[libGD] #79 [Comment added] arc's are drawn incorrectly (plus regression in 2.0.35RC2)

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FS#79 - arc's are drawn incorrectly (plus regression in 2.0.35RC2)
User who did this - Pierre Joye (Pierre)

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> I am seeing the problem with AA lines as well. AA lines at certain angles(?) are not drawn in true-color PNG. (Attached is a circle drawn using lines.) I'd like to use PNG output to support alpha anti-aliased text, which works well.

It is not a problem of the AA lines but the way we draw circles, ellipses (arc or full). We draw arcs using many lines. Extrems of the arc are drawn using single pixel lines mostl. Many of them overlap, blending ops are done many times within the same area. It ends to pure white when the drawing operation is finished.

> Is there a existing solution for drawing smooth/AA diagonal lines in true-color PNG?

You can draw AA lines at any angle, it works. But if you draw again again on the same area, the result will likely look like the background color.

A better approach to draw circles or ellipses is to use the Bresenham algorithm. I use it in my new implementation of the gdImageFilledEllipse function (already in 2.0.34 and later). That's what I use as well in the upcoming antialiased arcs functions.

What's about this change, does it work as you expect? (without AA, it cannot be done in 2.0.x but in 2.1.x).
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More information can be found at the following URL:
http://bugs.libgd.org/?do=details&task_id=79#comment245

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