Hyperion DRM VC4 screen grabber

This is an experimental attempt to capture a screenshot from a Raspberry Pi that is rendering using the Direct Rendering Manager. It currently works by opening the default card adapter, looping through all the planes and finding the underlying framebuffers. Using the framebuffer it is possible to determine the buffer handle for the underlying buffer object handle.

The buffer object handle can be mapped to memory using the VC4 specific DRM API's (see /usr/include/drm/vc4_drm.h), specifically using the ioctl drm_vc4_mmap_bo. The memory data is stored using XRGB8888 in little-endian 32 bit words, and is tiled in 32x32 bit squares (reference). There is also some other interlacing or similar I have not quite figured out yet.

The current implementation connects to Hyperion at 127.0.0.1:19400 and directly uploads the images.

Usage

1. Download the latest release archive.
2. Extract the archive, e.g. tar xvf drm-vc4-grabber-v0.1.0-aarch64-linux.tar.xz
3. Run the grabber in the background, e.g. nohup ./drm-vc4-grabber-v0.1.0-aarch64-linux/drm-vc4-grabber
4. Optionally use systemd to automatically start it in the background. On LibreELEC, copy systemd/drm-capture.service to ~/.config/system.d/ and then run systemctl enable drm-capture.service.

Compiling

1. Ensure rust is installed (with rustup and cargo).
2. Install the target toolchain for raspberry pi: rustup target install armv7-unknown-linux-gnueabihf.
3. Ensure the linker for this toolchain is installed, e.g. sudo apt install binutils-arm-none-eabi
4. Set the linker in your env var: export CARGO_TARGET_ARMV7_UNKNOWN_LINUX_GNUEABIHF_LINKER=/usr/bin/arm-linux-gnueabihf-gcc
5. Compile: cargo build --release --target armv7-unknown-linux-gnueabihf
6. The built file will be at target/armv7-unknown-linux-gnueabihf/release/drm-v4-capture

Example

The following is an example screen capture in the current codes state.

Debug Output

Driver: Driver { name: SmallOsString { data: [118, 99, 52, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], len: 3, as_ref(): "vc4" }, date: SmallOsString { data: [50, 48, 49, 52, 48, 54, 49, 54, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], len: 8, as_ref(): "20140616" }, desc: SmallOsString { data: [66, 114, 111, 97, 100, 99, 111, 109, 32, 86, 67, 52, 32, 103, 114, 97, 112, 104, 105, 99, 115, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], len: 21, as_ref(): "Broadcom VC4 graphics" } }
Plane Info: Info { handle: plane::Handle(84), crtc: Some(crtc::Handle(83)), fb: Some(framebuffer::Handle(207)), pos_crtcs: 15, formats: [0, 0, 0, 0, 0, 0, 0, 0], fmt_len: 8 }
  -> FB Info: Info { handle: framebuffer::Handle(207), size: (1920, 1080), pitch: 7680, bpp: 32, depth: 24, buffer: 1 }
  -> FB Info 2: drm_mode_fb_cmd2 { fb_id: 207, width: 1920, height: 1080, pixel_format: 875713112, flags: 2, handles: [2, 0, 0, 0], pitches: [7680, 0, 0, 0], offsets: [0, 0, 0, 0], modifier: [504403158265495553, 0, 0, 0] }
  -> Offset: 306663424
Plane Info: Info { handle: plane::Handle(90), crtc: None, fb: None, pos_crtcs: 15, formats: [0, 0, 0, 0, 0, 0, 0, 0], fmt_len: 8 }
Plane Info: Info { handle: plane::Handle(96), crtc: None, fb: None, pos_crtcs: 15, formats: [0, 0, 0, 0, 0, 0, 0, 0], fmt_len: 8 }
Plane Info: Info { handle: plane::Handle(102), crtc: None, fb: None, pos_crtcs: 15, formats: [0, 0, 0, 0, 0, 0, 0, 0], fmt_len: 8 }
Plane Info: Info { handle: plane::Handle(108), crtc: None, fb: None, pos_crtcs: 15, formats: [0, 0, 0, 0, 0, 0, 0, 0], fmt_len: 8 }
Plane Info: Info { handle: plane::Handle(114), crtc: None, fb: None, pos_crtcs: 15, formats: [0, 0, 0, 0, 0, 0, 0, 0], fmt_len: 8 }
Plane Info: Info { handle: plane::Handle(120), crtc: None, fb: None, pos_crtcs: 15, formats: [0, 0, 0, 0, 0, 0, 0, 0], fmt_len: 8 }
Plane Info: Info { handle: plane::Handle(126), crtc: None, fb: None, pos_crtcs: 15, formats: [0, 0, 0, 0, 0, 0, 0, 0], fmt_len: 8 }
Plane Info: Info { handle: plane::Handle(132), crtc: None, fb: None, pos_crtcs: 15, formats: [0, 0, 0, 0, 0, 0, 0, 0], fmt_len: 8 }
Plane Info: Info { handle: plane::Handle(138), crtc: None, fb: None, pos_crtcs: 15, formats: [0, 0, 0, 0, 0, 0, 0, 0], fmt_len: 8 }
Plane Info: Info { handle: plane::Handle(144), crtc: None, fb: None, pos_crtcs: 15, formats: [0, 0, 0, 0, 0, 0, 0, 0], fmt_len: 8 }
Plane Info: Info { handle: plane::Handle(150), crtc: None, fb: None, pos_crtcs: 15, formats: [0, 0, 0, 0, 0, 0, 0, 0], fmt_len: 8 }
Plane Info: Info { handle: plane::Handle(156), crtc: None, fb: None, pos_crtcs: 15, formats: [0, 0, 0, 0, 0, 0, 0, 0], fmt_len: 8 }
Plane Info: Info { handle: plane::Handle(162), crtc: None, fb: None, pos_crtcs: 15, formats: [0, 0, 0, 0, 0, 0, 0, 0], fmt_len: 8 }
Plane Info: Info { handle: plane::Handle(168), crtc: None, fb: None, pos_crtcs: 15, formats: [0, 0, 0, 0, 0, 0, 0, 0], fmt_len: 8 }
Plane Info: Info { handle: plane::Handle(174), crtc: None, fb: None, pos_crtcs: 15, formats: [0, 0, 0, 0, 0, 0, 0, 0], fmt_len: 8 }
CRTC Info: Info { handle: crtc::Handle(62), position: (0, 0), mode: None, fb: None, gamma_length: 256 }
CRTC Info: Info { handle: crtc::Handle(69), position: (0, 0), mode: None, fb: None, gamma_length: 256 }
CRTC Info: Info { handle: crtc::Handle(76), position: (0, 0), mode: None, fb: None, gamma_length: 256 }
CRTC Info: Info { handle: crtc::Handle(83), position: (0, 0), mode: Some(Mode { name: "1920x1080", clock: 148500, size: (1920, 1080), hsync: (2008, 2052, 2200), vsync: (1084, 1089, 1125), hskew: 0, vscan: 0, vrefresh: 60 }), fb: None, gamma_length: 256 }

Donations

I am in no way dependent on any donations, and am not asking for any support. However, if you would still like to show your appreciation you may do so using either of the following methods:

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