static String makeRgbaData(int width, int height, int bpp, boolean has_alpha) {
		final int CHECK_SIZE = 20;

		assert (bpp == 4);
		assert (has_alpha);

		int rowstride = width * bpp;

		char[] pixels = new char[height * rowstride];

		for (int y = 0; y < height; y++) {
			int i = 0;
			for (int x = 0; x < width; x++) {

				pixels[0 + y * rowstride + x * bpp] = pixels[1 + y * rowstride
						+ x * bpp] = pixels[2 + y * rowstride + x * bpp] = 0;
				pixels[3 + y * rowstride + x * bpp] = 0xff;

				// TODO
				if ((x % 2 == 1) && (y % 2 == 1) && (y % CHECK_SIZE == 1)
						&& (x % CHECK_SIZE == 1)) {
					if (x % CHECK_SIZE == 1) {
						if (++i > 3)
							i = 0;
					}
					pixels[i + y * rowstride + x * bpp] = 0xff;
				}
			}
		}

		return new String(pixels);
	}