Fill a part of an image

Question

Hi everybody,
I'm a new french iPhone developer
I'm searching since few days how to fill a part of an image for my iPhone application.
I think that I must use the CGContext functions but I found not anything... I understood how make few operations on my UiImageView. But I draw an eclipse, a rect... but not a "zone"?
I've an example for explain my idea :
http://uploads.bodin-hullin.net/41be0528efcdf5170b0acd18ebe210f6.png
The square is the UIImage.
When I touch the #1 circle, this circle is filled with my color.
When I touch the #2 circle, the same, with another color why not.
Can you help me ?
Thanks for all
Message was edited by: jacquesbh

Answer 1

Hi Jacques-
again, this isn't the only approach, but here's something that could work.
#1) Separate the individual shapes into individual images, white with black background. To make things easier, save in a format that does not have an alpha channel. (keeping each shape in its relative position within your bounds). I'd suggest trying a 50% gray for the lines and adjust later if needed. Just do this to a few images to try out the code.
#2) In the code fragment I posted before, set "image" to one of those saved files. This should give you a colorized image, keeping the black background.
#3) If you wish to remove the background, it's much more complex, but try the following:
add a method like so:
- (UIImage *)maskImg: (NSString *) filename
CGColorRef fillColor = [UIColor yellowColor].CGColor; // Yellow for test
CGImageRef baseImage = [[UIImage imageNamed:filename] CGImage];
CGImageRef maskImage;
CGContextRef context;
CGColorSpaceRef colorSpace;
colorSpace = CGColorSpaceCreateDeviceRGB();
// create a bitmap graphics context the size of the image
context = CGBitmapContextCreate (NULL, self.bounds.size.width, self.bounds.size.height, 8, 0, colorSpace, kCGImageAlphaPremultipliedLast);
// free the rgb colorspace
CGColorSpaceRelease(colorSpace);
if (context==NULL)
return NULL; // avoid errors
CGContextDrawImage(context, self.bounds, baseImage);
CGContextSetBlendMode (context, kCGBlendModeMultiply);
CGContextSetFillColorWithColor(context, fillColor);
CGContextFillRect(context, self.bounds);
CGContextSetBlendMode (context, kCGBlendModeNormal);
baseImage = CGBitmapContextCreateImage(context);
//baseImage = [self remAlpha:baseImage]; //should work without this line and method if images don't have an alpha channel
const float myMaskingColors[6] = { 0, 0, 0, 0, 0, 0 }; // can be a range, in this case we only want to mask out black
maskImage = CGImageCreateWithMaskingColors (baseImage, myMaskingColors);
CGContextRelease(context);
UIImage *img = [UIImage imageWithCGImage:maskImage];
//CGImageRelease(bitmap);
CGImageRelease(maskImage);
CGImageRelease(baseImage);
// return the image
return img;
and then in the drawRect, you'd just do something like:
UIImage *img = [self maskImg:@"test.jpg"]; //for testing
[img drawInRect:rect];
for your end purposes, you may want to add the color as another parameter of the maskImg method.... this stuff can be very tricky sometimes to setup... I know I experimented for hours getting no image, or a solid color block, etc... before perfecting this code.... hope this works for you..
I don't think you need to call this method if your images don't have an alpha channel, but I'm including it just in case:
-(CGImageRef)remAlpha:(CGImageRef)ref
//CGImageRef ref=img.CGImage;
int mWidth=CGImageGetWidth(ref);
int mHeight=CGImageGetHeight(ref);
int count=mWidthmHeight4;
void *bufferdata=malloc(count);
CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;
CGContextRef cgctx = CGBitmapContextCreate (bufferdata,mWidth,mHeight, 8,mWidth*4, colorSpaceRef, kCGImageAlphaPremultipliedLast);
CGRect rect = {0,0,mWidth,mHeight};
CGContextDrawImage(cgctx, rect, ref);
bufferdata = CGBitmapContextGetData (cgctx);
CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, bufferdata, mWidthmHeight4, NULL);
CGImageRef savedimageref = CGImageCreate(mWidth,mHeight, 8, 32, mWidth*4, colorSpaceRef, bitmapInfo,provider , NULL, NO, renderingIntent);
CFRelease(colorSpaceRef);
return savedimageref;