1 files changed, 56 insertions, 0 deletions
diff --git a/prev/image_unix.go b/prev/image_unix.go
new file mode 100644
index 0000000..c6ae397
--- /dev/null
+++ b/prev/image_unix.go
@@ -0,0 +1,56 @@
+// +build !windows,!darwin
+
+// 16 august 2014
+
+package ui
+
+import (
+	"fmt"
+	"image"
+	"unsafe"
+)
+
+// #include "gtk_unix.h"
+import "C"
+
+// this is what GtkFileChooserWidget uses
+// technically it uses max(width from that, height from that) if the call below fails and 16x16 otherwise, but we won't worry about that here (yet?)
+const scaleTo = C.GTK_ICON_SIZE_MENU
+
+func toIconSizedGdkPixbuf(img *image.RGBA) *C.GdkPixbuf {
+	var width, height C.gint
+
+	surface := C.cairo_image_surface_create(C.CAIRO_FORMAT_ARGB32,
+		C.int(img.Rect.Dx()),
+		C.int(img.Rect.Dy()))
+	if status := C.cairo_surface_status(surface); status != C.CAIRO_STATUS_SUCCESS {
+		panic(fmt.Errorf("cairo_create_image_surface() failed in toIconSizedGdkPixbuf(): %s\n",
+			C.GoString(C.cairo_status_to_string(status))))
+	}
+	C.cairo_surface_flush(surface)
+	toARGB(img, uintptr(unsafe.Pointer(C.cairo_image_surface_get_data(surface))),
+		int(C.cairo_image_surface_get_stride(surface)), false) // not NRGBA
+	C.cairo_surface_mark_dirty(surface)
+	basepixbuf := C.gdk_pixbuf_get_from_surface(surface, 0, 0, C.gint(img.Rect.Dx()), C.gint(img.Rect.Dy()))
+	if basepixbuf == nil {
+		panic(fmt.Errorf("gdk_pixbuf_get_from_surface() failed in toIconSizedGdkPixbuf() (no reason available)"))
+	}
+
+	if C.gtk_icon_size_lookup(scaleTo, &width, &height) == C.FALSE {
+		panic(fmt.Errorf("gtk_icon_size_lookup() failed in toIconSizedGdkPixbuf() (no reason available)"))
+	}
+	if int(width) == img.Rect.Dx() && int(height) == img.Rect.Dy() {
+		// just return the base pixbuf; we're good
+		C.cairo_surface_destroy(surface)
+		return basepixbuf
+	}
+	// else scale
+	pixbuf := C.gdk_pixbuf_scale_simple(basepixbuf, C.int(width), C.int(height), C.GDK_INTERP_NEAREST)
+	if pixbuf == nil {
+		panic(fmt.Errorf("gdk_pixbuf_scale_simple() failed in toIconSizedGdkPixbuf() (no reason available)"))
+	}
+
+	C.g_object_unref(C.gpointer(unsafe.Pointer(basepixbuf)))
+	C.cairo_surface_destroy(surface)
+	return pixbuf
+}