关于GTK用cairo绘图问题

cortex

我想用cairo绘制折线图，x坐标每次增加30，y坐标随机产生，每1秒刷新一次图像，但现在每次刷新使上次画布的东西都清空了，怎么回事呢
#include <cairo.h>
#include <gtk/gtk.h>
#include <glib.h>

gint x = 0, y = 0;
cairo_t *cr;
gint update(gpointer data) {
       gtk_widget_queue_draw((GtkWidget*) data);
}

static gboolean
on_expose_event(GtkWidget *widget,
        GdkEventExpose *event,
        gpointer data) {
   
    GRand *rand;
    gint x1 = 0, y1 = 0;
    rand = g_rand_new();

    cr = gdk_cairo_create(widget->window);
    cairo_set_source_rgb(cr, 0, 0, 0);
    cairo_set_line_width(cr, 2.0);

    cairo_move_to(cr, 100, 450);
    cairo_line_to(cr, 700, 450);

    cairo_move_to(cr, 100, 450);
    cairo_line_to(cr, 100, 50);
   
    cairo_move_to(cr, x1, y1);
    x += 30;
    y = g_rand_int_range(rand, 55, 400);
    cairo_line_to(cr, x, y);
   
    x1 = x;
    y1 = y;
   
    cairo_stroke(cr);
   
   
   
    //cairo_set_source_rgb(cr, 0, 0, 0);
    //cairo_arc(cr, x, y, 2, 0, 2 * 3.14);
    //cairo_clip(cr);
    //cairo_rectangle(cr, 0, 0, 256, 256);
    //cairo_fill(cr);
   
   
   
    cairo_select_font_face(cr, &quoturisa",
            CAIRO_FONT_SLANT_NORMAL,
            CAIRO_FONT_WEIGHT_BOLD);

    cairo_set_font_size(cr, 13);

    cairo_move_to(cr, 10, 50);
    cairo_show_text(cr, "温度（单位：℃）");
   
    cairo_move_to(cr, 700, 475);
    cairo_show_text(cr, "时间（单位：s）");
   

    cairo_stroke(cr);          //描绘轮廓
   // cairo_restore(cr);
    cairo_destroy(cr);          //销毁画笔
   
    return FALSE;
}

int main(int argc, char *argv[]) {
    GtkWidget *window;

    gtk_init(&argc, &argv);

    window = gtk_window_new(GTK_WINDOW_TOPLEVEL);

    g_signal_connect(window, "expose-event",
            G_CALLBACK(on_expose_event), NULL);
    g_signal_connect(window, "destroy",
            G_CALLBACK(gtk_main_quit), NULL);

    gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER);
    gtk_window_set_default_size(GTK_WINDOW(window), 800, 500);
    gtk_widget_set_app_paintable(window, TRUE);

    gtk_timeout_add(1000, update, window);

    gtk_widget_show_all(window);

    gtk_main();

    return 0;
}

mbt

可以试着在 绘制事件末尾加入 gtk_main_iteration()；