VertexShaderGen: Move the sonic epsilon hack to the vertex shader.

In the vertex shader we have control over the depth clipping planes,
so we don't have to offset every floating point value and lose accuracy.

1 files changed, 5 insertions, 2 deletions

diff --git a/Source/Core/VideoCommon/VertexShaderGen.cpp b/Source/Core/VideoCommon/VertexShaderGen.cpp
index a42f090716..7c4f558225 100644
--- a/Source/Core/VideoCommon/VertexShaderGen.cpp
+++ b/Source/Core/VideoCommon/VertexShaderGen.cpp
@@ -408,8 +408,11 @@ ShaderCode GenerateVertexShaderCode(APIType api_type, const vertex_shader_uid_da
 
     // Since we're adjusting z for the depth range before the perspective divide, we have to do our
     // own clipping. We want to clip so that -w <= z <= 0, which matches the console -1..0 range.
-    out.Write("o.clipDist0 = o.pos.z + o.pos.w;\n");  // Near: z < -w
-    out.Write("o.clipDist1 = -o.pos.z;\n");           // Far: z > 0
+    // We adjust our depth value for clipping purposes to match the perspective projection in the
+    // software backend, which is a hack to fix Sonic Adventure and Unleashed games.
+    out.Write("float clipDepth = o.pos.z * (1.0 - 1e-7);\n");
+    out.Write("o.clipDist0 = clipDepth + o.pos.w;\n");  // Near: z < -w
+    out.Write("o.clipDist1 = -clipDepth;\n");           // Far: z > 0
 
     // Adjust z for the depth range. We're using an equation which incorperates a depth inversion,
     // so we can map the console -1..0 range to the 0..1 range used in the depth buffer.