M2/Rendering

WIP

Blending Modes

All clients dating back to at least Wrath of the Lich King follow the state table below. The table is up to date with all blending modes present in the 7.1.0.22996 retail client. Not all blending modes are used, especially in older clients.

Wrath of the Lich King and Cataclysm do not use separate alpha blending. Legion does use separate alpha blending. It's currently unknown if Mists of Pandaria or Warlords of Draenor use separate alpha blending.

Blend_BlendAdd was added after Cataclysm.

Blend function enums are for OpenGL, but each has a Direct3D equivalent. Most pairings should be obvious, except: in Direct3D, CONSTANT_ALPHA is BLEND_FACTOR and ONE_MINUS_CONSTANT_ALPHA is INV_BLEND_FACTOR.

See this gist for code that converts OpenGL constants to Direct3D (excerpt from Chrome).

M2Material Blending Mode to blendStateIdx

In Wrath of the Lich King (and possibly newer clients), the blendStateIdx column does not directly match the M2Material blending_mode value present in M2 files. The value is translated through the following mapping table: { 0, 1, 2, 10, 3, 4, 5 }

Blend State Table

blendStateIdx	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	DST_ALPHA	ZERO
5	Blend_Mod2x	Enabled	DST_COLOR	SRC_COLOR	DST_ALPHA	SRC_ALPHA
6	Blend_ModAdd	Enabled	DST_COLOR	ONE	DST_ALPHA	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	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

Credits: Deamon, for unearthing blending mode names and laying out the original table; relaxok, for checking D3D state at runtime; schlumpf, for the initial reversing work; fallenoak, for mapping Deamon's table to OpenGL enums and verifying values across several expansion clients.

Fog Modes

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

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

In certain cases (possibly when the mesh or the camera is underwater), s_blendDisableUWFog may force fog mode 0 (disabled) to be selected based on blending mode. As of Mists of Pandaria, it appears this applies to Blend_Add and Blend_NoAlphaAdd.

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

Fog Mode	Action	Blending Modes
0	Disable fog logic in shader	-
1	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; use ViewSettings::s_fogInfo 2 or 3	-
6	? liquid plane related; use ViewSettings::s_fogInfo 3 or use CM2Lighting fog	-

Lighting Modes

Similar to fog modes above, blending modes also impact lighting. The client maps blending modes to lighting modes using s_shadedList.

M2Material flag 0x01 always causes lighting mode 0 (disabled) to be selected.

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

Lighting Mode	Action	Blending Modes
0	Disable lighting logic in shader, including local lights	Blend_Mod, Blend_Mod2x
1	Enable lighting logic in shader	Blend_Opaque, Blend_AlphaKey, Blend_Alpha, Blend_Add, possibly: Blend_NoAlphaAdd

M2Elements

An M2 is rendered as a series of M2Elements, which are constructed at runtime in CM2SceneRender::BeginDraw(), and sorted prior to drawing.

Element Alpha

For a given M2Element, whole-element alpha is calculated by multiplying the following things together:

• batch->color.alpha is the M2Batch animated color track alpha value (if present)

• batch->textureWeight is the M2Batch animated texture weight track value (if present); if batch->opCount is > 1, only the first textureWeight value is used

• m2->alpha is overall model opacity, which can be manipulated by things like distance fading and similar effects; default: 1.0

  element->alpha = batch->color.alpha * batch->textureWeight * m2->alpha;

Element Sorting

WIP

Alpha Testing

Alpha testing is enabled for most or all M2Elements being rendered. The alpha comparison function is always D3DCMP_GREATEREQUAL, which discards pixels with alpha values lower than the provided alphaRef.

For Blend_AlphaKey blending, the alphaRef value starts at a baseline, and is multiplied by the M2Element->alpha. This multiplication prevents inappropriate pixel discards during things like fades for distance culling. See the M2Element alpha section above for details on what can modify M2Element alpha.

For all other blending modes (ie !(Blend_AlphaKey), the alphaRef value is constant.

Blending Mode	alphaRef
!(Blend_AlphaKey)	All	1.0 / 255.0 (constant)
Blend_AlphaKey	>= Cata	(128.0 / 255.0) * element->alpha
	<= WotLK	(224.0 / 255.0) * element->alpha