Implement distance culling

[fallenoak]

After watching a few videos of people playing WotLK-era World of Warcraft, I'm almost certain that the client implements distance culling of some sort. In particular, it seems like small-ish map doodads are culled much earlier than large map doodads and WMOs.

Ideas

• Since WMOs will be portal culled, let's ignore them (and their doodads) for now: if WMOs are loaded, we'll render them
• Use the radius of the auto-computed bounding sphere to classify map doodads by size
• Define separate visibility radii (distance from camera) for culling small map doodads vs large map doodads
• Implement a culling function in VisibilityManager to cull map doodads based on these parameters
• Bonus points: make culling fade the doodad in / out rather than making it suddenly pop on the screen

Misc

Some client constants (from MoP):

• CWorldView::s_fadeDistDefault[] = [30.0, 100.0, 200.0, 650.0, 2100.0]
• CWorldView::s_fadeSizeDefault[] = [1.0, 4.0, 25.0, 100.0, 100000.0]
• CWorldView::s_fadeRangeDefault[] = [5.0, 10.0, 15.0, 20.0, 50.0]
• s_fadeDistScale = 1.0
• World::s_prevFarClip = 0.0
• World::s_farClip = 0.0
• World::s_minFarClip = 200.0 (set in World::InitializeStartup())

Potentially interesting client functions (from MoP):

• CWorldView::ScaleFadeDist()
• World::GetTerrainLodDist() -> return fmaxf(200.0, World::s_terrainLodDist);
• World::GetWmoLodDist() -> return fmaxf(200.0, World::s_wmoLodDist);

Other interesting code bits (from MoP):

int CWorldView::Update(*args)
{

  ...

  if (World::GetTerrainLod()) {
    if (World::GetTerrainLodDist() < s_fadeDistScale * CWorldView::s_fadeDistDefault) {
      CWorldView::s_fadeDistMax = LODWORD(World::GetTerrainLodDist());
    } else {
      CWorldView::s_fadeDistMax = s_fadeDistScale * CWorldView::s_fadeDistDefault;
    }
  }

  CWorldView::s_fadeDistMin = CWorldView::s_fadeDistMax - CWorldView::s_fadeRangeDefault;
  CWorldView::s_fadeDistMaxSqr = CWorldView::s_fadeDistMax * CWorldView::s_fadeDistMax;
  CWorldView::s_fadeDistMinSqr = CWorldView::s_fadeDistMin * CWorldView::s_fadeDistMin;

  ...

}

int World::GetTerrainLod()
{
  if (World::s_terrainLodDist >= 0.01) {
    return World::s_terrainLodDist <= fmaxf(World::s_farClip, World::s_minFarClip) * 0.6;
  } else {
    return 0;
  }
}

int World::GetWmoLod()
{
  if (World::s_wmoLodDist >= 0.01) {
    return World::s_wmoLodDist <= fmaxf(World::s_farClip, World::s_minFarClip) * 0.6;
  } else {
    return 0;
  }
}

long double World::GetHorizonFarClip()
{
  return (fmaxf(World::s_farClip, World::s_minFarClip) * World::s_horizonFarClipScale);
}

void World::SetMinFarClip(float minFarClip)
{
  if (minFarClip < 200.0) {
    World::s_minFarClip = 200.0;
  } else if (minFarClip > 2600.0) {
    World::s_minFarClip = 2600.0;
  } else {
    World::s_minFarClip = minFarClip;
  }

  return World::s_minFarClip;
}

[fallenoak]

According to schlumpf on #modcraft:

[10:28:48] [fallenoak] i seem to recall seeing doodads fading in as the camera approaches... but perhaps that's just from the files having to load?
[10:29:44] [schlumpf] should be based on their bounding box + distance, yes
[10:29:57] [fallenoak] right, so bigger objects would stay visible longer?
[10:30:11] [schlumpf] yes

As part of this issue, it might be worth spending some time hunting around IDA to see if there's anything to be gleaned about exactly how the official client handles the relationship between doodad bounding boxes and distance.