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PixelSampler.js
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PixelSampler.js
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// Copyright 2012 Google Inc. All Rights Reserved.
/**
* @fileoverview A class to facilitate sampling colors at particular pixels on a
* dygraph.
* @author danvk@google.com (Dan Vanderkam)
* @license MIT
*/
'use strict';
/**
* @constructor
*/
var PixelSampler = function(dygraph) {
this.dygraph_ = dygraph;
var canvas = dygraph.hidden_;
var ctx = canvas.getContext("2d");
this.imageData_ = ctx.getImageData(0, 0, canvas.width, canvas.height);
this.scale = canvas.width / dygraph.width_;
};
/**
* @param {number} x The screen x-coordinate at which to sample.
* @param {number} y The screen y-coordinate at which to sample.
* @return {Array.<number>} a 4D array: [R, G, B, alpha]. All four values
* are in [0, 255]. A pixel which has never been touched will be [0,0,0,0].
*/
PixelSampler.prototype.colorAtPixel = function(x, y) {
var i = 4 * (x * this.scale + this.imageData_.width * y * this.scale);
var d = this.imageData_.data;
return [d[i], d[i+1], d[i+2], d[i+3]];
};
/**
* Convenience wrapper around colorAtPixel if you only care about RGB (not A).
* @param {number} x The screen x-coordinate at which to sample.
* @param {number} y The screen y-coordinate at which to sample.
* @return {Array.<number>} a 3D array: [R, G, B]. All three values
* are in [0, 255]. A pixel which has never been touched will be [0,0,0].
*/
PixelSampler.prototype.rgbAtPixel = function(x, y) {
return this.colorAtPixel(x, y).slice(0, 3);
};
/**
* The method samples a color using data coordinates (not screen coordinates).
* This will round your data coordinates to the nearest screen pixel before
* sampling.
* @param {number} x The data x-coordinate at which to sample.
* @param {number} y The data y-coordinate at which to sample.
* @return {Array.<number>} a 4D array: [R, G, B, alpha]. All four values
* are in [0, 255]. A pixel which has never been touched will be [0,0,0,0].
*/
PixelSampler.prototype.colorAtCoordinate = function(x, y) {
var dom_xy = this.dygraph_.toDomCoords(x, y);
return this.colorAtPixel(Math.round(dom_xy[0]), Math.round(dom_xy[1]));
};
export default PixelSampler;