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/**
* Updates left and right projection matrices.
* Now, the convergence point is specified in real, physical meters, since the IPD is also specified
* in physical meters. That means, if the game-specific world scale is set correctly, a convergence
* value of 3.0f would mean that the virtual screen, neutral point or convergence point is 3 meters
* ahead of us.
* @param aspectRation The aspect ratio for the projection matrix.
***/
void ViewAdjustment::UpdateProjectionMatrices(float aspectRatio)
{
	t = 0.5f / aspectRatio;
	b = -0.5f / aspectRatio;

	D3DXMatrixPerspectiveOffCenterLH(&matProjection, l, r, b, t, n, f);
	D3DXMatrixInverse(&matProjectionInv, 0, &matProjection);
	
	// convergence frustum adjustment, based on NVidia explanations
	//
	// It is evident that the ratio of frustum shift to the near clipping plane is equal to the ratio of 
	// IOD/2 to the distance from the screenplane. (IOD=IPD) 
	// frustumAsymmetryInMeters = ((IPD/2) * nearClippingPlaneDistance) / convergence
	// <http://www.orthostereo.com/geometryopengl.html>
	//
	// (near clipping plane distance = physical screen distance)
	// (convergence = virtual screen distance)
	// ALL stated in meters here !
	const float nearClippingPlaneDistance = 1; // < TODO !! Assumption here : near clipping plane distance = 1 meter 
	float frustumAsymmetryInMeters = ((ipd/2) * nearClippingPlaneDistance) / convergence;

	// divide the frustum asymmetry by the assumed physical size of the physical screen
	const float physicalScreenSizeInMeters = 1; // < TODO !! Assumption here : physical screen size = 1 meter
	float frustumAsymmetryLeftInMeters = (frustumAsymmetryInMeters * LEFT_CONSTANT) / physicalScreenSizeInMeters;
	float frustumAsymmetryRightInMeters = (frustumAsymmetryInMeters * RIGHT_CONSTANT) / physicalScreenSizeInMeters;

	// get the horizontal screen space size and compute screen space adjustment
	float screenSpaceXSize = abs(l)+abs(r);
	float multiplier = screenSpaceXSize/1; // = 1 meter
	float frustumAsymmetryLeft = frustumAsymmetryLeftInMeters * multiplier;
	float frustumAsymmetryRight = frustumAsymmetryRightInMeters * multiplier;

	// now, create the re-projection matrices for both eyes using this frustum asymmetry
	D3DXMatrixPerspectiveOffCenterLH(&projectLeft, l+frustumAsymmetryLeft, r+frustumAsymmetryLeft, b, t, n, f);
	D3DXMatrixPerspectiveOffCenterLH(&projectRight, l+frustumAsymmetryRight, r+frustumAsymmetryRight, b, t, n, f);
}