Script API: get DrawingSurface for the room masks

[ivan-mogilko]

For #480.

This is a minor addition, but may have numerous practical uses.
There's already a DrawingSurface interface, and room areas - walkable areas, hotspots, regions and walk-behinds - are represented as 8-bit bitmap masks, so it's trivial to connect these.

The 4 new script functions allow to get corresponding room mask as a DrawingSurface, and do with it whatever a game developer wants.
Surfaces will be 8-bit, and each color index corresponds to an area ID. Color index = 0 is "no area", or eraser.
There are necessary safety tests in the engine to make sure that indexes beyond supported area limit are simply ignored (treated as "no area").

For example, following script will expand walkable area 1:

DrawingSurface* ds = GetDrawingSurfaceForWalkableArea();
ds.DrawingColor = 1; // drawing color = area ID
ds.DrawRectangle(100, 100, 200, 200);
ds.Release();

Changes made this way are not saved between room visit, which is in line with drawing upon a room background (this was done to prevent save data bloat). If user wants these changes to persist, the usual approach is to save custom data, and use it as an instruction, performing drawing on room load event.

[ericoporto]

OK, I had some fun with this. Click the gif below for full video.

AGS Project: maskDrawing.zip

I think it works, the only thing I wanted more when drawing was being able to see the other masks like we have the shortcut with Ctrl+A for walkbehinds, which I had to improvise with an overlay, but other than this, it appears to work.

On the video above, the houses are drawn in the background and the walkbehinds are updated, along with the walkable areas. The army of rogers will keep walking randomly, using pathfinder to avoid the non-walkable areas.

[ghost]

, the only thing I wanted more when drawing was being able to see the other masks like we have the shortcut with Ctrl+A for walkbehinds

There's a related ticket: #724