44 lines
1.4 KiB
HTML
44 lines
1.4 KiB
HTML
<!DOCTYPE html>
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<html>
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<head></head>
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<body>
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<canvas id="mycanvas" width="300" height="300"></canvas>
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<script>
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function rad2deg(x) {
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return x * 180 / Math.PI;
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}
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function ellipseUsingArc(context, x, y, radiusX, radiusY, rotation, startAngle, endAngle, anticlockwise)
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{
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var transform = new WebKitCSSMatrix();
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transform = transform.translate(x, y);
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transform = transform.rotate(rad2deg(rotation));
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transform = transform.scale(radiusX, radiusY);
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/*
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Use WebKitCSSMatrix instead of as follows, because using WebKitCSSMatrix computes float values more precisely.
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It is because we don't want to fail pixel comparison due to float precision.
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context.translate(x, y);
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context.rotate(rotation);
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context.scale(radiusX, radiusY);
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*/
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context.save();
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context.transform(transform.a, transform.b, transform.c, transform.d, transform.e, transform.f);
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context.arc(0, 0, 1, startAngle, endAngle, anticlockwise);
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context.restore();
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}
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var canvas = document.getElementById('mycanvas');
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var ctx = canvas.getContext('2d');
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ctx.fillStyle = '#0f0';
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ctx.fillRect(0, 0, canvas.width, canvas.height);
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ctx.lineJoin = 'bevel';
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ctx.lineWidth = 12;
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ctx.beginPath();
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ellipseUsingArc(ctx, 200, 150, 40, 80, -Math.PI / 6, Math.PI / 2, -Math.PI / 2, false);
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ellipseUsingArc(ctx, 100, 150, 40, 80, Math.PI / 6, Math.PI / 2, -Math.PI / 2, false);
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ctx.stroke();
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</script>
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</body>
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</html> |