水纹滤镜

    /*
            水波纹
            */
        function Ripple(imgData) {
            var width = imgData.width,
                height = imgData.height,
                pixelData = imgData.data,
                Center_X = height / 4,
                Center_Y = width / 4,
                wavelength = 20,
                phase = 0,
                amplitude = 3,
                radius = Math.min(height, width) / 2,
                radius2 = radius * radius;
            for (var i = 1; i < height; i++) {
                for (j = 1; j < width; j++) {
                    dx = i - Center_X;
                    dy = j - Center_Y;
                    distance2 = dx * dx + dy * dy;
                    if (distance2 > radius2) {
                        x = i;
                        y = j;
                    } else {
                        distance = Math.sqrt(distance2);
                        amount = amplitude * Math.sin(distance / wavelength * 2 * Math.PI - phase);
                        amount = amount * (radius - distance) / radius;
                        amount = amount * wavelength / (distance + 0.0001);

                        x = i + dx * amount;
                        y = j + dy * amount;
                    }


                    if (x > 1 && x < width && y < height && y > 1) {
                        x1 = Math.floor(x);
                        y1 = Math.floor(y);
                        p = x - x1;
                        q = y - y1;
                        var r0 = for_img(x1, y1, p, q, 0);
                        var g0 = for_img(x1, y1, p, q, 1);
                        var b0 = for_img(x1, y1, p, q, 2);
                        var p = i * canvas.width + j;
                        pixelData[p * 4 + 0] = r0;
                        pixelData[p * 4 + 1] = g0;
                        pixelData[p * 4 + 2] = b0;
                    }
                }
            }

            function for_img(x, y, p, q, n) {
                return pixelData[(x * width + y) * 4 + n] * (1 - p) * (1 - q) + pixelData[(x * width + y + 1) * 4 + n] * p * (1 - q) + pixelData[((x + 1) * width + y) * 4 + n] * q * (1 - p) + pixelData[((x + 1) * width + y + 1) * 4 + n] * p * q
            }


            imgData.data = pixelData;
            return imgData;
        }