C - X11 API: Graphics not Working in a While Loop

Question

I am trying to draw a background dynamically. The graphics work great normally...but:

int width, height;
GC gc_backcolor;
XGCValues gcv_backcolor;

width = c_values.width;
height = c_values.height;

gcv_backcolor.background = c_values.backcolor;
gcv_backcolor.foreground = c_values.backcolor;
gc_backcolor = XCreateGC(display, canvas, GCBackground | GCForeground, &gcv_backcolor);

int x = 0;
int y = 0;

while (y < height) {
    x = 0;

    while (x < width) {
        XDrawPoint(display, canvas, gc_backcolor, x, y);
        x++;
    }
    y++;
}

x = 0;
y = 0;

...for some reason, when I run it in a loop, it will not work. If anyone could explain to me why it is behaving this way, I would be grateful.

Could it be that I am calling this function on the canvas expose event?

  while(1) {
      XNextEvent(display, &event);

      if (event.xany.window == canvas) {
          if (event.type == Expose) {
              Canvas_Draw(display, canvas, c_values);
          }

       }
   }

Here is my main code:

#include <stdio.h>
#include <stdlib.h>
#include <X11/Xlib.h>
#include "Canvas.h"
#include "Extensions.h"

int main(int argc, char* argv[])
{
   Display* display;
   int screen;
   Window window;
   Window canvas;
   XEvent event;
   GC gc_canvas;

   //Canvas* canvas;

   display = XOpenDisplay(NULL);

   if (display == NULL) {
      fprintf(stderr, "Error trying to open display\n");
      exit(1);
   }

   screen = DefaultScreen(display);
   window = XCreateSimpleWindow(display, RootWindow(display, screen), 0, 0, 640, 480, 1, BlackPixel(display, screen), WhitePixel(display, screen));

   XSelectInput(display, window, ExposureMask | KeyPressMask);
   XMapWindow(display, window);

   /*   Create Canvas   */

   XGCValues gcv_canvas;
   CanvasValues c_values;

   gcv_canvas.foreground = 0xff00ff;
   gcv_canvas.background = 0xff00ff;

   canvas = XCreateSimpleWindow(display, window, 0, 0, 256, 256, 1, BlackPixel(display, screen), WhitePixel(display, screen));

   gc_canvas = XCreateGC(display, canvas, GCForeground | GCBackground, &gcv_canvas);

   XSelectInput(display, canvas, ExposureMask | KeyPressMask);
   XMapWindow(display, canvas);

   Canvas_Create_Content_Field(display, canvas, c_values);

   c_values.backcolor = 0x00ff00;

   //Canvas_Draw(display, canvas, c_values); this code only appears to work in the expose event

   /*   Create Canvas   */

   while(1) {
      XNextEvent(display, &event);

      if (event.xany.window == canvas) {
      if (event.type == Expose) {
          Canvas_Draw(display, canvas, c_values);
      }

       }
   }

   return 0;
}

Answer 1

I am sorry...it had nothing to do with the graphics, but the width and height integers were set to 0 due to an error in a function I made and used in the function that creates the data array for the image:

int width, height;
width = Window_Get_Width(display, canvas);  // Window_Get_Width had some errors and
height = Window_Get_Height(display, canvas);  // Window_Get_Height had the exact same errors

c_values->width = width;
c_values->height = height;

int field[width*height];

c_values->field = field;

I fixed the errors, and now everything is working out great! :D