如何从 Cairo 上下文创建 GtkImage？
我得到了一个使用 Cairo 上下文工作的绘制函数，最终结果应该是一个 GtkImage （没有中间图像创建）。我尝试使用 gdk_cairo_create 函数，但此代码：
...
GdkPixbuf *pixbuf = gdk_pixbuf_new (GDK_COLORSPACE_RGB, FALSE, 8, 22, 22);
GtkWidget *image = gtk_image_new_from_pixbuf (pixbuf);
GdkDrawable *drawable = image->window;
cairo_t *ctx = gdk_cairo_create (drawable);
my_cairo_paint_function (ctx);
...
失败并显示：
Gdk-CRITICAL **：IA__gdk_cairo_create：断言“GDK_IS_DRAWABLE（可绘制）”失败
与简单相同：
#include <gtk/gtk.h>
#include <cairo.h>
int
main (int argc, char *argv[])
{
gtk_init(&argc, &argv);
cairo_t *ctx = gdk_cairo_create (gtk_widget_get_window (gtk_image_new_from_file ("foobar.png")));
gtk_main();
return 0;
}
我不明白为什么会失败。任何帮助表示赞赏！
I got a paint function that works using a Cairo context and the end result should be a GtkImage (without intermediate image creation). I tried to use the gdk_cairo_create function but this code:
...
GdkPixbuf *pixbuf = gdk_pixbuf_new (GDK_COLORSPACE_RGB, FALSE, 8, 22, 22);
GtkWidget *image = gtk_image_new_from_pixbuf (pixbuf);
GdkDrawable *drawable = image->window;
cairo_t *ctx = gdk_cairo_create (drawable);
my_cairo_paint_function (ctx);
...
fails with:
Gdk-CRITICAL **: IA__gdk_cairo_create: assertion `GDK_IS_DRAWABLE (drawable)' failed
Same with a simple:
#include <gtk/gtk.h>
#include <cairo.h>
int
main (int argc, char *argv[])
{
gtk_init(&argc, &argv);
cairo_t *ctx = gdk_cairo_create (gtk_widget_get_window (gtk_image_new_from_file ("foobar.png")));
gtk_main();
return 0;
}
I don't understand why this fails. Any help is appreciated!
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GtkImage没有GdkWindow，因此调用gtk_widget_get_window()或访问widget->windowcode> 返回NULL。您可以将GtkImage放入GtkEventBox中，并在事件框的GdkWindow上进行绘制。尽管如此，看起来您正在尝试（使用
gdk_pixbuf_new）创建一个空白空间来绘制。在这种情况下，GtkImage不是您想要的小部件 - 请使用GtkDrawingArea。并且不要忘记在event-expose信号的处理程序中调用您的绘制函数！GtkImagedoesn't have aGdkWindow, so the call togtk_widget_get_window()or the access ofwidget->windowreturnsNULL. You can put theGtkImagein aGtkEventBoxand draw on the event box'sGdkWindow.Although, it looks like you're trying (with
gdk_pixbuf_new) to create an empty space to draw on. In that case,GtkImageis not the widget you want -- useGtkDrawingArea. And don't forget to call your paint function in the handler for theevent-exposesignal!