The GL native-wide present (Option B) did glFinish + glReadPixels of the whole
wide FBO to the CPU and re-uploaded it EVERY frame — a hard GPU pipeline stall +
round-trip that made OpenGL 16:9 run far slower than the software renderer (whose
wide path is pure CPU, no GPU sync). Confirmed by isolation: GL 4:3 smooth, GL
16:9 slow, independent of SS/AA.
Add gl_renderer_present_wide_fbo: blit the displayed buffer's wide FBO straight to
the window with glBlitFramebuffer (GPU-side, V-flipped, into the letterbox),
exactly like the canonical gl_renderer_present_vram — no readback, no glFinish,
no re-upload. main.cpp routes wide GL frames here (falling back to the CPU readout
only if the wide surface doesn't exist yet). USER-VALIDATED smooth. The CPU
readback path (glb_render_wide_display) stays as the fallback + the wide_shot
probe.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Matthew Stanley
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