CODEWITHSUNDEEP
iphoneiosipadopengl-esuiimage
automatom
automatom

Reputation: 275

Displaying stream of CGImage data as fast as possible

I am receiving a series of images over a network connection, and want to display them as fast as possible, up to 30 FPS. I have derived a UIView object (so I can override drawRect) and exposed a UIImage property called cameraImage. The frame data is arriving as fast as needed, but the actual drawing to screen takes far too much time (as a result of the lag from setNeedsDisplay), both creating lag in the video and slowing down the interaction with other controls. What is a better way to do this? I've though of using OpenGL, but the only examples I've seen aren't for drawing static images to the screen, but for adding texture to some rotating polygon.

- (void)drawRect:(CGRect)rect
{
  CGContextRef context = UIGraphicsGetCurrentContext();

  CGRect screenBounds = [[UIScreen mainScreen] bounds];
  [self.cameraImage drawInRect:screenBounds];

  // Drawing code
  //CGContextDrawImage(context, screenBounds, [self.cameraImage CGImage]); // Doesn't help
}

Upvotes: 0

Views: 558

Answers (1)

Kurt Revis
Kurt Revis

Reputation: 27984

Try setting a CALayer's contents to the image. Or, if you set it up with relatively sane parameters, setting a UIImageView's image shouldn't be much slower.

OpenGL is definitely an alternative, but it's much more difficult to work with, and it will still be limited by the same thing as the others: the texture upload speed.

(The way you're doing it (drawing in drawRect:), you have to let UIKit allocate a bitmap for you, then draw the image into the bitmap, then upload the bitmap to the video hardware. Best to skip the middleman and upload the image directly, if you can.)

It may also depend on where the CGImage came from. Is it backed by raw bitmap data (and if so, in what format?), or is it a JPEG or PNG? If the image has to be format-converted or decoded, it will take longer.

Also, how large is the CGImage? Make sure it isn't larger than it needs to be!

Upvotes: 3

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