HTML5 Canvas Notes For Professionals. 100+ pages of professional hints and tricks (GoalKicker.com) (Z-Library)

HTML5 Canvas Notes for ProfessionalsHTML5 Canvas Notes for Professionals GoalKicker.com Free Programming Books Disclaimer This is an unocial free book created for educational purposes and is not aliated with ocial HTML5 Canvas group(s) or company(s). All trademarks and registered trademarks are the property of their respective owners 100+ pages of professional hints and tricks

Contents About 1 ................................................................................................................................................................................... Chapter 1: Getting started with HTML5 Canvas 2 ............................................................................................ Section 1.1: Detecting mouse position on the canvas 2 ................................................................................................ Section 1.2: Canvas size and resolution 2 ....................................................................................................................... Section 1.3: Rotate 3 ......................................................................................................................................................... Section 1.4: Save canvas to image file 3 ........................................................................................................................ Section 1.5: How to add the Html5 Canvas Element to a webpage 4 ......................................................................... Section 1.6: An index to Html5 Canvas Capabilities & Uses 5 ...................................................................................... Section 1.7: O screen canvas 6 ...................................................................................................................................... Section 1.8: Hello World 6 ................................................................................................................................................. Chapter 2: Text 8 ............................................................................................................................................................... Section 2.1: Justified text 8 ............................................................................................................................................... Section 2.2: Justified paragraphs 13 .............................................................................................................................. Section 2.3: Rendering text along an arc 17 .................................................................................................................. Section 2.4: Text on curve, cubic and quadratic beziers 22 ......................................................................................... Section 2.5: Drawing Text 25 ........................................................................................................................................... Section 2.6: Formatting Text 26 ...................................................................................................................................... Section 2.7: Wrapping text into paragraphs 27 ............................................................................................................ Section 2.8: Draw text paragraphs into irregular shapes 28 ....................................................................................... Section 2.9: Fill text with an image 30 ............................................................................................................................ Chapter 3: Polygons 31 .................................................................................................................................................. Section 3.1: Render a rounded polygon 31 .................................................................................................................... Section 3.2: Stars 32 ......................................................................................................................................................... Section 3.3: Regular Polygon 33 ..................................................................................................................................... Chapter 4: Images 35 ..................................................................................................................................................... Section 4.1: Is "context.drawImage" not displaying the image on the Canvas? 35 ................................................... Section 4.2: The Tained canvas 35 ................................................................................................................................. Section 4.3: Image cropping using canvas 36 ............................................................................................................... Section 4.4: Scaling image to fit or fill 36 ....................................................................................................................... Chapter 5: Path (Syntax only) 39 .............................................................................................................................. Section 5.1: createPattern (creates a path styling object) 39 ...................................................................................... Section 5.2: stroke (a path command) 41 ..................................................................................................................... Section 5.3: fill (a path command) 45 ............................................................................................................................ Section 5.4: clip (a path command) 45 .......................................................................................................................... Section 5.5: Overview of the basic path drawing commands: lines and curves 47 .................................................. Section 5.6: lineTo (a path command) 49 ...................................................................................................................... Section 5.7: arc (a path command) 50 ........................................................................................................................... Section 5.8: quadraticCurveTo (a path command) 52 ................................................................................................. Section 5.9: bezierCurveTo (a path command) 53 ....................................................................................................... Section 5.10: arcTo (a path command) 54 ..................................................................................................................... Section 5.11: rect (a path command) 55 ......................................................................................................................... Section 5.12: closePath (a path command) 57 .............................................................................................................. Section 5.13: beginPath (a path command) 58 ............................................................................................................. Section 5.14: lineCap (a path styling attribute) 61 ........................................................................................................ Section 5.15: lineJoin (a path styling attribute) 62 ........................................................................................................ Section 5.16: strokeStyle (a path styling attribute) 63 .................................................................................................. Section 5.17: fillStyle (a path styling attribute) 65 .........................................................................................................

