Fix ellipse angles definition #24816
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As was found in whatwg/html#8408 the ellipse's `startAngle` and `endAngle` are not really angles on the ellipse, but angles on the eccentric circle of the ellipse. These are known as "eccentric angle", though this term *might* be a bit obscure at first sight, so I wouldn't mind a better proposition if reviewers have one. The specs got fixed in whatwg/html#8495 but as can be seen, the fix was quite verbose and I'm not sure the docs need to get that much details. So I hope this little fix is both enough to lead the ones that could get surprised by the actual behavior to the proper understanding, and not too obscure to lose in details the ones that wouldn't notice.
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(comment last updated: 2023-02-24 07:56:30) |
teoli2003
suggested changes
Feb 24, 2023
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This is a really good catch, and I learned some math stuff today (and I am giving maths lessons) |
Co-authored-by: Jean-Yves Perrier <jypenator@gmail.com>
Co-authored-by: Jean-Yves Perrier <jypenator@gmail.com>
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Description
This fixes a the Canvas2D
ellipse()methods angles definition.As was found in whatwg/html#8408 the ellipse's
startAngleandendAngleare not really angles on the ellipse, but angles on the eccentric circle of the ellipse.These are known as "eccentric angle" (e.g on Wolfram) , though this term might be a bit obscure at first sight, so I wouldn't mind a better proposition if reviewers have one.
Motivation
A couple of questions were opened on StackOverflow over this discrepancy between specs+docs vs implementations. (https://stackoverflow.com/questions/74111375, https://stackoverflow.com/questions/52149077)
Additional details
The specs got fixed in whatwg/html#8495 but as can be seen, the fix was quite verbose and I'm not sure the docs need to get into that much details. So I hope this little fix is both enough to lead the ones that could get surprised by the actual behavior to the proper understanding, and not too obscure to lose in details the ones that wouldn't notice.
Related issues and pull requests
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