我正在尝试使用 cairo 绘制一些弧线,但 gcc 警告我 gdk_cairo_create() is deprecated. Use gdk_window_begin_draw_frame() and gdk_drawing_context_get_cairo_context() instead
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为了解决这个问题,我做了一些研究,发现对于 gdk_window_begin_draw_frame() 我需要“GdkWindow”。我一直在我的窗口中使用 GtkWidget,所以我需要将“GtkWidget”转换为“GdkWindow”,但是 gtk_widget_get_window() 返回NULL 并导致段错误。
#include <gtk/gtk.h>
#include <cairo.h>
void main(int argc , char **argv){
gtk_init(&argc , &argv);
GtkWidget *win;
GdkWindow *gdkwin;
GdkDrawingContext *dc;
cairo_region_t *region;
cairo_t *cr;
win = gtk_window_new(GTK_WINDOW_TOPLEVEL);
region = cairo_region_create();
gdkwin = gtk_widget_get_window(GTK_WIDGET(win));
//Here gdkwin should contain a GdkWindow but it's NULL.
gc = gdk_window_begin_draw_frame(gdkwin , (const cairo_region_t*)®ion);
...
...
这是运行时错误:
(a.out:6852): Gdk-CRITICAL **: 23:53:06.042: gdk_window_begin_draw_frame: assertion 'GDK_IS_WINDOW (window)' failed
(a.out:6852): Gdk-CRITICAL **: 23:53:06.042: gdk_drawing_context_get_cairo_context: assertion 'GDK_IS_DRAWING_CONTEXT (context)' failed
Segmentation fault
我想获得一个 cairo 对象并将其用于 cairo_arc()。
谢谢。最好的问候。
最佳答案
下面是让 Cairo 在 GTK 3 下工作的完整源代码。它应该可以按原样编译。
正如其他人已经指出的那样,您必须使用绘制信号才能使事情正常进行。
#include <gtk/gtk.h>
#include <cairo.h>
// ------------------------------------------------------------
gboolean on_draw (GtkWidget *widget,
GdkEventExpose *event,
gpointer data)
{
// "convert" the G*t*kWidget to G*d*kWindow (no, it's not a GtkWindow!)
GdkWindow* window = gtk_widget_get_window(widget);
cairo_region_t * cairoRegion = cairo_region_create();
GdkDrawingContext * drawingContext;
drawingContext = gdk_window_begin_draw_frame (window,cairoRegion);
{
// say: "I want to start drawing"
cairo_t * cr = gdk_drawing_context_get_cairo_context (drawingContext);
{ // do your drawing
cairo_move_to(cr, 30, 30);
cairo_set_font_size(cr,15);
cairo_show_text(cr, "hello world");
}
// say: "I'm finished drawing
gdk_window_end_draw_frame(window,drawingContext);
}
// cleanup
cairo_region_destroy(cairoRegion);
return FALSE;
}
// ------------------------------------------------------------
int main (int argc, char * argv[]) {
gtk_init(&argc, &argv);
GtkWindow * window;
{ // window setup
window = (GtkWindow*)gtk_window_new(GTK_WINDOW_TOPLEVEL);
gtk_window_set_default_size (window, 200, 200);
gtk_window_set_position (window, GTK_WIN_POS_CENTER);
gtk_window_set_title (window, "Drawing");
g_signal_connect(window, "destroy", gtk_main_quit, NULL);
}
// create the are we can draw in
GtkDrawingArea* drawingArea;
{
drawingArea = (GtkDrawingArea*) gtk_drawing_area_new();
gtk_container_add(GTK_CONTAINER(window), (GtkWidget*)drawingArea);
g_signal_connect((GtkWidget*)drawingArea, "draw", G_CALLBACK(on_draw), NULL);
}
gtk_widget_show_all ((GtkWidget*)window);
gtk_main();
return 0;
}
// ------------------------------------------------------------
关于c - 如何在 GTK+3 的 gtk 窗口中创建 cairo 对象,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/57699050/