Re: [Gimp-developer] Important misfunction in gimp scaling tool

[Ofnuts <ofnuts laposte net>]

On 06/05/2012 06:41 PM, Liam R E Quin wrote:

On Mon, 2012-06-04 at 15:56 +0200, brefromjeu wrote:

[...]

. This is about the scale tool ( the one in the dock 
window ).
This function is missing the possibility of moving the center. A scale 
function is a homotetia ( not sure
of this word in english tho ) wich is defined by a ration and a center.

Since the scaling is linear, moving the origin would be equivalent to a
scale followed by a translation (a moving). The most useful part about
defining the centre (the origin) would be that it would remain in that
position after scaling.

I believe thew new redesigned transform tools will offer this in a
future version.

Yes, the interesting feature is that it would be the invariant point... however, I don't see anything like this in the proposal for the new transform tool:

scale

Scaling through scale handles means translating one corner points, with all sides at constant angles.

• dragging a scale handle shall translate its corner points by the vector of the drag;
• when the keep aspect transformation constraint is enabled, the translation shall only be along the diagonal that runs trough this corner point;
• when the from centre transformation constraint is enabled, the translation shall also translate the diagonally opposite corner points by the same distance, however with the angle of the vector 180 degrees rotated.

Scaling through side handles means translating one side, with it and the opposite side at constant angles.

• dragging a side handle shall translate its side by the vector of the drag, along the vector that runs perpendicular to the angle of the side;
• when the keep aspect transformation constraint is enabled, the two corners that are at the ends of the moving side(s) shall be kept on the diagonals that runs trough them;
• when the from centre transformation constraint is enabled, the translation shall also translate the opposite side by the same distance and the equally inward or outward, however along the vector that runs perpendicular to the angle of that opposite side.

The "when the from centre transformation constraint is enabled, the translation shall also translate the diagonally opposite corner points by the same distance, however with the angle of the vector 180 degrees rotated." tells me that the "centre" is the intersection of the diagonals and that you can't do anything about it.

This is more important than it looks, because if you can't define that invariant point on a combined rotation/scale, aligning two layers will be done in several successive align/rotate/scale steps, and each scale/rotate slighly blurs the picture, so it's a major usability gain to be able to do it in one single pass (fortunately there is also the exact-aligner plugin)