/* Flot plugin for drawing all elements of a plot on the canvas.
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Copyright (c) 2007-2014 IOLA and Ole Laursen.
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Licensed under the MIT license.
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Flot normally produces certain elements, like axis labels and the legend, using
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HTML elements. This permits greater interactivity and customization, and often
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looks better, due to cross-browser canvas text inconsistencies and limitations.
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It can also be desirable to render the plot entirely in canvas, particularly
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if the goal is to save it as an image, or if Flot is being used in a context
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where the HTML DOM does not exist, as is the case within Node.js. This plugin
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switches out Flot's standard drawing operations for canvas-only replacements.
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Currently the plugin supports only axis labels, but it will eventually allow
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every element of the plot to be rendered directly to canvas.
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The plugin supports these options:
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{
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canvas: boolean
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}
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The "canvas" option controls whether full canvas drawing is enabled, making it
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possible to toggle on and off. This is useful when a plot uses HTML text in the
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browser, but needs to redraw with canvas text when exporting as an image.
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*/
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(function($) {
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var options = {
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canvas: true
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};
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var render, getTextInfo, addText;
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// Cache the prototype hasOwnProperty for faster access
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var hasOwnProperty = Object.prototype.hasOwnProperty;
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function init(plot, classes) {
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var Canvas = classes.Canvas;
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// We only want to replace the functions once; the second time around
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// we would just get our new function back. This whole replacing of
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// prototype functions is a disaster, and needs to be changed ASAP.
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if (render == null) {
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getTextInfo = Canvas.prototype.getTextInfo,
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addText = Canvas.prototype.addText,
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render = Canvas.prototype.render;
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}
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// Finishes rendering the canvas, including overlaid text
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Canvas.prototype.render = function() {
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if (!plot.getOptions().canvas) {
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return render.call(this);
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}
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var context = this.context,
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cache = this._textCache;
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// For each text layer, render elements marked as active
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context.save();
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context.textBaseline = "middle";
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for (var layerKey in cache) {
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if (hasOwnProperty.call(cache, layerKey)) {
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var layerCache = cache[layerKey];
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for (var styleKey in layerCache) {
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if (hasOwnProperty.call(layerCache, styleKey)) {
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var styleCache = layerCache[styleKey],
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updateStyles = true;
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for (var key in styleCache) {
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if (hasOwnProperty.call(styleCache, key)) {
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var info = styleCache[key],
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positions = info.positions,
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lines = info.lines;
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// Since every element at this level of the cache have the
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// same font and fill styles, we can just change them once
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// using the values from the first element.
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if (updateStyles) {
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context.fillStyle = info.font.color;
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context.font = info.font.definition;
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updateStyles = false;
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}
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for (var i = 0, position; position = positions[i]; i++) {
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if (position.active) {
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for (var j = 0, line; line = position.lines[j]; j++) {
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context.fillText(lines[j].text, line[0], line[1]);
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}
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} else {
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positions.splice(i--, 1);
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}
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}
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if (positions.length == 0) {
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delete styleCache[key];
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}
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}
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}
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}
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}
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}
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}
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context.restore();
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};
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// Creates (if necessary) and returns a text info object.
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//
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// When the canvas option is set, the object looks like this:
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//
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// {
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// width: Width of the text's bounding box.
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// height: Height of the text's bounding box.
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// positions: Array of positions at which this text is drawn.
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// lines: [{
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// height: Height of this line.
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// widths: Width of this line.
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// text: Text on this line.
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// }],
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// font: {
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// definition: Canvas font property string.
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// color: Color of the text.
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// },
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// }
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//
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// The positions array contains objects that look like this:
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//
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// {
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// active: Flag indicating whether the text should be visible.
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// lines: Array of [x, y] coordinates at which to draw the line.
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// x: X coordinate at which to draw the text.
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// y: Y coordinate at which to draw the text.
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// }
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Canvas.prototype.getTextInfo = function(layer, text, font, angle, width) {
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if (!plot.getOptions().canvas) {
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return getTextInfo.call(this, layer, text, font, angle, width);
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}
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var textStyle, layerCache, styleCache, info;
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// Cast the value to a string, in case we were given a number
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text = "" + text;
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// If the font is a font-spec object, generate a CSS definition
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if (typeof font === "object") {
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textStyle = font.style + " " + font.variant + " " + font.weight + " " + font.size + "px " + font.family;
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} else {
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textStyle = font;
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}
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// Retrieve (or create) the cache for the text's layer and styles
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layerCache = this._textCache[layer];
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if (layerCache == null) {
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layerCache = this._textCache[layer] = {};
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}
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styleCache = layerCache[textStyle];
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if (styleCache == null) {
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styleCache = layerCache[textStyle] = {};
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}
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info = styleCache[text];
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if (info == null) {
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var context = this.context;
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// If the font was provided as CSS, create a div with those
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// classes and examine it to generate a canvas font spec.
