Instead of 4 MVP passes that double-draw at mirror boundaries (causing
bright seam from overlapping semi-transparent bars), expand the half-size
vertices into all 4 quadrants on the CPU by flipping coordinates. Draw
everything in a single pass with one full-screen ortho MVP. Each pixel is
now covered by exactly one quadrant's geometry — no overlap, no seam.
Also simplifies render: removes 4-pass loop, removes separate cepstrum
MVP slot (shares slot 0).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Same approach as the horizontal overlap (55% width) — the half-canvas
now extends 2 pixels past the midline so top/bottom quadrants overlap
slightly, covering rounding/rasterization gaps.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
pszsh