Merge pull request #4153 from stenzek/logicop-dstalpha

OGL: Handle case where both constant alpha and logic op is enabled

1 files changed, 16 insertions, 2 deletions

diff --git a/Source/Core/VideoBackends/OGL/VertexManager.cpp b/Source/Core/VideoBackends/OGL/VertexManager.cpp
index 0bc2e3a663..feb2351e49 100644
--- a/Source/Core/VideoBackends/OGL/VertexManager.cpp
+++ b/Source/Core/VideoBackends/OGL/VertexManager.cpp
@@ -10,6 +10,7 @@
 #include "Common/CommonTypes.h"
 #include "Common/FileUtil.h"
 #include "Common/GL/GLExtensions/GLExtensions.h"
+#include "Common/GL/GLInterfaceBase.h"
 #include "Common/StringUtil.h"
 
 #include "VideoBackends/OGL/ProgramShaderCache.h"
@@ -170,8 +171,15 @@ void VertexManager::vFlush(bool useDstAlpha)
 
   Draw(stride);
 
-  // run through vertex groups again to set alpha
-  if (useDstAlpha && !dualSourcePossible)
+  // If the GPU does not support dual-source blending, we can approximate the effect by drawing
+  // the object a second time, with the write mask set to alpha only using a shader that outputs
+  // the destination/constant alpha value (which would normally be SRC_COLOR.a).
+  //
+  // This is also used when logic ops and destination alpha is enabled, since we can't enable
+  // blending and logic ops concurrently.
+  bool logic_op_enabled = (bpmem.blendmode.logicopenable && !bpmem.blendmode.blendenable &&
+                           GLInterface->GetMode() == GLInterfaceMode::MODE_OPENGL);
+  if (useDstAlpha && (!dualSourcePossible || logic_op_enabled))
   {
     ProgramShaderCache::SetShader(DSTALPHA_ALPHA_PASS, m_current_primitive_type);
 
@@ -180,6 +188,9 @@ void VertexManager::vFlush(bool useDstAlpha)
 
     glDisable(GL_BLEND);
 
+    if (logic_op_enabled)
+      glDisable(GL_COLOR_LOGIC_OP);
+
     Draw(stride);
 
     // restore color mask
@@ -187,6 +198,9 @@ void VertexManager::vFlush(bool useDstAlpha)
 
     if (bpmem.blendmode.blendenable || bpmem.blendmode.subtract)
       glEnable(GL_BLEND);
+
+    if (logic_op_enabled)
+      glEnable(GL_COLOR_LOGIC_OP);
   }
 
 #if defined(_DEBUG) || defined(DEBUGFAST)