Section 5.18: lineWidth (A path styling attribute) 67 ..................................................................................................... Section 5.19: shadowColor, shadowBlur, shadowOsetX, shadowOsetY (path styling attributes) 68 .................. Section 5.20: createLinearGradient (creates a path styling object) 70 ...................................................................... Section 5.21: createRadialGradient (creates a path styling object) 73 ....................................................................... Chapter 6: Paths 77 .......................................................................................................................................................... Section 6.1: Ellipse 77 ........................................................................................................................................................ Section 6.2: Line without blurryness 78 .......................................................................................................................... Chapter 7: Navigating along a Path 80 ................................................................................................................. Section 7.1: Find point on curve 80 .................................................................................................................................. Section 7.2: Finding extent of Quadratic Curve 81 ....................................................................................................... Section 7.3: Finding points along a cubic Bezier curve 82 ........................................................................................... Section 7.4: Finding points along a quadratic curve 83 ............................................................................................... Section 7.5: Finding points along a line 84 ..................................................................................................................... Section 7.6: Finding points along an entire Path containing curves and lines 84 ...................................................... Section 7.7: Split bezier curves at position 91 ................................................................................................................ Section 7.8: Trim bezier curve 94 .................................................................................................................................... Section 7.9: Length of a Cubic Bezier Curve (a close approximation) 96 .................................................................. Section 7.10: Length of a Quadratic Curve 97 ............................................................................................................... Chapter 8: Dragging Path Shapes & Images on Canvas 98 ........................................................................ Section 8.1: How shapes & images REALLY(!) "move" on the Canvas 98 ................................................................... Section 8.2: Dragging circles & rectangles around the Canvas 99 ............................................................................. Section 8.3: Dragging irregular shapes around the Canvas 103 ................................................................................ Section 8.4: Dragging images around the Canvas 106 ................................................................................................ Chapter 9: Media types and the canvas 109 ....................................................................................................... Section 9.1: Basic loading and playing a video on the canvas 109 ............................................................................. Section 9.2: Capture canvas and Save as webM video 111 ........................................................................................ Section 9.3: Drawing an svg image 116 ......................................................................................................................... Section 9.4: Loading and displaying an Image 117 ...................................................................................................... Chapter 10: Animation 119 ............................................................................................................................................ Section 10.1: Use requestAnimationFrame() NOT setInterval() for animation loops 119 ......................................... Section 10.2: Animate an image across the Canvas 120 .............................................................................................. Section 10.3: Set frame rate using requestAnimationFrame 121 ................................................................................ Section 10.4: Easing using Robert Penners equations 121 ........................................................................................... Section 10.5: Animate at a specified interval (add a new rectangle every 1 second) 125 ........................................ Section 10.6: Animate at a specified time (an animated clock) 126 ........................................................................... Section 10.7: Don't draw animations in your event handlers (a simple sketch app) 127 ......................................... Section 10.8: Simple animation with 2D context and requestAnimationFrame 129 .................................................. Section 10.9: Animate from [x0,y0] to [x1,y1] 129 .......................................................................................................... Chapter 11: Collisions and Intersections 131 ........................................................................................................ Section 11.1: Are 2 circles colliding? 131 .......................................................................................................................... Section 11.2: Are 2 rectangles colliding? 131 .................................................................................................................. Section 11.3: Are a circle and rectangle colliding? 131 .................................................................................................. Section 11.4: Are 2 line segments intercepting? 131 ...................................................................................................... Section 11.5: Are a line segment and circle colliding? 133 ............................................................................................ Section 11.6: Are line segment and rectangle colliding? 133 ........................................................................................ Section 11.7: Are 2 convex polygons colliding? 134 ....................................................................................................... Section 11.8: Are 2 polygons colliding? (both concave and convex polys are allowed) 135 .................................... Section 11.9: Is an X,Y point inside an arc? 136 .............................................................................................................. Section 11.10: Is an X,Y point inside a wedge? 137 ......................................................................................................... Section 11.11: Is an X,Y point inside a circle? 138 .............................................................................................................

Section 11.12: Is an X,Y point inside a rectangle? 138 .................................................................................................... Chapter 12: Clearing the screen 139 ........................................................................................................................ Section 12.1: Rectangles 139 ............................................................................................................................................ Section 12.2: Clear canvas with gradient 139 ................................................................................................................ Section 12.3: Clear canvas using composite operation 139 ......................................................................................... Section 12.4: Raw image data 140 .................................................................................................................................. Section 12.5: Complex shapes 140 .................................................................................................................................. Chapter 13: Responsive Design 141 .......................................................................................................................... Section 13.1: Creating a responsive full page canvas 141 ............................................................................................ Section 13.2: Mouse coordinates after resizing (or scrolling) 141 ............................................................................... Section 13.3: Responsive canvas animations without resize events 142 .................................................................... Chapter 14: Shadows 144 .............................................................................................................................................. Section 14.1: Sticker eect using shadows 144 .............................................................................................................. Section 14.2: How to stop further shadowing 145 ......................................................................................................... Section 14.3: Shadowing is computationally expensive -- Cache that shadow! 145 .................................................. Section 14.4: Add visual depth with shadows 146 ......................................................................................................... Section 14.5: Inner shadows 146 ..................................................................................................................................... Chapter 15: Charts & Diagrams 151 ......................................................................................................................... Section 15.1: Pie Chart with Demo 151 ............................................................................................................................ Section 15.2: Line with arrowheads 152 .......................................................................................................................... Section 15.3: Cubic & Quadratic Bezier curve with arrowheads 153 ........................................................................... Section 15.4: Wedge 154 .................................................................................................................................................. Section 15.5: Arc with both fill and stroke 155 ............................................................................................................... Chapter 16: Transformations 157 .............................................................................................................................. Section 16.1: Rotate an Image or Path around it's centerpoint 157 ............................................................................. Section 16.2: Drawing many translated, scaled, and rotated images quickly 158 .................................................... Section 16.3: Introduction to Transformations 159 ....................................................................................................... Section 16.4: A Transformation Matrix to track translated, rotated & scaled shape(s) 160 ..................................... Chapter 17: Compositing 167 ....................................................................................................................................... Section 17.1: Draw behind existing shapes with "destination-over" 167 ...................................................................... Section 17.2: Erase existing shapes with "destination-out" 167 ................................................................................... Section 17.3: Default compositing: New shapes are drawn over Existing shapes 168 .............................................. Section 17.4: Clip images inside shapes with "destination-in" 168 ............................................................................... Section 17.5: Clip images inside shapes with "source-in" 168 ...................................................................................... Section 17.6: Inner shadows with "source-atop" 169 ..................................................................................................... Section 17.7: Change opacity with "globalAlpha" 169 ................................................................................................... Section 17.8: Invert or Negate image with "dierence" 170 ......................................................................................... Section 17.9: Black & White with "color" 170 .................................................................................................................. Section 17.10: Increase the color contrast with "saturation" 171 ................................................................................. Section 17.11: Sepia FX with "luminosity" 171 .................................................................................................................. Chapter 18: Pixel Manipulation with "getImageData" and "putImageData" 173 ............................. Section 18.1: Introduction to "context.getImageData" 173 ........................................................................................... Credits 175 ............................................................................................................................................................................ You may also like 176 ......................................................................................................................................................

