I am trying to transform a Sprite into a trapezoid, I don t really care about the interpolation even though I know without it my image will lose detail. All I really want to do is Transform my rectangular Sprite into a trapezoid like this:
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Has anyone done this with CGAffineTransforms or with cocos2d?
The transformation you re proposing is not affine. Affine transformations have to be undoable. So they can typically:
But they cannot "squeeze". Notice that the left and right sides of your trapezoid, if extended, would intersect at a particular spot. They re not parallel anymore. So you couldn t "undo" the transformation, because if there was anything to transform at that spot, you couldn t decide where they would transform to. In other words, if a transformation doesn t preserve parallelism, it pinches space, can t be undone, and isn t affine.
I don t know that much about transformations in Core Animation, so I hope that mathy stuff helps you find an alternative.
But I do know how you could do it in OpenGL, but it would require you to start over on how you draw your application:
If I m envisioning the result you want correctly, you want to build your rectangle in 3D, use an affine transformation to rotate it away a little bit, and use a (non-affine) projection transformation to flatten it into a 2D image.
If you re not looking for a 3D effect, but you really just want to pinch in the corners, then you can specify a GL_RECT with the points of your trapezoid and map your sprite onto it as a texture.
The easiest thing might be to pre-squeeze your image in a photo editor, save it as a .png with transparency, and draw a rectangle with that image.
You need to apply a CATransform3D to the layer of the UIView. To find out the right one, it is easier to use AGGeometryKit.
#import <AGGeometryKit/AGGeometryKit.h>
UIView *view = ...; // create a view
view.layer.anchorPoint = CGPointZero;
AGKQuad quad = view.layer.quadrilateral;
quad.tl.x += 20; // shift top left x-value with 20 pixels
quad.tr.x -= 20; // shift top right x-value with 20 pixels
view.layer.quadrilateral = quad; // the quad is converted to CATransform3D and applied
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