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91 lines
2.4 KiB
JavaScript
91 lines
2.4 KiB
JavaScript
/**
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* Construct representing a part of another {ImageWrapper}. Shares data
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* between the parent and the child.
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* @param from {ImageRef} The position where to start the {SubImage} from. (top-left corner)
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* @param size {ImageRef} The size of the resulting image
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* @param I {ImageWrapper} The {ImageWrapper} to share from
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* @returns {SubImage} A shared part of the original image
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*/
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function SubImage(from, size, I) {
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if (!I) {
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I = {
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data: null,
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size: size
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};
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}
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this.data = I.data;
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this.originalSize = I.size;
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this.I = I;
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this.from = from;
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this.size = size;
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}
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/**
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* Displays the {SubImage} in a given canvas
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* @param canvas {Canvas} The canvas element to write to
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* @param scale {Number} Scale which is applied to each pixel-value
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*/
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SubImage.prototype.show = function(canvas, scale) {
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var ctx,
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frame,
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data,
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current,
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y,
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x,
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pixel;
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if (!scale) {
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scale = 1.0;
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}
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ctx = canvas.getContext('2d');
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canvas.width = this.size.x;
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canvas.height = this.size.y;
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frame = ctx.getImageData(0, 0, canvas.width, canvas.height);
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data = frame.data;
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current = 0;
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for (y = 0; y < this.size.y; y++) {
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for (x = 0; x < this.size.x; x++) {
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pixel = y * this.size.x + x;
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current = this.get(x, y) * scale;
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data[pixel * 4 + 0] = current;
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data[pixel * 4 + 1] = current;
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data[pixel * 4 + 2] = current;
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data[pixel * 4 + 3] = 255;
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}
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}
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frame.data = data;
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ctx.putImageData(frame, 0, 0);
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};
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/**
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* Retrieves a given pixel position from the {SubImage}
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* @param x {Number} The x-position
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* @param y {Number} The y-position
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* @returns {Number} The grayscale value at the pixel-position
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*/
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SubImage.prototype.get = function(x, y) {
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return this.data[(this.from.y + y) * this.originalSize.x + this.from.x + x];
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};
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/**
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* Updates the underlying data from a given {ImageWrapper}
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* @param image {ImageWrapper} The updated image
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*/
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SubImage.prototype.updateData = function(image) {
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this.originalSize = image.size;
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this.data = image.data;
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};
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/**
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* Updates the position of the shared area
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* @param from {x,y} The new location
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* @returns {SubImage} returns {this} for possible chaining
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*/
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SubImage.prototype.updateFrom = function(from) {
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this.from = from;
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return this;
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};
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export default (SubImage);
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