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<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" >
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<head>
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<title>Approximation of an arc with bezier</title>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<script type="text/javascript">djConfig = { isDebug: true };</script>
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<script type="text/javascript" src="../../dojo.js"></script>
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<script type="text/javascript">dojo.require("dojo.debug.console");</script>
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<!--<script type="text/javascript" src="../../src/gfx/common.js"></script>-->
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<!--<script type="text/javascript" src="../../src/gfx/path.js"></script>-->
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<!--<script type="text/javascript" src="../../src/gfx/vml.js"></script>-->
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<!--<script type="text/javascript" src="../../src/gfx/svg.js"></script>-->
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<script type="text/javascript">
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dojo.require("dojo.gfx.*");
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makeShapes = function(){
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var surface = dojo.gfx.createSurface("test", 500, 300);
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var g = surface.createGroup();
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// create a reference ellipse
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var rx = 200;
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var ry = 100;
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var startAngle = 30;
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var arcAngle = 90;
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var axisAngle = 30;
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var e = g.createEllipse({rx: rx, ry: ry}).setStroke({});
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// calculate a bezier
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var alpha = dojo.math.degToRad(arcAngle) / 2; // half of our angle
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var cosa = Math.cos(alpha);
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var sina = Math.sin(alpha);
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// start point
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var p1 = {x: cosa, y: sina};
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// 1st control point
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var p2 = {x: cosa + (4 / 3) * (1 - cosa), y: sina - (4 / 3) * cosa * (1 - cosa) / sina};
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// 2nd control point (symmetric to the 1st one)
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var p3 = {x: p2.x, y: -p2.y};
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// end point (symmetric to the start point)
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var p4 = {x: p1.x, y: -p1.y};
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// rotate and scale poins as appropriate
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var s = dojo.gfx.matrix.normalize([dojo.gfx.matrix.scale(e.shape.rx, e.shape.ry), dojo.gfx.matrix.rotateg(startAngle + arcAngle / 2)]);
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p1 = dojo.gfx.matrix.multiplyPoint(s, p1);
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p2 = dojo.gfx.matrix.multiplyPoint(s, p2);
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p3 = dojo.gfx.matrix.multiplyPoint(s, p3);
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p4 = dojo.gfx.matrix.multiplyPoint(s, p4);
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// draw control trapezoid
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var t = g.createPath().setStroke({color: "blue"});
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t.moveTo(p1.x, p1.y);
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t.lineTo(p2.x, p2.y);
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t.lineTo(p3.x, p3.y);
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t.lineTo(p4.x, p4.y);
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t.lineTo(p1.x, p1.y);
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t.moveTo((p1.x + p4.x) / 2, (p1.y + p4.y) / 2);
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t.lineTo((p2.x + p3.x) / 2, (p2.y + p3.y) / 2);
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t.moveTo((p1.x + p2.x) / 2, (p1.y + p2.y) / 2);
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t.lineTo((p3.x + p4.x) / 2, (p3.y + p4.y) / 2);
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// draw a bezier
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var b = g.createPath().setStroke({color: "red"});
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b.moveTo(p1.x, p1.y);
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b.curveTo(p2.x, p2.y, p3.x, p3.y, p4.x, p4.y);
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// move everything in a middle
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g.setTransform([dojo.gfx.matrix.translate(250, 150), dojo.gfx.matrix.rotateg(axisAngle)]);
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};
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dojo.addOnLoad(makeShapes);
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</script>
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</head>
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<body>
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<p>Approximation of an arc with bezier</p>
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<!--<p><button onclick="makeShapes();">Make</button></p>-->
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<div id="test" style="width: 500px; height: 300px;"></div>
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<p>That's all Folks!</p>
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</body>
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</html>
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