WMO/Rendering

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Getting Started

Before reading through this page, ensure you've read through the material on the loading page first:

Lighting Queries

Lighting for interior WMO groups is prebaked into vertex colors.

This makes it easy to apply to static geometry, but introduces some challenges when lighting things like units and game objects that may be present in a WMO.

The client includes a suite of query functions that can be used to pull lighting colors out of the prebaked vertex colors given a particular position inside a WMO.

These functions are described below.

CMapObj::QueryLighting

In order to light entities like units, game objects, etc that exist within interior WMO groups, the game does the following:

  1. Query for the closest MOPY.
  2. Obtain the 3 relevant MOCV values for the MOPY.
  3. Create a CImVector color by interpolating the values based on the position of the entity relative to the MOPY (ie barycentric interpolation).

This queried color value is then fed in to the standard lighting logic.

Query with C3Segment

The following function is used to query lighting when the exact poly is not yet known. It uses a C3Segment to perform a ranged query against the BSP tree for relevant tris.

bool CMapObj::QueryLighting(CMapObj *this, uint32_t groupIndex, const C3Segment *seg, CImVector *color, bool *a5) {

  CMapObjGroup group = this->groupList[groupIndex];

  if (!this->unk6[16] || !(group->unk14 & 1) || group->flags & (SMOGroup::EXTERIOR | SMOGroup::EXTERIOR_LIT)) {

    return 0;

  }

  World::TriData::resultFlags = 0;
  World::TriData::nBatches = 0;
  World::TriData::nTriIndices = 0;
  World::TriData::nVertexIndices = 0;
  World::TriData::nMatrices = 0;

  float hitT = 1.0;

  // Query the BSP tree for the group to find appropriate tris

  bool triRes = CMapObjGroup::GetTris(group, seg, &hitT, 0, 0x8, (int)&a2 + 3, 0);

  if (!triRes) {

    return 0;

  }

  // Obtain point matching intersection between segment and tri

  C3Vector point;

  point.x = seg->start.x + hitT * (seg->end.x - seg->start.x);
  point.y = seg->start.y + hitT * (seg->end.y - seg->start.y);
  point.z = seg->start.z + hitT * (seg->end.z - seg->start.z);

  unsigned __int16 hitPoly = word_CD8094;

  bool lightRes = CMapObjGroup::QueryLighting(group, &point, hitPoly, color, a5);

  return lightRes;

}

Query with C3Vector and poly index

The following function is used to query lighting when the relevant poly is already known.

bool CMapObj::QueryLighting(CMapObj *this, uint32_t groupIndex, const C3Vector *point, uint16_t polyIdx, CImVector *color, bool *a5) {

  CMapObjGroup group = this->groupList[groupIndex];

  if (!this->unk6[16] || !(group->unk14 & 1) || group->flags & (SMOGroup::EXTERIOR | SMOGroup::EXTERIOR_LIT)) {

    return 0;

  }

  // Since the point and poly are already known, there's no need to query the BSP tree

  bool lightRes = CMapObjGroup::QueryLighting(group, point, polyIdx, color, a5);

  return lightRes;

}

CMapObjGroup::QueryLighting

Once a point and poly have been identified (see the other CMapObj lighting query functions), this function is used to calculate a CImVector color value.

Barycentric interpolation is used to combine the relevant vertex colors, and the CMapObj ambient color is added if the appropriate flag is set.

bool CMapObjGroup::QueryLighting(CMapObjGroup *this, const C3Vector *point, uint16_t polyIdx, CImVector *color, bool *a5) {

  // Poly is out of bounds

  if (polyIdx >= this->polyCount) {

    *color = this->parent->ambColor;
    *a5 = 0;

    return 1;

  }

  // Load xyAxisTable

  if (!(dword_D2DC18 & 1)) {

    dword_D2DC18 |= 1u;

    xyAxisTable[0] = { 1, 2 };
    xyAxisTable[1] = { 2, 0 };
    xyAxisTable[2] = { 0, 1 };

  }

  uint16_t* indices = &this->indexList[3 * polyIdx];

  C3Vector* vertices = this->vertexList;

  C3Vector* vert1 = &vertices[indices[0]];
  C3Vector* vert2 = &vertices[indices[1]];
  C3Vector* vert3 = &vertices[indices[2]];

  // Obtain normal for poly

  C4Plane plane;
  C4Plane::From3Pos(&plane, vert1, vert2, vert3);

  C3Vector::EAxis majAxis = C3Vector::MajorAxis(&plane.normal);

  // Obtain 2d coordinates for point and poly

  C2iVector xy = xyAxisTable[majAxis];

  C2Vector pt = { ((float *)(&point))[xy.x], ((float *)(&point))[xy.y] };
  C2Vector v1 = { ((float *)(&vert1))[xy.x], ((float *)(&vert1))[xy.y] };
  C2Vector v2 = { ((float *)(&vert2))[xy.x], ((float *)(&vert2))[xy.y] };
  C2Vector v3 = { ((float *)(&vert3))[xy.x], ((float *)(&vert3))[xy.y] };

