如何从开罗文档中绘制示例代码？

Question

我是一个完整的初学者，真的很想从和修补这些形状的放置。但是首先，我需要设置所有内容 - 仅复制代码不起作用。

/* a custom shape that could be wrapped in a function */
double x         = 25.6,        /* parameters like cairo_rectangle */
       y         = 25.6,
       width         = 204.8,
       height        = 204.8,
       aspect        = 1.0,     /* aspect ratio */
       corner_radius = height / 10.0;   /* and corner curvature radius */

double radius = corner_radius / aspect;
double degrees = M_PI / 180.0;

cairo_new_sub_path (cr);
cairo_arc (cr, x + width - radius, y + radius, radius, -90 * degrees, 0 * degrees);
cairo_arc (cr, x + width - radius, y + height - radius, radius, 0 * degrees, 90 * degrees);
cairo_arc (cr, x + radius, y + height - radius, radius, 90 * degrees, 180 * degrees);
cairo_arc (cr, x + radius, y + radius, radius, 180 * degrees, 270 * degrees);
cairo_close_path (cr);

cairo_set_source_rgb (cr, 0.5, 0.5, 1);
cairo_fill_preserve (cr);
cairo_set_source_rgba (cr, 0.5, 0, 0, 0.5);
cairo_set_line_width (cr, 10.0);
cairo_stroke (cr);

该代码应生成以下形状： 一个圆形的矩形，

但显然需要更多。因此，我决定运行以下代码，该代码可以创建一个窗口：

#include <X11/Xlib.h>
#include <X11/Xatom.h>
#include <X11/Xutil.h>
#include <cairo.h>
#include <cairo-xlib.h>

#include <stdio.h>
#include <stdlib.h>

/*! Simple Cairo/Xlib example.
 * @author Bernhard R. Fischer, 2048R/5C5FFD47 <[email protected]>.
 * @version 2014110801
 * Compile with
 * gcc -Wall $(pkg-config --libs --cflags cairo x11) -o cairo_xlib_simple cairo_xlib_simple.c
 */

/*! Check for Xlib Mouse/Keypress events. All other events are discarded.
 * @param sfc Pointer to Xlib surface.
 * @param block If block is set to 0, this function always returns immediately
 * and does not block. if set to a non-zero value, the function will block
 * until the next event is received.
 * @return The function returns 0 if no event occured (and block is set). A
 * positive value indicates that a key was pressed and the X11 key symbol as
 * defined in <X11/keysymdef.h> is returned. A negative value indicates a mouse
 * button event. -1 is button 1 (left button), -2 is the middle button, and -3
 * the right button.
 */
int cairo_check_event(cairo_surface_t *sfc, int block)
{
   char keybuf[8];
   KeySym key;
   XEvent e;

   for (;;)
   {
      if (block || XPending(cairo_xlib_surface_get_display(sfc)))
         XNextEvent(cairo_xlib_surface_get_display(sfc), &e);
      else
         return 0;

      switch (e.type)
      {
         case ButtonPress:
            return -e.xbutton.button;
         case KeyPress:
            XLookupString(&e.xkey, keybuf, sizeof(keybuf), &key, NULL);
            return key;
         default:
            fprintf(stderr, "Dropping unhandled XEevent.type = %d.\n", e.type);
      }
   }
}


/*! Open an X11 window and create a cairo surface base on that window.
 * @param x Width of window.
 * @param y Height of window.
 * @return Returns a pointer to a valid Xlib cairo surface. The function does
 * not return on error (exit(3)).
 */
cairo_surface_t *cairo_create_x11_surface0(int x, int y)
{
   Display *dsp;
   Drawable da;
   int screen;
   cairo_surface_t *sfc;

   if ((dsp = XOpenDisplay(NULL)) == NULL)
      exit(1);
   screen = DefaultScreen(dsp);
   da = XCreateSimpleWindow(dsp, DefaultRootWindow(dsp), 0, 0, x, y, 0, 0, 0);
   XSelectInput(dsp, da, ButtonPressMask | KeyPressMask);
   XMapWindow(dsp, da);

   sfc = cairo_xlib_surface_create(dsp, da, DefaultVisual(dsp, screen), x, y);
   cairo_xlib_surface_set_size(sfc, x, y);

   return sfc;
}


/*! Destroy cairo Xlib surface and close X connection.
 */
void cairo_close_x11_surface(cairo_surface_t *sfc)
{
   Display *dsp = cairo_xlib_surface_get_display(sfc);

   cairo_surface_destroy(sfc);
   XCloseDisplay(dsp);
}


int main(int argc, char **argv)
{
   cairo_surface_t *sfc;
   cairo_t *ctx;

   sfc = cairo_create_x11_surface0(500, 500);

   ctx = cairo_create(sfc);
   cairo_set_source_rgb(ctx, 1, 1, 1);
   cairo_paint(ctx);
   cairo_move_to(ctx, 20, 20);
   cairo_line_to(ctx, 200, 400);
   cairo_line_to(ctx, 450, 100);
   cairo_line_to(ctx, 20, 20);
   cairo_set_source_rgb(ctx, 0, 0, 1);
   cairo_fill_preserve(ctx);
   cairo_set_line_width(ctx, 5);
   cairo_set_source_rgb(ctx, 1, 1, 0);
   cairo_stroke(ctx);
   cairo_destroy(ctx);

   cairo_check_event(sfc, 1);

   cairo_close_x11_surface(sfc);

   return 0;
}

可以在此处访问输出：

我现在如何绘制形状和一些文字？

亲切的问候，

Answer 1

'ma完整的初学者，真的很想从 https：//www.cairographics中绘制一些形状。

最简单的方法不是打开图像，而是要绘制PNG。这是该页面第一个示例的示例。

#include <cairo.h>
#include <math.h> // For M_PI

int main() {
    cairo_surface_t *surface = cairo_image_surface_create (CAIRO_FORMAT_ARGB32, 300, 300);
    cairo_t *cr = cairo_create (surface);

    // Start of example
    double xc = 128.0;
    double yc = 128.0;
    double radius = 100.0;
    double angle1 = 45.0  * (M_PI/180.0);  /* angles are specified */
    double angle2 = 180.0 * (M_PI/180.0);  /* in radians           */

    cairo_set_line_width (cr, 10.0);
    cairo_arc (cr, xc, yc, radius, angle1, angle2);
    cairo_stroke (cr);

    /* draw helping lines */
    cairo_set_source_rgba (cr, 1, 0.2, 0.2, 0.6);
    cairo_set_line_width (cr, 6.0);

    cairo_arc (cr, xc, yc, 10.0, 0, 2*M_PI);
    cairo_fill (cr);

    cairo_arc (cr, xc, yc, radius, angle1, angle1);
    cairo_line_to (cr, xc, yc);
    cairo_arc (cr, xc, yc, radius, angle2, angle2);
    cairo_line_to (cr, xc, yc);
    cairo_stroke (cr);
    // End of example

    cairo_surface_write_to_png (surface, "example.png");
    cairo_destroy (cr);
    cairo_surface_destroy (surface);
    return 0;
}