Drawing an arrowhead on a line in canvas. Move mouse to move line. Similar to a marker tag in SVG.
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December 5, 2015 13:22
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Line Arrow
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| <html> | |
| <head> | |
| <title>Line Arrow</title> | |
| </head> | |
| <body> | |
| <script src="//d3js.org/d3.v3.min.js" charset="utf-8"></script> | |
| <script> | |
| var width = 960, | |
| height = 500, | |
| arrowLength = 10; | |
| var canvas = d3.select("body").append("canvas") | |
| .attr("width", width) | |
| .attr("height", height); | |
| var context = canvas.node().getContext("2d"); | |
| var origin = {x: width/2, y: height/2}; | |
| draw(width/4, height/4); | |
| canvas | |
| .on("mousemove", function() { | |
| var mouse = d3.mouse(this); | |
| var d = truncateVector([origin, {x: mouse[0], y: mouse[1]}], .8)[1]; | |
| draw(d.x, d.y); | |
| }); | |
| function draw(x, y) { | |
| var endPoint = {x, y}, | |
| arrowData = getArrowData([origin, endPoint]); | |
| context.clearRect(0, 0, width, height); | |
| path(context, [origin, endPoint]); | |
| path(context, [endPoint, arrowData.left]); | |
| path(context, [endPoint, arrowData.right]); | |
| } | |
| function path(context, data) { | |
| context.beginPath(); | |
| context.moveTo(data[0].x, data[0].y); | |
| data.slice(1).forEach(function(d) { | |
| context.lineTo(d.x, d.y); | |
| }); | |
| context.stroke(); | |
| context.closePath(); | |
| } | |
| function truncateVector(data, c) { | |
| var x0 = data[0].x, y0 = data[0].y, | |
| x1 = data[1].x, y1 = data[1].y, | |
| endPoint = { | |
| x: x0 + (x1-x0)*c, | |
| y: y0 + (y1-y0)*c | |
| }; | |
| return [data[0], endPoint]; | |
| } | |
| function getArrowData(data) { | |
| var data = data.slice(-2), | |
| x0 = data[0].x, y0 = data[0].y, | |
| x1 = data[1].x, y1 = data[1].y, | |
| t = Math.atan2(y1-y0, x1-x0), | |
| dt = Math.PI*(3/4); | |
| return { | |
| right: { | |
| x: arrowLength * Math.cos(t + dt) + x1, | |
| y: arrowLength * Math.sin(t + dt) + y1 | |
| }, | |
| left: { | |
| x: arrowLength * Math.cos(t - dt) + x1, | |
| y: arrowLength * Math.sin(t - dt) + y1 | |
| } | |
| }; | |
| } | |
| </script> | |
| </body> | |
| </html> |
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