Eevee: Add support for alpha background in viewport

Viewport now displays alpha checkerboard pattern like Cycles does when
film alpha is set to "Transparent".

Some small workarounds were necessary for Depth of Field and correct TAA
support.

1 files changed, 7 insertions, 2 deletions

diff --git a/source/blender/draw/engines/eevee/shaders/effect_dof_frag.glsl b/source/blender/draw/engines/eevee/shaders/effect_dof_frag.glsl
index 8a10962c6ef..d8cec17af58 100644
--- a/source/blender/draw/engines/eevee/shaders/effect_dof_frag.glsl
+++ b/source/blender/draw/engines/eevee/shaders/effect_dof_frag.glsl
@@ -5,6 +5,7 @@ uniform sampler2D colorBuffer;
 uniform sampler2D depthBuffer;
 
 uniform vec2 dofParams;
+uniform bool unpremult;
 
 #define dof_mul dofParams.x  /* distance * aperturesize * invsensorsize */
 #define dof_bias dofParams.y /* aperturesize * invsensorsize */
@@ -241,8 +242,12 @@ void main(void)
   fragColor = (far_col + near_col + focus_col) * inv_weight_sum;
 
 #  ifdef USE_ALPHA_DOF
-  /* Unpremult */
-  fragColor.rgb /= (fragColor.a > 0.0) ? fragColor.a : 1.0;
+  /* Sigh... viewport expect premult output but
+   * the final render output needs to be with
+   * associated alpha. */
+  if (unpremult) {
+    fragColor.rgb /= (fragColor.a > 0.0) ? fragColor.a : 1.0;
+  }
 #  endif
 }