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if (typeof font !== "object") {
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var element = $("<div> </div>")
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.css("position", "absolute")
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.addClass(typeof font === "string" ? font : null)
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.appendTo(this.getTextLayer(layer));
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font = {
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lineHeight: element.height(),
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style: element.css("font-style"),
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variant: element.css("font-variant"),
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weight: element.css("font-weight"),
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family: element.css("font-family"),
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color: element.css("color")
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};
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// Setting line-height to 1, without units, sets it equal
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// to the font-size, even if the font-size is abstract,
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// like 'smaller'. This enables us to read the real size
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// via the element's height, working around browsers that
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// return the literal 'smaller' value.
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font.size = element.css("line-height", 1).height();
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element.remove();
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}
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textStyle = font.style + " " + font.variant + " " + font.weight + " " + font.size + "px " + font.family;
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// Create a new info object, initializing the dimensions to
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// zero so we can count them up line-by-line.
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info = styleCache[text] = {
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width: 0,
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height: 0,
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positions: [],
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lines: [],
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font: {
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definition: textStyle,
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color: font.color
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}
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};
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context.save();
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context.font = textStyle;
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// Canvas can't handle multi-line strings; break on various
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// newlines, including HTML brs, to build a list of lines.
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// Note that we could split directly on regexps, but IE < 9 is
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// broken; revisit when we drop IE 7/8 support.
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var lines = (text + "").replace(/<br ?\/?>|\r\n|\r/g, "\n").split("\n");
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for (var i = 0; i < lines.length; ++i) {
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var lineText = lines[i],
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measured = context.measureText(lineText);
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info.width = Math.max(measured.width, info.width);
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info.height += font.lineHeight;
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info.lines.push({
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text: lineText,
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width: measured.width,
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height: font.lineHeight
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});
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}
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context.restore();
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}
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return info;
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};
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// Adds a text string to the canvas text overlay.
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Canvas.prototype.addText = function(layer, x, y, text, font, angle, width, halign, valign) {
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if (!plot.getOptions().canvas) {
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return addText.call(this, layer, x, y, text, font, angle, width, halign, valign);
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}
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var info = this.getTextInfo(layer, text, font, angle, width),
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positions = info.positions,
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lines = info.lines;
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// Text is drawn with baseline 'middle', which we need to account
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// for by adding half a line's height to the y position.
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y += info.height / lines.length / 2;
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// Tweak the initial y-position to match vertical alignment
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if (valign == "middle") {
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y = Math.round(y - info.height / 2);
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} else if (valign == "bottom") {
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y = Math.round(y - info.height);
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} else {
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y = Math.round(y);
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}
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// FIXME: LEGACY BROWSER FIX
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// AFFECTS: Opera < 12.00
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// Offset the y coordinate, since Opera is off pretty
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// consistently compared to the other browsers.
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if (!!(window.opera && window.opera.version().split(".")[0] < 12)) {
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y -= 2;
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}
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// Determine whether this text already exists at this position.
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// If so, mark it for inclusion in the next render pass.
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for (var i = 0, position; position = positions[i]; i++) {
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if (position.x == x && position.y == y) {
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position.active = true;
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return;
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}
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}
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// If the text doesn't exist at this position, create a new entry
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position = {
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active: true,
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lines: [],
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x: x,
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y: y
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};
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positions.push(position);
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// Fill in the x & y positions of each line, adjusting them
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// individually for horizontal alignment.
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for (var i = 0, line; line = lines[i]; i++) {
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if (halign == "center") {
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position.lines.push([Math.round(x - line.width / 2), y]);
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} else if (halign == "right") {
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position.lines.push([Math.round(x - line.width), y]);
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} else {
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position.lines.push([Math.round(x), y]);
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}
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y += line.height;
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}
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};
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}
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$.plot.plugins.push({
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init: init,
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options: options,
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name: "canvas",
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version: "1.0"
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});
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})(jQuery);
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