LOD Models

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This tutorial will help you creating Level of Detail Models in an efficient way. Efficient means that we want to increase the performance noticeably, spend as little time as possible and still keep our model visually appealing at all stages.

Contents

Planning stage

Before you begin you should ask if your model actually needs an LOD model; will it achieve a noticeable performance increase or just a waste of time?

When to use LOD models

It may be worth creating one or more LOD models if your model has:

  • small details which increase the polycount but cannot be seen at a distance
  • rounded or organic areas using a lot of polygons to suggest 'soft' edges
  • physic props - you never know where the player is going to carry them
  • expensive shaders (e.g. Normal Maps, Reflective Materials or the eye shader.)

Some cases in which an LOD model is unlikely provide any noticeable performance increase:

  • your model already has a small polycount or is low detail
  • you don't think you can reduce the polycount by at least 30% (the model has no round/organic features)
  • a static model that is only going to be used in areas with a good performance

Choosing where to draw the line is your decision; but it may be helpful to look at the HL2 models to see when Valve has created LOD models and when they thought it was unnecessary.

Modeling LODs

Tips

The work in the model editor should be kept to a minimum. You don't want to spend as much time on your LOD models as you did on the original model! Our goal is to make a few modifications on the model that will reduce the polycount within a few minutes. However, we don't want to make a whole new model, redo our UV map or something else that consumes a lot of time.

Get used to the fact that a LOD model can only be seen from a large distance. If a player wants to see details, he'll step closer. Since the player does not focus on the details, we can remove them without him noticing if it is done in a subtle way. Things you don't want to do:

  • Changing the outline of the model or anything that gives cover. You can remove the seats within a car, but don't remove the roof.
  • Moving details on the UV map. The texture will most likely get stretched during the process, however only if details move from one place to another it'll be noticeable.
  • Smoothing groups changing in a way that one large area turns from shadowed into brightened or similar.

Techniques

Removing small details

Often details are too small to be seen from a distance - they'll simply not be drawn with the resolution of modern day hardware or can't be noticed.

Reducing polys of complex surfaces

This can be done by using the tools your modeling package offers. It'll weld vertices without destroying the UV map.

Rebuilding complex geometry with very simple one

This is only recommend if the automatic tools fail as it is rather timeconsuming and needs a new UV map (use the same skin in any case). Rebuild the basic shape of the model (or a part of it) as low poly as possible.

Use .QC commands to simplify the model

By using pre-existing .QC Commands you can automatically remove or replace parts of your models mesh during compile without having to edit them yourself.

Use a low polycount mesh for your model's shadow

Often overlooked, you should create or re-use an existing low poly LOD mesh as the mesh used for dynamic shadow rendering. (prop_static casts lightmap shadows, useless in this case.)

Replace an expensive texture/shader with a simpler one

If your using an "expensive" shader, such as the eye shader or a normal map, on a model you can replace the texture which uses it with a less expensive one for specific LOD levels.

Simplify your models skeleton

More useful for character models, you can simplify the skeleton by replacing or collapsing bones when the model is a certain distance from the viewer. For example, you could simplify the hands by removing the finger bones leaving just the hand bone. This will result in the fingers being out straight, but at the distance the model is, the viewer wouldn't notice this.

Disable facial animation

For character models, it's pointless having the face animated when in the distance and it can't be seen.

Example (using 3DS Max)

The example model
This animated outdoor camera is high detailed. Bolts, Cables and the rotating camera-holder are small details with lot's of polys. The chassis of the motor is round and highly detailed as well.

The mounting on the wall is pretty straight forward. Not much polys are used here, an optimization is not necessary.

The goal is to make two different LOD models: One for a distance of 25 units per pixel and one for 50 units per pixel.
For the first one, some very small details (bolts, cable) are deleted. If we check the difference of the reference and the LOD model in the modelviewer, the missing bolts can not be noticed. The loss of the cable might seem a bit drastic, but in-game you'll most likely have a brighter background so the contrast between cable and wall will not be as big. Furthermore the player doesn't focus on the cable - he will simply not notice it.

Small details are deleted
Models compared in HLMV at 25 meter distance


Vertex Weld selected
In the second step, the camera-holder was deleted. Furthermore we want to reduce the number of polygons used on the chassis of the motor. The polygons have been selected and the vertex weld tool is used. By increasing the threshold, vertices are weld together and max adjusts the UV map. Try to find a good value which removes as much polys as possible while retaining the shape of the model.


