FillTrangle produces slightly different results if drawn in a BPicture

[jackburton]

As shown by the FlattenPictureTest test, FillTriangle produces a slightly different result when invoked inside a BPicture. This happens because there is no FILL_TRIANGLE op in the BPicture encoding, and FillTriangle is translated to a FillPolygon call. Now, I'd expect that FillPolygon(), when called with three points, would produce the same output that FillTriangle does.

[jackburton]

I've noticed that Painter::_DrawTriangle() (which is called for the fill_triangle op), aligns the points using the "_Align()" function with the "centerOffset" parameter set to true, while Painter::DrawPolygon() (called for the fill_polygon op) calls _Align() with the centerOffset parameter set to false. _Align(), if centerOffset is set to true, increments the point coordinates by 0.5. I don't know which one is correct, but it's what's causing this bug.

[stippi]

Thanks for investigating, Stefano! I'll try to have a look. The offsetting by 0.5 is to get a closer match to the original BeOS drawings. It should actually only happen when stroking, not when filling. I'll need to have a closer look, but of course it would be nice if FillTriangle() and FillPolygon() produce the exact same output for the same points.