Continuous framebuffer refresh: display new frames as they arrive on stdin#13
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[WIP] Add refresh functionality for framebuffer on new image
Continuous framebuffer refresh: display new frames as they arrive on stdin
May 23, 2026
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Pull request overview
This PR updates drm-framebuffer to support continuously reading frames from stdin and updating the display as each full frame arrives, and documents how to stream multiple frames and generate .fb files.
Changes:
- Refactors display logic into a helper and adds a
select()+signalfd()driven loop to read and display multiple frames fromstdin. - Updates README with a “Streaming multiple frames” example and an ImageMagick command for producing BGRA
.fbfiles.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 6 comments.
| File | Description |
|---|---|
| README.md | Documents multi-frame streaming usage and ImageMagick conversion to .fb. |
| main.c | Implements continuous frame ingestion from stdin and signal-driven termination. |
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Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details. Warning Firewall rules blocked me from connecting to one or more addresses (expand for details)I tried to connect to the following addresses, but was blocked by firewall rules:
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Instead of blocking with sigwait() after displaying the first frame, use signalfd() + select() to simultaneously monitor: - stdin for new frame data - SIGINT/SIGTERM for clean shutdown When a new complete frame is received on stdin it is immediately displayed. When stdin reaches EOF the last frame stays on screen and the program continues waiting for a signal. SIGINT or SIGTERM still causes a clean exit (restoring the original CRTC state). The display logic is extracted into a separate display_framebuffer() helper to avoid duplication. Co-authored-by: Stefan Eichenberger <eichest@gmail.com>
Co-authored-by: Stefan Eichenberger <eichest@gmail.com>
…andle pitch The inner read loop used `dumb_framebuffer.size` as the number of bytes to collect before displaying a frame. The kernel's DRM_IOCTL_MODE_CREATE_DUMB may align the pitch (row stride) beyond `width * bpp/8`, making `size` (`= pitch * height`) larger than the packed pixel data users actually supply. The code would therefore block waiting for phantom padding bytes until more data arrived, causing the "need 2 KB extra" symptom. Fix: - Compute `row_stride = width * bpp/8` (packed bytes per row). - Compute `image_size = row_stride * height` (bytes the user provides). - Read row-by-row: each `read()` targets at most the remaining bytes in the current row, written to `fb->data + row * pitch + col`. This places every row at the correct pitched offset in the mapped buffer, fixing the silent display corruption that would occur when pitch > row_stride. - Stop after `image_size` bytes, so a complete frame is displayed as soon as the last pixel byte arrives, with no extra data needed. Co-authored-by: Stefan Eichenberger <eichest@gmail.com>
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