Hi,

It uses GtkDrawingArea.

I don't see why you couldn't implement cropping with one of the GimpPreview widgets.

I tried to use GimpZoomPreview instead of GtkDrawingArea and want to tell you what I have found out.

As I understand it, GimpZoomPreview is designed to be very efficient for previewing various filters (in terms of required processing & memory). Unfortunately, it doesn't seem very usable as one might expect.

For a large preview widget uses area not larger than original image dimensions, so when you zoom in you see image only in that area and large parts of widget outside image area are drawn in background color. Moreover, it becomes unacceptably slow when scrolling. The design for small previews just doesn't seem to support large previews well. Therefore, chose GtkDrawingArea. BTW, is there any way to use gimp quick navigation widget with GtkScrollingWindow or ...?

In addition to this, GimpZoomPreview doesn't seem to work well with filters either. As far as I know, only nova.c (Supernova) uses it correctly, but it only renders based on a single selected point (it doesn't have to read & analize pixels, it only renders on them). If I understand GimpZoomPreview correctly, a plug-in has to scale pixel data outside preview viewport itself (it would be much harder to work if source & destination layers would have different dimensions). This is not a very easy task, if you don't scale the whole picture, but only required parts (for efficiency).

In conclusion, either I don't understand GimpZoomPreview (in that case some explanation would help) or its API should be improved to make it more usable.

Thanks.