DRW: Add DRW_STATE_BLEND_CUSTOM

This one enable dual source blending, enabling more fine tuned
blending parameters inside the shader.

2 files changed, 12 insertions, 5 deletions

diff --git a/source/blender/draw/intern/DRW_render.h b/source/blender/draw/intern/DRW_render.h
index 392362e73c5..a8f67e10a4d 100644
--- a/source/blender/draw/intern/DRW_render.h
+++ b/source/blender/draw/intern/DRW_render.h
@@ -347,12 +347,14 @@ typedef enum {
   DRW_STATE_BLEND_ALPHA_UNDER_PREMUL = (1 << 20),
   DRW_STATE_BLEND_OIT = (1 << 21),
   DRW_STATE_BLEND_MUL = (1 << 22),
+  /** Use dual source blending. WARNING: Only one color buffer allowed. */
+  DRW_STATE_BLEND_CUSTOM = (1 << 23),
 
-  DRW_STATE_CLIP_PLANES = (1 << 23),
-  DRW_STATE_WIRE_SMOOTH = (1 << 24),
-  DRW_STATE_FIRST_VERTEX_CONVENTION = (1 << 25),
+  DRW_STATE_CLIP_PLANES = (1 << 28),
+  DRW_STATE_WIRE_SMOOTH = (1 << 29),
+  DRW_STATE_FIRST_VERTEX_CONVENTION = (1 << 30),
   /** DO NOT USE. Assumed always enabled. Only used internally. */
-  DRW_STATE_PROGRAM_POINT_SIZE = (1 << 26),
+  DRW_STATE_PROGRAM_POINT_SIZE = (1u << 31),
 } DRWState;
 
 #define DRW_STATE_DEFAULT \
diff --git a/source/blender/draw/intern/draw_manager_exec.c b/source/blender/draw/intern/draw_manager_exec.c
index 2596570c022..949d3e1d38b 100644
--- a/source/blender/draw/intern/draw_manager_exec.c
+++ b/source/blender/draw/intern/draw_manager_exec.c
@@ -225,7 +225,7 @@ void drw_state_set(DRWState state)
     if (CHANGED_ANY_STORE_VAR(DRW_STATE_BLEND_ALPHA | DRW_STATE_BLEND_ALPHA_PREMUL |
                                   DRW_STATE_BLEND_ADD | DRW_STATE_BLEND_MUL |
                                   DRW_STATE_BLEND_ADD_FULL | DRW_STATE_BLEND_OIT |
-                                  DRW_STATE_BLEND_ALPHA_UNDER_PREMUL,
+                                  DRW_STATE_BLEND_ALPHA_UNDER_PREMUL | DRW_STATE_BLEND_CUSTOM,
                               test)) {
       if (test) {
         glEnable(GL_BLEND);
@@ -262,6 +262,11 @@ void drw_state_set(DRWState state)
           /* Let alpha accumulate. */
           glBlendFunc(GL_ONE, GL_ONE);
         }
+        else if ((state & DRW_STATE_BLEND_CUSTOM) != 0) {
+          /* Custom blend parameters using dual source blending.
+           * Can only be used with one Draw Buffer. */
+          glBlendFunc(GL_ONE, GL_SRC1_COLOR);
+        }
         else {
           BLI_assert(0);
         }