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POscreenshot using openGL and/or X11
 

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  1. POscreenshot using openGL and/or X11
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    <p>i am trying to get a screenshot of the screen or a window. I tried using functions from X11 and it works fine. The problem is that getting the pixels from XImage takes a lot of time. Than i tried to look for some answers on how to do it using openGL. Here's what i've got:</p> <pre><code>#include &lt;stdlib.h&gt; #include &lt;stdio.h&gt; #include &lt;cstdio&gt; #include &lt;GL/glut.h&gt; #include &lt;GL/gl.h&gt; #include &lt;GL/glx.h&gt; #include &lt;X11/Xlib.h&gt; int main(int argc, char **argv) { int width=1200; int height=800; //_____________________________---- Display *dpy; Window root; GLint att[] = { GLX_RGBA, GLX_DEPTH_SIZE, 24, GLX_DOUBLEBUFFER, None }; XVisualInfo *vi; GLXContext glc; dpy = XOpenDisplay(NULL); if ( !dpy ) { printf("\n\tcannot connect to X server\n\n"); exit(0); } root = DefaultRootWindow(dpy); vi = glXChooseVisual(dpy, 0, att); if (!vi) { printf("\n\tno appropriate visual found\n\n"); exit(0); } glXMakeCurrent(dpy, root, glc); glc = glXCreateContext(dpy, vi, NULL, GL_TRUE); printf("vendor: %s\n", (const char*)glGetString(GL_VENDOR)); //____________________________________________ glXMakeCurrent(dpy, root, glc); glEnable(GL_DEPTH_TEST); GLubyte* pixelBuffer = new GLubyte[sizeof(GLubyte)*width*height*3*3]; glReadBuffer(GL_FRONT); GLint ReadBuffer; glGetIntegerv(GL_READ_BUFFER,&amp;ReadBuffer); glPixelStorei(GL_READ_BUFFER,GL_RGB); GLint PackAlignment; glGetIntegerv(GL_PACK_ALIGNMENT,&amp;PackAlignment); glPixelStorei(GL_PACK_ALIGNMENT,1); glReadPixels(0, 0, width, height, GL_RGB, GL_UNSIGNED_INT, pixelBuffer); int i; for (i=0;i&lt;100;i++) printf("%u\n",((unsigned int *)pixelBuffer)[i]); return 0; } </code></pre> <p>when i run the program it returns an error: X Error of failed request: BadAccess (attempt to access private resource denied) Major opcode of failed request: 199 () Minor opcode of failed request: 26 Serial number of failed request: 20 Current serial number in output stream: 20</p> <p>if i comment the line with glXMakeCurrent(dpy, root, glc); before glc = glXCreateContext(dpy, vi, NULL, GL_TRUE); it returns no erros, but all the pixels are 0.</p> <p>How should i go about this problem? I am new to openGL and maybe i am missing something important here. Maybe also another way of getting pixels from the screen or specific window exists?</p>
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    1. USgenpfault
    1. USJaka
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    1. PO
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    1. VO
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      1. POscreenshot using openGL and/or X11
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    2. VO
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    1. COWhat makes you thing that using GL will make it faster? It should be the same.
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      1. USMatias Valdenegro
    2. COHow much time is it taking? Is there network transmission involved? Are you just viewing stdout in a terminal? Try redirecting to a file and use the `time` command. Printing characters to the terminal uses the same X server that's desperately trying to copy an image and marshall it over a protocol. Heisenberg may apply; your inspection technique may be distorting the very information you seek.
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      1. USluser droog
 

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