Tim, John, Bert, et al,
if you look at e.g. resizing code in the platforms/iOS code (in e.g. platforms/iOS//vm/OSX/sqSqueakOSXOpenGLView.m) the code accesses the display bits by looking up the display object installed via primitiveBeDisplay in the specialObjectsArray:
- (void) performDraw: (CGRect)rect { sqInt form = interpreterProxy->displayObject(); // Form
CGContextRef context = (CGContextRef)[[NSGraphicsContext currentContext] graphicsPort]; CGContextSaveGState(context);
int width = interpreterProxy->positive32BitValueOf(interpreterProxy->fetchPointerofObject(1, form)); int height = interpreterProxy->positive32BitValueOf(interpreterProxy->fetchPointerofObject(2, form)); sqInt formBits = interpreterProxy->fetchPointerofObject(0, form); // bits void* bits = (void*)interpreterProxy->firstIndexableField(formBits); // bits int bitSize = interpreterProxy->byteSizeOf(formBits); int bytePerRow = 4*width;
This is really unsafe. If it gets called while the VM is compacting, or doing a become, then potentially boom!
Storing the display in the specialObjectsArray stops it form being GCed, but it doesn't stop it moving around, and it doesn't stop a become altering the location of the objects surrounding it, etc.
Surely a better approach is to inform the VM of the location, depth and extent of the bits via some ioSetDisplayBits function and then cacheing those values somewhere in the VM. Thoughts?
P.S. John McIntosh tells me that you, Tim R, may have written such code in the past.
_,,,^..^,,,_ best, Eliot