使用X11配合cairo实现图形绘制，pango实现文字输出

X11的绘图和输出文字功能不仅使用麻烦，而且效果很差，因此建议使用第三方图形库实现绘图和输出文字功能。cairo是GTK2和GTK3使用的图形库，支持C语言，也可配合X11使用，使用非常简单。但是cairo的文字输出只是演示用途，基本没法用，输出文字一般使用pango这种文字渲染库。

ubuntu配置开发环境的命令：

sudo apt install build-essential libx11-dev libcairo2-dev libpango1.0-dev

编译的命令：

gcc -o xdrawstr xdrawstr.c -lX11 `pkg-config --cflags --libs pangocairo`

xdrawstr.c源代码： 

#include <stdio.h>
#include <stdlib.h>
#include <X11/Xlib.h>
#include <X11/Xlocale.h>
#include <cairo.h>
#include <cairo-xlib.h>
#include <pango/pangocairo.h>

int main(int argc, char **argv)
{
	Display *dpy;
	Window w;
	int i;
	GC gc;
	XEvent xe;

	int width = 300;
	int height = 200;

	cairo_surface_t *surface;
	PangoFontDescription *font_description;

	dpy = XOpenDisplay(NULL);
	w = XCreateSimpleWindow(dpy, RootWindow(dpy, 0), 50, 50, width, height, 5,
			BlackPixel(dpy, 0), WhitePixel(dpy, 0));

	surface = cairo_xlib_surface_create(
			dpy, w, DefaultVisual(dpy, DefaultScreen(dpy)),
			width, height);
	font_description = pango_font_description_new();
	pango_font_description_set_family(font_description, "sans-serif");
	pango_font_description_set_weight (font_description, PANGO_WEIGHT_BOLD);
	pango_font_description_set_absolute_size(font_description, 16 * PANGO_SCALE);

	XSelectInput(dpy, w, ExposureMask|StructureNotifyMask|
			KeyPressMask|ButtonPressMask);

	XMapWindow(dpy, w);

	XFlush(dpy);

	while (True)
	{
		XNextEvent(dpy, &xe);
		switch (xe.type) {
		case Expose:
			if (1)
			{
				cairo_t *cr = cairo_create(surface);
				PangoLayout *layout = pango_cairo_create_layout(cr);
				pango_layout_set_font_description(layout, font_description);
				pango_layout_set_text(layout, "你好，世界！", -1);
				cairo_set_source_rgb(cr, 0.0, 0.0, 1.0);
				cairo_move_to(cr, 10.0, 50.0);
				pango_cairo_show_layout(cr, layout);
				g_object_unref(layout);
				cairo_destroy(cr);
			}
			break;
		case ConfigureNotify:
			if (1)
			{
				XConfigureEvent *ce = (XConfigureEvent *)&xe;
				width = ce->width;
				height = ce->height;
				cairo_xlib_surface_set_size(surface, width, height);
			}
			break;
		case KeyPress:
			break;
		case ButtonPress:
			if (1)
			{
				XButtonEvent *be = (XButtonEvent *)&xe;
				if (be->button == Button3)
					exit(0);
			}
			break;
		default:
			break;
		}
	}
	return 0;
}