x11 - XPutImage to a DefaultRootWindow() gives nothing -


i'm trying write screensaver compatible "xscreensaver"-package. requires program draw in root-window. program runs fine when create non-root-window myself, e.g.:

window window = xcreatesimplewindow(display, rootwindow(display, 0), 0, 0, width, height, 1, 0, 0);

drawing a

window window = defaultrootwindow(display);

instead gives nothing. tried running xscreensaver-demo, xterm, environment without window manager give black. in terminal start it, no x11 errors shown. error-handler not triggered. guess biggest problem can't find (not google) how debug this.

any appreciated!

here's code:

#include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <x11/xlib.h> #include <x11/xutil.h>  void draw(char *rgb_out, int w, int h) {         for(int i=0; i<w*h*4; i++)                 *rgb_out++ = rand(); }  ximage *create_ximage(display *display, visual *visual, int width, int height) {         char *image32 = (char *)malloc(width * height * 4);         draw(image32, width, height);         return xcreateimage(display, visual, 24, zpixmap, 0, image32, width, height, 32, 0); }  int x11_err_handler(display *pd, xerrorevent *pxev) {         char msg[4096] = { 0 };         xgeterrortext(pd, pxev -> error_code, msg, sizeof(msg));         printf("%s\n", msg);         return 0; }  int main(int argc, char **argv) {         display *display = xopendisplay(getenv("display"));          window window = defaultrootwindow(display);          xwindowattributes wa;         xgetwindowattributes(display, window, &wa);         int width = wa.width, height = wa.height;         printf("res: %dx%d\n", width, height);          gc gc = xcreategc(display, window, 0, null);         visual *visual = defaultvisual(display, 0);          xseterrorhandler(x11_err_handler);          for(;;)         {                 ximage *ximage = create_ximage(display, visual, width, height);                 xputimage(display, window, gc, ximage, 0, 0, 0, 0, width, height);                 xdestroyimage(ximage);                  xflush(display);                  usleep(50000);         }          return 0; }

it can compiled using:

g++ -o3 -lx11 -lxpm so.cpp

your code works fine me, tested xephyr. guess (as commented) in setup root window obscured de, example in ubuntu there 'nautilus' running full screen provide desktop / icons / dnd / rubber band selection functionality.


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