cairo 绘制水印背景图片

绘制的水印图片，可以添加到应用程序。我是添加到gedit上的（GTK3.0）

#include <cairo.h>
#include <math.h>
cairo_surface_t *surface;
cairo_t *cr;
void clear_surface (void)
{
	cairo_t *cr;
	cr = cairo_create (surface);
	cairo_set_source_rgb (cr, 1, 1, 1); /* 白色 */
	cairo_paint (cr);
	cairo_destroy (cr);
}

int main(int argc, char *argv[])
{
	int  width = 0, height = 0;
	surface = cairo_image_surface_create(CAIRO_FORMAT_ARGB32, 340, 80);//创建一个图像外观
	cr = cairo_create(surface);	
	cairo_select_font_face(cr, "serif", CAIRO_FONT_SLANT_NORMAL, CAIRO_FONT_WEIGHT_BOLD);//设置字体
	cairo_set_font_size(cr, 25.0);//设置字体大小
	clear_surface();//设置背景色为白色
	cairo_move_to(cr, 10.0, 30.0);//从10  30 开始绘制
	cairo_set_source_rgb (cr, 0.9, 0.9, 0.9); /* 设置字体颜色 */
	cairo_show_text(cr, "机密文件！请勿外传！");
	cairo_destroy(cr);
	cairo_surface_write_to_png(surface, "timg.png");
	cairo_surface_destroy(surface);
	
	cairo_surface_t *image;
	cairo_pattern_t *pattern;
	surface = cairo_image_surface_create(CAIRO_FORMAT_ARGB32, 1440, 900);

        cr = cairo_create(surface);
	image = cairo_image_surface_create_from_png ("timg.png");
	width = cairo_image_surface_get_width (image);
	height = cairo_image_surface_get_height (image);
	pattern = cairo_pattern_create_for_surface (image);
	cairo_pattern_set_extend (pattern, CAIRO_EXTEND_REPEAT);//平铺 
	cairo_rotate (cr, M_PI / 4);//旋转多少
	cairo_scale (cr, 2, 2);//x指宽度缩放倍数，y指高度缩放的倍数
	cairo_translate (cr, -(width+110), -(height+420));
	cairo_set_source (cr, pattern);
	cairo_rectangle (cr, 0, 0, 1440, 900);//绘制一个矩形，起点是0,0，长1440，宽900  
	cairo_fill (cr);
	cairo_destroy(cr);
	cairo_pattern_destroy (pattern);
	cairo_surface_destroy (image);
	cairo_surface_write_to_png(surface, "timg.png");
	cairo_surface_destroy(surface);

	return 0;
}
#inclu