用Xlib库进行基本图形编程(3)
陈着
posted @ Nov 06, 2009 09:53:52 AM
in GTK+
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5.编译基于Xlib的程序
编译基于Xlib的需要把他们和Xlib库进行链接。这是通过使用如下的编译命令行来完成的：
cc prog.c -o prog -lX11
如果编译器抱怨它找不到X11库，尝试加上‘-L’标志，像这样:
cc prog.c -o prog -L/usr/X11/lib -lX11
或者也许是这样(对于用X11的release 6的系统)：
cc prog.c -o prog -L/usr/X11R6/lib -lX11
在SunOs 4系统上，X库被放置于/usr/openwin/lib：
cc prog.c -o prog -L/usr/openwin/lib -lX11
6.打开和关闭连接到X服务器的连接
X程序首先需要打开连接到X服务器的连接。在我们完成这件工作的时候，我们需要指定运行 X服务器的机器的地址，以及display号码。X window系统能够支持全部连接于同一个机器的 好几个display。然而，通常只有一个这样的display，它的display号是‘0’。如果我们想 要连接到本地display(也就是我们客户程序所运行的机器的display)，我们可以指定displa y为’:0‘。要连接到地址为”simey“的机器的第一个display，我们能够使用地址”simey :0“。这儿是连接是如何被打开的：
#include <X11/Xlib.h> /* defines common Xlib functions and structs. */
.
.
/* this variable will contain the pointer to the Display structure */
/* returned when opening a connection. */
Display* display;
/* open the connection to the display "simey:0". */
display = XOpenDisplay("simey:0");
if (display == NULL) {
fprintf(stderr, "Cannot connect to X server %s\n", "simey:0");
exit (-1);
}
.
.
/* this variable will contain the pointer to the Display structure */
/* returned when opening a connection. */
Display* display;
/* open the connection to the display "simey:0". */
display = XOpenDisplay("simey:0");
if (display == NULL) {
fprintf(stderr, "Cannot connect to X server %s\n", "simey:0");
exit (-1);
}
注意，对于X程序来说检查系统变量‘DISPLAY’是否被定义了是很常见的，而且如果是的话 ，使用它的内容作为XOpenDisplay()函数的参数。
当程序完成了它的使命并且需要关闭连接到X服务器的连接的时候，它如下动作：
XCloseDisplay(display);
这将导致所有由程序创造的窗口(如果还有剩下的话)自动被服务器关闭，而且为了客户的利 益任何留在服务器上的资源－将被释放。注意这将不会导致我们的客户程序终止－我们使用 普通的exit()函数来完成。
7.检查关于Display的基本信息
一旦我们打开了一个连接到X服务器的连接，我们应当检查有关它的一些基本信息：他有什 么样的屏幕，尺寸是多少(宽和高)，它支持多少颜色(黑白？灰度？256色？更多？)，以及 等等。我们将展示一些作一些这样检查的代码片段，以及在使用中解释每个函数的注释。我 们假定‘display’是一个指向‘Display’的结构的指针，由前面对XOpenDisplay()的调用 返回的。
/* this variable will be used to store the "default" screen of the */
/* X server. usually an X server has only one screen, so we're only */
/* interested in that screen. */
int screen_num;
/* these variables will store the size of the screen, in pixels. */
int screen_width;
int screen_height;
/* this variable will be used to store the ID of the root window of our */
/* screen. Each screen always has a root window that covers the whole */
/* screen, and always exists. */
Window root_window;
/* these variables will be used to store the IDs of the black and white */
/* colors of the given screen. More on this will be explained later. */
unsigned long white_pixel;
unsigned long black_pixel;
/* check the number of the default screen for our X server. */
screen_num = DefaultScreen(display);
/* find the width of the default screen of our X server, in pixels. */
screen_width = DisplayWidth(display, screen_num);
/* find the height of the default screen of our X server, in pixels. */
screen_height = DisplayHeight(display, screen_num);
/* find the ID of the root window of the screen. */
root_window = RootWindow(display, screen_num);
/* find the value of a white pixel on this screen. */
white_pixel = WhitePixel(display, screen_num);
/* find the value of a black pixel on this screen. */
black_pixel = BlackPixel(display, screen_num);
/* X server. usually an X server has only one screen, so we're only */
/* interested in that screen. */
int screen_num;
/* these variables will store the size of the screen, in pixels. */
int screen_width;
int screen_height;
/* this variable will be used to store the ID of the root window of our */
/* screen. Each screen always has a root window that covers the whole */
/* screen, and always exists. */
Window root_window;
/* these variables will be used to store the IDs of the black and white */
/* colors of the given screen. More on this will be explained later. */
unsigned long white_pixel;
unsigned long black_pixel;
/* check the number of the default screen for our X server. */
screen_num = DefaultScreen(display);
/* find the width of the default screen of our X server, in pixels. */
screen_width = DisplayWidth(display, screen_num);
/* find the height of the default screen of our X server, in pixels. */
screen_height = DisplayHeight(display, screen_num);
/* find the ID of the root window of the screen. */
root_window = RootWindow(display, screen_num);
/* find the value of a white pixel on this screen. */
white_pixel = WhitePixel(display, screen_num);
/* find the value of a black pixel on this screen. */
black_pixel = BlackPixel(display, screen_num);
有各种其他的宏来得到关于屏幕的更多信息，你可以从任何Xlib参考书中得到它们。还有和 这些宏完成相同功能的函数(例如XWhitePixel，它和WhitePixel干一样的事情)。
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