UIGraphicsBeginImageContext vs CGBitmapContextCreate

Je suis en train de changer de couleur d'une image dans un thread d'arrière-plan.

Apple doc a dit UIGraphicsBeginImageContext ne peut être appelé à partir de thread principal, et je suis en train d'utiliser CGBitmapContextCreate:

contexte = CGBitmapContextCreate
(bitmapData,
pixelsWide,
pixelsHigh,
8, //bits par composante

                             bitmapBytesPerRow,
                             colorSpace,
                             kCGImageAlphaPremultipliedFirst);

J'ai deux versions de "changeColor" premier à utiliser UIGraphisBeginImageContext, le second, à l'aide de CGBitmapContextCreate.

Le premier correctement les changements de couleur, mais le second ne l'est pas.

Pourquoi est-ce?

- (UIImage*) changeColor: (UIColor*) aColor
{
    if(aColor == nil)
        return self;

    UIGraphicsBeginImageContext(self.size);

    CGRect bounds;
    bounds.origin = CGPointMake(0,0);
    bounds.size = self.size;
    [aColor set];

    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextTranslateCTM(context, 0, self.size.height);
    CGContextScaleCTM(context, 1.0, -1.0);

    CGContextClipToMask(context, bounds, [self CGImage]);
    CGContextFillRect(context, bounds);

    UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return img;
}

---

- (UIImage*) changeColor: (UIColor*) aColor
{
    if(aColor == nil)
        return self;

    CGContextRef context = CreateARGBBitmapContext(self.size);

    CGRect bounds;
    bounds.origin = CGPointMake(0,0);
    bounds.size = self.size;

    CGColorRef colorRef = aColor.CGColor;
    const CGFloat *components = CGColorGetComponents(colorRef);
    float red = components[0];
    float green = components[1];
    float blue = components[2];

    CGContextSetRGBFillColor(context, red, green, blue, 1);


    CGContextClipToMask(context, bounds, [self CGImage]);
    CGContextFillRect(context, bounds);

    CGImageRef imageRef = CGBitmapContextCreateImage(context);
    UIImage* img = [UIImage imageWithCGImage: imageRef];
    unsigned char* data = (unsigned char*)CGBitmapContextGetData (context);  
    CGContextRelease(context);
    free(data);

    return img;
}

---

CGContextRef CreateARGBBitmapContext(CGSize size)
{
CGContextRef    context = NULL;
CGColorSpaceRef colorSpace;
void *          bitmapData;
int             bitmapByteCount;
int             bitmapBytesPerRow;
//Get image width, height. We'll use the entire image.                                                                                                                                                                                 
size_t pixelsWide = size.width;
size_t pixelsHigh = size.height;
//Declare the number of bytes per row. Each pixel in the bitmap in this                                                                                                                                                                
//example is represented by 4 bytes; 8 bits each of red, green, blue, and                                                                                                                                                              
//alpha.                                                                                                                                                                                                                               
bitmapBytesPerRow   = (pixelsWide * 4);
bitmapByteCount     = (bitmapBytesPerRow * pixelsHigh);
//Use the generic RGB color space.                                                                                                                                                                                                     
colorSpace = CGColorSpaceCreateDeviceRGB();
if (colorSpace == NULL)
{
fprintf(stderr, "Error allocating color space\n");
return NULL;
}
//Allocate memory for image data. This is the destination in memory                                                                                                                                                                    
//where any drawing to the bitmap context will be rendered.                                                                                                                                                                            
bitmapData = malloc( bitmapByteCount );
if (bitmapData == NULL)
{
fprintf (stderr, "Memory not allocated!");
CGColorSpaceRelease( colorSpace );
return NULL;
}
//Create the bitmap context. We want pre-multiplied ARGB, 8-bits                                                                                                                                                                       
//per component. Regardless of what the source image format is                                                                                                                                                                         
//(CMYK, Grayscale, and so on) it will be converted over to the format                                                                                                                                                                 
//specified here by CGBitmapContextCreate.                                                                                                                                                                                             
context = CGBitmapContextCreate (bitmapData,
pixelsWide,
pixelsHigh,
8,      //bits per component                                                                                                                                                                          
bitmapBytesPerRow,
colorSpace,
kCGImageAlphaPremultipliedFirst);
if (context == NULL)
{
free (bitmapData);
fprintf (stderr, "Context not created!");
}
//Make sure and release colorspace before returning                                                                                                                                                                                    
CGColorSpaceRelease( colorSpace );
return context;
}

OriginalL'auteur eugene | 2011-01-13