Region-of-interest frames render on the CPU path; the viewer keeps main's
frame drawing (Show Channel, exposure, ROI) and reads GPU-composited frames
back. Keeping frames as native egui-wgpu textures stays implemented behind
RenderSource::gpu_display (off).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
The desktop viewer builds the GPU compositor on egui-wgpu's device and,
with Mercury GPU Acceleration, renders frames into RGBA8 textures that are
registered with egui-wgpu and drawn directly (no readback); the RAM preview
cache holds them under a video-memory budget. Pixels are read back only on
demand (Info panel, eyedroppers, histograms). Project Settings gets the
Video Rendering and Effects renderer choice. ui_gpu test: GPU viewer frame
matches the CPU one (skips without an adapter).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
