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iosipadquartz-2d

iOS Quartz 2D How to expand layer beyond screen frame

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Is there a way to expand layer (the area where you draw), to be larger. At first i thought that (0,0) is the center, but it seems that it is a starting point for layer. I was planning to draw content at (0,0) then to translate it as necessary.

Or, must i draw whatever i have in center of layer (width/2, height/2) and then translate as necessary?

EDIT_01: The offset of layer is made by panning gesture recognizer. That is on purpose, since app must have panning of content.

Solution

  • Answers

    At first i thought that (0,0) is the center, but it seems that it is a starting point for layer

    (0,0) in iOS begins at the top left of the layer, and gets greater going right and down. In OS X, (0,0) begins in the bottom left, and gets greater going right and up.

    Is there a way to expand layer (the area where you draw), to be larger

    The question I have is, do you need to? This can have performance issues, as you're rendering and storing drawing data when you don't really need to, causing more memory to be used. It looks like your layer is filling the screen correctly, it's just translated incorrectly. If you move it to the correct place, you shouldn't need to expand the layer off screen.

    This doesn't mean you can't translate other layers off screen, of course you can. But really you don't want to expand the size of your drawing area to expand off screen.

    Must i draw whatever i have in center of layer (width/2, height/2) and then translate as necessary?

    If you want them drawn into the center, then yes. You can create your own method to translate your own co-ordinate space into the co-ordinate space of the layer, to make this easier for you.

    Documentation

    I'd suggest reading this, to get a greater grasp of the geometry workings of CALayer: https://developer.apple.com/library/ios/#documentation/Cocoa/Conceptual/CoreAnimation_guide/Articles/Layers.html#//apple_ref/doc/uid/TP40006082-SW1

    ...and this to get an understanding of drawing techniques: https://developer.apple.com/library/ios/#documentation/graphicsimaging/conceptual/drawingwithquartz2d/dq_layers/dq_layers.html