Home/ Questions/Q 8163583
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-06-06T19:05:48+00:00

I have two ImageViews, one called imageView and the other called subView (which is

  • 0

I have two ImageViews, one called imageView and the other called subView (which is a subview of imageView).

I want to blend the images on these views together, with the user being able to switch the alpha of the blend with a pan. My code works, but right now, the code is slow as we are redrawing the image each time the pan gesture is moved. Is there a faster/more efficient way of doing this?

BONUS Q: I want to allow for my subView image to drawn zoomed in. Currently I’ve set my subView to be UIViewContentModeCenter, however I can’t seem to draw a zoomed in part of my image with this content mode. Is there any way around this?

My drawrect:

- (void)drawRect:(CGRect)rect
{
float xCenter = self.center.x - self.currentImage1.size.width/2.0;
float yCenter = self.center.y - self.currentImage1.size.height/2.0;

subView.alpha = self.blendAmount;  // Customize the opacity of the top image.

UIGraphicsBeginImageContext(self.currentImage1.size);

CGContextRef c = UIGraphicsGetCurrentContext();

CGContextSetBlendMode(c, kCGBlendModeColorBurn);
[imageView.layer renderInContext:c];

self.blendedImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
[self.blendedImage drawAtPoint:CGPointMake(xCenter,yCenter)];

}
Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    You need to use GPU for image processing which is far faster than using CPU (as you’re doing right now).

    You can use Core Image framework which is very fast and easy to use but requires iOS 5, or you can use Open GL directly but you need to be experienced and have some knowledge about Open GL Shading.

    • 0