color-drawing.c

一系列在X窗口环境图形化编程的范例。基于GTK。看完这个教程

/*
 * color-drawing.c - demonstrate drawing of pixels, lines, arcs, etc, using
 *		      different foreground colors, in a window.
 */

#include <X11/Xlib.h>

#include <stdio.h>
#include <stdlib.h>		/* getenv(), etc. */
#include <unistd.h>		/* sleep(), etc.  */

/*
 * function: create_simple_window. Creates a window with a white background
 *           in the given size.
 * input:    display, size of the window (in pixels), and location of the window
 *           (in pixels).
 * output:   the window's ID.
 * notes:    window is created with a black border, 2 pixels wide.
 *           the window is automatically mapped after its creation.
 */
Window
create_simple_window(Display* display, int width, int height, int x, int y)
{
  int screen_num = DefaultScreen(display);
  int win_border_width = 2;
  Window win;

  /* create a simple window, as a direct child of the screen's */
  /* root window. Use the screen's black and white colors as   */
  /* the foreground and background colors of the window,       */
  /* respectively. Place the new window's top-left corner at   */
  /* the given 'x,y' coordinates.                              */
  win = XCreateSimpleWindow(display, RootWindow(display, screen_num),
                            x, y, width, height, win_border_width,
                            BlackPixel(display, screen_num),
                            WhitePixel(display, screen_num));

  /* make the window actually appear on the screen. */
  XMapWindow(display, win);

  /* flush all pending requests to the X server. */
  XFlush(display);

  return win;
}

GC
create_gc(Display* display, Window win, int reverse_video)
{
  GC gc;				/* handle of newly created GC.  */
  unsigned long valuemask = 0;		/* which values in 'values' to  */
					/* check when creating the GC.  */
  XGCValues values;			/* initial values for the GC.   */
  unsigned int line_width = 2;		/* line width for the GC.       */
  int line_style = LineSolid;		/* style for lines drawing and  */
  int cap_style = CapButt;		/* style of the line's edje and */
  int join_style = JoinBevel;		/*  joined lines.		*/
  int screen_num = DefaultScreen(display);

  gc = XCreateGC(display, win, valuemask, &values);
  if (gc < 0) {
	fprintf(stderr, "XCreateGC: \n");
  }

  /* allocate foreground and background colors for this GC. */
  if (reverse_video) {
    XSetForeground(display, gc, WhitePixel(display, screen_num));
    XSetBackground(display, gc, BlackPixel(display, screen_num));
  }
  else {
    XSetForeground(display, gc, BlackPixel(display, screen_num));
    XSetBackground(display, gc, WhitePixel(display, screen_num));
  }

  /* define the style of lines that will be drawn using this GC. */
  XSetLineAttributes(display, gc,
                     line_width, line_style, cap_style, join_style);

  /* define the fill style for the GC. to be 'solid filling'. */
  XSetFillStyle(display, gc, FillSolid);

  return gc;
}

void
main(int argc, char* argv[])
{
  Display* display;		/* pointer to X Display structure.           */
  int screen_num;		/* number of screen to place the window on.  */
  Window win;			/* pointer to the newly created window.      */
  unsigned int display_width,
               display_height;	/* height and width of the X display.        */
  unsigned int width, height;	/* height and width for the new window.      */
  char *display_name = getenv("DISPLAY");  /* address of the X display.      */
  GC gc;			/* GC (graphics context) used for drawing    */
				/*  in our window.			     */
  Colormap screen_colormap;     /* color map to use for allocating colors.   */
  XColor red, brown, blue, yellow, green;
				/* used for allocation of the given color    */
				/* map entries.                              */
  Status rc;			/* return status of various Xlib functions.  */

  /* open connection with the X server. */
  display = XOpenDisplay(display_name);
  if (display == NULL) {
    fprintf(stderr, "%s: cannot connect to X server '%s'\n",
            argv[0], display_name);
    exit(1);
  }

  /* get the geometry of the default screen for our display. */
  screen_num = DefaultScreen(display);
  display_width = DisplayWidth(display, screen_num);
  display_height = DisplayHeight(display, screen_num);

  /* make the new window occupy 1/9 of the screen's size. */
  width = (display_width / 3);
  height = (display_height / 3);
  printf("window width - '%d'; height - '%d'\n", width, height);