A first reducement of the polys, but there are still too much polys.
Messed up, don't trust the automatic tools blindly.
The final setting. Polys drastically reduced.


Checking in the modelviewer once again, the difference is once again hardly noticeable, but the polygon count is significantly lowered.

Models compared in HLMV at 50 meter distance


.QC file specific techniques

To use LOD levels, you need to add some extra commands to your .QC file.

First of all, you need to specify the $lod <units per pixel> { ... } command. This denotes that further commands between the braces should be applied to your model for that specific LOD level.

Replacing the model

The most common command is replacemodel (model name) (replacement model). You can specify which model is to be replaced and which .smd is to be used for the replacement.

// LOD 1 
$lod 25
{
      replacemodel "mymodelreference.smd" "mymodel_LOD1.smd"
}

// LOD 2 
$lod 50
{
      replacemodel "mymodelreference.smd" "mymodel_LOD2.smd"
}

Here our highest polycount model (mymodelreference.smd) is being replaced with a simpler, lower polycount version after 25 units per pixel and 50 units per pixel.

Note:For each LOD level definition, we are replacing the original mesh we defined with $model or $body. LOD commands don't replace the meshes of any previously defined LOD level.

Using a lowpoly model for the shadow

There is also a $shadowlod { ... } command which contains instructions which specific model is to be used for rendering the model's shadow.

// Shadow LOD 
$shadowlod
{
      replacemodel "mymodelreference.smd" "mymodel_shadow.smd"
}
Bug:Placing the opening brace on the same line as the $shadowlod command will cause an unrecoverable error during compile. Always add a line break!

A simple .QC example

$modelname mymodelfolder/mymodelcompiled.mdl
$cdmaterials modeltextures/mytexturefolder
$surfaceprop metal
$body studio "mymodelreference.smd"
$sequence idle "mymodelreference.smd" loop fps 15
$collisionmodel "mymodel_phy.smd" {
      Mass 5
}

$lod 15
{
      replacemodel "mymodelreference" "mymodel_lod1"
}

$lod 40
{
      replacemodel "mymodelreference" "mymodel_lod2"
}

$shadowlod
{
      replacemodel "mymodelreference" "mymodel_lod2"
}

The above gives a very simple example of using LOD levels. Two LOD models are used to reduce the polys at distance. The second LOD model was also used for the shadow LOD model.

However there are are a number of additional .QC Commands you can use within $lod groups to improve performance even more.

Replacing or removing a specific mesh

The above example demonstrates the use of the QC command replacemodel which replaces one SMD mesh with another. You can optionally choose to completely remove that mesh either by using blank as the replacment mesh name or alternatively using the removemodel.

The following example is for a fictional character model which comprises of two meshes - one for the body, one for the characters equipment packs. At distance, we choose to remove the equipment mesh entirely.

// LOD 0 - main models
$model soldier_body "body.smd"
$model soldier_kit  "kit.smd"

// LOD 1 
$lod 25
{
      replacemodel "body.smd" "body_LOD1.smd"
      replacemodel "kit.smd"  "kit_LOD1.smd"
}

// LOD 2 
$lod 50
{
      replacemodel "body.smd" "body_LOD2.smd"
      removemodel  "kit.smd"
      // alternate method
      // replacemodel "kit.smd" blank
}

Replacing a texture or using different shaders

Expensive shaders often have a big performance impact as well. Disabling them after a certain distance is an easy way to increase the performance.

To do this you use the replacematerial .QC Command which replaces one VMT material with another. An example of this would be replacing the eye material/shader on a character model with something simpler such as a VertexLitGeneric texture.

In the following example the materials righteye.vmt and lefteye.vmt use the expensive eye shader and are replaced at LOD level 30 with the material named face.vmt. The result would look odd close up but as the model will be sufficiently far away from the viewer, they are unlikely to notice.

Note:While it might seem odd to replace the eye textures with the face texture it's actually quite smart as the face texture is already loaded into memory and a new texture won't need to be fetched. Every little counts.
$lod 30 
{
	replacematerial "righteye" "face"
	replacematerial "lefteye"  "face"
}

Another technique is to simply remove the parts of the mesh that use a certain material or shader. For example, on a character model viewed at a great distance you would not be able to make out the eyes or mouth at all so it may be beneficial to simply just remove them. This can be achieved with the removemesh command which will remove any faces in the models mesh which use the specified texture, helping to reduce polycount.

