piscrn

A screenshot server, library, and command-line utility for the Raspberry Pi

Components

• libpiscrn is a library which provides a function for taking a PNG screenshot of the Raspberry Pi video output and writing it to a file, stdout, or memory.
• piscrn is a command-line interface to libpiscrn.
• piscrnd is an HTTP daemon which replies to GET /screenshot requests with a screenshot.

Building

piscrn uses CMake as its build system. You can compile it for the Raspberry Pi with a CMake Toolchain File like so:

mkdir build
cd build
cmake -G Ninja -DCMAKE_TOOLCHAIN_FILE=my-raspberry-pi-toolchain.cmake ..
ninja
ninja install

Usage

piscrnd

To serve requests to GET /screenshot at port 3001:

./piscrnd

Full options

Usage: piscrnd [--port <port>] [--quiet]

    --port,-p - port to listen on(default is 3001)
    --quiet,-q - quiet mode(default is off)
    --help,-h - print this usage information

piscrn

To take a screenshot and save it to "snapshot.png"

./piscrn

Full options

Usage: piscrn [--pngname name] [--width <width>] [--height <height>] 
              [--compression <level>] [--delay <delay>] [--display <number>] [--stdout] [--help]

    --pngname,-p - name of png file to create (default is snapshot.png)
    --height,-h - image height (default is screen height)
    --width,-w - image width (default is screen width)
    --compression,-c - PNG compression level (0 - 9)
    --delay,-d - delay in seconds (default 0)
    --display,-D - Raspberry Pi display number (default 0)
    --stdout,-s - write file to stdout
    --help,-H - print this usage information

libpiscrn

libpiscrn provides a single entry point:

piscrn_error_code piscrn_take_screenshot(piscrn_screenshot_params const *params);

Examples

Output to Memory

  piscrn_screenshot_params params = piscrn_default_params;
  params.output.choice = PISCRN_OUTPUT_MEMORY;
  const char *pngBuffer;
  size_t pngSize;
  params.output.memoryOut = &pngBuffer;
  params.output.sizeOut = &pngSize;
  piscrn_take_screenshot(&params);

Output to "my_output.png" File

  piscrn_screenshot_params params = piscrn_default_params;
  params.output.choice = PISCRN_OUTPUT_FILE;
  params.output.fileName = "my_output.png";
  piscrn_take_screenshot(&params);

piscrn_screenshot_params struct members

• piscrn_output_descriptor output: description of where to output the png (default: "snapshot.png")
• uint32_t displayNumber: which RPi display to use (default: 0)
• int compression: zlib compression level (default: -1)
• int32_t requestedHeight: requested height of png (default: display height)
• int32_t requestedWidth: requested height of png (default: display width)
• int delay: delay before taking screenshot in ms (default: 0ms)

piscrn_output_descriptor struct members

• piscrn_output_choice choice - which output method to use
• const char** memoryOut - where to store the resulting data if outputting to memory (NOTE: BE SURE TO free THIS)
• size_t* sizeOut - where to store the size of the resulting data if outputting to memory
• const char* fileName - filename to use if outputting to a file

prscrn_output_choice enum members

• PISCRN_OUTPUT_STDOUT: output png to stdout
• PISCRN_OUTPUT_FILE: output png to a file
• PISCRN_OUTPUT_MEMORY: output png to memory

prscrn_default_params

An instance of piscrn_screenshot_params with defaults filled in.

Dependencies

Depends upon libpng. This can be installed using vcpkg.

Licences

Uses jeremycw/httpserver.h, which uses an MIT license.

Screenshot code is adapted from AndrewFromMelbourne/raspi2png, which uses as MIT license.