[Kstars-devel] Performance of KStars Lite

[Artem Fedoskin]

Dear developers of KStars,

While porting lines (Equator, EquatorialCoordinateGrid,
HorizontalCoordinateGrid,
ConstellationLines etc.) I noticed that performance of Android version fell
down pretty significant. Profiler shows that sincos is called a lot and at
least on my tablet this causes very laggy slewing.
I thought that we could use SkyMesh to see what lines have to be updated
and call toScreenVec accordingly but it turns out that SkyMesh doesn't
always return visible Trixels correctly. I'm doing the following:

   1. Call SkyMesh::aperture(focus, radius)
   2. Iterate over visible trixels with MeshIterator region (mesh,DRAW_BUF);

On minimum zoom when the whole half sphere is visible I get all 512 trixels.
I thought that in this case it has to be around 256 trixels. Also when I
don't draw lines based on what trixels are visible, some of lines in
visible area are not drawn. Is it a normal behavior or a bug?

Is it possible to minimize the number of calls to Projector::toScreenVec()?
Can we modify Projector::checkVisibility() so that we don't call toScreenVec()
if we now that the SkyPoint is not visible?

I committed all the changes so feel free to test them on your device and
measure the performance. Also, if someone has experience with shaders I
would appreciate helping me as Qt Quick Scene Graph doesn't support drawing
dashed lines out of a box and I would like to use shaders for that but have
a few questions.

Regards, Artem
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