drm-gbm: present via vsynced page flips instead of per-frame SetCrtc#25
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drm-gbm: present via vsynced page flips instead of per-frame SetCrtc#25lhoward wants to merge 1 commit into
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NativeWindowDrmGbm::SwapBuffers() called drmModeSetCrtc every frame, which is not vsynced -- the CRTC re-latches its scanout buffer immediately, not at vblank. On slower panels with high-contrast transitions the seam is plainly visible as tearing. Refs sony#136. Use drmModePageFlip with DRM_MODE_PAGE_FLIP_EVENT after the initial modeset. WaitForPageFlip() drains the previous flip event before the next is queued, and a release-on-flip handshake (bo_release_after_flip_ -> bo_pending_release_) ensures a displaced BO is freed only after the kernel has stopped scanning it out. No explicit GPU wait is needed: eglSwapBuffers attaches an implicit dma-buf exclusive fence to the rendered BO, which the legacy page-flip path already honours -- the kernel will not latch a framebuffer whose fence has not signalled. Resize() drains the in-flight flip and re-arms modeset for the fresh GBM surface; the destructor drains before restoring the original CRTC. enable_vsync_ remains a gate -- passing enableVSync: false in the Swift wrapper restores the legacy synchronous SetCrtc path. Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com> Co-authored-by: Amp <amp@ampcode.com> Amp-Thread-ID: https://ampcode.com/threads/T-019df5d6-7d1c-755a-9be1-e10d54295a9f
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NativeWindowDrmGbm::SwapBuffers()calleddrmModeSetCrtcevery frame, which is not vsynced -- the CRTC re-latches its scanout buffer immediately, not at vblank. On slower panels with high-contrast transitions the seam is plainly visible as tearing. Refs sony#136.Use
drmModePageFlipwithDRM_MODE_PAGE_FLIP_EVENTafter the initial modeset.WaitForPageFlip()drains the previous flip event before the next is queued, and a release-on-flip handshake (bo_release_after_flip_ -> bo_pending_release_) ensures a displaced BO is freed only after the kernel has stopped scanning it out.No explicit GPU wait is needed:
eglSwapBuffersattaches an implicit dma-buf exclusive fence to the rendered BO, which the legacy page-flip path already honours -- the kernel will not latch a framebuffer whose fence has not signalled.Resize() drains the in-flight flip and re-arms modeset for the fresh GBM surface; the destructor drains before restoring the original CRTC. enable_vsync_ remains a gate -- passing enableVSync: false in the Swift wrapper restores the legacy synchronous SetCrtc path.