  /* create a simple window, as a direct child of the screen's   */
  /* root window. Use the screen's white color as the background */
  /* color of the window. Place the new window's top-left corner */
  /* at the given 'x,y' coordinates.                             */
  win = create_simple_window(display, width, height, 0, 0);

  /* allocate a new GC (graphics context) for drawing in the window. */
  gc = create_gc(display, win, 0);
  XSync(display, False);

  /* get access to the screen's color map. */
  screen_colormap = DefaultColormap(display, DefaultScreen(display));

  /* allocate the set of colors we will want to use for the drawing. */
  rc = XAllocNamedColor(display, screen_colormap, "red", &red, &red);
  if (rc == 0) {
    fprintf(stderr, "XAllocNamedColor - failed to allocated 'red' color.\n");
    exit(1);
  }
  rc = XAllocNamedColor(display, screen_colormap, "brown", &brown, &brown);
  if (rc == 0) {
    fprintf(stderr, "XAllocNamedColor - failed to allocated 'brown' color.\n");
    exit(1);
  }
  rc = XAllocNamedColor(display, screen_colormap, "blue", &blue, &blue);
  if (rc == 0) {
    fprintf(stderr, "XAllocNamedColor - failed to allocated 'blue' color.\n");
    exit(1);
  }
  rc = XAllocNamedColor(display, screen_colormap, "yellow", &yellow, &yellow);
  if (rc == 0) {
    fprintf(stderr, "XAllocNamedColor - failed to allocated 'yellow' color.\n");
    exit(1);
  }
  rc = XAllocNamedColor(display, screen_colormap, "green", &green, &green);
  if (rc == 0) {
    fprintf(stderr, "XAllocNamedColor - failed to allocated 'green' color.\n");
    exit(1);
  }
  
  /* draw one pixel near each corner of the window */
  /* draw the pixels in a red color. */
  XSetForeground(display, gc, red.pixel);
  XDrawPoint(display, win, gc, 5, 5);
  XDrawPoint(display, win, gc, 5, height-5);
  XDrawPoint(display, win, gc, width-5, 5);
  XDrawPoint(display, win, gc, width-5, height-5);

  /* draw two intersecting lines, one horizontal and one vertical, */
  /* which intersect at point "50,100".                            */
  /* draw the line in a brown color. */
  XSetForeground(display, gc, brown.pixel);
  XDrawLine(display, win, gc, 50, 0, 50, 200);
  XDrawLine(display, win, gc, 0, 100, 200, 100);

  /* now use the XDrawArc() function to draw a circle whose diameter */
  /* is 30 pixels, and whose center is at location '50,100'.         */
  /* draw the arc in a blue color. */
  XSetForeground(display, gc, blue.pixel);
  XDrawArc(display, win, gc, 50-(30/2), 100-(30/2), 30, 30, 0, 360*64);

  {
    XPoint points[] = {
      {0, 0},
      {15, 15},
      {0, 15},
      {0, 0}
    };
    int npoints = sizeof(points)/sizeof(XPoint);

    /* draw a small triangle at the top-left corner of the window. */
    /* the triangle is made of a set of consecutive lines, whose   */
    /* end-point pixels are specified in the 'points' array.       */
    /* draw the triangle in a yellow color. */
    XSetForeground(display, gc, yellow.pixel);
    XDrawLines(display, win, gc, points, npoints, CoordModeOrigin);
  }

  /* draw a rectangle whose top-left corner is at '120,150', its width is */
  /* 50 pixels, and height is 60 pixels.                                  */
  /* draw the rectangle in a black color. */
  XSetForeground(display, gc, BlackPixel(display, screen_num));
  XDrawRectangle(display, win, gc, 120, 150, 50, 60);

  /* draw a filled rectangle of the same size as above, to the left of the */
  /* previous rectangle.                                                   */
  /* draw the rectangle in a green color. */
  XSetForeground(display, gc, green.pixel);
  XFillRectangle(display, win, gc, 60, 150, 50, 60);

  /* flush all pending requests to the X server. */
  XFlush(display);

  /* make a delay for a short period. */
  sleep(4);

  /* close the connection to the X server. */
  XCloseDisplay(display);
}