GoalKicker.com – HTML5 Canvas Notes for Professionals 1 About Please feel free to share this PDF with anyone for free, latest version of this book can be downloaded from: https://goalkicker.com/HTML5CanvasBook This HTML5 Canvas Notes for Professionals book is compiled from Stack Overflow Documentation, the content is written by the beautiful people at Stack Overflow. Text content is released under Creative Commons BY-SA, see credits at the end of this book whom contributed to the various chapters. Images may be copyright of their respective owners unless otherwise specified This is an unofficial free book created for educational purposes and is not affiliated with official HTML5 Canvas group(s) or company(s) nor Stack Overflow. All trademarks and registered trademarks are the property of their respective company owners The information presented in this book is not guaranteed to be correct nor accurate, use at your own risk Please send feedback and corrections to web@petercv.com

GoalKicker.com – HTML5 Canvas Notes for Professionals 2 Chapter 1: Getting started with HTML5 Canvas Section 1.1: Detecting mouse position on the canvas This example will show how to get the mouse position relative to the canvas, such that (0,0) will be the top-left hand corner of the HTML5 Canvas. The e.clientX and e.clientY will get the mouse positions relative to the top of the document, to change this to be based on the top of the canvas we subtract the left and right positions of the canvas from the client X and Y. var canvas = document.getElementById("myCanvas"); var ctx = canvas.getContext("2d"); ctx.font = "16px Arial"; canvas.addEventListener("mousemove", function(e) { var cRect = canvas.getBoundingClientRect(); // Gets CSS pos, and width/height var canvasX = Math.round(e.clientX - cRect.left); // Subtract the 'left' of the canvas var canvasY = Math.round(e.clientY - cRect.top); // from the X/Y positions to make ctx.clearRect(0, 0, canvas.width, canvas.height); // (0,0) the top left of the canvas ctx.fillText("X: "+canvasX+", Y: "+canvasY, 10, 20); }); Runnable Example The use of Math.round is due to ensure the x,y positions are integers, as the bounding rectangle of the canvas may not have integer positions. Section 1.2: Canvas size and resolution The size of a canvas is the area it occupies on the page and is defined by the CSS width and height properties. canvas { width : 1000px; height : 1000px; } The canvas resolution defines the number of pixels it contains. The resolution is set by setting the canvas element width and height properties. If not specified the canvas defaults to 300 by 150 pixels. The following canvas will use the above CSS size but as the width and height is not specified the resolution will be 300 by 150. <canvas id="my-canvas"></canvas> This will result in each pixel being stretched unevenly. The pixel aspect is 1:2. When the canvas is stretched the browser will use bilinear filtering. This has an effect of blurring out pixels that are stretched. For the best results when using the canvas ensure that the canvas resolution matches the display size. Following on from the CSS style above to match the display size add the canvas with the width and height set to the same pixel count as the style defines. <canvas id = "my-canvas" width = "1000" height = "1000"></canvas>

