[Xr] Xr API comments: Arcs

Paul Sladen xr at paul.sladen.org
Sat May 31 04:43:48 PDT 2003

On Mon, 26 May 2003, Carl Worth wrote:
> The only remaining problem is that I need an implementation that can
> break an elliptical arc into a sufficient number of cubic splines [...]

Arcs (including 360^ ones) need direct support.  The reason that Arcs
exist in every low-level drawing API is because they /cannot/ be accurately
approximated with Cubics...

Secondly, on scanline devices circular/elliptical arcs can be rendered
*incrementally* and do not need the overhead of converting to line-segments.

> I haven't planned to add rounded rectangles,

These are paths composed of 4 arcs and 4 lines.  This stuff is high-level...

> but the XrArcTo

Look very carefully at the Quartz support for Arcs, the two forms: {centre,
axial-radius, angle} and {point, point, point} are a nightmare to convert
between.  Both should probably be provided--with functions available in a
support-library to translate between the two.


War is inconsistent with Truth.  Nottingham, GB

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