无法在C中使用XCB绘制多边形

问题描述

刚开始使用C进行XCB编程。我编写了这段代码，该代码将创建一个窗口并绘制一些点和一个矩形：

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

int main() {
    xcb_connection_t *connection = xcb_connect(NULL,NULL);
    if (xcb_connection_has_error(connection)) {
        printf("Error setting up connection to X\n");
        exit(1);
    }
    const xcb_setup_t *setup = xcb_get_setup(connection);
    xcb_screen_t *screen = xcb_setup_roots_iterator(setup).data;

    // Create wndow
    xcb_window_t window_id = xcb_generate_id(connection);
    uint32_t prop_name = XCB_CW_BACK_PIXEL | XCB_CW_EVENT_MASK;
    uint32_t prop_value[2];
    prop_value[0] = screen->white_pixel;
    prop_value[1] = XCB_EVENT_MASK_BUTTON_PRESS | XCB_EVENT_MASK_KEY_PRESS | XCB_EVENT_MASK_EXPOSURE;
    xcb_create_window(connection,screen->root_depth,window_id,screen->root,100,500,400,1,XCB_WINDOW_CLASS_INPUT_OUTPUT,screen->root_visual,prop_name,&prop_value);
    xcb_map_window(connection,window_id);
    xcb_flush(connection);

    uint32_t gc_value_mask = XCB_GC_FOREGROUND | XCB_GC_GRAPHICS_EXPOSURES;
    uint32_t gc_value_list[2];
    gc_value_list[0] = screen->black_pixel;
    gc_value_list[1] = 0;
    xcb_drawable_t drawable_window = screen->root;
    xcb_gcontext_t context_id = xcb_generate_id(connection);
    xcb_void_cookie_t cookie = xcb_create_gc(connection,context_id,drawable_window,gc_value_mask,gc_value_list);

    // Create polygons
    xcb_point_t points[5] = {{10,10},{10,50},{40,70},{70,40},{50,10}};
    xcb_rectangle_t rect = {50,50,50};

    // Main loop
    xcb_generic_event_t *event;
    while ((event = xcb_wait_for_event(connection))) {
        switch (event->response_type) {
            case XCB_KEY_PRESS:
                break;
            case XCB_BUTTON_PRESS:
                break;
            case XCB_EXPOSE:
                printf("Expose event called\n");
                // Draw polygons
                xcb_poly_point(connection,XCB_COORD_MODE_ORIGIN,4,points);
                xcb_poly_fill_rectangle(connection,&rect);
                xcb_flush(connection);
            default:
                break;
        }
        free(event);
    }

    return 0;
}

它已正确编译，并且在运行时没有警告或错误。但是，我只是得到一个没有图形的窗口。我在做什么错了？

解决方法

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c xcb