Trapezoid!

Performance Tuning
#1

I was wondering if there are any fast algorithms out there for taking an image and morphing it into the shape of a trapezoid (trapezium).

I found this method:

	private final float A = W * 0.08f;
	private final float B = W * (1f - 0.08f);

	private final void createTrapezium(BufferedImage src, BufferedImage out) {
		int[] pix = ((DataBufferInt) src.getRaster().getDataBuffer()).getData();
		int[] pix2 = ((DataBufferInt) out.getRaster().getDataBuffer()).getData();
		Arrays.fill(pix2, 0);
		for (int y = 0; y < HEIGHT; y++) {
			int yw = y * W;
			float y_to_h = y / (float) HEIGHT;
			float C_A_offset = A * (1 - y_to_h);
			float trapeziumLine = -C_A_offset + B + (W - B) * y_to_h;
			float k = trapeziumLine / W;
			for (int x = 0; x < W; x++) {
				int destX = (int) (C_A_offset + x * k);
				pix2[yw + destX] = pix[yw + x];
			}
		}
	}

But it’s pretty CPU intensive (using this in real-time for a changing background image at 30 FPS)… Is there an alternative to using JAI?

#2

You mention JAI, so I assume you’ve seen the thread at http://stackoverflow.com/questions/2500489/fast-perspective-transform-in-java-advanced-imaging-api … unfortunately you’re not going to get anywhere with an Affine transform, so you’re kinda out of luck as built-in features go.

If you’re looking to do a transition, like screens swiping from one to the next, you could always pre-render them and just animate through those. Otherwise the only really viable alternative that’ll get you any reasonable quality at decent speed is to go 3d and use OpenGL.

#3

It seems that JAI has to be installed, that’s why I don’t want to use it… Is there a version that you can just bundle with a project (with native libs)?

#4

You could try ImageMagick bindings, I’m pretty sure that has a perspective transform in it. There’s also JavaCV, which should be able to do anything you imagine once you figure it out. Neither of those are going to be real-time either.

#5

Ugh. Would it be possible to have a 3D background and a 2D foreground if I switch to OpenGL? Time to look up tutorials.

Thanks!