From 92a4551bb296e67726c2b4e2939defdf092527de Mon Sep 17 00:00:00 2001
From: Connor McLaughlin <stenzek@gmail.com>
Date: Tue, 10 Nov 2020 20:36:17 +1000
Subject: [PATCH] GPU/OpenGL: Support GL_EXT_blend_func_extended for
 dual-source blend

---
 src/core/gpu_hw.h          | 15 +++++++++++++++
 src/core/gpu_hw_opengl.cpp | 14 +++++++-------
 src/core/shadergen.cpp     |  2 ++
 3 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/src/core/gpu_hw.h b/src/core/gpu_hw.h
index 2bd162845..10d2694f6 100644
--- a/src/core/gpu_hw.h
+++ b/src/core/gpu_hw.h
@@ -225,6 +225,21 @@ protected:
     }
   }
 
+  /// Returns true if alpha blending should be enabled for drawing the current batch.
+  ALWAYS_INLINE bool UseAlphaBlending(TransparencyMode transparency_mode, BatchRenderMode render_mode) const
+  {
+    if (m_texture_filtering == GPUTextureFilter::Bilinear || m_texture_filtering == GPUTextureFilter::JINC2 ||
+        m_texture_filtering == GPUTextureFilter::xBR)
+    {
+      return true;
+    }
+
+    if (transparency_mode == TransparencyMode::Disabled || render_mode == BatchRenderMode::OnlyOpaque)
+      return false;
+
+    return true;
+  }
+
   void FillVRAM(u32 x, u32 y, u32 width, u32 height, u32 color) override;
   void UpdateVRAM(u32 x, u32 y, u32 width, u32 height, const void* data) override;
   void CopyVRAM(u32 src_x, u32 src_y, u32 dst_x, u32 dst_y, u32 width, u32 height) override;
diff --git a/src/core/gpu_hw_opengl.cpp b/src/core/gpu_hw_opengl.cpp
index 6e0281a39..3aee7b2e9 100644
--- a/src/core/gpu_hw_opengl.cpp
+++ b/src/core/gpu_hw_opengl.cpp
@@ -240,7 +240,8 @@ void GPU_HW_OpenGL::SetCapabilities(HostDisplay* host_display)
   int max_dual_source_draw_buffers = 0;
   glGetIntegerv(GL_MAX_DUAL_SOURCE_DRAW_BUFFERS, &max_dual_source_draw_buffers);
   m_supports_dual_source_blend =
-    (max_dual_source_draw_buffers > 0) && (GLAD_GL_VERSION_3_3 || GLAD_GL_ARB_blend_func_extended);
+    (max_dual_source_draw_buffers > 0) &&
+    (GLAD_GL_VERSION_3_3 || GLAD_GL_ARB_blend_func_extended || GLAD_GL_EXT_blend_func_extended);
   if (!m_supports_dual_source_blend)
     Log_WarningPrintf("Dual-source blending is not supported, this may break some mask effects.");
 
@@ -588,12 +589,7 @@ void GPU_HW_OpenGL::DrawBatchVertices(BatchRenderMode render_mode, u32 base_vert
 
 void GPU_HW_OpenGL::SetBlendMode()
 {
-  if (m_texture_filtering == GPUTextureFilter::Nearest && (m_current_transparency_mode == TransparencyMode::Disabled ||
-                                                           m_current_render_mode == BatchRenderMode::OnlyOpaque))
-  {
-    glDisable(GL_BLEND);
-  }
-  else
+  if (UseAlphaBlending(m_current_transparency_mode, m_current_render_mode))
   {
     glEnable(GL_BLEND);
     glBlendEquationSeparate(m_current_transparency_mode == TransparencyMode::BackgroundMinusForeground ?
@@ -602,6 +598,10 @@ void GPU_HW_OpenGL::SetBlendMode()
                             GL_FUNC_ADD);
     glBlendFuncSeparate(GL_ONE, m_supports_dual_source_blend ? GL_SRC1_ALPHA : GL_SRC_ALPHA, GL_ONE, GL_ZERO);
   }
+  else
+  {
+    glDisable(GL_BLEND);
+  }
 }
 
 void GPU_HW_OpenGL::SetDepthFunc()
diff --git a/src/core/shadergen.cpp b/src/core/shadergen.cpp
index 1cd886dc6..be6d7aa12 100644
--- a/src/core/shadergen.cpp
+++ b/src/core/shadergen.cpp
@@ -89,6 +89,8 @@ void ShaderGen::WriteHeader(std::stringstream& ss)
     // Enable EXT_blend_func_extended for dual-source blend on OpenGL ES.
     if (GLAD_GL_EXT_blend_func_extended)
       ss << "#extension GL_EXT_blend_func_extended : require\n";
+    if (GLAD_GL_ARB_blend_func_extended)
+      ss << "#extension GL_ARB_blend_func_extended : require\n";
   }
   else if (m_render_api == HostDisplay::RenderAPI::OpenGL)
   {