I can draw a "solid color" sprite for each surface and put it on top of the track (set to invisible). That would be ideal assuming construct will discard the transparent pixels in the sprite. I thought it could only use the collision polygon.
Are you saying it can?
Just tested and No. It only detects the collision polygon.
So the best way seems to be; import the track segments and hand draw the collision polygon for each.
PS: Multiple collision polygons per sprite (like adding image points) would be a nice feature. Even better if the collision mask could be drawn with a "block" brush (4x4, 8x8, ...)
And its nagging me that i shouldnt go over 8 collision points per sprite, bummer.