Creating a NSBitmapImageRep
Creating a NSBitmapImageRep
- Subject: Creating a NSBitmapImageRep
- From: Richard Schreyer <email@hidden>
- Date: Tue, 2 Jul 2002 23:24:04 -0700
I'm trying to create a NSBitmapImageRep with the following bit of code:
NSImage* image = [[NSImage alloc] initWithSize: size];
NSBitmapImageRep* bitmap = [[NSBitmapImageRep alloc]
initWithBitmapDataPlanes: nil
pixelsWide: size.width pixelsHigh: size.height
bitsPerSample: 8 samplesPerPixel: 4
hasAlpha: YES isPlanar: NO
colorSpaceName: NSCalibratedRGBColorSpace
bytesPerRow: 0 bitsPerPixel: 32];
unsigned char* imageBytes = [bitmap bitmapData];
int x, y;
[image addRepresentation: bitmap];
for (y = size.height-1; y >= 0; y--) {
for (x = size.width-1; x >= 0; x--) {
int pixIndex = 4 * (y*(int)size.width+x);
imageBytes[pixIndex] = 0; // red
imageBytes[pixIndex+1] = 0; // green
imageBytes[pixIndex+2] = 255; // blue
imageBytes[pixIndex+3] = 128; // alpha
}
}
Right now, I would just like to be able to create an image of a
transparent color. Once that works, I'm going to vary the alpha to
create a gradient. This is based on some code I found in the list
archives.
The problem is the image isn't getting created correctly. If I give it
an alpha of 255, everything works, and I get the desired color. If I
set the alpha to 254, and then display the image, it draws black lines
across the color in-line with the white portions of the pinstripes
behind it. If I set the alpha to 253 or lower, I end up with
transparent gray, it's transparency varying with the alpha.
Does anyone know what might be causing this?
Richard Schreyer
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