OGL: Handle cases where reversed depth is already used.

Source/Core/VideoBackends/D3D/main.cpp

@@ -72,6 +72,7 @@ void VideoBackend::InitBackendInfo()
   g_Config.backend_info.bSupportsPaletteConversion = true;
   g_Config.backend_info.bSupportsClipControl = true;
   g_Config.backend_info.bSupportsDepthClamp = true;
+  g_Config.backend_info.bSupportsReversedDepthRange = false;
 
   IDXGIFactory* factory;
   IDXGIAdapter* ad;

Source/Core/VideoBackends/D3D12/main.cpp

@@ -75,6 +75,7 @@ void VideoBackend::InitBackendInfo()
   g_Config.backend_info.bSupportsPaletteConversion = true;
   g_Config.backend_info.bSupportsClipControl = true;
   g_Config.backend_info.bSupportsDepthClamp = true;
+  g_Config.backend_info.bSupportsReversedDepthRange = false;
 
   IDXGIFactory* factory;
   IDXGIAdapter* ad;

Source/Core/VideoBackends/OGL/Render.cpp

@@ -1160,9 +1160,16 @@ void Renderer::SetViewport()
   // value supported by the console GPU. If not, we simply clamp the near/far values
   // themselves to the maximum value as done above.
   if (g_ActiveConfig.backend_info.bSupportsDepthClamp)
-    glDepthRangef(GX_MAX_DEPTH, 0.0f);
+  {
+    if (xfmem.viewport.zRange < 0.0f)
+      glDepthRangef(0.0f, GX_MAX_DEPTH);
+    else
+      glDepthRangef(GX_MAX_DEPTH, 0.0f);
+  }
   else
+  {
     glDepthRangef(GLFar, GLNear);
+  }
 }
 
 void Renderer::ClearScreen(const EFBRectangle& rc, bool colorEnable, bool alphaEnable, bool zEnable,

Source/Core/VideoBackends/OGL/main.cpp

@@ -102,6 +102,7 @@ void VideoBackend::InitBackendInfo()
   g_Config.backend_info.bSupports3DVision = false;
   g_Config.backend_info.bSupportsPostProcessing = true;
   g_Config.backend_info.bSupportsSSAA = true;
+  g_Config.backend_info.bSupportsReversedDepthRange = true;
 
   // Overwritten in Render.cpp later
   g_Config.backend_info.bSupportsDualSourceBlend = true;

Source/Core/VideoCommon/VertexShaderManager.cpp

@@ -392,8 +392,26 @@ void VertexShaderManager::SetConstants()
     // because the standard depth range equation pushes all depth values towards
     // the back of the depth buffer where conventionally depth buffers have the
     // least precision.
-    constants.pixelcentercorrection[2] = xfmem.viewport.zRange / 16777215.0f;
-    constants.pixelcentercorrection[3] = 1.0f - xfmem.viewport.farZ / 16777215.0f;
+    if (g_ActiveConfig.backend_info.bSupportsReversedDepthRange)
+    {
+      // For backends that support reversing the depth range we also support cases
+      // where the console also uses reversed depth with the same accuracy. We need
+      // to make sure the depth range is positive here and then reverse the depth in
+      // the backend viewport.
+      constants.pixelcentercorrection[2] = abs(xfmem.viewport.zRange) / 16777215.0f;
+      if (xfmem.viewport.zRange < 0.0f)
+        constants.pixelcentercorrection[3] = xfmem.viewport.farZ / 16777215.0f;
+      else
+        constants.pixelcentercorrection[3] = 1.0f - xfmem.viewport.farZ / 16777215.0f;
+    }
+    else
+    {
+      // For backends that don't support reversing the depth range we can still render
+      // cases where the console uses reversed depth correctly. But we simply can't
+      // provide the same accuracy as the console.
+      constants.pixelcentercorrection[2] = xfmem.viewport.zRange / 16777215.0f;
+      constants.pixelcentercorrection[3] = 1.0f - xfmem.viewport.farZ / 16777215.0f;
+    }
 
     dirty = true;
     // This is so implementation-dependent that we can't have it here.

Source/Core/VideoCommon/VideoConfig.h

@@ -172,6 +172,7 @@ struct VideoConfig final
     bool bSupportsClipControl;  // Needed by VertexShaderGen, so must stay in VideoCommon
     bool bSupportsSSAA;
     bool bSupportsDepthClamp;  // Needed by VertexShaderGen, so must stay in VideoCommon
+    bool bSupportsReversedDepthRange;
   } backend_info;
 
   // Utility