Auto-height dialogs need one frame to measure their content height before they
can be centered. Previously that first frame was drawn near the top, so a
first-ever open flashed off-center for a frame before snapping to center.
On the measuring frame, lay the content out (so the child's auto-height is still
measured) but clip the whole card to a zero rect and skip the glass panel — the
card draws nothing while the blur backdrop still shows, then it appears already
centered on the next frame. Clip covers both ImGui widgets and hand-drawn
content; layout/measurement is unaffected (verified migrate / about / import-key
still render centered at the settled frame).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
DanS
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