SUMMARY 1. The Image -> Resize Canvas tool gives fine and detailed adjustment and has a small thumbnail type indicator which can be dragged for coarse position adjustment. However, there is no feedback outline shown on the canvas which would be a useful improvement if it could be done. 2a. Further to that, a Resize To Selection function would be useful for easy and quick adjustment of the final canvas size and position. This would be similar to Trim To Selection except that it wouldn't remove any content. 2b. If this Resize to Selection function initially brought up the Resize Canvas tool, with values set to those defined by the selection outline, the Resize canvas tool could then be used for further fine numerical adjustment, with its feedback outline shown on canvas. For 2a and 2b above, the selection should be deselected after resizing since it's only purpose is as a simple way to drag out a defined area. 3. Another function could be Resize To Layer. This would be similar to Trim to Layer except that it wouldn't remove any content. This would enable you to set up individual layers (under the background layer probably or anywhere you like) that define 'viewports' in the form of rectangular (filled or not filled) areas which could later be used with Resize To Layer to remake the canvas size and position.
1. agreed that would be useful for feedback 2a. Resize Canvas to selection would be nice too, but maybe as an aditional context menu entry. 2b. it could be, but as vector selections can be fine tuned ill be more in favor of avoiding the extra step of showing the canvas resize dialog.} 3.While I see the usage of this, the usage falls a little into an obscure area of relying on pixels below the "grey area". Which would cause confusion in the long run as some operations do clear the pixels outside de view area.
@vanyossi re. Comment 1 2b) The vector selection can be numerically fine tuned (only in heigth and width, not x/y offset) but this doesn't happen in real-time with immediate visual feedback, unlike the Resize Canvas function which does this. I've tried fine tuning in this way and it's an awkward and clumsy process for fine adjustment of a selection. If you do Edit Selection on an initial manual selection (vector or raster) then you do have the real time feedback of a transformed global selection mask. You then have to switch back to 'marching ants' by turning off the global selection mask but that's not a problem. Resizing the canvas in this way (or any way) would not be frequent operation. 3) It would be useful and interesting to know which operations clear pixels outside the view area, apart from Trim operations obviously. If this were regarded as 'not a suitable/sensible function' then I could do a workaround by using the Similar Colour Selection Tool on a 'viewport rectangle' to give a selection and then use Resize To Selection (assuming it was implemented). Any consequences from operations that cleared pixels outside the current canvas would be my fault and my problem.