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Subject: Re: [office] How to calculate the start and end point of an elliptical arc from given angles.
Hi Regina, thanks for another detailed analysis here - you wrote: > But the specification does not describe, how to calculate the start > and end point. I have tested it with some applications and found, > that actually two methods are used. > > (1) Used by LibreOffice 4.0 and PowerPoint 2013 Preview > Draw an angle with the given value (here 30deg and 315deg). > Calculate the intersection of the leg of the angle with the full > ellipse (here center (3000|1000) and size (6000|2000)). > That at least appears to be the simplest interpretation. Also note that those enhanced paths are more-or-less a bijection of those binary ppt autoshape things (see also 20.1.9 in ISO 29500), and keeping that mapping lossless and/or preventing excessive recalculation seems desirable. > I have no proposal, because both methods are reasonable. > I wonder how wide-spread those commands are - where did you notice the difference, I presume there is a bug report somewhere? > (C) The applications agree in which direction they draw the arc. But > it looks not like "clockwise", although "clockwise" is specified. > That looks like an easy fix then. > (D) The applications agree use the angle direction as positive from > positive x-axis to negative y-axis. That is against mathematical > definition. Again a problem of insufficient angle definitions in the > specification. > Seems uncontroversial to fix, too? Kind regards, -- Thorsten Behrens SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg; GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer, HRB 16746 (AG Nürnberg)
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