Unable to move compositor backdrop image using manipulator if outside of view area
Open, ConfirmedPublic

Description

Blender 2.8
Windows 64 bits

If you use the backdrop image and move the display image using the manipulator outside the view area, you cannot move again the image because the scroll bars don't move the image.

See this video: https://www.dropbox.com/s/7zv4tc0oxtivs7r/UI_Compo_problem.mp4?dl=0

Details

Type
Bug
Campbell Barton (campbellbarton) triaged this task as Confirmed priority.Mon, Feb 19, 1:10 AM

Confirmed on Blender 2.8 - Arch Linux x64.

It's also possible to see that there is no strong association between using the manipulators or the backdrop's toolbar on the right.
More specifically, when you drag the backdrop, there is no change in the offset until you hover the sidebar also when you use the Move button and the handlers don't move with it (only when you deselect and select the view node).

Reading more of the code I've seen this piece that could cause part of the problem above:
WM_manipulator_types.h:303

        /* Returns the final transformation which may be different from the 'matrix',
	 * depending on the manipulator.
	 * Notes:
	 * - Scale isn't applied (wmManipulator.scale/user_scale).
	 * - Offset isn't applied (wmManipulator.matrix_offset).
	 */
	wmManipulatorFnMatrixBasisGet matrix_basis_get;

Watching the code, I've seen that @Campbell Barton (campbellbarton) wrote part of the manipulators. Maybe he could give some insights.

Also, what would be the best approach to avoid missing the manipulators on the scene ? Or should we just guarantee the consistency of the toolbar and manipulators information?