Quick test of CGBitmapContextCreate's CGImageAlphaInfo modes, for http://stackoverflow.com/questions/19674740/opengl-es2-premultiplied-vs-straight-alpha-blending/23256585#comments-23256585

TestCGBitmapContextCreate_iOSTests.m

#import "TestCGBitmapContextCreate_iOSTests.h"



@implementation TestCGBitmapContextCreate_iOSTests


- (void)setUp
{
    [super setUp];
    
    _colorSpace = CGColorSpaceCreateDeviceRGB();
}

- (void)tearDown
{
    CGColorSpaceRelease(_colorSpace);
    
    [super tearDown];
}

static const size_t kWidth = 512, kHeight = 512;
static const size_t kBitsPerComponent = 8;
static const size_t kComponentsPerPixel = 4;

- (void)subTestCGImageAlphaMode:(CGImageAlphaInfo)alphaMode expectSuccess:(BOOL)shouldBeSuccessful
{
	size_t bytesPerRow = kBitsPerComponent * kComponentsPerPixel * kWidth / 8;
	CGContextRef cgContext = CGBitmapContextCreate(
		NULL, // data
		kWidth, kHeight,
		kBitsPerComponent, bytesPerRow,
		_colorSpace,
		alphaMode
	);
	
	NSLog(@"\t" @"cgContext with CGImageAlphaInfo %d: %@", alphaMode, cgContext);
	if (shouldBeSuccessful)
		STAssertNotNil((__bridge id)cgContext, @"Unable to create context with CGImageAlphaInfo %d", alphaMode);
	else
		STAssertNil((__bridge id)cgContext, @"Unexpectedly created context with CGImageAlphaInfo %d", alphaMode);
	
	CGContextRelease(cgContext);
}
- (void)subTestCGImageAlphaMode:(CGImageAlphaInfo)alphaMode {
	[self subTestCGImageAlphaMode:alphaMode expectSuccess:YES];
}

- (void)testAllCGImageAlphaModes
{
	[self subTestCGImageAlphaMode:kCGImageAlphaNone];
	[self subTestCGImageAlphaMode:kCGImageAlphaPremultipliedLast];
	[self subTestCGImageAlphaMode:kCGImageAlphaPremultipliedFirst];
	[self subTestCGImageAlphaMode:kCGImageAlphaLast];
	[self subTestCGImageAlphaMode:kCGImageAlphaFirst];
	[self subTestCGImageAlphaMode:kCGImageAlphaNoneSkipLast];
	[self subTestCGImageAlphaMode:kCGImageAlphaNoneSkipFirst];
	[self subTestCGImageAlphaMode:kCGImageAlphaOnly];
}

- (void)testInvalidCGImageAlphaModes
{
	unsigned int highestCGImageAlphaMode = 0;
	highestCGImageAlphaMode = (kCGImageAlphaNone > highestCGImageAlphaMode) ? kCGImageAlphaNone : highestCGImageAlphaMode;
	highestCGImageAlphaMode = (kCGImageAlphaPremultipliedLast > highestCGImageAlphaMode) ? kCGImageAlphaPremultipliedLast : highestCGImageAlphaMode;
	highestCGImageAlphaMode = (kCGImageAlphaPremultipliedFirst > highestCGImageAlphaMode) ? kCGImageAlphaPremultipliedFirst : highestCGImageAlphaMode;
	highestCGImageAlphaMode = (kCGImageAlphaLast > highestCGImageAlphaMode) ? kCGImageAlphaLast : highestCGImageAlphaMode;
	highestCGImageAlphaMode = (kCGImageAlphaFirst > highestCGImageAlphaMode) ? kCGImageAlphaFirst : highestCGImageAlphaMode;
	highestCGImageAlphaMode = (kCGImageAlphaNoneSkipLast > highestCGImageAlphaMode) ? kCGImageAlphaNoneSkipLast : highestCGImageAlphaMode;
	highestCGImageAlphaMode = (kCGImageAlphaNoneSkipFirst > highestCGImageAlphaMode) ? kCGImageAlphaNoneSkipFirst : highestCGImageAlphaMode;
	highestCGImageAlphaMode = (kCGImageAlphaOnly > highestCGImageAlphaMode) ? kCGImageAlphaOnly : highestCGImageAlphaMode;
	
	for (int invalidModeI = (highestCGImageAlphaMode + 1); invalidModeI <= kCGBitmapAlphaInfoMask; ++invalidModeI) {
		[self subTestCGImageAlphaMode:invalidModeI expectSuccess:NO];
	}
}

@end