Simulate the openGL triangle primitive but with non-linear projection

Registered by Fabien Chéreau

When openGL triangles are currently rendered using a non-linear projection, only the corner vertices have the proper position, and the inside texture is linearly interpolated between the 3 points. This can cause annoying distortions for large triangles.

If you want to see this problem into effect, use a 360 deg FOV with the Hammer Aitoff distortion, and activate the constellations art. You will see at the top that the distortions look ugly.

A solution is to sub-tessellate the triangles at the time of rendering into smaller triangles when needed, until the distortions reach a value making them less visible.
The same technique is applied when rendering arcs in StelPainter::drawSmallCircleArc()

Blueprint information

Status:
Complete
Approver:
None
Priority:
Undefined
Drafter:
None
Direction:
Needs approval
Assignee:
None
Definition:
Approved
Series goal:
None
Implementation:
Implemented
Milestone target:
None
Started by
Fabien Chéreau
Completed by
Fabien Chéreau

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