$lod 60
{
	removemesh "righteye"
	removemesh "lefteye"
}

Simplify your models skeleton

Another way to improve performance on things like character models is to simplifiy the models skeleton based on its distance. This can be done via the .QC Commands bonetreecollapse and replacebone.

bonetreecollapse will collapse, or remove, all the bones which are a child of the one you specify. For example, collapsing ValveBiped.Bip01_L_Hand will remove all the finger bones. Any vertices weighted to those bones are re-assigned to the hand bone and move with it. This will mean that the fingers will no longer be animated but as the model is in the distance, this wont be noticed.

The following example removes the finger bones on the left and right hands of our character model at LOD level 30.

$lod 30 
{
        bonetreecollapse "ValveBiped.Bip01_L_Hand"
        bonetreecollapse "ValveBiped.Bip01_R_Hand"
}

replacebone works in a similar way to bonetreecollapse, but only replaces one bone with another. This can be useful for such things as removing helper bones (Ulna, Wrist, Elbow, etc) and attaching the vertices that used them to another.

The following example removes the helper bones from a character rig by re-assigning the vertices attached to them to other bones in the basic skeleton:

$lod 30 
{
	replacebone "ValveBiped.Bip01_L_Elbow" "ValveBiped.Bip01_L_upperarm"
	replacebone "ValveBiped.Bip01_R_Elbow" "ValveBiped.Bip01_R_upperarm"
	replacebone "ValveBiped.Bip01_L_Ulna" "ValveBiped.Bip01_L_Forearm"
	replacebone "ValveBiped.Bip01_R_Ulna" "ValveBiped.Bip01_R_Forearm"
	replacebone "ValveBiped.Bip01_L_Shoulder" "ValveBiped.Bip01_L_upperarm"	
	replacebone "ValveBiped.Bip01_R_Shoulder" "ValveBiped.Bip01_R_upperarm"
	replacebone "ValveBiped.Bip01_L_Trapezius" "ValveBiped.Bip01_L_upperarm"
	replacebone "ValveBiped.Bip01_R_Trapezius" "ValveBiped.Bip01_R_upperarm"
	replacebone "ValveBiped.Bip01_L_Wrist" "ValveBiped.Bip01_L_Forearm"
	replacebone "ValveBiped.Bip01_R_Wrist" "ValveBiped.Bip01_R_Forearm"
	replacebone "ValveBiped.Bip01_L_Bicep" "ValveBiped.Bip01_L_upperarm"
	replacebone "ValveBiped.Bip01_R_Bicep" "ValveBiped.Bip01_R_upperarm"
}

Disable facial animation

Character models at a distance are often so small that the viewer would never make out any facial animation on them. When this is the case, you can use the .QC Command nofacial to disable face animation for that LOD level.

$lod 30 
{
	nofacial
}

A complete character .QC example

The following is an example of a complete .QC file for a humanoid character model. You'll see we define 5 LOD levels, a specific shadow LOD and the texture and skeleton simplification methods.

// *** mode and material paths *** //
//
$cd .\
$modelname candy.mdl
$cdmaterials models\candy\
$cdmaterials models\human\female
$mostlyopaque

// *** start eye/face/body data *** //
//
$eyeposition 0.000 0.000 70.000
$illumposition 1.165 -0.000 34.196

// *** head controllers *** //
//
$attachment "eyes" "ValveBiped.Bip01_Head1" -0.0454 -3.2682 67.3843 absolute
$attachment "mouth" "ValveBiped.Bip01_Head1" 0.80 -5.50 0.10 rotate 0 -80 -90
$attachment "chest" "ValveBiped.Bip01_Spine2" 5.00 4.00 0.00 rotate 0 90 90

// *** include anims *** //
//
$includemodel humans/female_shared.mdl
$includemodel humans/female_ss.mdl
$includemodel humans/female_gestures.mdl
$includemodel humans/female_postures.mdl

// *** head mesh and rig body *** //
//
$model candy_body ".\shared\candy_body_ref.smd"
$model candy_head ".\shared\candy_face_ref.smd"

// *** set-up LOD *** //
//

// LOD 1
$lod 10
{
        // replace LOD 0 meshes with our lower poly ones
	replacemodel ".\shared\candy_face_ref.smd" ".\shared\candy_face_ref_LOD1.smd"
	replacemodel ".\shared\candy_body_ref.smd" ".\shared\candy_body_ref_LOD1.smd"
}

// LOD 2
$lod 20 
{
	replacemodel ".\shared\candy_face_ref.smd" ".\shared\candy_face_ref_LOD2.smd"
	replacemodel ".\shared\candy_body_ref.smd" ".\shared\candy_body_ref_LOD2.smd"
}

