From 0c4ee9e13d489f40159596db9026e17e6404ea3c Mon Sep 17 00:00:00 2001
From: Sebastian Parborg <darkdefende@gmail.com>
Date: Mon, 5 Aug 2019 18:49:24 +0200
Subject: [PATCH] Fix T67665 "Affect Alpha" in Texture Paint mode doesn't work
 as expected

The "alpha lock" check was missing for the smear and soften brush.
Added checks to make sure that the alpha values are kept the same.

Reviewed By: Brecht

Differential Revision: http://developer.blender.org/D5416
---
 .../editors/sculpt_paint/paint_image_proj.c   | 52 +++++++++++--------
 1 file changed, 30 insertions(+), 22 deletions(-)

diff --git a/source/blender/editors/sculpt_paint/paint_image_proj.c b/source/blender/editors/sculpt_paint/paint_image_proj.c
index e5527e7210d..58283655270 100644
--- a/source/blender/editors/sculpt_paint/paint_image_proj.c
+++ b/source/blender/editors/sculpt_paint/paint_image_proj.c
@@ -5092,6 +5092,22 @@ static void image_paint_partial_redraw_expand(ImagePaintPartialRedraw *cell,
   cell->y2 = max_ii(cell->y2, (int)projPixel->y_px + 1);
 }
 
+static void copy_original_alpha_channel(ProjPixel *pixel, bool is_floatbuf)
+{
+  /* Use the original alpha channel data instead of the modified one */
+  if (is_floatbuf) {
+    /* slightly more involved case since floats are in premultiplied space we need
+     * to make sure alpha is consistent, see T44627 */
+    float rgb_straight[4];
+    premul_to_straight_v4_v4(rgb_straight, pixel->pixel.f_pt);
+    rgb_straight[3] = pixel->origColor.f_pt[3];
+    straight_to_premul_v4_v4(pixel->pixel.f_pt, rgb_straight);
+  }
+  else {
+    pixel->pixel.ch_pt[3] = pixel->origColor.ch_pt[3];
+  }
+}
+
 /* Run this for single and multi-threaded painting. */
 static void do_projectpaint_thread(TaskPool *__restrict UNUSED(pool),
                                    void *ph_v,
@@ -5263,17 +5279,7 @@ static void do_projectpaint_thread(TaskPool *__restrict UNUSED(pool),
           }
 
           if (lock_alpha) {
-            if (is_floatbuf) {
-              /* slightly more involved case since floats are in premultiplied space we need
-               * to make sure alpha is consistent, see T44627 */
-              float rgb_straight[4];
-              premul_to_straight_v4_v4(rgb_straight, projPixel->pixel.f_pt);
-              rgb_straight[3] = projPixel->origColor.f_pt[3];
-              straight_to_premul_v4_v4(projPixel->pixel.f_pt, rgb_straight);
-            }
-            else {
-              projPixel->pixel.ch_pt[3] = projPixel->origColor.ch_pt[3];
-            }
+            copy_original_alpha_channel(projPixel, is_floatbuf);
           }
 
           last_partial_redraw_cell = last_projIma->partRedrawRect + projPixel->bb_cell_index;
@@ -5478,17 +5484,7 @@ static void do_projectpaint_thread(TaskPool *__restrict UNUSED(pool),
               }
 
               if (lock_alpha) {
-                if (is_floatbuf) {
-                  /* slightly more involved case since floats are in premultiplied space we need
-                   * to make sure alpha is consistent, see T44627 */
-                  float rgb_straight[4];
-                  premul_to_straight_v4_v4(rgb_straight, projPixel->pixel.f_pt);
-                  rgb_straight[3] = projPixel->origColor.f_pt[3];
-                  straight_to_premul_v4_v4(projPixel->pixel.f_pt, rgb_straight);
-                }
-                else {
-                  projPixel->pixel.ch_pt[3] = projPixel->origColor.ch_pt[3];
-                }
+                copy_original_alpha_channel(projPixel, is_floatbuf);
               }
             }
 
@@ -5504,11 +5500,17 @@ static void do_projectpaint_thread(TaskPool *__restrict UNUSED(pool),
     for (node = smearPixels; node; node = node->next) { /* this wont run for a float image */
       projPixel = node->link;
       *projPixel->pixel.uint_pt = ((ProjPixelClone *)projPixel)->clonepx.uint;
+      if (lock_alpha) {
+        copy_original_alpha_channel(projPixel, false);
+      }
     }
 
     for (node = smearPixels_f; node; node = node->next) {
       projPixel = node->link;
       copy_v4_v4(projPixel->pixel.f_pt, ((ProjPixelClone *)projPixel)->clonepx.f);
+      if (lock_alpha) {
+        copy_original_alpha_channel(projPixel, true);
+      }
     }
 
     BLI_memarena_free(smearArena);
@@ -5518,11 +5520,17 @@ static void do_projectpaint_thread(TaskPool *__restrict UNUSED(pool),
     for (node = softenPixels; node; node = node->next) { /* this wont run for a float image */
       projPixel = node->link;
       *projPixel->pixel.uint_pt = projPixel->newColor.uint;
+      if (lock_alpha) {
+        copy_original_alpha_channel(projPixel, false);
+      }
     }
 
     for (node = softenPixels_f; node; node = node->next) {
       projPixel = node->link;
       copy_v4_v4(projPixel->pixel.f_pt, projPixel->newColor.f);
+      if (lock_alpha) {
+        copy_original_alpha_channel(projPixel, true);
+      }
     }
 
     BLI_memarena_free(softenArena);