Material optimization

When working with materials, there are a couple performance bottlenecks to keep in mind: fillrate (which usually affects all DirectX levels), and reducing vertex processing (which only is a bottleneck on DirectX7). As a level designer, the only real choice that you've got to combat any of these performance bottlenecks is to either reduce the amount of a particular expensive material on screen, or to turn off some of the expensive features in the material (like bumpmapping, for example). Note that you can make different choices about which features to use at each separate DirectX support level.

One other important aspect of dealing with performance bottlenecks is that you're going to have to measure framerates to see how well you're doing. For Half-Life 2, we used 3 target machines (determined based on looking at our hardware survey stats) for measuring performance at various DirectX levels. These were:

DX (DirectX) Level	Minimum Platform
DX9	ATI 9800, 1 GB, P4 3.0 GHz
DX8	NVidia GeForce4 Ti4600, 512 MB, P4 2.0 GHz
DX7	NVidia GeForce2 MX, 256MB, P4 1.2 GHz

Shader fallbacks

Here's how you specify different material parameters for different DX support levels: Each shader has a specific fallback shader it uses if the shader determines it can't run on the particular DX level on the card currently being run. Within the definition of your material, you add a field with the same name as the fallback shader and a sub-block of fields which are the values of those fields that you want to use if that fallback shader is being used. A list of the most commonly used shaders and their fallback shaders is shown below.

Here's an example:

LightmappedGeneric
{
	$basetexture	metal/metalwall063a
	$surfaceprop	metal
	$envmap			env_cubemap

	LightmappedGeneric_DX9
	{
		$bumpmap					metal/metalwall063a_normal
		$normalmapalphaenvmapmask	1
	}

	LightmappedGeneric_DX8
	{
		$basetexture			metal/citadel_metalwall063a
		$basealphaenvmapmask	1
	}

	LightmappedGeneric_DX6
	{
		$fallbackmaterial	metal/metalwall063b
	}
}

In this example, the $envmap field is used no matter what DirectX level the game is being run at. The $basetexture field metal/metalwall063a is used for every fallback shader except LightmappedGeneric_dx8 (used for running under DX8), which uses metal/citadel_metalwall063a for its $basetexture. Also under DX8 only, we add a field specifying that the special base texture used by dx8 has an envmap mask in its alpha channel. When using the LightmappedGeneric_DX9 shader (used by DX9), we add a bumpmap and specify that the envmap mask is in the alpha channel of the bumpmap. Note that it's also possible to cause the material system to use a completely different material with a totally different set of shaders by specifying a $fallbackmaterial in a fallback block, which is done in this example when falling back to the LightmappedGeneric_DX6 shader (used by DX7 and DX6).

For a listing of all of the fallback shaders used in Half-Life 2, see the document Half-Life 2 Shader Fallbacks.

Overdraw

Fillrate refers to the number of pixels that a video card can shove into its memory per second, independently of the time needed to decide what colour they should be. It becomes an issue when the user tries to run a game at a higher resolution than the card is capable of, or more commonly when pixels are processed multiple times.

This effect is known as 'overdraw' and occurs when a material is translucent (particles are dreadful), uses normal mapping, uses specular reflections and/or is refractive. You can spot overdraw by checking showbudget for an unusually large 'Swap Buffer' bar. (Objects/surfaces that are drawn despite being behind another object are technically overdraw too, but are normally discounted because it would be more expensive to cull them.)

The only real solution to overdraw is reducing the number of pixels that needs to be re-processed, usually with a shader fallback or by creating fewer, larger objects, but there are still a few tricks that can be employed to a limited effect.

Refraction

Any object that crosses the plane of a refractive material will be rendered twice: once for the direct view, and again for the refracted view (

Todo: What about reflection?

). This becomes avoidable when the water is obscured - for instance, if the object is embedded in a displacement sand drift. By raising the model or cutting the water brush so that it doesn't extend beneath the displacement, the second rendering can be avoided.

You can examine what is being rendered for refraction with mat_showwatertextures 1.

Normal mapping

LightmappedGeneric materials are the prime suspects here. To help a little you can add $nodiffusebumplighting 1 to the material in question, which turns off albedo normal mapping without affecting specular, but as ever the only true solution is a fallback.

Tip:When creating DirectX 8 fallbacks, use LightmappedGeneric_NoBump_DX8 to differentiate between video cards that have and haven't been deemed suitable for normal mapping by Valve.

Water

With Water overdraw is caused by both refraction and reflection, often over a large area. You can disable them if needed perhaps in conjunction with another shader fallback:

$forcecheap 1

Disables both reflection and refraction.

$refracttexture

$reflecttexture

Not specifying a texture bypasses one or both passes.

If you've got fillrate and CPU to burn, you can forcibly make the water do local reflections (regardless of video config settings) by specifying $forceexpensive 1, and you can forcibly make the water reflect entities by specifying $reflectentities 1.

Special materials

nodraw

tools\toolsnodraw prevents a surface from being drawn at all, prevents lightmaps from being compiled for it, and prevents it from reflecting light (it still casts shadows). Use it on surfaces that will never be seen by the player but can't be sealed off by another brush, such as the tops of roofs and ledges or the far side of building in inaccessible areas, particularly those in background maps.

black, white

Two materials that behave like nodraw, but have a color value. Use at the bottom of deep pits, behind bright lights, etc.

skybox_2d

A 3D skybox is drawn in full whenever the tools\toolsskybox material is being drawn. You can avoid this by using tools\toolsskybox2d in its place. Obviously, this only has an effect when the normal skybox material isn't visible!

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