ML-186: improve presto redraw performance with partial updates

2026-05-16 21:29:02 +01:00
parent d61dd6c7b8
commit aab16b2c66
3 changed files with 358 additions and 49 deletions
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+---
+id: ML-186
+title: Improve Presto display redraw performance
+status: Done
+assignee:
+  - Codex
+created_date: "2026-05-16 20:14"
+updated_date: "2026-05-16 20:22"
+labels:
+  - presto
+  - performance
+dependencies: []
+references:
+  - "https://github.com/pimoroni/presto/issues/56"
+documentation:
+  - "https://github.com/pimoroni/presto/blob/main/docs/presto.md"
+modified_files:
+  - presto/main.py
+  - presto/tests/test_screens.py
+priority: medium
+ordinal: 22000
+---
+
+## Description
+
+<!-- SECTION:DESCRIPTION:BEGIN -->
+
+Use Pimoroni Presto partial display updates for bounded redraws in the MicroPython app where doing so preserves existing behavior. The current app performs full-screen updates for all draws; the desired outcome is to reduce display transfer work for high-frequency or small-area updates without changing visible UI behavior or making physical-device claims without on-device verification.
+
+<!-- SECTION:DESCRIPTION:END -->
+
+## Acceptance Criteria
+
+<!-- AC:BEGIN -->
+
+- [x] #1 Bounded UI redraws use partial display updates when the Presto firmware supports them and safely fall back to full updates otherwise.
+- [x] #2 Scrollable fixed-header views continue to render correctly during drag and release redraws.
+- [x] #3 Search input and scrobble feedback preserve existing visible behavior while avoiding unnecessary full-screen display transfers where practical.
+- [x] #4 Headless smoke tests pass, and any unverified physical-device behavior is clearly not claimed.
+<!-- AC:END -->
+
+## Implementation Plan
+
+<!-- SECTION:PLAN:BEGIN -->
+
+1. Add safe display update helpers in `presto/main.py`: a full update wrapper, a partial update wrapper with fallback, and named rectangles for the scroll viewport/search input/scrobble button.
+2. Keep full-screen updates for full state transitions and broad redraws, but use partial updates for bounded areas where the buffer content can be refreshed independently.
+3. For fixed-header scrollable views, add a bounded redraw mode that clears/redraws only the viewport below the header and calls `partial_update` for that region during drag redraws.
+4. For small feedback updates, redraw only the search input field after query text changes and redraw only the scrobble button area when its state changes.
+5. Add focused tests around fallback/partial-update behavior if the emulator can observe it, then run the Presto smoke test suite.
+<!-- SECTION:PLAN:END -->
+
+## Implementation Notes
+
+<!-- SECTION:NOTES:BEGIN -->
+
+Implemented safe partial display update helpers with full-update fallback, viewport-only redraws for scrollable fixed-header views, query-field partial redraws, and scrobble-button partial redraws. After user correction, kept the detail cover layout at `DETAIL_COVER_SIZE = px(200)` and updated tests/docs that incorrectly described the cover as 460px.
+
+<!-- SECTION:NOTES:END -->
+
+## Final Summary
+
+<!-- SECTION:FINAL_SUMMARY:BEGIN -->
+
+Implemented bounded display update support for the Presto MicroPython app. Full-screen transitions still use full updates, while scroll redraws now refresh only the content viewport, search typing refreshes only the query field row, and scrobble loading/done feedback refreshes only the visible button region. Added tests for partial-update dispatch, fallback behavior, scroll viewport updates, search field updates, and scrobble button updates. Kept the detail cover layout at `DETAIL_COVER_SIZE = px(200)` and updated stale tests/docs that incorrectly described the detail cover as 460px.
+
+Verification: `python3 -c "import py_compile; py_compile.compile('main.py', cfile='/tmp/main.pyc', doraise=True)"`; `python3 -m py_compile tests/test_screens.py`; `mise run test` (14 passed). Physical Presto behavior was not verified on-device.
+
+<!-- SECTION:FINAL_SUMMARY:END -->