* Started porting back keyframe editing tools for the Action Editor/Dopesheet. Currently, only Snap (Shift-S) and Mirror (Shift-M) are functional.
* Added keyframe-editing API method for ensuring that all IPO-curves are left in a valid state after modifiying the values of their keyframes.
* Added operator-register flags for most of the operators. Only mouse-select doesn't have it for now (as there's not much useful info stored, and no exec callback).
User Notes (for using tools whose behaviour has changed):
* Mouse Selection Tools:
1) Click on keyframe to modify its selection. Holding the 'Shift' modifier when doing so, will result in keyframe selection being toggled instead of replacing existing selections.
2) Click on either side of the current frame indicator while holding the 'Alt' modifier. This will select only all the keyframes on the relevant side of the current frame indicator.
3) Click on a keyframe while holding the 'Ctrl' modifier. This will select all the keyframes that fall on that frame.
* Borderselect Tools
1) BKEY selects all the keyframes within the specified range (as per normal)
2) ALT-BKEY will select either all the keyframes in the frame-range specified or the channel range specified, depending on which axis of the select region was larger. This method is prejudiced towards frame-range selection.
Code Notes:
* Finished porting over all of the remaining keyframe selection tools, and recoded the ported ones to make them easier to use (after running into some technical limitations)
* Simplified the way to check if 'animation context' is valid by moving a necessary check into that function.
* Refactored internal keyframe-looping tools to reduce the amount of code needed per tool to edit keyframes, removing a lot of the unnecessary bulk. Now, the ipo/icu_keys_bezier_loop functions recieve a few more arguments (1st arg is pointer to generic customdata, and another defines a validation callback which makes it easier to reuse some of the select callbacks).
* Added 'totrect' adjustment for number of channels being shown in Action Editor, so that scrolling will be limited to where there is data (and also so that scroller displays more relevant context info).
For this to work, filtering channels now returns the number of channels extracted. This may come into use for other tools if there's such a need.
* I still need to port over some code for markers, which is required for some of the tools which use them. For now, those tools do nothing.
* Grease-Pencil editing mode in Action Editor is currently non-functional (code is commented out due to missing dependencies). This is currently pending the re-implementation of Grease Pencil in 2.5
Ported the following tools
* borderselect
* invert selection
Note: while porting these, I noticed a few issues with some stuff that still needs to be cleaned up.
Events handling in scrollers won't work yet, for the useful select all in frame(-range) or select all in channel(s). We should probably review ways to expose this more clearly in the UI too.
* Brought back backend for editing keyframes IPO/IPO-Curves. Did some refactoring work here that will still have to be verified when operators using them are added.
* Animation channel filtering code now returns the number of channels filtered (for Action Editor to set totrect of channels - TODO still!)
* View2D - made function to check if mouse is in View2D scrollers an API function
* Renamed keyframe related files. The old names were too clumsy.
* Started porting click-select operators for Action Editor. These don't work currently, as the events are being stolen by the markers. This needs to be fixed ASAP.
