XnView Software

Currently the free rotation dialogue consist of a ruler and a arrow that we can move with either the mouse or the keyboard.
Moving the arrow on the ruler is not easy, sometime too reactive.
Also, the rotation is always centred with the image, which is not always optimal. For example the main subject could be in the left side. The rotation should preserve the maximum of the original picture in this area.

Suggestion is to allow to rotate the image with the mouse in 2 phases:
- 1st step to define the axe of the rotation. The axe is materialised by a point or a star. It should not make any trouble as - by definition - there is no movement here. By default it is at the center of the image and it can be changed with the mouse.
- 2nd step, with the mouse click on either side (or top° of the image and move up/down (right/left from the top) to adjust the angle. This method is a bit less precise than the current one but is more efficient. If need, a final adjustment can be made with the arrows

The new dialogue would just consist of 2 arrows (horizontal, rounded arrows for left/right), an angle indicator + the options (except "Apply to image as this is required)

You might look at this earlier thread: Horizon Straightener Needed

And in relation to the detailed user interface, particularly at my post concerning the ScanTailor rotation interface.

I didn't knew that

Steps:

1. Double-click on an image to open in Viewer
2. Edit | Crop (or press Shift + X)
3. Select an area around the "horizon" - take care to have an edge close to "horizon"
4. Go with the mouse NEAR to the one of the corners of the crop rectangle till you'll see a "rotating" cursor (like "Refresh"). Now you can rotate the crop rectangle.
5. Rotate & adjust till you have the margin exactly parallel with the horizon
6. Expand the margins of the rectangle as desired.

From time to time I noticed the small rotating cursors but never understood, never tried to click on them. Now I did and found it better than the rotation tool, for basic rotation jobs. The drawback is some options are missing. The good news is the code is available, it just need implementation on the rotation dialogue.

PS: Based on the above as an alternate proposal to my original, we may remove the "Free rotation tool" and implement the options Show grid, Auto crop, Smooth to an improved "Crop - and Rotate" tool. That's a big change on the features and user interface.