Posted by Henrik Nergaard on Jul 07, 2016; 9:06pm
URL: https://forum.world.st/VM-Crash-tp4905304p4905497.html

That dump looks familiar..

----
| surface morph formCanvas |

surface := AthensCairoSurface extent: 100@100.

surface drawDuring: [ :athCan |
 athCan
  setShape: (0 asPoint corner: 100 asPoint);
  setPaint: Color orange;
  draw.
].

morph := surface asForm asMorph.

"comment out these two lines, and it draws fine"
surface := nil.
Smalltalk garbageCollect.

formCanvas := FormCanvas extent: 100 asPoint.

morph fullDrawOn: formCanvas .
morph debugDrawError
---

AthensCairoCanvas >>#asForm do not actually return a "valid" form, but an "external" that holds an index to a Surface, instead of the actual bits, and somewhere during drawing there is a machinery which finds the surface based on this index, and copy those bits. That way #asForm do not need to allocate any bits itself, but at the expense that the lifetime of the surface must be longer then the form.

I guess you can try to use AthensCairoSurface>>#displayOnMorphicCanvas:at: in TRMorph>>#drawOn: instead of how it is done now, this should assure that the Surface is still alive when drawing.

I also think that changing the extent of the surface should be moved from #layoutChanged to the start of #drawOn:. The layoutChanged/ morph extent change could happen more than once in between draw calls,  which could cause unnecessary recreations of the surface. It should also ensure that the surface cannot be recreated while inside #drawOn:.

Hope this helps.

Best regards,
Henrik