GTK3學習筆記4 Drawing
阿新 • • 發佈:2019-01-27
原文介紹可見這裡。
這篇介紹一個很好玩的視窗,一個可以進行繪圖的視窗。換句話說,可以做一個簡單的繪圖軟體。
效果見下面的動畫:
雖然很粗糙,不過,做出這麼個簡單的繪圖視窗算是很有成就感了吧。
關於程式碼:
不過程式碼也是比較長的,我將原文中的程式碼分成了兩部分,即標頭檔案mygtk.h和源程式main.c。
mygtk.h:
#ifndef MYGTK_H_INCLUDED #define MYGTK_H_INCLUDED /* 建立一個surface(我翻譯為“表面”),用於儲存當前的塗鴉*/ 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().*/ /* 將 surface 初始化為白色*/ 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); } /* 創造一個新的、大小適當的 surface 去儲存我們的塗鴉 */ 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)); /* 將 surface 初始化為白色*/ clear_surface (); /* 我們做了處理後,不必再做進一步的處理 */ return TRUE; } /*通過 surface 重繪螢幕。 * 接收一個現有的 cairo_t 物件,繪製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; } /*在指定的位置繪製一個矩形 */ 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); /* 構圖 */ 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); /*訊號“ configure-event“被髮射了 , *則所繫結構件的大小、位置與次序棧都被捕獲了。 */ 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; }
這裡需要做些說明:
對於標頭檔案中的後兩個函式我還沒有弄得太懂,不過大致跟按鈕press捕捉有關,至於其詳細特性,需要檢視標頭檔案中的宣告。如果在codeblocks中查詢宣告顯示找不到,應該是編譯器選項的搜尋路徑沒有新增上或者新增完全,大致應該如圖:
即:新增你的GTK目錄下include的所有目錄及其子目錄到搜尋路徑,這樣就能找到函式聲明瞭。