option to lock alpha while projection painting.

(commit 27538 by Campbell from render25 branch)

release/scripts/ui/space_view3d_toolbar.py

@@ -592,6 +592,11 @@ class VIEW3D_PT_tools_brush(PaintPanel):
 
             col.prop(brush, "blend", text="Blend")
 
+            col = layout.column()
+            col.active = (brush.blend not in ('ERASE_ALPHA', 'ADD_ALPHA'))
+            col.prop(brush, "use_alpha")
+            
+
         # Weight Paint Mode #
 
         elif context.weight_paint_object and brush: