Check if font exists.
API bool OverlayIsFontID(uint id);
id: Font ID.
returns: True font exists.

Check if font exists.
API bool OverlayIsFontName(wcstr name);
name: Font name.
returns: True font exists.

Check if atlas exists.
API bool OverlayIsAtlasID(uint id);
id: Atlas ID.
returns: True if atlas exists.

Check if atlas exists.
API bool OverlayIsAtlasName(wcstr name);
name: Atlas name.
returns: True if atlas exists.

Get atlas dims.
API S2i OverlayGetAtlasDims(uint atlasID);
atlasID: Atlas ID.
returns: Atlas dims.

Get font height.
API uint OverlayGetFontHeight(uint fontID);
fontID: Font ID.
returns: Font height.

Get character width.
API uint OverlayGetCharWidth(uint fontID, wchar c);
fontID: Font ID.
c: Character.
returns: Character width.

Get character advance.
API uint OverlayGetCharAdvance(uint fontID, wchar c);
fontID: Font ID.
c: Character.
returns: Character advance.

Get entities.
API Entities OverlayGetEntities();
returns: Entities.

Get caller defined data.
API void *OverlayGetData();
returns: Caller define data.

Get font ID.
API uint OverlayGetFont(wcstr name);
name: Font name.
returns: Font ID.

Get atlas ID.
API uint OverlayGetAtlas(wcstr name);
name: Atlas name.
returns: Atlas ID.

Set clip region.
API void OverlaySetClip(MetaPos metaPos, B2i pRect);
metaPos: Meta position object.
pRect: Parent rect.

Reset clip region to entire overlay.
API void OverlayResetClip();

Erase overlay.
API void OverlayErase();

Manual forward update.
API void OverlayForward();

Manual reverse udpate.
API void OverlayReverse();

Begin new overlay.
API void OverlayBegin(Assets assets, uint dataSize, uint blockSize, uint incr, FUpdateCB Forward, FUpdateCB Reverse, FDestructCB Destruct);
assets: Overlay.
assets: Assets.
dataSize: Caller defined data size.
blockSize: Block size.
incr: Increment size.
Forward: Forward callback, or 0.
Reverse: Reverse callback, or 0.
Destruct: Destruct callback, or 0.