Mask Editor: Add mask blending factor for combined overlay

This adds a new parameter to the "Combined" overlay mode of the mask editor.
The "blending factor" allows users to blend the mask exterior with the original
footage to visualise the content of the mask in a more intuitive way.  The
"Alpha" overlay is unaffected by this change.

The existing "Combined" overlay is used like before (covering everything
outside the mask in black), but can be blended with the slider in the mask
overlay to look at the exterior.

This is part of an effort to make mask editing more intuitive & easy to use:
https://developer.blender.org/T93097

Differential Revision: https://developer.blender.org/D13284

1 files changed, 16 insertions, 5 deletions

diff --git a/source/blender/editors/mask/mask_draw.c b/source/blender/editors/mask/mask_draw.c
index aab4007854f..1bd224fe763 100644
--- a/source/blender/editors/mask/mask_draw.c
+++ b/source/blender/editors/mask/mask_draw.c
@@ -663,6 +663,7 @@ void ED_mask_draw_region(
     const char draw_flag,
     const char draw_type,
     const eMaskOverlayMode overlay_mode,
+    const float blend_factor,
     /* convert directly into aspect corrected vars */
     const int width_i,
     const int height_i,
@@ -721,12 +722,14 @@ void ED_mask_draw_region(
   }
 
   if (draw_flag & MASK_DRAWFLAG_OVERLAY) {
-    const float red[4] = {1.0f, 0.0f, 0.0f, 0.0f};
+    float buf_col[4] = {1.0f, 0.0f, 0.0f, 0.0f};
     float *buffer = mask_rasterize(mask_eval, width, height);
 
     if (overlay_mode != MASK_OVERLAY_ALPHACHANNEL) {
       /* More blending types could be supported in the future. */
-      GPU_blend(GPU_BLEND_MULTIPLY);
+      GPU_blend(GPU_BLEND_ALPHA);
+      buf_col[0] = -1.0f;
+      buf_col[3] = 1.0f;
     }
 
     GPU_matrix_push();
@@ -737,10 +740,18 @@ void ED_mask_draw_region(
     }
     IMMDrawPixelsTexState state = immDrawPixelsTexSetup(GPU_SHADER_2D_IMAGE_SHUFFLE_COLOR);
     GPU_shader_uniform_vector(
-        state.shader, GPU_shader_get_uniform(state.shader, "shuffle"), 4, 1, red);
-    immDrawPixelsTexTiled(
-        &state, 0.0f, 0.0f, width, height, GPU_R16F, false, buffer, 1.0f, 1.0f, NULL);
+        state.shader, GPU_shader_get_uniform(state.shader, "shuffle"), 4, 1, buf_col);
 
+    if (overlay_mode == MASK_OVERLAY_COMBINED) {
+      const float blend_col[4] = {0.0f, 0.0f, 0.0f, blend_factor};
+
+      immDrawPixelsTexTiled(
+          &state, 0.0f, 0.0f, width, height, GPU_R16F, false, buffer, 1.0f, 1.0f, blend_col);
+    }
+    else {
+      immDrawPixelsTexTiled(
+          &state, 0.0f, 0.0f, width, height, GPU_R16F, false, buffer, 1.0f, 1.0f, NULL);
+    }
     GPU_matrix_pop();
 
     if (overlay_mode != MASK_OVERLAY_ALPHACHANNEL) {