Add a "Unified interaction" option to the 3D Transform tool, and a
corresponding "unified" property to GimpToolTransform3DGrid. When
active, all three interaction modes of the grid (camera, move, and
rotate) are available simultaneously, regardless of the active
dialog page. In this mode, the inner and outer regions of the item
are used for moving and rotation, respectively, and the vanishing-
point is controlled through through a handle.
(cherry picked from commit 30132fc2da)
In GimpToolTransform3DGrid, fix the test for determining which side
of the plane is facing the viewer, affecting the direction of
rotation when rotating around the local Z axis.
(cherry picked from commit bcaaa453c4)
Add a new GimpToolTransform3DGrid tool widget, subclassed from
GimpToolTransformGrid, which can be used to perform 3D
transformations.
The widget can be in one of three modes:
CAMERA - allows adjusting the primary vanishing point by moving a
handle.
MOVE - allows moving the object through dragging.
ROTATE - allows rotating the object through dragging.
By default, controlling the transformation through dragging applies
to the X and Y axes. Holding Shift (or setting the "constrain-
axis" property) restricts the motion to only one of the axes.
For the MOVE and ROTATE mode, holding Ctrl (or setting the "z-axis"
property) allows controlling the Z axis instead.
For the same modes, holding Alt (or setting the "local-frame"
property), applies the adjustments in the object's local frame of
reference, instead of the display's global frame of reference.