  // Calculate barycentric weights
  // https://stackoverflow.com/a/26567573/6770172

  C2Vector sv2 = { v2.x - v1.x, v2.y - v1.y };
  C2Vector sv3 = { v3.x - v1.x, v3.y - v1.y };
  C2Vector spt = { pt.x - v1.x, pt.y - v1.y };

  // total area = cross(sub(v2, v1), sub(v3, v1))
  float at = sv2.x * sv3.y - sv2.y * sv3.x;

  // a3 = cross(sub(v2, v1), sub(pt, v1)) / total area
  float a3 = (sv2.x * spt.y - sv2.y * spt.x) / at;

  // a2 = cross(sub(pt, v1), sub(v3, v1)) / total area
  float a2 = (spt.x * sv3.y - spt.y * sv3.x) / at;

  // Calculate color weights

  int w3 = (a3 * 256.0) - 0.5;
  int w2 = (a2 * 256.0) - 0.5;
  int w1 = 256 - w3 - w2;

  // Adjust weights in cases where point is outside poly

  if (w3 < 0) {

    int o3 = (w3 * w2) / (w1 + w2);

    w2 += o3;
    w1 += w3 - o3;

    w3 = 0;

  }

  if (w2 < 0) {

    int o2 = (w2 * w3) / (w1 + w3);

    w3 += o2;
    w1 += w2 - o2;

    w2 = 0;

  }

  if (w1 < 0) {

    int o1 = (w1 * w2) / (w2 + w3);

    w2 += o1;
    w3 += w1 - o1;

    w1 = 0;

  }

  CImVector c1 = this->colorVertexList[indices[0]];
  CImVector c2 = this->colorVertexList[indices[1]];
  CImVector c3 = this->colorVertexList[indices[2]];

  // Interpolate color by weight

  color->a = (uint16_t)(w1 * c1.a + w2 * c2.a + w3 * c3.a) / 256;
  color->r = (uint16_t)(w1 * c1.r + w2 * c2.r + w3 * c3.r) / 256;
  color->g = (uint16_t)(w1 * c1.g + w2 * c2.g + w3 * c3.g) / 256;
  color->b = (uint16_t)(w1 * c1.b + w2 * c2.b + w3 * c3.b) / 256;

  // Double color RGB values -- not sure why?

  uint32_t v49 = 2 * color->r;
  uint32_t v50 = 2 * color->g;
  uint32_t v51 = 2 * color->b;

  // If MOHD.flags & 0x02, add CMapObj ambient color

  if (this->parent->header->flags & 0x2) {

    v49 += this->parent->ambColor.r;
    v50 += this->parent->ambColor.g;
    v51 += this->parent->ambColor.b;

  }

  // Clamp final color to 255

  color->r = v49 >= 0xFF ? 0xFF : v49;
  color->g = v50 >= 0xFF ? 0xFF : v50;
  color->b = v51 >= 0xFF ? 0xFF : v51;

  // MOPY.flags & 0x01 -- what is this used for?

  *a5 = this->polyList[polyIdx].flags & 0x1;

  return 1;

}

Color Adjustments

CMapObj::AttenTransVerts

TODO

Group Rendering (WotLK)

This section is applicable to Wrath of the Lich King. Cataclysm significantly changed the CMapObjGroup rendering paths.

Rendering of CMapObjGroups is handled by a pair of functions.

In Wrath of the Lich King, RenderGroup_Int handles groups with MOCV chunks present, and RenderGroup_Ext handles groups that lack the MOCV chunk.

These functions can be replaced by debug rendering functions when CMapObj::s_renderMode is set to one of the various debug rendering modes.

Render Mode

Various debug rendering modes are available via CMapObj::s_renderMode.

Value CMapObj::s_renderMode Notes
0 collision SMOPoly->flags & 0x08
1 detail SMOPoly->flags & 0x04
2 render (SMOPoly->flags & 0x20) && !(SMOPoly->flags & 0x04)
3 trans (SMOPoly->flags & 0x01) && (SMOPoly->flags & 0x04 | 0x20)
4  ?  ?
5 - Default rendering path

Lighting Mode

Depending on material flags, the client selects from 4 potential lighting modes.

These lighting modes control the lighting values fed into the vertex shaders.

Note that the lighting mode 3 is only used when the unified rendering path is executed.

Value CMapObj::s_lightingMode ambColor dirColor
0 unlit vec3(0.0, 0.0, 0.0) vec3(0.0, 0.0, 0.0)
1 ext lit DNInfo->lightInfo->ambColor DNInfo->lightInfo->dirColor
2 window lit DNInfo->lightInfo->windowAmbColor DNInfo->lightInfo->windowDirColor
3 int lit CMapObj->header->ambColor vec3(0.0, 0.0, 0.0)

CMapObj::RenderGroup_Int

CMapObj::RenderGroup_Ext