Cleanup: GPU: Move towards an explicit Blend state

This make use of the GLStateStack functions for:
- `GPU_blend()`
- `GPU_blend_set_func()`
- `GPU_blend_set_func_separate()`

The goal is to unify them using an explicit state setting.
This will remove the need to use obscure blend functions

1 files changed, 26 insertions, 3 deletions

diff --git a/source/blender/gpu/intern/gpu_state.cc b/source/blender/gpu/intern/gpu_state.cc
index 485aa3b852e..d2aa0816a3f 100644
--- a/source/blender/gpu/intern/gpu_state.cc
+++ b/source/blender/gpu/intern/gpu_state.cc
@@ -35,8 +35,17 @@
 
 #include "gpu_state_private.hh"
 
+/* TODO remove */
+#include "gl_state.hh"
+
 using namespace blender::gpu;
 
+// /* This should replace GPU_blend, GPU_blend_set_func and GPU_blend_set_func_separate. */
+// void GPU_blend_set(eGPUBlend blend)
+// {
+//   GLStateStack::set_blend(blend);
+// }
+
 static GLenum gpu_get_gl_blendfunction(eGPUBlendFunction blend)
 {
   switch (blend) {
@@ -59,16 +68,30 @@ static GLenum gpu_get_gl_blendfunction(eGPUBlendFunction blend)
 void GPU_blend(bool enable)
 {
   if (enable) {
-    glEnable(GL_BLEND);
+    GLStateStack::set_blend(GPU_BLEND_ALPHA);
   }
   else {
-    glDisable(GL_BLEND);
+    GLStateStack::set_blend(GPU_BLEND_NONE);
   }
 }
 
 void GPU_blend_set_func(eGPUBlendFunction sfactor, eGPUBlendFunction dfactor)
 {
-  glBlendFunc(gpu_get_gl_blendfunction(sfactor), gpu_get_gl_blendfunction(dfactor));
+  if (sfactor == GPU_ONE && dfactor == GPU_ONE) {
+    GLStateStack::set_blend(GPU_BLEND_ADDITIVE);
+  }
+  else if (sfactor == GPU_ONE && dfactor == GPU_ONE_MINUS_SRC_ALPHA) {
+    GLStateStack::set_blend(GPU_BLEND_ALPHA_PREMULT);
+  }
+  else if (sfactor == GPU_SRC_ALPHA && dfactor == GPU_ONE_MINUS_SRC_ALPHA) {
+    GLStateStack::set_blend(GPU_BLEND_ALPHA);
+  }
+  else if (sfactor == GPU_DST_COLOR && dfactor == GPU_ZERO) {
+    GLStateStack::set_blend(GPU_BLEND_MULTIPLY);
+  }
+  else {
+    BLI_assert(0);
+  }
 }
 
 void GPU_blend_set_func_separate(eGPUBlendFunction src_rgb,