Easier single-stepping of frames with keyboard and mouse

[mgkuhn]

When viewing a 3D volume (e.g., movie, CT, MRI), at the moment the only way to move from one single frame/slice to the next one seems to be via clicking the |<< and >>| buttons in the “player” widget at the bottom of the window. This can be quite inconvenient when searching for some feature in a 3D or 4D volume. Repeatedly clicking on a button while focusing the eyeballs on another part of the screen can be difficult, as the mouse can easily move off the button, and switching direction requires each time re-tasking ones eyeballs to search the other button, risking loosing whatever feature the eyeballs were tracking in the image.

It would be useful if there were also alternatives to single-step through slices that do not require moving the eyeballs off the image, such as

• Keyboard shortcuts. For example, some video players use the comma key for single-stepping backwards, and the full-stop key for single-stepping forwards, so my suggestion would be comma and full-stop for single-stepping in the third dimension, and perhaps n and m for single-stepping in the fourth dimension?
• A modifier key that causes the mouse wheel to change to the next/previous slice. We have already Ctrl-mouse-wheel for zoom, as well as unmodified-mouse-wheel and shift-mouse-wheel for panning in the first and second dimension (along with click+drag). So could we not add e.g. Alt-mouse-wheel and Shift-Alt-mouse-wheel for single-stepping in the third and fourth dimension, respectively?

(Ultimately, such mouse-wheel mappings may have to be user configurable, as some of them may already have been hijacked by some desktop environments for other purposes.)

[timholy]

Sorry I missed this. I'd definitely support keyboard or mouse-wheel interaction to navigate. Would appreciate a pull request if that's possible. I might get to it eventually but it is not high on the priority list.