// LOD 3
$lod 30 
{
	replacemodel ".\shared\candy_face_ref.smd" ".\shared\candy_face_ref_LOD3.smd"
	replacemodel ".\shared\candy_body_ref.smd" ".\shared\candy_body_ref_LOD3.smd"

	// collapse the hands down to the hand bone, removing the fingers
        bonetreecollapse "ValveBiped.Bip01_L_Hand"
        bonetreecollapse "ValveBiped.Bip01_R_Hand"

	// remove our eye material/shader with something simpler
        replacematerial "candy_righteye" "candy_face"
	replacematerial "candy_lefteye" "candy_face"

        // turn off facial animation
	nofacial
}

// LOD 4
$lod 45 
{
	replacemodel ".\shared\candy_face_ref.smd" ".\shared\candy_face_ref_LOD4.smd"
	replacemodel ".\shared\candy_body_ref.smd" ".\shared\candy_body_ref_LOD4.smd"

        // simplifiy our skeleton further by collapsing extremities
        bonetreecollapse "ValveBiped.Bip01_L_Forearm"
        bonetreecollapse "ValveBiped.Bip01_R_Forearm"
        bonetreecollapse "ValveBiped.Bip01_L_Calf"
        bonetreecollapse "ValveBiped.Bip01_R_Calf"
        bonetreecollapse "ValveBiped.Bip01_Neck1"

        // simplifiy the spine
        replacebone "ValveBiped.Bip01_Neck1" "ValveBiped.Bip01_Spine2"
        replacebone "ValveBiped.Bip01_Spine4" "ValveBiped.Bip01_Spine2"
        replacebone "ValveBiped.Bip01_Spine1" "ValveBiped.Bip01_Spine"
        replacebone "ValveBiped.Bip01_Spine" "ValveBiped.Bip01_Spine2"

	// simplifiy by removing the helper bones
     	replacebone "ValveBiped.Bip01_L_Elbow" "ValveBiped.Bip01_L_upperarm"
	replacebone "ValveBiped.Bip01_R_Elbow" "ValveBiped.Bip01_R_upperarm"
	replacebone "ValveBiped.Bip01_L_Ulna" "ValveBiped.Bip01_L_Forearm"
	replacebone "ValveBiped.Bip01_R_Ulna" "ValveBiped.Bip01_R_Forearm"
	replacebone "ValveBiped.Bip01_L_Shoulder" "ValveBiped.Bip01_L_upperarm"	
	replacebone "ValveBiped.Bip01_R_Shoulder" "ValveBiped.Bip01_R_upperarm"
	replacebone "ValveBiped.Bip01_L_Trapezius" "ValveBiped.Bip01_L_upperarm"
	replacebone "ValveBiped.Bip01_R_Trapezius" "ValveBiped.Bip01_R_upperarm"
	replacebone "ValveBiped.Bip01_L_Wrist" "ValveBiped.Bip01_L_Forearm"
	replacebone "ValveBiped.Bip01_R_Wrist" "ValveBiped.Bip01_R_Forearm"
	replacebone "ValveBiped.Bip01_L_Bicep" "ValveBiped.Bip01_L_upperarm"
	replacebone "ValveBiped.Bip01_R_Bicep" "ValveBiped.Bip01_R_upperarm"
	
	replacematerial "candy_righteye" "candy_face"
	replacematerial "candy_lefteye" "candy_face"

        // remove any meshes covered by the eye textures
	removemesh "models\candy\candy_righteye"
	removemesh "models\candy\candy_lefteye"

	nofacial
}

// LOD 5
$lod 70 
{
	replacemodel ".\shared\candy_face_ref.smd" ".\shared\candy_face_ref_LOD5.smd"
	replacemodel ".\shared\candy_body_ref.smd" ".\shared\candy_body_ref_LOD5.smd"

        bonetreecollapse "ValveBiped.Bip01_L_Forearm"
        bonetreecollapse "ValveBiped.Bip01_R_Forearm"
        bonetreecollapse "ValveBiped.Bip01_L_Calf"
        bonetreecollapse "ValveBiped.Bip01_R_Calf"
        bonetreecollapse "ValveBiped.Bip01_Neck1"
        replacebone "ValveBiped.Bip01_Neck1" "ValveBiped.Bip01_Spine2"
        replacebone "ValveBiped.Bip01_Spine4" "ValveBiped.Bip01_Spine2"
        replacebone "ValveBiped.Bip01_Spine1" "ValveBiped.Bip01_Spine"
        replacebone "ValveBiped.Bip01_Spine" "ValveBiped.Bip01_Spine2"
	
