[whatwg] Canvas arcTo method

Michael Day mikeday at yeslogic.com
Sun Aug 19 20:10:11 PDT 2012


The camvas arcTo method generates an arc that touches two tangent lines. 
The first tangent line is from the last point in the previous subpath to 
the first point passed to the arcTo method.

What happens in this situation:

ctx.lineTo(100, 100);
ctx.scale(2, 1);
ctx.arcTo(100, 100, 100, 200, 100);

The current transformation matrix should be used to transform the 
generated arc, not to transform its control points.

However, in this case the first untransformed control point is equal to 
the last point in the previous subpath, which means it must generate a 
straight line and not an arc.

Firefox and Chrome do not do this, as can be seen by viewing the 
attached HTML file.

What is the correct behaviour in this case?

Best regards,


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