GoalKicker.com – HTML5 Canvas Notes for Professionals 3 Section 1.3: Rotate The rotate(r) method of the 2D context rotates the canvas by the specified amount r of radians around the origin. HTML <canvas id="canvas" width=240 height=240 style="background-color:#808080;"> </canvas> <button type="button" onclick="rotate_ctx();">Rotate context</button> JavaScript var canvas = document.getElementById("canvas"); var ctx = canvas.getContext("2d"); var ox = canvas.width / 2; var oy = canvas.height / 2; ctx.font = "42px serif"; ctx.textAlign = "center"; ctx.textBaseline = "middle"; ctx.fillStyle = "#FFF"; ctx.fillText("Hello World", ox, oy); rotate_ctx = function() { // translate so that the origin is now (ox, oy) the center of the canvas ctx.translate(ox, oy); // convert degrees to radians with radians = (Math.PI/180)*degrees. ctx.rotate((Math.PI / 180) * 15); ctx.fillText("Hello World", 0, 0); // translate back ctx.translate(-ox, -oy); }; Live demo on JSfiddle Section 1.4: Save canvas to image file You can save a canvas to an image file by using the method canvas.toDataURL(), that returns the data URI for the canvas' image data. The method can take two optional parameters canvas.toDataURL(type, encoderOptions): type is the image format (if omitted the default is image/png); encoderOptions is a number between 0 and 1 indicating image quality (default is 0.92). Here we draw a canvas and attach the canvas' data URI to the "Download to myImage.jpg" link. HTML <canvas id="canvas" width=240 height=240 style="background-color:#808080;"> </canvas> <p></p> <a id="download" download="myImage.jpg" href="" onclick="download_img(this);">Download to myImage.jpg</a> JavaScript var canvas = document.getElementById("canvas");

GoalKicker.com – HTML5 Canvas Notes for Professionals 4 var ctx = canvas.getContext("2d"); var ox = canvas.width / 2; var oy = canvas.height / 2; ctx.font = "42px serif"; ctx.textAlign = "center"; ctx.textBaseline = "middle"; ctx.fillStyle = "#800"; ctx.fillRect(ox / 2, oy / 2, ox, oy); download_img = function(el) { // get image URI from canvas object var imageURI = canvas.toDataURL("image/jpg"); el.href = imageURI; }; Live demo on JSfiddle. Section 1.5: How to add the Html5 Canvas Element to a webpage Html5-Canvas ... Is an Html5 element. Is supported in most modern browsers (Internet Explorer 9+). Is a visible element that is transparent by default Has a default width of 300px and a default height of 150px. Requires JavaScript because all content must be programmatically added to the Canvas. Example: Create an Html5-Canvas element using both Html5 markup and JavaScript: <!doctype html> <html> <head> <style> body{ background-color:white; } #canvasHtml5{border:1px solid red; } #canvasJavascript{border:1px solid blue; } </style> <script> window.onload=(function(){ // add a canvas element using javascript var canvas=document.createElement('canvas'); canvas.id='canvasJavascript' document.body.appendChild(canvas); }); // end $(function(){}); </script> </head> <body> <!-- add a canvas element using html --> <canvas id='canvasHtml5'></canvas> </body> </html>

GoalKicker.com – HTML5 Canvas Notes for Professionals 5 Section 1.6: An index to Html5 Canvas Capabilities & Uses Capabilities of the Canvas Canvas lets you programmatically draw onto your webpage: Images, Texts, Lines and Curves. Canvas drawings can be extensively styled: stroke width, stroke color, shape fill color, opacity, shadowing, linear gradients and radial gradients, font face, font size, text alignment, text may be stroked, filled or both stroked & filled, image resizing, image cropping, compositing Uses of the Canvas Drawings can be combined and positioned anywhere on the canvas so it can be used to create: Paint / Sketch applications, Fast paced interactive games, Data analyses like charts, graphs, Photoshop-like imaging, Flash-like advertising and Flashy web content. Canvas allows you to manipulate the Red, Green, Blue & Alpha component colors of images. This allows canvas to manipulate images with results similar to Photoshop. Recolor any part of an image at the pixel level (if you use HSL you can even recolor an image while retaining the important Lighting & Saturation so the result doesn't look like someone slapped paint on the image), "Knockout" the background around a person/item in an image, Detect and Floodfill part of an image (eg, change the color of a user-clicked flower petal from green to yellow -- just that clicked petal!), Do Perspective warping (e.g. wrap an image around the curve of a cup), Examine an image for content (eg. facial recognition), Answer questions about an image: Is there a car parked in this image of my parking spot?, Apply standard image filters (grayscale, sepia, etc) Apply any exotic image filter you can dream up (Sobel Edge Detection), Combine images. If dear Grandma Sue couldn't make it to the family reunion, just "photoshop" her into the reunion image. Don't like Cousin Phil -- just "photoshop him out, Play a video / Grab a frame from a video, Export the canvas content as a .jpg | .png image (you can even optionally crop or annotate the image and

