GTK3学习笔记4 Drawing

原文介绍可见这里。

这篇介绍一个很好玩的窗口，一个可以进行绘图的窗口。换句话说，可以做一个简单的绘图软件。
效果见下面的动画：

        

虽然很粗糙，不过，做出这么个简单的绘图窗口算是很有成就感了吧。

关于代码：

不过代码也是比较长的，我将原文中的代码分成了两部分，即头文件mygtk.h和源程序main.c。

mygtk.h:

#ifndef MYGTK_H_INCLUDED#define MYGTK_H_INCLUDED/* 建立一个surface（我翻译为“表面”），用于存储当前的涂鸦*/static cairo_surface_t *surface = NULL;/* 摘自cairo.h，A cairo_surface_t represents an image, either as the destination * of a drawing operation or as source when drawing onto another * surface.  To draw to a #cairo_surface_t, create a cairo context * with the surface as the target, using cairo_create().*//* 将 surface 初始化为白色*/static void clear_surface (void){    cairo_t *cr;    cr = cairo_create (surface);    cairo_set_source_rgb (cr, 1, 1, 1);    cairo_paint (cr);    cairo_destroy (cr);}/* 创造一个新的、大小适当的 surface 去存储我们的涂鸦 */static gboolean configure_event_cb (GtkWidget  *widget,                    GdkEventConfigure *event,                    gpointer           data){    if (surface)        cairo_surface_destroy (surface);    surface = gdk_window_create_similar_surface (gtk_widget_get_window (widget),              CAIRO_CONTENT_COLOR,              gtk_widget_get_allocated_width (widget),              gtk_widget_get_allocated_height (widget));    /* 将 surface 初始化为白色*/    clear_surface ();    /* 我们做了处理后，不必再做进一步的处理 */    return TRUE;} /*通过 surface 重绘屏幕。 * 接收一个现有的 cairo_t 对象，绘制widget的暴露部分。 */static gboolean draw_cb (GtkWidget *widget,         cairo_t   *cr,         gpointer   data){    cairo_set_source_surface (cr, surface, 0, 0);    cairo_paint (cr);    return FALSE;}/*在指定的位置绘制一个矩形 */static void draw_brush (GtkWidget *widget,            gdouble    x,            gdouble    y){    cairo_t *cr;    /* Paint to the surface, where we store our state */    cr = cairo_create (surface);    cairo_rectangle (cr, x - 3, y - 3, 6, 6);    cairo_fill (cr);    cairo_destroy (cr);    /* Now invalidate the affected region of the drawing area. */    gtk_widget_queue_draw_area (widget, x - 3, y - 3, 6, 6);}/* Handle button press events by either drawing a rectangle * or clearing the surface, depending on which button was pressed. * The ::button-press signal handler receives a GdkEventButton * struct which contains this information. */static gboolean button_press_event_cb (GtkWidget      *widget,                       GdkEventButton *event,                       gpointer        data){    /* paranoia check, in case we haven't gotten a configure event */    if (surface == NULL)        return FALSE;    if (event->button == GDK_BUTTON_PRIMARY)    {        draw_brush (widget, event->x, event->y);    }    else if (event->button == GDK_BUTTON_SECONDARY)    {        clear_surface ();        gtk_widget_queue_draw (widget);    }    /* We've handled the event, stop processing */    return TRUE;}/* Handle motion events by continuing to draw if button 1 is * still held down. The ::motion-notify signal handler receives * a GdkEventMotion struct which contains this information. */static gboolean motion_notify_event_cb (GtkWidget      *widget,                        GdkEventMotion *event,                        gpointer        data){    /* paranoia check, in case we haven't gotten a configure event */    if (surface == NULL)        return FALSE;    if (event->state & GDK_BUTTON1_MASK)        draw_brush (widget, event->x, event->y);    /* We've handled it, stop processing */    return TRUE;}static void close_window (void){    if (surface)        cairo_surface_destroy (surface);    gtk_main_quit ();}#endif // MYGTK_H_INCLUDED

main.c:

#include <gtk/gtk.h>#include "mygtk.h"int main (int argc, char *argv[]){    GtkWidget *window, *frame, *da;    gtk_init (&argc, &argv);    /* 构图 */    window = gtk_window_new (GTK_WINDOW_TOPLEVEL);    gtk_window_set_title (GTK_WINDOW (window), "Drawing Area");    g_signal_connect (window, "destroy", G_CALLBACK (close_window), NULL);    gtk_container_set_border_width (GTK_CONTAINER (window), 8);    frame = gtk_frame_new (NULL);    gtk_frame_set_shadow_type (GTK_FRAME (frame), GTK_SHADOW_IN);    gtk_container_add (GTK_CONTAINER (window), frame);    da = gtk_drawing_area_new ();    /* set a minimum size */    gtk_widget_set_size_request (da, 100, 100);    gtk_container_add (GTK_CONTAINER (frame), da);    /* Signals used to handle the backing surface */    g_signal_connect (da, "draw",                      G_CALLBACK (draw_cb), NULL);    /*信号“ configure-event“被发射了 ，     *则所绑定构件的大小、位置与次序栈都被捕获了。     */    g_signal_connect (da,"configure-event",                      G_CALLBACK (configure_event_cb), NULL);    /* Event signals */    g_signal_connect (da, "motion-notify-event",                      G_CALLBACK (motion_notify_event_cb), NULL);    g_signal_connect (da, "button-press-event",                      G_CALLBACK (button_press_event_cb), NULL);    /* Ask to receive events the drawing area doesn't normally     * subscribe to. In particular, we need to ask for the     * button press and motion notify events that want to handle.     */    gtk_widget_set_events (da, gtk_widget_get_events (da)                           | GDK_BUTTON_PRESS_MASK                           | GDK_POINTER_MOTION_MASK);    gtk_widget_show_all (window);    gtk_main ();    return 0;}

这里需要做些说明：

对于头文件中的后两个函数我还没有弄得太懂，不过大致跟按钮press捕捉有关，至于其详细特性，需要查看头文件中的声明。

如果在codeblocks中查找声明显示找不到，应该是编译器选项的搜索路径没有添加上或者添加完全，大致应该如图：

即：添加你的GTK目录下include的所有目录及其子目录到搜索路径，这样就能找到函数声明了。