xcb+cairo hello world window

xcr.c

//xcr.c
//cc -o xcr $(pkg-config --cflags --libs cairo xcb xcb-icccm) xcr.c -lcairo -lxcb -lxcb-icccm
#include <stdlib.h>
#include <string.h>
#include <cairo.h>
#include <cairo-xcb.h>
#include <xcb/xcb.h>
#include <xcb/xcb_image.h>
#include <xcb/xcb_aux.h>
#include <xcb/xcb_icccm.h>

typedef struct {
    int width, height;
    int scrno;
    xcb_screen_t *scr;
    xcb_connection_t *connection;
    xcb_drawable_t win;
    unsigned int white;
    xcb_visualtype_t *visual_type;

    cairo_surface_t *surface;
    cairo_t *cr;
} Window;
Window window;

int makewindow()
{
    xcb_screen_iterator_t iter;
    xcb_depth_iterator_t depth_iter;

    window.width = 300;
    window.height = 200;

    window.connection = xcb_connect(NULL,&window.scrno);
    iter = xcb_setup_roots_iterator(xcb_get_setup(window.connection));
    for (; iter.rem; --window.scrno, xcb_screen_next(&iter))
        if (window.scrno == 0)
        {
            window.scr = iter.data;
            break;
        }
    window.win = xcb_generate_id(window.connection);
    window.white = window.scr->white_pixel;
    xcb_create_window(window.connection, XCB_COPY_FROM_PARENT,
            window.win, window.scr->root,
            0, 0,
            window.width, window.height,
            5,
            XCB_WINDOW_CLASS_INPUT_OUTPUT,
            window.scr->root_visual,
            XCB_CW_BACK_PIXEL,
            &window.white);
    xcb_icccm_set_wm_name(window.connection, window.win, XCB_ATOM_STRING, 8, strlen("xcr"), "xcr");
    xcb_map_window(window.connection, window.win);
    xcb_flush(window.connection);

    depth_iter = xcb_screen_allowed_depths_iterator(window.scr);
    for (; depth_iter.rem; xcb_depth_next(&depth_iter)) {
        xcb_visualtype_iterator_t visual_iter;

        visual_iter = xcb_depth_visuals_iterator(depth_iter.data);
        for (; visual_iter.rem; xcb_visualtype_next(&visual_iter)) {
            if (window.scr->root_visual == visual_iter.data->visual_id) {
                window.visual_type = visual_iter.data;
                goto visual_found;
            }
        }
    }
visual_found: ;

    {
        window.surface = cairo_xcb_surface_create (window.connection, window.win, window.visual_type, window.width, window.height);
        window.cr = cairo_create (window.surface);

        cairo_select_font_face (window.cr, "serif", CAIRO_FONT_SLANT_NORMAL, CAIRO_FONT_WEIGHT_BOLD);
        cairo_set_font_size (window.cr, 32.0);
        cairo_set_source_rgb (window.cr, 0.0, 0.0, 1.0);
        cairo_move_to (window.cr, 10.0, 50.0);
        cairo_show_text (window.cr, "Hello, world");

        cairo_surface_flush(window.surface);
        xcb_flush(window.connection);
    }
    return 0;
}

int destroywindow() {
    cairo_destroy (window.cr);
    cairo_surface_destroy (window.surface);
    xcb_disconnect(window.connection);
    return 0;
}

int main(int argc, char **argv)
{

    makewindow();
    sleep(100);
    destroywindow();

    return 0;
}

Thank You for publishing this example. It does work, but there are some things I want to notice.

In order to compile You also should add #include <unistd.h> (for sleep() function).

It is unnecessary to pass -l... flags, pkg-config already does it.

After resizing window gets filled in white. I am not familiar with XCB and I cannot suggest how to fix it. If this example don't tries to handle resize event - please, make it clear, write this information in a comment.

The image gets filled with white after resizing because the code is setting the XCB_CW_BACK_PIXEL of the xcb_window_t to white. Instead of a single color as background for windows, you can also set an X pixmap, using XCB_CW_BACK_PIXMAP instead of XCB_CW_BACK_PIXEL. In general, xcb is poorly documented, but for the most part it's a thin wrapper around the X protocol to help you send requests (using the X protocol) to the X server. Once you begin understanding the X protocol itself, you will find that most xcb calls correspond very nicely to X protocol requests, replies, events, and errors (these are the 4 types of packets that the X server understands).