Created
October 9, 2013 13:38
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An extension to the CanvasRenderingContext2D's fillText method that supports line breaks and automatically fits the text into a specified bounding box.
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| <!DOCTYPE html> | |
| <html> | |
| <body> | |
| <canvas id="canvas" width="800" height="400" style="border: 1px solid #333;"></canvas> | |
| <script type="text/javascript"> | |
| // Based on: | |
| // http://www.html5canvastutorials.com/tutorials/html5-canvas-wrap-text-tutorial | |
| CanvasRenderingContext2D.prototype.textLines = function(x, y, w, h, text, | |
| hard_wrap) { | |
| var ctx = this; | |
| var lines = Array(); | |
| var hard_lines = text.trim().split("\n"); | |
| hard_lines.forEach(function(hard_line) { | |
| if(ctx.measureText(hard_line).width > w) { | |
| var line = ""; | |
| var words = hard_line.split(" "); | |
| words.forEach(function(word) { | |
| var nline = line + word + " "; | |
| if(ctx.measureText(nline).width > w) { | |
| lines.push(line); | |
| if(ctx.measureText(word).width > w && hard_wrap) { | |
| line = ""; | |
| var chars = word.split(""); | |
| chars.forEach(function(char) { | |
| var nline = line + char; | |
| if(ctx.measureText(nline).width > w) { | |
| lines.push(line); | |
| line = char; | |
| } else { | |
| line = nline; | |
| } | |
| }); | |
| line += " "; | |
| } else { | |
| line = word + " "; | |
| } | |
| } else { | |
| line = nline; | |
| } | |
| }); | |
| lines.push(line); | |
| } else { | |
| lines.push(hard_line); | |
| } | |
| }); | |
| return lines; | |
| }; | |
| CanvasRenderingContext2D.prototype.boxedFillText = function(x, y, w, h, text, | |
| hard_wrap) { | |
| var ctx = this; | |
| var lines = ctx.textLines(x, y, w, h, text, hard_wrap); | |
| var lineHeight = parseInt(ctx.font.split("px")[0]) * 1.2; | |
| var min_y = y; | |
| var max_y = y + h; | |
| var ll = lines.length - 1; | |
| switch(ctx.textBaseline.toLowerCase()) { | |
| case "bottom": | |
| min_y = y - h + lineHeight; | |
| max_y = y; | |
| y -= ll * lineHeight; | |
| if(y < min_y) | |
| y = min_y; | |
| break; | |
| case "middle": | |
| min_y = y - h / 2 + lineHeight / 2; | |
| max_y = y + h / 2 - lineHeight / 2; | |
| y -= (ll / 2) * lineHeight; | |
| if(y < min_y) | |
| y = min_y; | |
| break; | |
| default: | |
| break; | |
| } | |
| console.log(ctx.textBaseline); | |
| lines.forEach(function(line) { | |
| if(y <= max_y) { | |
| ctx.fillText(line, x, y); | |
| } | |
| y += lineHeight; | |
| }); | |
| }; | |
| var canvas = document.getElementById("canvas"); | |
| var ctx = canvas.getContext("2d"); | |
| ctx.fillStyle = "#0F0"; | |
| ctx.fillRect(20, 20, 200, 150); | |
| ctx.fillRect(20, 220, 200, 150); | |
| ctx.font = "20px Arial"; | |
| ctx.fillStyle = "#000"; | |
| ctx.textBaseline = "middle"; | |
| var text = "This is\nsome nice text WithAVeryLongWordInItThatIsTooLong.."; | |
| ctx.boxedFillText(20, 95, 200, 150, text); | |
| ctx.boxedFillText(20, 295, 200, 150, text, true); | |
| </script> | |
| </body> | |
| </html> |
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