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aferreira
06-12-2016, 03:25 PM
Hey guys,

I'm trying to implement CSM in my engine but i'm having trouble with the frustums cameras (which is the sun).

The problem is that in the first frame the shadows are correctly working but as soon as i rotate the viewers camera, each camera rotates to the opposite side of what it should. For example if i look to the left, each frustum rotates to the right (from the viewers perspective) which causes the depth map to be looking at the wrong spot. Besides this the camera does not seem to track the user position in the world, i.e., it will always look at the opengl center (0,0,0) if i just step backwards without rotating the camera.

The code that i have to calculate the MVP matrix for each cascaded camera is:


void deferredRenderer::calcOrthoProjections(openGLCamer a::Camera lightCamera, openGLCamera::Camera camera)
{

float lambda = 0.5; // Lambda value for split distance calc. (based on GPU gems paralel splits by nvidia)
float n = camera.getNearClip();
float f = camera.getFarClip();

m_cascadeEnd[0] = camera.getNearClip();


glm::mat4 invCameraView = glm::inverse(camera.View);

// Get the light view transform (lookat is always (0,0-1)
glm::mat4 lightView = glm::lookAt(glm::vec3(0), lightCamera.getCameraLookAt(), glm::vec3(0,1,0));

float ar = 1.0f/camera.GetAspectRatio();

float tanHalfHFOV = tanf(glm::radians((camera.GetFOV()) / 2.0f));
float tanHalfVFOV = tanf(glm::radians((camera.GetFOV() * ar) / 2.0f));


// Projection information
openGLCamera::shadowOrthoProjInfo m_shadowOrthoProjInfo;

for (uint i = 0 ; i < nShadowMaps ; i++)
{

// Calculate the split distance (based on GPU gems parallel splits by novidia)
float cuni = n + ((f-n)*((i+1)/(float)nShadowMaps));
float clog = n * std::powf(f/n, (i+1)/(float)nShadowMaps);
float c = lambda*cuni + (1-lambda)*clog;
m_cascadeEnd[i+1] = c;


float xn = m_cascadeEnd[i] * tanHalfHFOV;
float xf = m_cascadeEnd[i + 1] * tanHalfHFOV;
float yn = m_cascadeEnd[i] * tanHalfVFOV;
float yf = m_cascadeEnd[i + 1] * tanHalfVFOV;

// These corners are view space vectors
glm::vec4 frustumCorners[8] =
{
// near face
glm::vec4(xn, yn, m_cascadeEnd[i], 1.0),
glm::vec4(-xn, yn, m_cascadeEnd[i], 1.0),
glm::vec4(xn, -yn, m_cascadeEnd[i], 1.0),
glm::vec4(-xn, -yn, m_cascadeEnd[i], 1.0),

// far face
glm::vec4(xf, yf, m_cascadeEnd[i + 1], 1.0),
glm::vec4(-xf, yf, m_cascadeEnd[i + 1], 1.0),
glm::vec4(xf, -yf, m_cascadeEnd[i + 1], 1.0),
glm::vec4(-xf, -yf, m_cascadeEnd[i + 1], 1.0)
};


glm::vec4 frustumCornersL[8];

float minX = std::numeric_limits<float>::max();
float maxX = std::numeric_limits<float>::min();
float minY = std::numeric_limits<float>::max();
float maxY = std::numeric_limits<float>::min();
float minZ = std::numeric_limits<float>::max();
float maxZ = std::numeric_limits<float>::min();

// Rotate the camera so its facing from up -> down
glm::mat4 modelMatrix = glm::rotate(glm::mat4(1), 3.1415f/3.0f, glm::vec3(1,0,0));

for (uint j = 0 ; j < 8 ; j++)
{
// Transform the frustum coordinate from view to world space
glm::vec4 vW = invCameraView * frustumCorners[j];

// Transform the frustum coordinate from world to light space
frustumCornersL[j] = lightView * vW;

minX = std::min(minX, frustumCornersL[j].x);
maxX = std::max(maxX, frustumCornersL[j].x);
minY = std::min(minY, frustumCornersL[j].y);
maxY = std::max(maxY, frustumCornersL[j].y);
minZ = std::min(minZ, frustumCornersL[j].z);
maxZ = std::max(maxZ, frustumCornersL[j].z);
}

m_shadowOrthoProjInfo.l = minX;
m_shadowOrthoProjInfo.r = maxX;
m_shadowOrthoProjInfo.b = minY;
m_shadowOrthoProjInfo.t = maxY;
m_shadowOrthoProjInfo.n = minZ;
m_shadowOrthoProjInfo.f = maxZ;

glm::mat4 Projection = glm::ortho(m_shadowOrthoProjInfo.l, m_shadowOrthoProjInfo.r,
m_shadowOrthoProjInfo.b, m_shadowOrthoProjInfo.t,
m_shadowOrthoProjInfo.n, m_shadowOrthoProjInfo.f);

lightProjView[i] = Projection * lightView * modelMatrix;

}
}

Any information that you need i will gladly provide. Thank you in advance.