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- // returns a function that calculates lanczos weight
- function lanczosCreate(lobes) {
- return function(x) {
- if (x > lobes)
- return 0;
- x *= Math.PI;
- if (Math.abs(x) < 1e-16)
- return 1;
- var xx = x / lobes;
- return Math.sin(x) * Math.sin(xx) / x / xx;
- };
- }
- // elem: canvas element, img: image element, sx: scaled width, lobes: kernel radius
- function thumbnailer(elem, img, sx, lobes) {
- this.canvas = elem;
- elem.width = img.width;
- elem.height = img.height;
- elem.style.display = "none";
- this.ctx = elem.getContext("2d");
- this.ctx.drawImage(img, 0, 0);
- this.img = img;
- this.src = this.ctx.getImageData(0, 0, img.width, img.height);
- this.dest = {
- width : sx,
- height : Math.round(img.height * sx / img.width),
- };
- this.dest.data = new Array(this.dest.width * this.dest.height * 3);
- this.lanczos = lanczosCreate(lobes);
- this.ratio = img.width / sx;
- this.rcp_ratio = 2 / this.ratio;
- this.range2 = Math.ceil(this.ratio * lobes / 2);
- this.cacheLanc = {};
- this.center = {};
- this.icenter = {};
- setTimeout(this.process1, 0, this, 0);
- }
- thumbnailer.prototype.process1 = function(self, u) {
- self.center.x = (u + 0.5) * self.ratio;
- self.icenter.x = Math.floor(self.center.x);
- for (var v = 0; v < self.dest.height; v++) {
- self.center.y = (v + 0.5) * self.ratio;
- self.icenter.y = Math.floor(self.center.y);
- var a, r, g, b;
- a = r = g = b = 0;
- for (var i = self.icenter.x - self.range2; i <= self.icenter.x + self.range2; i++) {
- if (i < 0 || i >= self.src.width)
- continue;
- var f_x = Math.floor(1000 * Math.abs(i - self.center.x));
- if (!self.cacheLanc[f_x])
- self.cacheLanc[f_x] = {};
- for (var j = self.icenter.y - self.range2; j <= self.icenter.y + self.range2; j++) {
- if (j < 0 || j >= self.src.height)
- continue;
- var f_y = Math.floor(1000 * Math.abs(j - self.center.y));
- if (self.cacheLanc[f_x][f_y] == undefined)
- self.cacheLanc[f_x][f_y] = self.lanczos(Math.sqrt(Math.pow(f_x * self.rcp_ratio, 2)
- + Math.pow(f_y * self.rcp_ratio, 2)) / 1000);
- weight = self.cacheLanc[f_x][f_y];
- if (weight > 0) {
- var idx = (j * self.src.width + i) * 4;
- a += weight;
- r += weight * self.src.data[idx];
- g += weight * self.src.data[idx + 1];
- b += weight * self.src.data[idx + 2];
- }
- }
- }
- var idx = (v * self.dest.width + u) * 3;
- self.dest.data[idx] = r / a;
- self.dest.data[idx + 1] = g / a;
- self.dest.data[idx + 2] = b / a;
- }
- if (++u < self.dest.width)
- setTimeout(self.process1, 0, self, u);
- else
- setTimeout(self.process2, 0, self);
- };
- thumbnailer.prototype.process2 = function(self) {
- self.canvas.width = self.dest.width;
- self.canvas.height = self.dest.height;
- self.ctx.drawImage(self.img, 0, 0, self.dest.width, self.dest.height);
- self.src = self.ctx.getImageData(0, 0, self.dest.width, self.dest.height);
- var idx, idx2;
- for (var i = 0; i < self.dest.width; i++) {
- for (var j = 0; j < self.dest.height; j++) {
- idx = (j * self.dest.width + i) * 3;
- idx2 = (j * self.dest.width + i) * 4;
- self.src.data[idx2] = self.dest.data[idx];
- self.src.data[idx2 + 1] = self.dest.data[idx + 1];
- self.src.data[idx2 + 2] = self.dest.data[idx + 2];
- }
- }
- self.ctx.putImageData(self.src, 0, 0);
- self.canvas.style.display = "block";
- };
- img.onload = function() {
- var canvas = document.createElement("canvas");
- new thumbnailer(canvas, img, 188, 3); //this produces lanczos3
- document.body.appendChild(canvas);
- };
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