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5 Scaling pixbufs and scaling and compositing pixbufs
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9 The &gdk-pixbuf; contains functions to scale pixbufs, to scale
10 pixbufs and composite against an existing image, and to scale
11 pixbufs and composite against a solid color or checkerboard.
12 Compositing a checkerboard is a common way to show an image with
13 an alpha channel in image-viewing and editing software.
17 Since the full-featured functions (gdk_pixbuf_scale(),
18 gdk_pixbuf_composite(), and gdk_pixbuf_composite_color()) are
19 rather complex to use and have many arguments, two simple
20 convenience functions are provided, gdk_pixbuf_scale_simple() and
21 gdk_pixbuf_composite_color_simple() which create a new pixbuf of a
22 given size, scale an original image to fit, and then return the
27 The following example demonstrates handling an expose event by
28 rendering the appropriate area of a source image (which is scaled
29 to fit the widget) onto the widget's window. The source image is
30 rendered against a checkerboard, which provides a visual
31 representation of the alpha channel if the image has one. If the
32 image doesn't have an alpha channel, calling
33 gdk_pixbuf_composite_color() function has exactly the same effect
34 as calling gdk_pixbuf_scale().
39 expose_cb (GtkWidget *widget, GdkEventExpose *event, gpointer data)
43 gdk_window_set_back_pixmap (widget->window, NULL, FALSE);
45 dest = gdk_pixbuf_new (GDK_COLORSPACE_RGB, FALSE, 8, event->area.width, event->area.height);
47 gdk_pixbuf_composite_color (pixbuf, dest,
48 0, 0, event->area.width, event->area.height,
49 -event->area.x, -event->area.y,
50 (double) widget->allocation.width / gdk_pixbuf_get_width (pixbuf),
51 (double) widget->allocation.height / gdk_pixbuf_get_height (pixbuf),
52 GDK_INTERP_BILINEAR, 255,
53 event->area.x, event->area.y, 16, 0xaaaaaa, 0x555555);
55 gdk_pixbuf_render_to_drawable (dest, widget->window, widget->style->fg_gc[GTK_STATE_NORMAL],
56 0, 0, event->area.x, event->area.y,
57 event->area.width, event->area.height,
58 GDK_RGB_DITHER_NORMAL, event->area.x, event->area.y);
60 gdk_pixbuf_unref (dest);
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