From e86d7cbc999223ca113af7b4c0aac6850c1854fe Mon Sep 17 00:00:00 2001
From: Jules Blok <jules.blok@gmail.com>
Date: Wed, 17 Aug 2016 20:12:44 +0200
Subject: [PATCH] OGL: Workaround gl_ClipDistance bug on Mesa i965.

---
 Source/Core/VideoBackends/OGL/Render.cpp      |  4 +---
 Source/Core/VideoCommon/DriverDetails.h       |  7 ++++---
 Source/Core/VideoCommon/GeometryShaderGen.cpp | 10 ++++++++++
 3 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/Source/Core/VideoBackends/OGL/Render.cpp b/Source/Core/VideoBackends/OGL/Render.cpp
index 78d5d106b7..d637c308ca 100644
--- a/Source/Core/VideoBackends/OGL/Render.cpp
+++ b/Source/Core/VideoBackends/OGL/Render.cpp
@@ -482,9 +482,7 @@ Renderer::Renderer()
       GLExtensions::Supports("GL_ARB_shading_language_420pack");
 
   // Clip distance support is useless without a method to clamp the depth range
-  g_Config.backend_info.bSupportsDepthClamp =
-      GLExtensions::Supports("GL_ARB_depth_clamp") &&
-      !DriverDetails::HasBug(DriverDetails::BUG_BROKENCLIPDISTANCE);
+  g_Config.backend_info.bSupportsDepthClamp = GLExtensions::Supports("GL_ARB_depth_clamp");
 
   g_ogl_config.bSupportsGLSLCache = GLExtensions::Supports("GL_ARB_get_program_binary");
   g_ogl_config.bSupportsGLPinnedMemory = GLExtensions::Supports("GL_AMD_pinned_memory");
diff --git a/Source/Core/VideoCommon/DriverDetails.h b/Source/Core/VideoCommon/DriverDetails.h
index 414ef03390..b6dcf87963 100644
--- a/Source/Core/VideoCommon/DriverDetails.h
+++ b/Source/Core/VideoCommon/DriverDetails.h
@@ -205,12 +205,13 @@ enum Bug
   // everywhere else.
   BUG_SLOWGETBUFFERSUBDATA,
 
-  // Bug: Broken lines in geometry shaders when writing to gl_ClipDistance
+  // Bug: Broken lines in geometry shaders when writing to gl_ClipDistance in the vertex shader
   // Affected Devices: Mesa i965
   // Started Version: -1
   // Ended Version: -1
-  // Mesa hasn't tested geometry shaders on i965 with user-defined clipping planes.
-  // Causes misrenderings on a large amount of things that draw lines.
+  // Writing to gl_ClipDistance in both the vertex shader and the geometry shader will break
+  // the geometry shader. Current workaround is to make sure the geometry shader always consumes
+  // the gl_ClipDistance inputs from the vertex shader.
   BUG_BROKENCLIPDISTANCE,
 };
 
diff --git a/Source/Core/VideoCommon/GeometryShaderGen.cpp b/Source/Core/VideoCommon/GeometryShaderGen.cpp
index 2630a422fa..83b30943bc 100644
--- a/Source/Core/VideoCommon/GeometryShaderGen.cpp
+++ b/Source/Core/VideoCommon/GeometryShaderGen.cpp
@@ -7,6 +7,7 @@
 
 #include "Common/CommonTypes.h"
 #include "VideoCommon/BPMemory.h"
+#include "VideoCommon/DriverDetails.h"
 #include "VideoCommon/GeometryShaderGen.h"
 #include "VideoCommon/LightingShaderGen.h"
 #include "VideoCommon/VideoCommon.h"
@@ -211,6 +212,15 @@ ShaderCode GenerateGeometryShaderCode(APIType ApiType, const geometry_shader_uid
   {
     out.Write("\tVS_OUTPUT f;\n");
     AssignVSOutputMembers(out, "f", "vs[i]", uid_data->numTexGens, uid_data->pixel_lighting);
+
+    if (g_ActiveConfig.backend_info.bSupportsDepthClamp &&
+        DriverDetails::HasBug(DriverDetails::BUG_BROKENCLIPDISTANCE))
+    {
+      // On certain GPUs we have to consume the clip distance from the vertex shader
+      // or else the other vertex shader outputs will get corrupted.
+      out.Write("\tf.clipDist0 = gl_in[i].gl_ClipDistance[0];\n");
+      out.Write("\tf.clipDist1 = gl_in[i].gl_ClipDistance[1];\n");
+    }
   }
   else
   {