GoalKicker.com – HTML5 Canvas Notes for Professionals 6 export the result as a new image), About moving and editing canvas drawings (for example to create an action game): After something has been drawn on the canvas, that existing drawing cannot be moved or edited. This common misconception that canvas drawings are movable is worth clarifying: Existing canvas drawings cannot be edited or moved! Canvas draws very, very quickly. Canvas can draw hundreds of images, texts, lines & curves in a fraction of a second. It uses the GPU when available to speed up drawing. Canvas creates the illusion of motion by quickly and repeatedly drawing something and then redrawing it in a new position. Like television, this constant redrawing gives the eye the illusion of motion. Section 1.7: O screen canvas Many times when working with the canvas you will need to have a canvas to hold some intrum pixel data. It is easy to create an offscreen canvas, obtain a 2D context. An offscreen canvas will also use the available graphics hardware to render. The following code simply creates a canvas and fills it with blue pixels. function createCanvas(width, height){ var canvas = document.createElement("canvas"); // create a canvas element canvas.width = width; canvas.height = height; return canvas; } var myCanvas = createCanvas(256,256); // create a small canvas 256 by 256 pixels var ctx = myCanvas.getContext("2d"); ctx.fillStyle = "blue"; ctx.fillRect(0,0,256,256); Many times the offscreen canvas will be used for many tasks, and you may have many canvases. To simplify the use of the canvas you can attach the canvas context to the canvas. function createCanvasCTX(width, height){ var canvas = document.createElement("canvas"); // create a canvas element canvas.width = width; canvas.height = height; canvas.ctx = canvas.getContext("2d"); return canvas; } var myCanvas = createCanvasCTX(256,256); // create a small canvas 256 by 256 pixels myCanvas.ctx.fillStyle = "blue"; myCanvas.ctx.fillRect(0,0,256,256); Section 1.8: Hello World HTML <canvas id="canvas" width=300 height=100 style="background-color:#808080;"> </canvas> JavaScript var canvas = document.getElementById("canvas");

GoalKicker.com – HTML5 Canvas Notes for Professionals 7 var ctx = canvas.getContext("2d"); ctx.font = "34px serif"; ctx.textAlign = "center"; ctx.textBaseline="middle"; ctx.fillStyle = "#FFF"; ctx.fillText("Hello World",150,50); Result

GoalKicker.com – HTML5 Canvas Notes for Professionals 8 Chapter 2: Text Section 2.1: Justified text This example renders justified text. It adds extra functionality to the CanvasRenderingContext2D by extending its prototype or as a global object justifiedText (optional see Note A). Example rendering. Code to render this image is in the usage examples at the bottom. The Example The function as a anonymous immediately invoked function. (function(){ const FILL = 0; // const to indicate filltext render const STROKE = 1; const MEASURE = 2; var renderType = FILL; // used internal to set fill or stroke text var maxSpaceSize = 3; // Multiplier for max space size. If greater then no justificatoin applied var minSpaceSize = 0.5; // Multiplier for minimum space size var renderTextJustified = function(ctx,text,x,y,width){ var words, wordsWidth, count, spaces, spaceWidth, adjSpace, renderer, i, textAlign, useSize, totalWidth; textAlign = ctx.textAlign; // get current align settings ctx.textAlign = "left"; wordsWidth = 0; words = text.split(" ").map(word => { var w = ctx.measureText(word).width; wordsWidth += w; return { width : w, word : word,

GoalKicker.com – HTML5 Canvas Notes for Professionals 9 }; }); // count = num words, spaces = number spaces, spaceWidth normal space size // adjSpace new space size >= min size. useSize Resulting space size used to render count = words.length; spaces = count - 1; spaceWidth = ctx.measureText(" ").width; adjSpace = Math.max(spaceWidth * minSpaceSize, (width - wordsWidth) / spaces); useSize = adjSpace > spaceWidth * maxSpaceSize ? spaceWidth : adjSpace; totalWidth = wordsWidth + useSize * spaces if(renderType === MEASURE){ // if measuring return size ctx.textAlign = textAlign; return totalWidth; } renderer = renderType === FILL ? ctx.fillText.bind(ctx) : ctx.strokeText.bind(ctx); // fill or stroke switch(textAlign){ case "right": x -= totalWidth; break; case "end": x += width - totalWidth; break; case "center": // intentional fall through to default x -= totalWidth / 2; default: } if(useSize === spaceWidth){ // if space size unchanged renderer(text,x,y); } else { for(i = 0; i < count; i += 1){ renderer(words[i].word,x,y); x += words[i].width; x += useSize; } } ctx.textAlign = textAlign; } // Parse vet and set settings object. var justifiedTextSettings = function(settings){ var min,max; var vetNumber = (num, defaultNum) => { num = num !== null && num !== null && !isNaN(num) ? num : defaultNum; if(num < 0){ num = defaultNum; } return num; } if(settings === undefined || settings === null){ return; } max = vetNumber(settings.maxSpaceSize, maxSpaceSize); min = vetNumber(settings.minSpaceSize, minSpaceSize); if(min > max){ return; } minSpaceSize = min; maxSpaceSize = max; } // define fill text var fillJustifyText = function(text, x, y, width, settings){ justifiedTextSettings(settings);

