Fix T80603 Workbench: Inverted alpha when rendering

This was caused by a left over DRWPass->state modification
that made the subsequent samples redraw without Blending enabled.
This led to incorrect blending.

The fix is to use the new API for pass instancing.

3 files changed, 20 insertions, 12 deletions

diff --git a/source/blender/draw/engines/workbench/workbench_private.h b/source/blender/draw/engines/workbench/workbench_private.h
index 8983826f16f..d377f09ac73 100644
--- a/source/blender/draw/engines/workbench/workbench_private.h
+++ b/source/blender/draw/engines/workbench/workbench_private.h
@@ -131,6 +131,9 @@ typedef struct WORKBENCH_PassList {
   struct DRWPass *transp_accum_ps;
   struct DRWPass *transp_accum_infront_ps;
 
+  struct DRWPass *transp_depth_infront_ps;
+  struct DRWPass *transp_depth_ps;
+
   struct DRWPass *shadow_ps[2];
 
   struct DRWPass *merge_infront_ps;
diff --git a/source/blender/draw/engines/workbench/workbench_transparent.c b/source/blender/draw/engines/workbench/workbench_transparent.c
index 1c8575ddc12..94fcd8b5a9d 100644
--- a/source/blender/draw/engines/workbench/workbench_transparent.c
+++ b/source/blender/draw/engines/workbench/workbench_transparent.c
@@ -91,16 +91,18 @@ void workbench_transparent_cache_init(WORKBENCH_Data *vedata)
   {
     int transp = 1;
     for (int infront = 0; infront < 2; infront++) {
-      DRWState state = DRW_STATE_WRITE_COLOR | DRW_STATE_DEPTH_LESS_EQUAL | DRW_STATE_BLEND_OIT;
+      DRWState state = DRW_STATE_WRITE_COLOR | DRW_STATE_DEPTH_LESS_EQUAL | DRW_STATE_BLEND_OIT |
+                       wpd->cull_state | wpd->clip_state;
 
       DRWPass *pass;
       if (infront) {
-        DRW_PASS_CREATE(psl->transp_accum_infront_ps, state | wpd->cull_state | wpd->clip_state);
-        pass = psl->transp_accum_infront_ps;
+        psl->transp_accum_infront_ps = pass = DRW_pass_create("transp_accum_infront", state);
+        DRW_PASS_INSTANCE_CREATE(
+            psl->transp_depth_infront_ps, pass, state | DRW_STATE_WRITE_DEPTH);
       }
       else {
-        DRW_PASS_CREATE(psl->transp_accum_ps, state | wpd->cull_state | wpd->clip_state);
-        pass = psl->transp_accum_ps;
+        psl->transp_accum_ps = pass = DRW_pass_create("transp_accum", state);
+        DRW_PASS_INSTANCE_CREATE(psl->transp_depth_ps, pass, state | DRW_STATE_WRITE_DEPTH);
       }
 
       for (eWORKBENCH_DataType data = 0; data < WORKBENCH_DATATYPE_MAX; data++) {
@@ -159,20 +161,17 @@ void workbench_transparent_draw_depth_pass(WORKBENCH_Data *data)
   const bool do_transparent_depth_pass = psl->outline_ps || wpd->dof_enabled || do_xray_depth_pass;
 
   if (do_transparent_depth_pass) {
-    DRWState state = DRW_STATE_WRITE_COLOR | DRW_STATE_WRITE_DEPTH | DRW_STATE_DEPTH_LESS_EQUAL;
 
-    if (!DRW_pass_is_empty(psl->transp_accum_ps)) {
+    if (!DRW_pass_is_empty(psl->transp_depth_ps)) {
       GPU_framebuffer_bind(fbl->opaque_fb);
       /* TODO(fclem) Disable writing to first two buffers. Unnecessary waste of bandwidth. */
-      DRW_pass_state_set(psl->transp_accum_ps, state | wpd->cull_state | wpd->clip_state);
-      DRW_draw_pass(psl->transp_accum_ps);
+      DRW_draw_pass(psl->transp_depth_ps);
     }
 
-    if (!DRW_pass_is_empty(psl->transp_accum_infront_ps)) {
+    if (!DRW_pass_is_empty(psl->transp_depth_infront_ps)) {
       GPU_framebuffer_bind(fbl->opaque_infront_fb);
       /* TODO(fclem) Disable writing to first two buffers. Unnecessary waste of bandwidth. */
-      DRW_pass_state_set(psl->transp_accum_infront_ps, state | wpd->cull_state | wpd->clip_state);
-      DRW_draw_pass(psl->transp_accum_infront_ps);
+      DRW_draw_pass(psl->transp_depth_infront_ps);
     }
   }
 }
diff --git a/source/blender/draw/intern/draw_manager_data.c b/source/blender/draw/intern/draw_manager_data.c
index 81842f5d2ec..ca5d5170262 100644
--- a/source/blender/draw/intern/draw_manager_data.c
+++ b/source/blender/draw/intern/draw_manager_data.c
@@ -1962,6 +1962,8 @@ DRWPass *DRW_pass_create(const char *name, DRWState state)
   return pass;
 }
 
+/* Create an instance of the original pass that will execute the same drawcalls but with its own
+ * DRWState. */
 DRWPass *DRW_pass_create_instance(const char *name, DRWPass *original, DRWState state)
 {
   DRWPass *pass = DRW_pass_create(name, state);
@@ -1980,6 +1982,10 @@ void DRW_pass_link(DRWPass *first, DRWPass *second)
 
 bool DRW_pass_is_empty(DRWPass *pass)
 {
+  if (pass->original) {
+    return DRW_pass_is_empty(pass->original);
+  }
+
   LISTBASE_FOREACH (DRWShadingGroup *, shgroup, &pass->shgroups) {
     if (!DRW_shgroup_is_empty(shgroup)) {
       return false;