Drawing pixmaps using libX11

drawing-pixmaps.c

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <unistd.h>
#include <string.h>
#include <math.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <X11/Xlib.h>
#include <X11/extensions/XShm.h>

XImage *CreatePixmapImage(Display *display, Visual *visual, void ** data, int width, int height) {
	static XShmSegmentInfo shminfo;
	XImage *image = XShmCreateImage(display, visual, 24, ZPixmap, 0, &shminfo, width, height); 
	
	shminfo.shmid = shmget(IPC_PRIVATE, image->bytes_per_line * image->height,IPC_CREAT|0777);
	shminfo.shmaddr = image->data = *data = shmat(shminfo.shmid, 0, 0);
	shminfo.readOnly = False;

	XShmAttach(display, &shminfo);
	return image;
}

void redrawImage(unsigned char *image, int width, int height) {
    int i, j;
    static double time = 0;
    //unsigned char *image32=(unsigned char *)malloc(width*height*4);
    unsigned char *p=image;
    double ttime = sin(time)*256;
    for(i=0; i<width; i++)
    {
        for(j=0; j<height; j++)
        {
         
            *p++=i%256; // blue
            *p++=j%256; // green
            *p++=ttime; // red
         
            p++;
        }
    }
    time+=0.06;
    if (time >= M_PI) time = 0;
}

void processEvent(Display *display, Window window, Visual* visual, int width, int height) {
    XEvent ev;
    XImage *ximage;
    
    if (XPending(display)) {
		XNextEvent(display, &ev);
		switch(ev.type) {
			case Expose:		break;
			case ButtonPress:
			case KeyPress:		exit(0); break;
		}
	}
}

int main(int argc, char **argv)
{
    int width=512, height=512;
    Display *display=XOpenDisplay(NULL);
    Visual *visual=DefaultVisual(display, 0);
    Window window=XCreateSimpleWindow(display, RootWindow(display, 0), 0, 0, width, height, 1, 0, 0);
    XImage *ximage;
    uint8_t *image;
    if(visual->class!=TrueColor)
    {
        fprintf(stderr, "Cannot handle non true color visual ...\n");
        exit(1);
    }
    
    XSelectInput(display, window, ButtonPressMask|ExposureMask|KeyPressMask);
    XMapWindow(display, window);
    
    ximage = CreatePixmapImage(display, visual, (void**) &image, width, height);
    
    while(1)
    {
        processEvent(display, window, visual, width, height);
		redrawImage(image, width, height);
		XPutImage(display, window, DefaultGC(display, 0), ximage, 0, 0, 0, 0, width, height);
		usleep(10000);
    }
}