GoalKicker.com – HTML5 Canvas Notes for Professionals 10 renderType = FILL; renderTextJustified(this, text, x, y, width); } // define stroke text var strokeJustifyText = function(text, x, y, width, settings){ justifiedTextSettings(settings); renderType = STROKE; renderTextJustified(this, text, x, y, width); } // define measure text var measureJustifiedText = function(text, width, settings){ justifiedTextSettings(settings); renderType = MEASURE; return renderTextJustified(this, text, 0, 0, width); } // code point A // set the prototypes CanvasRenderingContext2D.prototype.fillJustifyText = fillJustifyText; CanvasRenderingContext2D.prototype.strokeJustifyText = strokeJustifyText; CanvasRenderingContext2D.prototype.measureJustifiedText = measureJustifiedText; // code point B // optional code if you do not wish to extend the CanvasRenderingContext2D prototype /* Uncomment from here to the closing comment window.justifiedText = { fill : function(ctx, text, x, y, width, settings){ justifiedTextSettings(settings); renderType = FILL; renderTextJustified(ctx, text, x, y, width); }, stroke : function(ctx, text, x, y, width, settings){ justifiedTextSettings(settings); renderType = STROKE; renderTextJustified(ctx, text, x, y, width); }, measure : function(ctx, text, width, settings){ justifiedTextSettings(settings); renderType = MEASURE; return renderTextJustified(ctx, text, 0, 0, width); } } to here*/ })(); Note A: If you do not wish to extend the CanvasRenderingContext2D prototype Remove from the example all code between // code point A and // code point B and uncomment the code marked /* Uncomment from here to the closing comment How to use Three functions are added to the CanvasRenderingContext2D and are available to all 2D context objects created. ctx.fillJustifyText( text, x, y, width, [settings]); ctx.strokeJustifyText( text, x, y, width, [settings]); ctx.measureJustifiedText( text, width, [settings]); Fill and stroke text function fill or stroke text and use the same arguments. measureJustifiedText will return the

GoalKicker.com – HTML5 Canvas Notes for Professionals 11 actual width that text would be rendered at. This may be equal, less, or greater than the argument width depending on current settings. Note: Arguments inside [ and ] are optional. Function arguments text: String containing the text to be rendered. x, y: Coordinates to render the text at. width: Width of the justified text. Text will increase/decrease spaces between words to fit the width. If the space between words is greater than maxSpaceSize (default = 6) times normal spacing will be used and the text will not fill the required width. If the spacing is less than minSpaceSize (default = 0.5) time normal spacing then the min space size is used and the text will overrun the width requested settings: Optional. Object containing min and max space sizes. The settings argument is optional and if not included text rendering will use the last setting defined or the default (shown below). Both min and max are the min and max sizes for the [space] character separating words. The default maxSpaceSize = 6 means that when the space between characters is > 63 * ctx.measureText(" ").width text will not be justified. If text to be justified has spaces less than minSpaceSize = 0.5 (default value 0.5) * ctx.measureText(" ").width the spacing will be set to minSpaceSize * ctx.measureText(" ").width and the resulting text will overrun the justifying width. The following rules are applied, min and max must be numbers. If not then the associate values will not be changed. If minSpaceSize is larger than maxSpaceSize both input setting are invalid and min max will not be changed. Example setting object with defaults settings = { maxSpaceSize : 6; // Multiplier for max space size. minSpaceSize : 0.5; // Multiplier for minimum space size }; NOTE: These text functions introduce a subtle behaviour change for the textAlign property of the 2D context. 'Left', 'right', 'center' and 'start' behave as is expected but 'end' will not align from the right of the function argument x but rather from the right of x + width Note: settings (min and max space size) are global to all 2D context objects. USAGE Examples var i = 0; text[i++] = "This text is aligned from the left of the canvas."; text[i++] = "This text is near the max spacing size"; text[i++] = "This text is way too short."; text[i++] = "This text is too long for the space provied and will overflow#";

