From 0bdf4e2f2d1cd9538ac0196db8c302c21d49c860 Mon Sep 17 00:00:00 2001
From: Jeroen Bakker <jbakker>
Date: Sat, 5 Oct 2019 17:18:41 +0200
Subject: Show Background Image Beneath Transparent Objects (Cycles only)

Camera background images were not shown under transparent objects.
This patch performs an alpha under for background images for cycles.

In order to see the difference the Film transparency needs to be turned on.

Note that workbench and EEVEE still needs to be adapted as they don't
write store alpha value in the viewport.

Side note. This implementation is already an improvement of the current behavior, what users are requesting. (Show background images underneath cycles viewport rendering.) It is clear that this patch still needs to be extended to workbench and eevee. For now that should be marked as a known limitation.

Reviewed By: fclem

Differential Revision: https://developer.blender.org/D5437
---
 source/blender/draw/intern/draw_view.c | 38 ++++++++--------------------------
 1 file changed, 9 insertions(+), 29 deletions(-)

(limited to 'source/blender/draw/intern/draw_view.c')

diff --git a/source/blender/draw/intern/draw_view.c b/source/blender/draw/intern/draw_view.c
index 7aa2e007f79..58643eb12a8 100644
--- a/source/blender/draw/intern/draw_view.c
+++ b/source/blender/draw/intern/draw_view.c
@@ -41,11 +41,9 @@
 #include "BKE_object.h"
 #include "BKE_paint.h"
 
-#include "DRW_render.h"
-
 #include "view3d_intern.h"
 
-#include "draw_view.h"
+#include "draw_manager.h"
 
 /* ******************** region info ***************** */
 
@@ -60,18 +58,17 @@ void DRW_draw_region_info(void)
 }
 
 /* ************************* Background ************************** */
+void DRW_clear_background()
+{
+  GPU_clear_color(0.0, 0.0, 0.0, 0.0);
+  GPU_clear(GPU_COLOR_BIT | GPU_DEPTH_BIT | GPU_STENCIL_BIT);
+}
 
 void DRW_draw_background(bool do_alpha_checker)
 {
-  /* Just to make sure */
-  glDepthMask(GL_TRUE);
-  glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
-  glStencilMask(0xFF);
-
+  drw_state_set(DRW_STATE_WRITE_COLOR | DRW_STATE_BLEND_ALPHA_UNDER_PREMUL);
   if (do_alpha_checker) {
     /* Transparent render, do alpha checker. */
-    GPU_depth_test(false);
-
     GPU_matrix_push();
     GPU_matrix_identity_set();
     GPU_matrix_identity_projection_set();
@@ -79,18 +76,11 @@ void DRW_draw_background(bool do_alpha_checker)
     imm_draw_box_checker_2d(-1.0f, -1.0f, 1.0f, 1.0f);
 
     GPU_matrix_pop();
-
-    GPU_clear(GPU_DEPTH_BIT | GPU_STENCIL_BIT);
-
-    GPU_depth_test(true);
   }
-  else if (UI_GetThemeValue(TH_SHOW_BACK_GRAD)) {
+  else {
     float m[4][4];
     unit_m4(m);
 
-    /* Gradient background Color */
-    GPU_depth_test(false);
-
     GPUVertFormat *format = immVertexFormat();
     uint pos = GPU_vertformat_attr_add(format, "pos", GPU_COMP_F32, 2, GPU_FETCH_FLOAT);
     uint color = GPU_vertformat_attr_add(
@@ -103,8 +93,8 @@ void DRW_draw_background(bool do_alpha_checker)
 
     immBindBuiltinProgram(GPU_SHADER_2D_SMOOTH_COLOR_DITHER);
 
-    UI_GetThemeColor3ubv(TH_BACK_GRAD, col_lo);
     UI_GetThemeColor3ubv(TH_BACK, col_hi);
+    UI_GetThemeColor3ubv(UI_GetThemeValue(TH_SHOW_BACK_GRAD) ? TH_BACK_GRAD : TH_BACK, col_lo);
 
     immBegin(GPU_PRIM_TRI_FAN, 4);
     immAttr3ubv(color, col_lo);
@@ -119,16 +109,6 @@ void DRW_draw_background(bool do_alpha_checker)
     immUnbindProgram();
 
     GPU_matrix_pop();
-
-    GPU_clear(GPU_DEPTH_BIT | GPU_STENCIL_BIT);
-
-    GPU_depth_test(true);
-  }
-  else {
-    /* Solid background Color */
-    UI_ThemeClearColorAlpha(TH_BACK, 1.0f);
-
-    GPU_clear(GPU_COLOR_BIT | GPU_DEPTH_BIT | GPU_STENCIL_BIT);
   }
 }
 
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