CODEWITHSUNDEEP
iphoneimagecore-graphicsshadow
Lars Petersen
Lars Petersen

Reputation: 622

Hot can I add a shadow to an image using CoreGraphics on the iPhone?

I have a problem concerning Core Graphics drawing a shadow under my masked image.

I wrote a method to turn a grey image (actually it's an icon) into a white using a mask. Now I want to draw a shadow underneath it.

That's my code so far:

CGContextRef context = CGBitmapContextCreate(NULL, imageRect.size.width, imageRect.size.height, 8, 0, CGImageGetColorSpace(image.CGImage), kCGImageAlphaPremultipliedLast);

CGContextSetRGBFillColor(context, 1, 1, 1, 1);
CGContextFillRect(context, imageRect);

CGContextClipToMask(context, imageRect, image.CGImage);

CGContextSetRGBFillColor(context, 0, 0, 0, 1);
CGContextFillRect(context, imageRect);

CGImageRef bwCGImage = CGBitmapContextCreateImage(context);
UIImage *bwImage = [UIImage imageWithCGImage:bwCGImage scale:image.scale orientation:image.imageOrientation];

CGContextRelease(context);
CGImageRelease(bwCGImage);


UIGraphicsBeginImageContextWithOptions(image.size, NO, 0.0);
[[UIColor whiteColor] set];
UIRectFill(CGRectMake(0, 0, image.size.width, image.size.height));

UIImage *normalBackgroundImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();


CGImageRef imageMask = CGImageMaskCreate(CGImageGetWidth(bwImage.CGImage), CGImageGetHeight(bwImage.CGImage), CGImageGetBitsPerComponent(bwImage.CGImage), CGImageGetBitsPerPixel(bwImage.CGImage), CGImageGetBytesPerRow(bwImage.CGImage), CGImageGetDataProvider(bwImage.CGImage), NULL, YES);

CGImageRef normalImageRef = CGImageCreateWithMask(normalBackgroundImage.CGImage, imageMask);

UIImage *normalImage = [UIImage imageWithCGImage:normalImageRef scale:image.scale orientation:image.imageOrientation];


CGImageRelease(imageMask);
CGImageRelease(normalImageRef);

Actually everything is working fine. Only the shadow is missing. How can I draw it?

Upvotes: 0

Views: 1847

Answers (1)

Henrik P. Hessel
Henrik P. Hessel

Reputation: 36617

I always recommend the great Quartz 2D Guide by Apple. Considering your question you should read the Shadows Chapter

It includes a great demo (including comments) 

void MyDrawWithShadows (CGContextRef myContext, // 1
                         float wd, float ht);
{
    CGSize          myShadowOffset = CGSizeMake (-15,  20);// 2
    float           myColorValues[] = {1, 0, 0, .6};// 3
    CGColorRef      myColor;// 4
    CGColorSpaceRef myColorSpace;// 5

    CGContextSaveGState(myContext);// 6

    CGContextSetShadow (myContext, myShadowOffset, 5); // 7
    // Your drawing code here// 8
    CGContextSetRGBFillColor (myContext, 0, 1, 0, 1);
    CGContextFillRect (myContext, CGRectMake (wd/3 + 75, ht/2 , wd/4, ht/4));

    myColorSpace = CGColorSpaceCreateDeviceRGB ();// 9
    myColor = CGColorCreate (myColorSpace, myColorValues);// 10
    CGContextSetShadowWithColor (myContext, myShadowOffset, 5, myColor);// 11
    // Your drawing code here// 12
    CGContextSetRGBFillColor (myContext, 0, 0, 1, 1);
    CGContextFillRect (myContext, CGRectMake (wd/3-75,ht/2-100,wd/4,ht/4));

    CGColorRelease (myColor);// 13
    CGColorSpaceRelease (myColorSpace); // 14

    CGContextRestoreGState(myContext);// 15
}

Upvotes: 2

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