     	replacebone "ValveBiped.Bip01_L_Elbow" "ValveBiped.Bip01_L_upperarm"
	replacebone "ValveBiped.Bip01_R_Elbow" "ValveBiped.Bip01_R_upperarm"
	replacebone "ValveBiped.Bip01_L_Ulna" "ValveBiped.Bip01_L_Forearm"
	replacebone "ValveBiped.Bip01_R_Ulna" "ValveBiped.Bip01_R_Forearm"
	replacebone "ValveBiped.Bip01_L_Shoulder" "ValveBiped.Bip01_L_upperarm"	
	replacebone "ValveBiped.Bip01_R_Shoulder" "ValveBiped.Bip01_R_upperarm"
	replacebone "ValveBiped.Bip01_L_Trapezius" "ValveBiped.Bip01_L_upperarm"
	replacebone "ValveBiped.Bip01_R_Trapezius" "ValveBiped.Bip01_R_upperarm"
	replacebone "ValveBiped.Bip01_L_Wrist" "ValveBiped.Bip01_L_Forearm"
	replacebone "ValveBiped.Bip01_R_Wrist" "ValveBiped.Bip01_R_Forearm"
	replacebone "ValveBiped.Bip01_L_Bicep" "ValveBiped.Bip01_L_upperarm"
	replacebone "ValveBiped.Bip01_R_Bicep" "ValveBiped.Bip01_R_upperarm"

	replacematerial "candy_righteye" "candy_face"
	replacematerial "candy_lefteye" "candy_face"

	removemesh "models\candy\candy_righteye"
	removemesh "models\candy\candy_lefteye"

	nofacial
}

// SHADOW
$shadowlod
{
        // use our existing LOD 4 mesh as a simpler mesh for rendering the models shadow
        //
	replacemodel ".\shared\candy_face_ref.smd" ".\shared\candy_face_ref_LOD4.smd"
	replacemodel ".\shared\candy_body_ref.smd" ".\shared\candy_body_ref_LOD4.smd"

        bonetreecollapse "ValveBiped.Bip01_L_Forearm"
        bonetreecollapse "ValveBiped.Bip01_R_Forearm"
        bonetreecollapse "ValveBiped.Bip01_L_Calf"
        bonetreecollapse "ValveBiped.Bip01_R_Calf"
        bonetreecollapse "ValveBiped.Bip01_Neck1"
        replacebone "ValveBiped.Bip01_Neck1" "ValveBiped.Bip01_Spine2"
        replacebone "ValveBiped.Bip01_Spine4" "ValveBiped.Bip01_Spine2"
        replacebone "ValveBiped.Bip01_Spine1" "ValveBiped.Bip01_Spine"
        replacebone "ValveBiped.Bip01_Spine" "ValveBiped.Bip01_Spine2"
	
     	replacebone "ValveBiped.Bip01_L_Elbow" "ValveBiped.Bip01_L_upperarm"
	replacebone "ValveBiped.Bip01_R_Elbow" "ValveBiped.Bip01_R_upperarm"
	replacebone "ValveBiped.Bip01_L_Ulna" "ValveBiped.Bip01_L_Forearm"
	replacebone "ValveBiped.Bip01_R_Ulna" "ValveBiped.Bip01_R_Forearm"
	replacebone "ValveBiped.Bip01_L_Shoulder" "ValveBiped.Bip01_L_upperarm"	
	replacebone "ValveBiped.Bip01_R_Shoulder" "ValveBiped.Bip01_R_upperarm"
	replacebone "ValveBiped.Bip01_L_Trapezius" "ValveBiped.Bip01_L_upperarm"
	replacebone "ValveBiped.Bip01_R_Trapezius" "ValveBiped.Bip01_R_upperarm"
	replacebone "ValveBiped.Bip01_L_Wrist" "ValveBiped.Bip01_L_Forearm"
	replacebone "ValveBiped.Bip01_R_Wrist" "ValveBiped.Bip01_R_Forearm"
	replacebone "ValveBiped.Bip01_L_Bicep" "ValveBiped.Bip01_L_upperarm"
	replacebone "ValveBiped.Bip01_R_Bicep" "ValveBiped.Bip01_R_upperarm"

	replacematerial "candy_righteye" "candy_face"
	replacematerial "candy_lefteye" "candy_face"

	removemesh "models\candy\candy_righteye"
	removemesh "models\candy\candy_lefteye"

	nofacial
}
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