On Thu, Feb 7, 2019 at 08:10 PM, Jon Welch wrote:

Looks like it's a bug in the OS then

But via what mechanism?  As you know the 2D 'drawing' routines (specifically the bezierColor function in this case) are in the SDL2_gfx library which is statically linked with BBCSDL, not part of Android.  So it's not clear to me how differences in the 'OS' can affect what pixels are plotted, even though the evidence would suggest that is exactly what is happening.

I do hope you will continue to investigate, perhaps by trying to devise a workaround if that is the only solution.  Out of curiosity, what is the effect of changing the number of line segments that are used to draw the Bezier curves (fifth parameter of bezierColor)?  Does increasing it from 3 to 4 (or more) make the problem better, worse, or no difference?  Can you tell (perhaps by changing the colours) whether the 'holes' are within the Bezier curves or between them?  If they are between them there is more opportunity for patching them.

If the problem cannot be fixed I will obviously have to remove the angled ellipse library from BBCSDL because it is not acceptable to include a library which isn't genuinely 'cross platform'.