[Bf-blender-cvs] [18c4fcb9a34] greasepencil-refactor: DRW: Add subtract blend logic

[Clément Foucault]

Commit: 18c4fcb9a34b05da4854b34509b3641b793eda6b
Author: Clément Foucault
Date:   Fri Dec 13 19:31:02 2019 +0100
Branches: greasepencil-refactor
https://developer.blender.org/rB18c4fcb9a34b05da4854b34509b3641b793eda6b

DRW: Add subtract blend logic

This is to support subtract blending with Multiple Render Targets

===================================================================

M	source/blender/draw/intern/DRW_render.h
M	source/blender/draw/intern/draw_manager_exec.c

===================================================================

diff --git a/source/blender/draw/intern/DRW_render.h b/source/blender/draw/intern/DRW_render.h
index f00bf61cbb7..d84a8a66810 100644
--- a/source/blender/draw/intern/DRW_render.h
+++ b/source/blender/draw/intern/DRW_render.h
@@ -305,8 +305,9 @@ typedef enum {
   DRW_STATE_BLEND_ALPHA_UNDER_PREMUL = (1 << 20),
   DRW_STATE_BLEND_OIT = (1 << 21),
   DRW_STATE_BLEND_MUL = (1 << 22),
+  DRW_STATE_BLEND_SUB = (1 << 23),
   /** Use dual source blending. WARNING: Only one color buffer allowed. */
-  DRW_STATE_BLEND_CUSTOM = (1 << 23),
+  DRW_STATE_BLEND_CUSTOM = (1 << 24),
 
   DRW_STATE_IN_FRONT_SELECT = (1 << 25),
   DRW_STATE_LOGIC_INVERT = (1 << 26),
diff --git a/source/blender/draw/intern/draw_manager_exec.c b/source/blender/draw/intern/draw_manager_exec.c
index 977bec92cba..bd378d78780 100644
--- a/source/blender/draw/intern/draw_manager_exec.c
+++ b/source/blender/draw/intern/draw_manager_exec.c
@@ -233,11 +233,11 @@ void drw_state_set(DRWState state)
   /* Blending (all buffer) */
   {
     int test;
-    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_CUSTOM,
-                              test)) {
+    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_CUSTOM | DRW_STATE_BLEND_SUB,
+            test)) {
       if (test) {
         glEnable(GL_BLEND);
 
@@ -273,6 +273,9 @@ void drw_state_set(DRWState state)
           /* Let alpha accumulate. */
           glBlendFunc(GL_ONE, GL_ONE);
         }
+        else if ((state & DRW_STATE_BLEND_SUB) != 0) {
+          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. */
@@ -281,6 +284,13 @@ void drw_state_set(DRWState state)
         else {
           BLI_assert(0);
         }
+
+        if ((state & DRW_STATE_BLEND_SUB) != 0) {
+          glBlendEquation(GL_FUNC_REVERSE_SUBTRACT);
+        }
+        else {
+          glBlendEquation(GL_FUNC_ADD);
+        }
       }
       else {
         glDisable(GL_BLEND);