SimpleScreenshot

A small library I created for a need in my OCR projects.

The Screenshot class stores an area of the screen (x, y, width, height) where it is expected to take frequent screenshots (see Usage).

The Screenshot class returns Raw Image data of that area when called with operator() or takeScreenshot().

This Raw Image can then be used to create a desired image object. e.g: cv::Mat (see Usage).

The raw image data is a 2-dimensional array containing one uchar element per channel, representing (R, G, B, A) of the pixel at that point:

  *img_data[x][y][0] = (uchar)255; // (RED)
  *img_data[x][y][1] = (uchar)255; // (GREEN)
  *img_data[x][y][2] = (uchar)255; // (BLUE)
  *img_data[x][y][3] = (uchar)0;   // (ALPHA)

You can get width and height from Screenshot class members.

SimpleScreenshot is compatible with Linux and Windows ( only tested cross-compiling with mingw and running with Wine.)

Prerequisites

• g++, cmake
• X11, xshm ( for Linux )

Arch Linux: sudo pacman -S libx11 libxext

Ubuntu: sudo apt-get install libx11-dev libxext-dev

Usage

• CMakeLists:

    add_subdirectory(SimpleScreenshot)
    include_directories(SimpleScreenshot/include)
    target_link_libraries(
        ${EXECUTABLE}
        simplescreenshot)

• C++

    #include <Screenshot/Screenshot.h>

    // This is just initialization of the area where you would take screenshots
    Screenshot screenshot{x, y, width, height};
    
    // Takes the screenshot and returns raw Image data  width*height*(8bits RGBA)
    void *data = screenshot(); // or screenshoot.takeScreenshot();

    // Creating a OpenCV Matrix ( 8bit RGBA Image)
    cv::Mat img = cv::Mat(screen.height, screen.width, CV_8UC4, (unsigned char*)data);

Build Test

A very simple test:

#include <Screenshot/Screenshot.h>
#include <opencv2/core.hpp>
#include <opencv2/highgui.hpp>
#include <opencv2/imgcodecs.hpp>

#include <assert.h>

int main() {
    // Initialize
    sh::Screenshot screen{100, 100, 100, 100};

    // Grab screenshot
    void *data = screen();
    // or alternatively:
    // void *data = screen.takeScreenshot();

    // Create cv::Mat 8bit RGBA
    cv::Mat img = cv::Mat(screen.height, screen.width, CV_8UC4, (unsigned char*)data);

    assert(!img.empty());

    cv::imshow("raw", img);
    cv::waitKey(0);

    img.release();

    return 0;
};

Requires OpenCV:

sudo pacman -S opencv

or

sudo apt-get install libopencv-dev

Build with:

    cd build
    cmake .. -DBUILD_TESTS=ON
    cmake --build .

or

    ./build.sh run

License

Copyright 2015,2020 Joaqim Planstedt

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see http://www.gnu.org/licenses/.