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Xperience

Shadow Mapping Perspective Projection

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Hi,

I have a problem with rendering shadows. If I created orthographics projection matrix or perspective projection matrix, it works , shadows are created, but it causes that in shadows are lighter places. They showing in random positions and it is really unpleasant(specially in moving, or with rotating lights). Here is a picture:

 

rmqj44.jpg

 

Here is  code for creating lights:

void Lights::Build()
{
	XMVECTOR Direction = XMLoadFloat3(&m_DirectionalLight.Direction);
	XMVECTOR Position = -1.f * m_BoundingScene.Radius * Direction;
	XMVECTOR Target = XMLoadFloat3(&m_BoundingScene.Center);
	XMVECTOR Up = XMVectorSet(0.f, 1.f, 0.f, 0.f);

	XMMATRIX V = XMMatrixLookAtLH(Position, Target, Up);

	XMFLOAT3 CenterOfTheSceneLS;
	XMStoreFloat3(&CenterOfTheSceneLS, XMVector3TransformCoord(Target, V));

	float l = CenterOfTheSceneLS.x - m_BoundingScene.Radius;
	float r = CenterOfTheSceneLS.x + m_BoundingScene.Radius;
	float b = CenterOfTheSceneLS.y - m_BoundingScene.Radius;
	float t = CenterOfTheSceneLS.y + m_BoundingScene.Radius;
	float n = CenterOfTheSceneLS.z - m_BoundingScene.Radius;
	float f = CenterOfTheSceneLS.z + m_BoundingScene.Radius;

	//XMMATRIX P = XMMatrixOrthographicOffCenterLH(l, r, b, t, n, f);          

	//XMMATRIX P = XMMatrixPerspectiveOffCenterLH(l, r, b, t, n, f);                 // Result is the same here

	XMMATRIX P = XMMatrixPerspectiveFovLH(0.5f * XM_PI, 1.f, 10.f, 400.f);             // and here

	XMMATRIX T = XMMatrixSet(
		0.5f, 0.f, 0.f, 0.f,
		0.f, -0.5f, 0.f, 0.f,
		0.f, 0.f, 1.f, 0.f,
		0.5f, 0.5f, 0.f, 1.f);
	XMMATRIX ShadowTransform = XMMatrixMultiply(XMMatrixMultiply(V, P), T);

	XMStoreFloat4x4(&m_View, V);
	XMStoreFloat4x4(&m_Proj, P);
	XMStoreFloat4x4(&m_ShadowTransform, ShadowTransform);
}

Here is shader code for sampling shadow map:

static const float SMAP_SIZE = 2048.f;
static const float SMAP_DX = 1.f / SMAP_SIZE;

float ComputePCF(SamplerComparisonState comparisonState, Texture2D ShadowMap, float4 ShadowPosH)
{
	ShadowPosH.xyz /= ShadowPosH.w;

	float2 Offsets[9] = {
		float2(-SMAP_DX, SMAP_DX), float2(0.f, SMAP_DX), float2(SMAP_DX, SMAP_DX),
		float2(-SMAP_DX, 0.f), float2(0.f, 0.f), float2(SMAP_DX, 0.f),
		float2(-SMAP_DX, -SMAP_DX), float2(0.f, -SMAP_DX), float2(SMAP_DX, -SMAP_DX)
	};

	float PercList = 0.f;
	[unroll]
	for (int i = 0; i < 9; i++)
		PercList += ShadowMap.SampleCmpLevelZero(comparisonState, ShadowPosH.xy + Offsets[i], ShadowPosH.z).r;
	return PercList / 9.f;
}

I tried different bias(or none), different samplers and different positions but nothing works. Thanks for advice

 

 

 

 

 

EDIT:

Problem solved, if someone has same problem, here is solution:

 

Problem with rendering shadows caused tessellation, more precisely tessellation factors.I've computed a tessellation factor inside Vertex Shader(based on distance to the camera). In the Hull shader I transfer tessellation factors from Vertices to the edges(through average = (A + B) * 0.5f), but I've had a bad order:

// Bad

pt.EdgeTessFactor[0] = 0.5f * (Patch[2].TessFactor + Patch[0].TessFactor);
pt.EdgeTessFactor[1] = 0.5f * (Patch[0].TessFactor + Patch[1].TessFactor);
pt.EdgeTessFactor[2] = 0.5f * (Patch[1].TessFactor + Patch[2].TessFactor);
pt.InsideTessFactor = pt.EdgeTessFactor[0];


// This one Works

pt.EdgeTessFactor[0] = 0.5f * (Patch[1].TessFactor + Patch[2].TessFactor);
pt.EdgeTessFactor[1] = 0.5f * (Patch[2].TessFactor + Patch[0].TessFactor);
pt.EdgeTessFactor[2] = 0.5f * (Patch[0].TessFactor + Patch[1].TessFactor);
pt.InsideTessFactor = pt.EdgeTessFactor[0];

I don't know exactly why first one didn't work and second one yes(if someone can explain why, I will be pleasured).
 

Edited by Xperience

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Funny this has an impact on the shadow. I rather expect cracks in the mesh for wrong factors (which I don't see). Anyway: Which edge is which when tesselating ?.

Additional recommendation: Use average (or min or max) of the edge factors for the inside tesselation factor, not just the value from one edge.

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