Columns: Make sure the ClipRect is valid.

[szreder]

When a window with columns is dragged horizontally outside of the viewport, the ClipRect of a column may fall entirely outside ClipRect of the containing window. Intersecting those ClipRects using ClipWith() member function may cause the resulting rectangle to be invalid (meaning: ClipRect.Min.x > ClipRect.Max.x).

Fix this issue by using ClipWithFull() instead.

[ocornut]

Hello,
Thanks for the PR. I think the fix is fine as is for this specific case, however the way things are designed, an “inverted” rectangle should be perfectly valid as “null” rectangle.

So my question is: could you describe which issue you are getting which made you dig into this fix?

Thank you!

[szreder]

Hello,
the "inverted" rectangle gets passed to the ImDrawCmd for which I assumed (based on related IM_ASSERT()s sprinkled here and there) that its ClipRect need to be valid (non-inverted). My renderer balked at such inverted rectangles, which caused me to investigate the issue in the first place.

At first I though about hackfixing the renderer to accept such rectangles, but after diving into ImGui's code and noticing the aforementioned asserts, I came to the conclusion that the proper fix is to use ClipWithFull(). My conviction was further strenghtened after reading comments beside struct ImRect ClipWith() and ClipWithFull() member functions.

Best regards

[ocornut]

the "inverted" rectangle gets passed to the ImDrawCmd

I can't repro that in the unmodified demo, because high-level primitives are clipped, making the ImDrawCmd empty and culled before it gets a chance to reach the rendering back-end. However, I can see that adding e.g. unclipped ImDrawList calls create the situation you mention.

ImDrawList::PushClipRect() does the equivalent of ClipWithFull() so the culprit is that custom code calling the optimized shortcut SetWindowClipRectBeforeSetChannel() needs to pass a positive or null ClipRect.

I'll merge you fix and will make sure other users of SetWindowClipRectBeforeSetChannel() also perform clipping the expected way.