Added some comments. Fixed a crash when composite-blending a pastecanvas onto an...

[synfig.git] / synfig-core / trunk / src / synfig / layer_pastecanvas.cpp

diff --git a/synfig-core/trunk/src/synfig/layer_pastecanvas.cpp b/synfig-core/trunk/src/synfig/layer_pastecanvas.cpp
index edc3d0b..e632f26 100644 (file)
--- a/synfig-core/trunk/src/synfig/layer_pastecanvas.cpp
+++ b/synfig-core/trunk/src/synfig/layer_pastecanvas.cpp
@@ -343,14 +343,21 @@ Layer_PasteCanvas::accelerated_render(Context context,Surface *surface,int quali
        const Rect full_bounding_rect(canvas->get_context().get_full_bounding_rect());
        bool blend_using_straight = false; // use 'straight' just for the central blit
 
+       // we have rendered what's under us, if necessary
        if(context->empty())
        {
+               // if there's nothing under us, and we're blending 'onto', then we've finished
                if (Color::is_onto(blend_method)) return true;
-               if (blend_method==Color::BLEND_COMPOSITE) blend_method=Color::BLEND_STRAIGHT;
+
+               // there's nothing under us, so using straight blending is
+               // faster than and equivalent to using composite, but we don't
+               // want to blank the surrounding areas
+               if (blend_method==Color::BLEND_COMPOSITE) blend_using_straight = true;
        }
 
        if (!etl::intersect(context.get_full_bounding_rect(),full_bounding_rect+origin))
        {
+               // if there's no intersection between the context and our surface, and we're rendering 'onto', then we're done
                if (Color::is_onto(blend_method)) return true;
 
                /* 'straight' is faster than 'composite' and has the same