How to distort an image to any quadrangle?

Question

Do any of you have an idea, how to distort an image in any quadrangle? I want to implement an image, which you can pull any corner in any direction, distorting the image. A

Answer 1

There is an issue with your code. Although it is the correct method, you have inverted the float[] parameters, as appears in Android documentation:

public boolean setPolyToPoly (float[] src, int srcIndex, float[] dst, int dstIndex, int pointCount)
WHERE
src: The array of src [x,y] pairs (points)
...
dst: The array of dst [x,y] pairs (points)

So, according with your code, the matrix should be created as:

matrix.setPolyToPoly(
        new float[] {
            x0, y0,
            x1, y1,
            x2, y2,
            x3, y3},
    0,
new float[] { 
        0, 0, 
        bitmap.getWidth(), 0
        0, bitmap.getHeight(),
        bitmap.getWidth(), bitmap.getHeight() 
    }, 0, 
    4);

In this way, the app works fine, as shown in the image:

By the other hand, regarding of what user2498079 says in his comment about the computational problem in low end devices, you can use some easy-to-do techniques to reduce the source image size (and color depth, for example) before matrix conversion calculation. It'd make it easier for the low end phone to realize this task.