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?