M2/Rendering

Blending Modes

Wrath of the Lich King and Cataclysm do not use separate alpha blending. Later expansion clients likely do use separate alpha blending.

Blend_BlendAdd was added after Cataclysm.

Values for functions match OpenGL, but each has a D3D equivalent.

State Idx	Mode	Blending Enabled	Src Color	Dest Color	Src Alpha	Dest Alpha
0	Blend_Opaque	Disabled	ONE	ZERO	ONE	ZERO
1	Blend_AlphaKey	Disabled	ONE	ZERO	ONE	ZERO
2	Blend_Alpha	Enabled	SRC_ALPHA	ONE_MINUS_SRC_ALPHA	ONE	ONE_MINUS_SRC_ALPHA
3	Blend_Add	Enabled	SRC_ALPHA	ONE	ZERO	ONE
4	Blend_Mod	Enabled	DST_COLOR	ZERO	?	ZERO
5	Blend_Mod2x	Enabled	DST_COLOR	SRC_COLOR	?	SRC_ALPHA
6	Blend_ModAdd	Enabled	DST_COLOR	ONE	?	ONE
7	Blend_InvSrcAlphaAdd	Enabled	ONE_MINUS_SRC_ALPHA	ONE	ONE_MINUS_SRC_ALPHA	ONE
8	Blend_InvSrcAlphaOpaque	Enabled	ONE_MINUS_SRC_ALPHA	ZERO	ONE_MINUS_SRC_ALPHA	ZERO
9	Blend_SrcAlphaOpaque	Enabled	SRC_ALPHA	ZERO	SRC_ALPHA	ZERO
10	Blend_NoAlphaAdd	Enabled	ONE	ONE	ZERO	ONE
11	Blend_ConstantAlpha	Enabled	CONSTANT_ALPHA	ONE_MINUS_CONSTANT_ALPHA	?	?
12	Blend_Screen	Enabled	ONE_MINUS_DST_COLOR	ONE	ONE	ZERO
13	Blend_BlendAdd	Enabled	ONE	ONE_MINUS_SRC_ALPHA	ONE	ONE_MINUS_SRC_ALPHA

Fog Modes

Because blending modes adjust how color is applied during a draw call, fog color often has to be modified accordingly.

The M2Material flag 0x02 causes fog mode 0 (disabled) to always be selected, regardless of blending mode.

The following fog modes were taken from Mists of Pandaria (build 15662).

Fog Mode	Action	Blending Modes
0	Disable fog logic in shader	-
1	? possibly: use fog color without changes ?	Blend_Opaque, Blend_AlphaKey, Blend_Alpha
2	Override fog color to 0x000000 (black)	Blend_Add, possibly: Blend_NoAlphaAdd
3	Override fog color to 0xFFFFFF (white)	Blend_Mod
4	Override fog color to 0x808080 (half white)	Blend_Mod2x
5	? submerged camera related ?	-
6	? liquid plane related ?	-