libX11：XPutImage第一次調用

Question

我已經使用XCreateImage創建了XImage，並使用XPutImage在窗口上顯示它，但XPutImage僅在第二次調用它時顯示此圖片。爲什麼會發生？

#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) 
{ 
     int i = 0; 

     for (i = 0;i < w*h;i += 4) { 
       rgb_out[i + 1] = 0; 
       rgb_out[i + 2] = 0; 
       rgb_out[i + 3] = 0; 
     } 

     return; 
} 

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 main(int argc, char **argv) 
{ 
     int win_b_color; 
     int win_w_color; 
     XEvent xev; 
     Window window; 
     GC gc; 
     Display *display = XOpenDisplay(NULL); 
     Visual *visual; 
     XImage *ximage; 

     win_b_color = BlackPixel(display, DefaultScreen(display)); 
     win_w_color = BlackPixel(display, DefaultScreen(display)); 
     window = XCreateSimpleWindow(display, 
           DefaultRootWindow(display), 
           0, 0, 600, 400, 0, 
           win_b_color, win_w_color); 

     gc = XCreateGC(display, window, 0, NULL); 
     visual = DefaultVisual(display, 0); 

     XMapWindow(display, window); 
     XFlush(display); 
     ximage = create_ximage(display, visual, 100, 100); 
     while (1) { 
       int r; 

       r = XPutImage(display, window, 
         gc, ximage, 0, 0, 0, 0, 
         100, 100); 
       printf("RES: %i\n", r); 
       XSync(display, 1); 
       XFlush(display); 
       getchar(); 
     } 

     return 0; 
} 

Answer 1

關鍵是要等待該窗口映射。您可以通過Expose事件來做到這一點。

int main(int argc, char **argv) 
{ 
     int win_b_color; 
     int win_w_color; 
     XEvent xev; 
     Window window; 
     GC gc; 
     Display *display = XOpenDisplay(NULL); 
     Visual *visual; 
     XImage *ximage; 

     win_b_color = BlackPixel(display, DefaultScreen(display)); 
     win_w_color = BlackPixel(display, DefaultScreen(display)); 
     window = XCreateSimpleWindow(display, 
           DefaultRootWindow(display), 
           0, 0, 600, 400, 0, 
           win_b_color, win_w_color); 

     visual = DefaultVisual(display, 0); 

     XSelectInput(display, window, ExposureMask | KeyPressMask); 

     XMapWindow(display, window); 
     XFlush(display); 
     gc = XCreateGC(display, window, 0, NULL); 
     ximage = create_ximage(display, visual, 100, 100); 
     XEvent event; 
     bool exit = false; 

     while (!exit) { 
       int r; 

       XNextEvent(display, &event); 

       if (event.type == Expose) 
       { 
        r = XPutImage(display, window, 
          gc, ximage, 0, 0, 0, 0, 
          100, 100); 
        printf("RES: %i\n", r); 
       } 
       else if (event.type == KeyPress) 
        exit = true; 
     } 

     return 0; 
}