Signal: assetAboutToBeExported #3984

Is your feature request related to a problem? Please describe. I've got an extension that listens to assetAboutToBeSaved to do last-minute corrections. Examples:

• ensuring that polygon vertices are in counter-clockwise winding order
• ensuring that vertices are snapped to the nearest pixel coordinate
• apply rotation and offset

This works well, but the signal is not triggered when exporting. Thus, when changes are made since the last save and a user then hits export, an invalid file can be generated

Describe the solution you'd like A new signal assetAboutToBeExported that works the same way as assetAboutToBeSaved. For consistency perhaps assetExported as well

Describe alternatives you've considered

• An objectEdited signal emitted whenever anything about an object changes. But there are usecases for layers, tilesets etc. too.
• Doing the corrections to the map in the write function of a map format. Not allowed; the map is read-only.
• Completely parsing the map and writing it to a custom format, doing checks and fixes along the way. Lots of work, plus the result is not visible to the user since it is only applied to the exported file; not the map
• Doing the checks in the write function of a map format and returning an error message "please save before exporting" when issues are found. That seems a bit annoying when the issues could be fixed automatically.