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August 9, 2024 20:38
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The Case of the Missing Pixel.
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| // | |
| // main.m | |
| // TheCaseOfTheMissingPixel | |
| // | |
| // Created by August Mueller on 3/13/24. | |
| // | |
| #import <AppKit/AppKit.h> | |
| /* | |
| FB13687028 | |
| clang -x objective-c -framework AppKit main.m; ./a.out | |
| Drawing an RGB image to a GenericGrayGamma2_2 CGBitmapContext inserts artifacts | |
| We're going to draw a single vertical line on an 8x8 RGB white bitmap context | |
| Then we're going to make a CGImageRef from that context, and then draw that to a | |
| 8x8 GenericGrayGamma2_2 bitmap context. | |
| What happens is an extra pixel is then thrown in the bottom right corner. | |
| Which is bad. | |
| */ | |
| void writeAndOpenImageAtPath(CGImageRef img, NSString *path); | |
| int main(int argc, const char * argv[]) { | |
| @autoreleasepool { | |
| CGColorSpaceRef cs = CGColorSpaceCreateWithName(kCGColorSpaceSRGB); | |
| CGBitmapInfo options = (CGBitmapInfo)kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big; | |
| size_t bitsPerComponent = 8; | |
| size_t width = 8; | |
| size_t height = 8; | |
| CGContextRef bitmapContext = CGBitmapContextCreate(nil, width, height, bitsPerComponent, 0, cs, options); | |
| assert(bitmapContext); | |
| CGContextSetBlendMode(bitmapContext, kCGBlendModeCopy); | |
| CGContextSetRGBFillColor(bitmapContext, 1, 1, 1, 1); | |
| CGContextFillRect(bitmapContext, CGRectMake(0, 0, width, height)); | |
| CGContextSetRGBFillColor(bitmapContext, 0, 0, 0, 1); | |
| CGContextFillRect(bitmapContext, CGRectMake(width-2, 0, 1, height)); | |
| CGImageRef rgbImage = CGBitmapContextCreateImage(bitmapContext); | |
| writeAndOpenImageAtPath(rgbImage, @"/tmp/rgbImage.png"); | |
| CGColorSpaceRef greycs = CGColorSpaceCreateWithName(kCGColorSpaceGenericGrayGamma2_2); | |
| CGContextRef greyBitmapContext = CGBitmapContextCreate(nil, width, height, bitsPerComponent, 0, greycs, (CGBitmapInfo)kCGImageAlphaPremultipliedLast); | |
| assert(greyBitmapContext); | |
| CGContextDrawImage(greyBitmapContext, CGRectMake(0, 0, width, height), rgbImage); | |
| CGImageRef grayImage = CGBitmapContextCreateImage(greyBitmapContext); | |
| writeAndOpenImageAtPath(grayImage, @"/tmp/grayImage.png"); | |
| printf("All done!\n"); | |
| } | |
| return 0; | |
| } | |
| void writeAndOpenImageAtPath(CGImageRef img, NSString *path) { | |
| system([[NSString stringWithFormat:@"rm %@", path] UTF8String]); | |
| NSURL *writeURL = [NSURL fileURLWithPath:path]; | |
| CGImageDestinationRef imageDestination = CGImageDestinationCreateWithURL((__bridge CFURLRef)writeURL, (__bridge CFStringRef)@"public.png", 1, NULL); | |
| CGImageDestinationAddImage(imageDestination, img, (__bridge CFDictionaryRef)@{}); | |
| assert(CGImageDestinationFinalize(imageDestination)); | |
| system([[NSString stringWithFormat:@"open %@", path] UTF8String]); | |
| } |
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