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, 42 insertions, 0 deletions

diff --git a/source/blender/draw/engines/eevee/eevee_effects.c b/source/blender/draw/engines/eevee/eevee_effects.c
index 79b4cb231a8..a4d3bc5b276 100644
--- a/source/blender/draw/engines/eevee/eevee_effects.c
+++ b/source/blender/draw/engines/eevee/eevee_effects.c
@@ -168,6 +168,11 @@ void EEVEE_effects_init(EEVEE_ViewLayerData *sldata,
     effects->enabled_effects |= EFFECT_NORMAL_BUFFER;
   }
 
+  /* Alpha checker if background is not drawn in viewport. */
+  if (!DRW_state_is_image_render() && !DRW_state_draw_background()) {
+    effects->enabled_effects |= EFFECT_ALPHA_CHECKER;
+  }
+
   /**
    * Ping Pong buffer
    */
@@ -361,6 +366,23 @@ void EEVEE_effects_cache_init(EEVEE_ViewLayerData *sldata, EEVEE_Data *vedata)
     DRW_shgroup_uniform_mat4(grp, "pastPersmat", effects->velocity_past_persmat);
     DRW_shgroup_call_add(grp, quad, NULL);
   }
+
+  if ((effects->enabled_effects & EFFECT_ALPHA_CHECKER) != 0) {
+    psl->alpha_checker = DRW_pass_create("Alpha Checker",
+                                         DRW_STATE_WRITE_COLOR | DRW_STATE_BLEND_PREMUL_UNDER);
+
+    GPUShader *checker_sh = GPU_shader_get_builtin_shader(GPU_SHADER_2D_CHECKER);
+
+    DRWShadingGroup *grp = DRW_shgroup_create(checker_sh, psl->alpha_checker);
+
+    copy_v4_fl4(effects->color_checker_dark, 0.15f, 0.15f, 0.15f, 1.0f);
+    copy_v4_fl4(effects->color_checker_light, 0.2f, 0.2f, 0.2f, 1.0f);
+
+    DRW_shgroup_uniform_vec4(grp, "color1", effects->color_checker_dark, 1);
+    DRW_shgroup_uniform_vec4(grp, "color2", effects->color_checker_light, 1);
+    DRW_shgroup_uniform_int_copy(grp, "size", 8);
+    DRW_shgroup_call_add(grp, quad, NULL);
+  }
 }
 
 #if 0 /* Not required for now */
@@ -491,6 +513,26 @@ void EEVEE_downsample_cube_buffer(EEVEE_Data *vedata, GPUTexture *texture_src, i
   DRW_stats_group_end();
 }
 
+void EEVEE_draw_alpha_checker(EEVEE_Data *vedata)
+{
+  EEVEE_PassList *psl = vedata->psl;
+  EEVEE_StorageList *stl = vedata->stl;
+  EEVEE_EffectsInfo *effects = stl->effects;
+
+  if ((effects->enabled_effects & EFFECT_ALPHA_CHECKER) != 0) {
+    float mat[4][4];
+    unit_m4(mat);
+
+    /* Fragile, rely on the fact that GPU_SHADER_2D_CHECKER
+     * only use the persmat. */
+    DRW_viewport_matrix_override_set(mat, DRW_MAT_PERS);
+
+    DRW_draw_pass(psl->alpha_checker);
+
+    DRW_viewport_matrix_override_unset(DRW_MAT_PERS);
+  }
+}
+
 void EEVEE_draw_effects(EEVEE_ViewLayerData *UNUSED(sldata), EEVEE_Data *vedata)
 {
   EEVEE_PassList *psl = vedata->psl;