specular lighting and render system

[bishopnator]

Hi, I found, that ogre has always turned-on specular lighting in DX render system:

Code: Select all

	//---------------------------------------------------------------------
	void D3D9RenderSystem::_beginFrame()
	{
		HRESULT hr;

		if( !mActiveViewport )
			OGRE_EXCEPT( Exception::ERR_INTERNAL_ERROR, "Cannot begin frame - no viewport selected.", "D3D9RenderSystem::_beginFrame" );

		if( FAILED( hr = mpD3DDevice->BeginScene() ) )
		{
			String msg = DXGetErrorDescription9(hr);
			OGRE_EXCEPT(Exception::ERR_RENDERINGAPI_ERROR, "Error beginning frame :" + msg, "D3D9RenderSystem::_beginFrame" );
		}

		if(!mBasicStatesInitialised)
		{
			// First-time 
			// setup some defaults
			// Allow specular
			hr = __SetRenderState(D3DRS_SPECULARENABLE, TRUE);
			if (FAILED(hr))
			{
				String msg = DXGetErrorDescription9(hr);
				OGRE_EXCEPT(Exception::ERR_RENDERINGAPI_ERROR, "Error enabling alpha blending option : " + msg, "D3D9RenderSystem::_beginFrame");
			}
			mBasicStatesInitialised = true;
		}

	}

I found in DX documentation in 'Performance Optimizations' section following tip:

Specular highlights almost double the cost of a light. Use them only when you must. Set the D3DRS_SPECULARENABLE render state to 0, the default value, whenever possible. When defining materials, you must set the specular power value to zero to turn off specular highlights for that material; just setting the specular color to 0,0,0 is not enough.

I wrote "simple" shader for calculating lighting on my model with specularity and difference in fps was significant - if I added specular color calculation fps decreased from 200 to 100fps (GeForce 8600GT). I didn't test it with fixed pipeline, but with older cards I remember, that it significaly decreased fps. So my question is if somebody though about this issue and why specular calculations are always enabled? (maybe I missed something, but I found D3DRS_SPECULARENABLE only in _beginFrame method)

[sinbad]

Hmm, this is interesting. I'm surprised it even made a difference when you had shaders enabled though, since fixed function should not be used. I'll see if we can make this conditional.

[bishopnator]

I tried this:
diffuse+ambient (200fps):

Code: Select all

	// per vertex lightning calculation - like D3D implementation
	float4 fvDiffuse = lightDiffuse * saturate(dot(normLightDir, worldNormal));
	o.vColor = lightAmbient + fvDiffuse;

diffuse+ambient+specular(100fps):

Code: Select all

	// per vertex lightning calculation - like D3D implementation
	float4 fvDiffuse = lightDiffuse * saturate(dot(normLightDir, worldNormal));
	o.vColor = lightAmbient + fvDiffuse;
	float3 fvH = normalize(normalize(eyePos - vPosition.xyz) + normLightDir);		
	float4 fvSpecular = lightSpecular * pow(dot(worldNormal, fvH), matShininess);	
   o.vColor += fvSpecular;

I only suppose that in fixed pipeline if specular lighting is enabled than it is always calculated. Then I search DX API and I found performance tip which I pasted here in this thread. I didn't try to modify ogre (remove enabling specular lighting) and compare fps with and without specular in fixed pipeline.

[sinbad]

Ah ok. Yes, no guarantee that turning it off in fixed-function will make a measurable difference, probably depends on the driver. We can check though.