Taking a screenshot using imagemagick API

问题

I'm using GCC 4.7.2, C89, and ImageMagick-6.8.0-4.

I am trying to take a screen shot using the ImageMagick API. I have downloaded, compiled, and installed the headers and libraries.

However, I can't see in the documentation the API calls to do the screen shot. I will be linking and including the headers so that I can call the API from my C program. I just want the name of the function I will have to use to do this.

Can anyone point me in the right direction? Can ImageMagick take screenshots?

回答1:

Using 'x:' Special File Format

If you want a no-thrill screen grab; you can invoke ImageMagick's import command by passing "x:root" as the source argument in MagickReadImage. The x: format allows for a full screenshot or a single window by passing a pid or window label. Additional modifiers can capture regions & paging.

#include <wand/MagickWand.h>

int main(int argc, char **argv) 
{
    MagickWandGenesis();
    MagickWand *wand = NULL;
    wand = NewMagickWand();
    MagickReadImage(wand,"x:root"); // <-- Invoke ImportImageCommand
    MagickWriteImage(wand,"screen_shot.png");
    if(wand)wand = DestroyMagickWand(wand);
    MagickWandTerminus();
    return 0;
}

Use Additional 'magick' Libraries

Outside of wand libraries, magick/xwindow.h allows you to import images by use of XImportImage, XImportInfo & XGetImportInfo methods. You can examine how these methods work in ImageMagick's source files wand/import.c.

Working Directly with X and Pixel Iterator

MagickWand also includes PixelWand; which, can iterate over an image-pointer in memory. A little more work, but greater flexibility.

#include <stdio.h>
#include <wand/MagickWand.h>
#include <X11/Xlib.h>

int main(int argc, char **argv) {
    int x,y;
    unsigned long pixel;
    char hex[128];

    // X11 items
    Display *display = XOpenDisplay(NULL);
    Window root = DefaultRootWindow(display);
    XWindowAttributes attr;
    XGetWindowAttributes(display, root, &attr);

    // MagickWand items
    MagickWand *wand = NULL;
    PixelWand *pwand = NULL;
    PixelIterator *pitr = NULL;
    PixelWand **wand_pixels = NULL;

    // Set-up Wand
    MagickWandGenesis();
    pwand = NewPixelWand();
    PixelSetColor(pwand,"white"); // Set default;
    wand = NewMagickWand();
    MagickNewImage(wand,attr.width,attr.height,pwand);
    pitr = NewPixelIterator(wand);

    // Get image from display server
    XImage *image = XGetImage(display,root, 0,0 , 
                                attr.width, attr.height,
                                XAllPlanes(), ZPixmap);

    unsigned long nwands; // May also be size_t

    for (y=0; y < image->height; y++) {
        wand_pixels=PixelGetNextIteratorRow(pitr,&nwands);
            for ( x=0; x < image->width; x++) {
                pixel = XGetPixel(image,x,y);
                sprintf(hex, "#%02x%02x%02x",
                                pixel>>16,           // Red
                                (pixel&0x00ff00)>>8, // Green
                                pixel&0x0000ff       // Blue
                                );
                PixelSetColor(wand_pixels[x],hex);
            }
            (void) PixelSyncIterator(pitr);
    }

    // Write to disk
    MagickWriteImages(wand,"screen_test.png");

    // Clean-Up
    XDestroyImage(image);
    pitr=DestroyPixelIterator(pitr);
    wand=DestroyMagickWand(wand);
    MagickWandTerminus();
    XCloseDisplay(display);
    return 0;
}

Helpful Hints

Ensure that ImageMagick is able to connect to your display system. Try a few import CLI commands to verify your local install is working. This question is a good example.

import -display localhost:0.0 -window root test_out.png
import -display ::0 -window root test_out.png
import -display :0.0 -window root test_out.png
import -display :0 -window root test_out.png

回答2:

cli program import from imagemagick can take screenshots by running like this:

import -window root screenshot.png

So input image can be specified as file or as -window root

回答3:

type: import fileName.fileType (Example: import screen.png)
A cross cursor will appear: Click and drag it over the part of the screen you wish to capture (Be sure the terminal window does not cover what you wish to capture)

来源：https://stackoverflow.com/questions/13219710/taking-a-screenshot-using-imagemagick-api

标签

ImageMagick