2.2.2. Background effect flags

This flag is used by most functions that modify a cell background color. It defines how the console's current background color is used to modify the cell's existing background color :
TCOD_BKGND_NONE : the cell's background color is not modified.
TCOD_BKGND_SET : the cell's background color is replaced by the console's default background color : newbk = curbk.
TCOD_BKGND_MULTIPLY : the cell's background color is multiplied by the console's default background color : newbk = oldbk * curbk
TCOD_BKGND_LIGHTEN : newbk = MAX(oldbk,curbk)
TCOD_BKGND_DARKEN : newbk = MIN(oldbk,curbk)
TCOD_BKGND_SCREEN : newbk = white - (white - oldbk) * (white - curbk) // inverse of multiply : (1-newbk) = (1-oldbk)*(1-curbk)
TCOD_BKGND_COLOR_DODGE : newbk = curbk / (white - oldbk)
TCOD_BKGND_COLOR_BURN : newbk = white - (white - oldbk) / curbk
TCOD_BKGND_ADD : newbk = oldbk + curbk
TCOD_BKGND_ADDALPHA(alpha) : newbk = oldbk + alpha*curbk
TCOD_BKGND_BURN : newbk = oldbk + curbk - white
TCOD_BKGND_OVERLAY : newbk = curbk.x <= 0.5 ? 2*curbk*oldbk : white - 2*(white-curbk)*(white-oldbk)
TCOD_BKGND_ALPHA(alpha) : newbk = (1.0f-alpha)*oldbk + alpha*(curbk-oldbk)
TCOD_BKGND_DEFAULT : use the console's default background flag
Note that TCOD_BKGND_ALPHA and TCOD_BKGND_ADDALPHA are MACROS that needs a float parameter between (0.0 and 1.0). TCOD_BKGND_ALPH and TCOD_BKGND_ADDA should not be used directly (else they will have the same effect as TCOD_BKGND_NONE).
For Python, remove TCOD_ : libtcod.BKGND_NONE
For C# : None, Set, Multiply, Lighten, Darken, Screen, ColodDodge, ColorBurn, Add, Burn Overlay, Default
With lua, use tcod.None, ..., tcod.Default, BUT tcod.console.Alpha(value) and tcod.console.AddAlpha(value)