gtk: present on demand (Repainter), not every tick - #94
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The GTK back-end blitted a full frame every vsync — one layout + texture upload + recompose at 60 Hz even on an idle, unchanged window. Implement window.Repainter instead, the policy the Cocoa back-end already uses: Repaint() raises a flag (cheap, callable from any goroutine, no GTK call off the main thread, no callback allocation), and the frame clock — the one persistent main-thread pump — presents only when the flag is set. go-widgets/application's present loop calls Repaint at up to 60 Hz gated by the handler's NeedsPresent, so a still window draws nothing. Measured with the reader under Xvfb: idle presents fall from ~100% of ticks to ~7% (heartbeat + spinner cadence) — a ~15× cut in idle uploads — with the UI unchanged. A compile-time assertion pins the capability; TestRepaintGating pins the present-once-per-Repaint contract without a display.
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The GTK backend blitted a full frame every vsync — layout + texture upload + recompose at 60 Hz even on an idle window. Implement
window.Repainter(the policy the Cocoa backend already uses):Repaint()raises a flag (cheap, any goroutine, no GTK call off the main thread, no callback allocation), and the frame clock — one persistent main-thread pump — presents only when the flag is set.go-widgets/application's present loop callsRepaintgated by the handler'sNeedsPresent, so a still window draws nothing.Measured with the reader under Xvfb: idle presents fall from ~100% of ticks to ~7% (heartbeat + spinner cadence) — a ~15× cut in idle uploads — UI unchanged. Compile-time assertion pins the capability;
TestRepaintGatingpins the present-once-per-Repaint contract display-free.