Drawing into CGImageRef

问题:

I want to create a CGImageRef and draw points to it.

What context to use to create an empty CGImageRef and be able to draw onto it. CGContextRef or CGBitmapContextRef?

If you can provide code to create an empty CGImageRef image and draw to it I would appreciate.

回答1:

#define HIRESDEVICE (((int)rintf([[[UIScreen mainScreen] currentMode] size].width/[[UIScreen mainScreen] bounds].size.width )>1))


- (CGImageRef) blerg
    {
    CGFloat imageScale = (CGFloat)1.0;
    CGFloat width = (CGFloat)180.0;
    CGFloat height = (CGFloat)180.0;

    if ( HIRESDEVICE )
        {
        imageScale = (CGFloat)2.0;
        }

    // Create a bitmap graphics context of the given size
    //
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(NULL, width * imageScale, height * imageScale, 8, 0, colorSpace, kCGImageAlphaPremultipliedLast);


    // Draw ...
    //
    CGContextSetRGBFillColor(context, (CGFloat)0.0, (CGFloat)0.0, (CGFloat)0.0, (CGFloat)1.0 );
    // …


    // Get your image
    //
    CGImageRef cgImage = CGBitmapContextCreateImage(context);

    CGColorSpaceRelease(colorSpace);
    CGContextRelease(context);

    return cgImage;
    }