Question

在X11显示编程的情况下，我想知道如何在显示窗口时擦除结构。让我们说我想画一条直线，矩形和圆形。但是，我希望在绘制矩形之前消除直线，依此类推。这样做有什么功能吗？

代码：

#include <stdlib.h>
#include <stdio.h>
#include <X11/Xlib.h>
#include <math.h>
#include "time.h"
#include "sys/time.h"

 // Global variables
 Display *display;
 Window  window;
 XSetWindowAttributes attributes;
 XGCValues gr_values;
 XFontStruct *fontinfo;
 GC gr_context;
 Visual *visual;
 int depth;
 int screen;
 XEvent event;
 XColor    color, dummy;

 main (argc, argv)
 char   *argv[];
 int     argc;
 {

 display = XOpenDisplay(NULL);
 screen = DefaultScreen(display);
 visual = DefaultVisual(display,screen);
 depth  = DefaultDepth(display,screen);
 attributes.background_pixel = XWhitePixel(display,screen);

 window = XCreateWindow( display,XRootWindow(display,screen),
                        200, 200, 1050, 1200, 5, depth,  InputOutput,
                        visual ,CWBackPixel, &attributes);
 XSetStandardProperties(display,window,"Welcome","Hi",None,NULL,0,NULL);
  XSelectInput(display,window,ExposureMask | KeyPressMask) ;
  fontinfo = XLoadQueryFont(display,"6x10");//6*10

   XAllocNamedColor(display, DefaultColormap(display, screen),"red",
                  &color,&dummy);

   gr_values.font = fontinfo->fid;
   gr_values.foreground = color.pixel;

   gr_context=XCreateGC(display,window,GCFont+GCForeground, &gr_values);

   // gr_context2=XCreateGC(display,window,GCFont+GCForeground, &gr_values);


 XFlush(display);
 XMapWindow(display,window);
 XFlush(display);
int i,j,a,b,h,w,angle1,angle2;
 while(1){
    XNextEvent(display,&event);

    switch(event.type){
    case Expose:
     //Straight line

        XDrawLine(display,window,gr_context,800,800, 400, 450);
        XFlush(display);
        usleep(50000);

    // Which function should I write here to make the line vanished??

     //Rectangle

        XDrawRectangle(display,window,gr_context,102,103, 200, 150);
        XFlush(display);
        usleep(50000);

     //Arc and Circle

      a = 600, b = 700;
      h = 100, w = 100;
      angle1 = 0, angle2 = 360*64;
      XDrawArc(display, window, gr_context, a-(w/2), b-(h/2), w, h, angle1,   angle2);
     XFlush(display);
        usleep(50000);

          break;

       case KeyPress: 
           XCloseDisplay(display); 
            exit(0);

         }
       }
     }

更新的代码：关注 - 显示两次，然后删除第一个

  #include <stdlib.h>
  #include <stdio.h>
  #include <X11/Xlib.h>
  #include <math.h>
  #include "time.h"
  #include "sys/time.h"



 // Global variables
 Display *display;
 Window  window;
 XSetWindowAttributes attributes;
 XGCValues gr_values;
 XFontStruct *fontinfo;
 GC gr_context;
 Visual *visual;
 int depth;
 int screen;
 XEvent event;
 XColor    color, dummy;

 main (argc, argv)
 char   *argv[];
 int     argc;
  { 
   display = XOpenDisplay(NULL);
   screen = DefaultScreen(display);
    visual = DefaultVisual(display,screen);
   depth  = DefaultDepth(display,screen);
   attributes.background_pixel = XWhitePixel(display,screen);

   window = XCreateWindow( display,XRootWindow(display,screen),
                        200, 200, 1050, 1200, 5, depth,  InputOutput,
                        visual ,CWBackPixel, &attributes);
   XSetStandardProperties(display,window,"Welcome","Hi",None,NULL,0,NULL);
   XSelectInput(display,window,ExposureMask | KeyPressMask) ;
   fontinfo = XLoadQueryFont(display,"6x10");
   XAllocNamedColor(display, DefaultColormap(display, screen),"cyan",
                  &color,&dummy);


   gr_values.font = fontinfo->fid;
   gr_values.foreground = color.pixel;
   gr_values.function   = GXxor;

   gr_context=XCreateGC(display,window,GCFont+GCForeground+GCFunction,   &gr_values);



   XFlush(display);
   XMapWindow(display,window);
   XFlush(display);
   int i,j,a,b,h,w,angle1,angle2;
    while(1){
    XNextEvent(display,&event);

    switch(event.type){
    case Expose:
    XDrawLine(display,window,gr_context,800,800, 400, 450);
    XFlush(display);
   usleep(500000);
     XDrawRectangle(display,window,gr_context,102,103, 200, 150);
    XFlush(display);
   usleep(500000);

         break;

    case KeyPress: 
         XCloseDisplay(display); 
         exit(0);

    }
  }
}

Answer 1

没有直接的方法，因为X11不存储可以从显示列表中删除的对象，就像更高级别的图形库可能支持的那样。

最简单的解决方法是使用XOR图形。

以下是代码中应该更改的内容，以便使用此方法实现您的目标：

***************
*** 38,40 ****

!    XAllocNamedColor(display, DefaultColormap(display, screen),"cyan",
                    &color,&dummy);
--- 38,40 ----

!    XAllocNamedColor(display, DefaultColormap(display, screen),"red",
                    &color,&dummy);
***************
*** 43,47 ****
     gr_values.foreground = color.pixel;
-    gr_values.function   = GXxor;

!    gr_context=XCreateGC(display,window,GCFont+GCForeground+GCFunction, &gr_values);

--- 43,46 ----
     gr_values.foreground = color.pixel;

!    gr_context=XCreateGC(display,window,GCFont+GCForeground, &gr_values);

***************
*** 66,68 ****
      // Which function should I write here to make the line vanished??
-         XDrawLine(display,window,gr_context,800,800, 400, 450);

--- 65,66 ----
***************

绘图颜色从红色变为青色，xor渲染在白色背景下保持红色。
图形上下文现在包含GXxor函数。
在延迟之后添加具有相同参数的行的第二个绘图。第二个调用“中和”前一个调用，因此屏幕恢复到原来的状态。

或者，您可以使用双缓冲，但这意味着您需要重绘除备用缓冲区上已删除对象之外的所有内容。

如何在多物体/结构X11显示的情况下从窗口擦除对象？

1 个答案: