{
-					N += depthBias;
+					N += context->depthBias;
 				}
 
 				if(complementaryDepthBuffer)
@@ -583,7 +583,7 @@
 				data->halfPixelX = replicate(0.5f / W);
 				data->halfPixelY = replicate(0.5f / H);
 				data->viewportHeight = abs(viewport.height);
-				data->slopeDepthBias = slopeDepthBias;
+				data->slopeDepthBias = context->slopeDepthBias;
 				data->depthRange = Z;
 				data->depthNear = N;
 				draw->clipFlags = clipFlags;
@@ -2447,12 +2447,12 @@
 
 	void Renderer::setDepthBias(float bias)
 	{
-		depthBias = bias;
+		context->depthBias = bias;
 	}
 
 	void Renderer::setSlopeDepthBias(float slopeBias)
 	{
-		slopeDepthBias = slopeBias;
+		context->slopeDepthBias = slopeBias;
 	}
 
 	void Renderer::setRasterizerDiscard(bool rasterizerDiscard)

src/Renderer/SetupProcessor.cpp

diff --git a/src/Renderer/SetupProcessor.cpp b/src/Renderer/SetupProcessor.cpp
index 772327f..bc456e9 100644
--- a/src/Renderer/SetupProcessor.cpp
+++ b/src/Renderer/SetupProcessor.cpp
@@ -85,7 +85,7 @@
 		state.pointSprite = context->pointSpriteActive();
 		state.cullMode = context->cullMode;
 		state.twoSidedStencil = context->stencilActive() && context->twoSidedStencil;
-		state.slopeDepthBias = slopeDepthBias != 0.0f;
+		state.slopeDepthBias = context->slopeDepthBias != 0.0f;
 		state.vFace = context->pixelShader && context->pixelShader->isVFaceDeclared();
 
 		state.positionRegister = Pos;

src/Renderer/SetupProcessor.hpp

diff --git a/src/Renderer/SetupProcessor.hpp b/src/Renderer/SetupProcessor.hpp
index 2750d4c..be0adc7 100644
--- a/src/Renderer/SetupProcessor.hpp
+++ b/src/Renderer/SetupProcessor.hpp
@@ -95,9 +95,6 @@
 
 		void setRoutineCacheSize(int cacheSize);
 
-		float depthBias;
-		float slopeDepthBias;
-
 	private:
 		Context *const context;