An app our company is developing is showing odd behavior and crashes
under 10.6, but not under 10.5.
I've done some digging and figured out that a major contributor to the
crash is the following routine:
(I've changed it slightly to get rid of unimportant details and make
it more readable:
-(void) eraseImageRep: (NSBitmapImageRep*) theImageRep;
{
NSSize imageSize = [theImageRep size];
unsigned long dataSize = [theImageRep bytesPerRow] * imageSize.height;
void* theData = [theImageRep bitmapData];
bzero(theData, dataSize);
}
Our app deals with indexed color images. We create a custom NSImage
that contains an NSBitmapImageRep set up specifically to be non-
planar, RGBA, 8 bits/channel. We then have code that converts back and
forth between our indexed color document data and the byte format of
our custom image rep.
The above call is used when we don't want to set context to the
offscreen image and draw into it, but want to do a fast block erase.
After making this call in 10.6, the target NSImage stops drawing
correctly, and and some future time a call to NSRectFill for this
image crashes.
All the code to manipulate the image data of the image rep works
perfectly, and if I replace the routine above with code that erases
the image with code like this:
[NSGraphicsContext setCurrentContext: offscreenImageContext];
[[NSColor clearColor] setFill];
NSRectFill(aRect);
It works perfectly.
I can certainly refactor our code to always clear our offscreen image
(image rep) by setting context and doing Cocoa calls, but I want to
understand why the routine above makes our app crash under 10.5 and
not 10.6.
I thought we might be getting into trouble because we write to ALL the
bytes in the image rep's bitmapData including padding bytes at the end
of each row. I rewrote the routine above to only write to actual pixel
bytes for each row and leave the padding bytes alone, but the app
still crashes in 10.6.
That changed code looks like this: (again edited to simplify)
-(void) eraseImageRep: (NSBitmapImageRep*) theImageRep;
{
NSSize imageSize = [theImageRep size];
void* dataPtr;
NSUInteger index;
NSUInteger bytesPerRow = [theImageRep bytesPerRow];
unsigned long rowSize = size.width * 4;
void* theData = [theImageRep bitmapData];
dataPtr = theData;
for (index = 0; index < imageSize.height; index++)
{
memset(dataPtr, 0, rowSize);
dataPtr += bytesPerRow;
}
}
Interestingly, our app calls the above routine in several places, and
it is only one of the calls that causes us problems. I have not been
able to figure out what it is about this particular use of the erase
routine that causes the problem.
The code that creates our NSImage and image rep looks like this:
tempDisplayImageRecord.theImageRep =
[[[NSBitmapImageRep alloc]
initWithBitmapDataPlanes: NULL
pixelsWide: size.width
pixelsHigh: size.height
bitsPerSample: 8 //1 byte for R, G,
B, and A
samplesPerPixel: 4 //Specify RGBA
hasAlpha: YES //Ask for an alpha
channel
isPlanar: NO //RGBA data is mixed
together for each pixel.
//If planar, there are separate buffers for r, g, b, and a values
colorSpaceName: NSDeviceRGBColorSpace //Use device color. This
avoids color profile matching
bytesPerRow: 0 //Let the system
decide how many bytes/row.
//This way it can add padding so rows begin on memory boundaries
bitsPerPixel: 0] autorelease]; //Let the system calculate this
(but it's 32 bits/pixel)
if (!tempDisplayImageRecord.theImageRep) return -1; //>>>>>>ERROR!
<<<<<< Report to user!!!!
[(tempDisplayImageRecord.theImage = [[TestImage allocWithZone:[self
zone]] initWithSize:size])
addRepresentation:tempDisplayImageRecord.theImageRep];
if (!tempDisplayImageRecord.theImage) return -1; //>>>>>>ERROR!
<<<<<< Report to user!!!!
tempDisplayImageRecord.theContext = [NSGraphicsContext
graphicsContextWithBitmapImageRep: tempDisplayImageRecord.theImageRep];
if (!tempDisplayImageRecord.theContext) return -1; //>>>>>>ERROR!
<<<<<< Report to user!!!!
Does anybody out there have any idea what's going on, and why we are
seeing different behavior from 10.5 and 10.6? This has me stumped.
Regards,
Duncan Champney
WareTo
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