GoalKicker.com – HTML5 Canvas Notes for Professionals 12 text[i++] = "This text is aligned using 'end' and starts at x + width"; text[i++] = "This text is near the max spacing size"; text[i++] = "This text is way too short."; text[i++] = "#This text is too long for the space provied and will overflow"; text[i++] = "This is aligned with 'center' and is placed from the center"; text[i++] = "This text is near the max spacing size"; text[i++] = "This text is way too short."; text[i++] = "This text is just too long for the space provied and will overflow"; // ctx is the 2d context // canvas is the canvas ctx.clearRect(0,0,w,h); ctx.font = "25px arial"; ctx.textAlign = "center" var left = 20; var center = canvas.width / 2; var width = canvas.width-left*2; var y = 40; var size = 16; var i = 0; ctx.fillText("Justified text examples.",center,y); y+= 40; ctx.font = "14px arial"; ctx.textAlign = "left" var ww = ctx.measureJustifiedText(text[0], width); var setting = { maxSpaceSize : 6, minSpaceSize : 0.5 } ctx.strokeStyle = "red" ctx.beginPath(); ctx.moveTo(left,y - size * 2); ctx.lineTo(left, y + size * 15); ctx.moveTo(canvas.width - left,y - size * 2); ctx.lineTo(canvas.width - left, y + size * 15); ctx.stroke(); ctx.textAlign = "left"; ctx.fillStyle = "red"; ctx.fillText("< 'left' aligned",left,y - size) ctx.fillStyle = "black"; ctx.fillJustifyText(text[i++], left, y, width, setting); // settings is remembered ctx.fillJustifyText(text[i++], left, y+=size, width); ctx.fillJustifyText(text[i++], left, y+=size, width); ctx.fillJustifyText(text[i++], left, y+=size, width); y += 2.3*size; ctx.fillStyle = "red"; ctx.fillText("< 'end' aligned from x plus the width -------------------->",left,y - size) ctx.fillStyle = "black"; ctx.textAlign = "end"; ctx.fillJustifyText(text[i++], left, y, width); ctx.fillJustifyText(text[i++], left, y+=size, width); ctx.fillJustifyText(text[i++], left, y+=size, width); ctx.fillJustifyText(text[i++], left, y+=size, width); y += 40; ctx.strokeStyle = "red" ctx.beginPath(); ctx.moveTo(center,y - size * 2); ctx.lineTo(center, y + size * 5); ctx.stroke(); ctx.textAlign = "center";

GoalKicker.com – HTML5 Canvas Notes for Professionals 13 ctx.fillStyle = "red"; ctx.fillText("'center' aligned",center,y - size) ctx.fillStyle = "black"; ctx.fillJustifyText(text[i++], center, y, width); ctx.fillJustifyText(text[i++], center, y+=size, width); ctx.fillJustifyText(text[i++], center, y+=size, width); ctx.fillJustifyText(text[i++], center, y+=size, width); Section 2.2: Justified paragraphs Renders text as justified paragraphs. REQUIRES the example Justified text Example render Top paragraph has setting.compact = true and bottom false and line spacing is 1.2 rather than the default 1.5. Rendered by code usage example bottom of this example. Example code // Requires justified text extensions (function(){ // code point A if(typeof CanvasRenderingContext2D.prototype.fillJustifyText !== "function"){ throw new ReferenceError("Justified Paragraph extension missing requiered CanvasRenderingContext2D justified text extension"); } var maxSpaceSize = 3; // Multiplier for max space size. If greater then no justificatoin applied var minSpaceSize = 0.5; // Multiplier for minimum space size var compact = true; // if true then try and fit as many words as possible. If false then try to get the spacing as close as possible to normal var lineSpacing = 1.5; // space between lines const noJustifySetting = { // This setting forces justified text off. Used to render last line of paragraph. minSpaceSize : 1, maxSpaceSize : 1, }

GoalKicker.com – HTML5 Canvas Notes for Professionals 14 // Parse vet and set settings object. var justifiedTextSettings = function(settings){ var min, max; var vetNumber = (num, defaultNum) => { num = num !== null && num !== null && !isNaN(num) ? num : defaultNum; return num < 0 ? defaultNum : num; } if(settings === undefined || settings === null){ return; } compact = settings.compact === true ? true : settings.compact === false ? false : compact; max = vetNumber(settings.maxSpaceSize, maxSpaceSize); min = vetNumber(settings.minSpaceSize, minSpaceSize); lineSpacing = vetNumber(settings.lineSpacing, lineSpacing); if(min > max){ return; } minSpaceSize = min; maxSpaceSize = max; } var getFontSize = function(font){ // get the font size. var numFind = /[0-9]+/; var number = numFind.exec(font)[0]; if(isNaN(number)){ throw new ReferenceError("justifiedPar Cant find font size"); } return Number(number); } function justifiedPar(ctx, text, x, y, width, settings, stroke){ var spaceWidth, minS, maxS, words, count, lines, lineWidth, lastLineWidth, lastSize, i, renderer, fontSize, adjSpace, spaces, word, lineWords, lineFound; spaceWidth = ctx.measureText(" ").width; minS = spaceWidth * minSpaceSize; maxS = spaceWidth * maxSpaceSize; words = text.split(" ").map(word => { // measure all words. var w = ctx.measureText(word).width; return { width : w, word : word, }; }); // count = num words, spaces = number spaces, spaceWidth normal space size // adjSpace new space size >= min size. useSize Resulting space size used to render count = 0; lines = []; // create lines by shifting words from the words array until the spacing is optimal. If compact // true then will true and fit as many words as possible. Else it will try and get the spacing as // close as possible to the normal spacing while(words.length > 0){ lastLineWidth = 0; lastSize = -1; lineFound = false; // each line must have at least one word. word = words.shift(); lineWidth = word.width; lineWords = [word.word]; count = 0; while(lineWidth < width && words.length > 0){ // Add words to line word = words.shift(); lineWidth += word.width; lineWords.push(word.word); count += 1; spaces = count - 1; adjSpace = (width - lineWidth) / spaces;

