From dc35083392fe04935f8d0395aeb59903b1afe6e5 Mon Sep 17 00:00:00 2001
From: baldurk <baldurk@baldurk.org>
Date: Mon, 1 Mar 2021 11:38:04 +0000
Subject: [PATCH] Check for clip origin on GL to enable Y-flipping for output
 meshes

---
 renderdoc/driver/gl/gl_postvs.cpp | 19 +++++++++++++++++++
 renderdoc/driver/gl/gl_replay.h   |  2 ++
 2 files changed, 21 insertions(+)

diff --git a/renderdoc/driver/gl/gl_postvs.cpp b/renderdoc/driver/gl/gl_postvs.cpp
index 33f07a461..dc3b2883b 100644
--- a/renderdoc/driver/gl/gl_postvs.cpp
+++ b/renderdoc/driver/gl/gl_postvs.cpp
@@ -739,6 +739,17 @@ void GLReplay::InitPostVSBuffers(uint32_t eventId)
   if(HasExt[ARB_transform_feedback2])
     drv.glBindTransformFeedback(eGL_TRANSFORM_FEEDBACK, DebugData.feedbackObj);
 
+  bool flipY = false;
+
+  if(HasExt[ARB_clip_control])
+  {
+    GLenum clipOrigin = eGL_LOWER_LEFT;
+    GL.glGetIntegerv(eGL_CLIP_ORIGIN, (GLint *)&clipOrigin);
+
+    if(clipOrigin == eGL_UPPER_LEFT)
+      flipY = true;
+  }
+
   GLuint idxBuf = 0;
 
   if(vsRefl->outputSignature.empty())
@@ -1867,6 +1878,8 @@ void GLReplay::InitPostVSBuffers(uint32_t eventId)
 
       m_PostVSData[eventId].gsout.useIndices = false;
 
+      m_PostVSData[eventId].gsout.flipY = flipY;
+
       m_PostVSData[eventId].gsout.hasPosOut = hasPosition;
 
       m_PostVSData[eventId].gsout.idxBuf = 0;
@@ -1877,6 +1890,10 @@ void GLReplay::InitPostVSBuffers(uint32_t eventId)
       m_PostVSData[eventId].gsout.instData = instData;
     }
   }
+  else
+  {
+    m_PostVSData[eventId].vsout.flipY = flipY;
+  }
 
   // delete temporary program we made
   drv.glDeleteProgram(feedbackProg);
@@ -1989,6 +2006,8 @@ MeshFormat GLReplay::GetPostVSBuffers(uint32_t eventId, uint32_t instID, uint32_
   ret.nearPlane = s.nearPlane;
   ret.farPlane = s.farPlane;
 
+  ret.flipY = s.flipY;
+
   if(instID < s.instData.size())
   {
     GLPostVSData::InstData inst = s.instData[instID];
diff --git a/renderdoc/driver/gl/gl_replay.h b/renderdoc/driver/gl/gl_replay.h
index 1a8286e96..bba676f25 100644
--- a/renderdoc/driver/gl/gl_replay.h
+++ b/renderdoc/driver/gl/gl_replay.h
@@ -62,6 +62,8 @@ struct GLPostVSData
     GLuint idxBuf = 0;
     uint32_t idxByteWidth = 0;
 
+    bool flipY = false;
+
     bool hasPosOut = false;
 
     float nearPlane = 0.0f;