GoalKicker.com – HTML5 Canvas Notes for Professionals 15 if(minS > adjSpace){ // if spacing less than min remove last word and finish line lineFound = true; words.unshift(word); lineWords.pop(); }else{ if(!compact){ // if compact mode if(adjSpace < spaceWidth){ // if less than normal space width if(lastSize === -1){ lastSize = adjSpace; } // check if with last word on if its closer to space width if(Math.abs(spaceWidth - adjSpace) < Math.abs(spaceWidth - lastSize)){ lineFound = true; // yes keep it }else{ words.unshift(word); // no better fit if last word removes lineWords.pop(); lineFound = true; } } } } lastSize = adjSpace; // remember spacing } lines.push(lineWords.join(" ")); // and the line } // lines have been worked out get font size, render, and render all the lines. last // line may need to be rendered as normal so it is outside the loop. fontSize = getFontSize(ctx.font); renderer = stroke === true ? ctx.strokeJustifyText.bind(ctx) : ctx.fillJustifyText.bind(ctx); for(i = 0; i < lines.length - 1; i ++){ renderer(lines[i], x, y, width, settings); y += lineSpacing * fontSize; } if(lines.length > 0){ // last line if left or start aligned for no justify if(ctx.textAlign === "left" || ctx.textAlign === "start"){ renderer(lines[lines.length - 1], x, y, width, noJustifySetting); ctx.measureJustifiedText("", width, settings); }else{ renderer(lines[lines.length - 1], x, y, width); } } // return details about the paragraph. y += lineSpacing * fontSize; return { nextLine : y, fontSize : fontSize, lineHeight : lineSpacing * fontSize, }; } // define fill var fillParagraphText = function(text, x, y, width, settings){ justifiedTextSettings(settings); settings = { minSpaceSize : minSpaceSize, maxSpaceSize : maxSpaceSize, }; return justifiedPar(this, text, x, y, width, settings); } // define stroke var strokeParagraphText = function(text, x, y, width, settings){ justifiedTextSettings(settings);

GoalKicker.com – HTML5 Canvas Notes for Professionals 16 settings = { minSpaceSize : minSpaceSize, maxSpaceSize : maxSpaceSize, }; return justifiedPar(this, text, x, y, width, settings,true); } CanvasRenderingContext2D.prototype.fillParaText = fillParagraphText; CanvasRenderingContext2D.prototype.strokeParaText = strokeParagraphText; })(); NOTE this extends the CanvasRenderingContext2D prototype. If you do not wish this to happen use the example Justified text to work out how to change this example to be part of the global namespace. NOTE Will throw a ReferenceError if this example can not find the function CanvasRenderingContext2D.prototype.fillJustifyText How to use ctx.fillParaText(text, x, y, width, [settings]); ctx.strokeParaText(text, x, y, width, [settings]); See Justified text for details on arguments. Arguments between [ and ] are optional. The settings argument has two additional properties. compact: Default true. If true tries to pack as many words as possible per line. If false the tries to get the word spacing as close as possible to normal spacing. lineSpacing Default 1.5. Space per line default 1.5 the distance from on line to the next in terms of font size Properties missing from the settings object will default to their default values or to the last valid values. The properties will only be changed if the new values are valid. For compact valid values are only booleans true or false Truthy values are not considered valid. Return object The two functions return an object containing information to help you place the next paragraph. The object contains the following properties. nextLine Position of the next line after the paragraph pixels. fontSize Size of the font. (please note only use fonts defined in pixels eg 14px arial) lineHeight Distance in pixels from one line to the next This example uses a simple algorithm that works one line at to time to find the best fit for a paragraph. This does not mean that it the best fit (rather the algorithm's best) You may wish to improve the algorithm by creating a multi pass line algorithm over the generated lines. Moving words from the end of one line to the start of the next, or from the start back to the end. The best look is achieved when the spacing over the entire paragraph has the smallest variation and is the closest to the normal text spacing. As this example is dependent on the Justified text example the code is very similar. You may wish to move the two into one function. Replace the function justifiedTextSettings in the other example with the one used in this example. Then copy all the rest of the code from this example into the anonymous function body of the Justified text example. You will no longer need to test for dependencies found at // Code point A It can be removed.