• Create Account

We're offering banner ads on our site from just \$5!

# gcard28

Member Since 15 Sep 2006
Offline Last Active Aug 19 2013 12:10 PM

### Topics I've Started

17 July 2013 - 10:01 PM

I've been working furiously and so far stable cascaded shadow maps are mocking me..... I can't seem to get this working for the life of me.....

So I will run through my algorithm and perhaps some kind soul will take pity on me and show me the error of my ways......

[1] I calculate the split frustum values for FOUR cascades.

I use this equation:

```    // get the currently active camera
ICamera *pcCamera = getCurrentCamera ();
vsAssert (pcCamera != NULL);

if (m_fSplitNearZ < pcCamera->getNearZ ())
{
m_fSplitNearZ = pcCamera->getNearZ ();
}

for (vsInt32 iSplit = 1; iSplit < NUM_CASCADE_SPLITS; iSplit++)
{
vsFloat32 fStep = iSplit / (vsFloat32) NUM_CASCADE_SPLITS;

vsFloat32 fLogSplit = m_fSplitNearZ * powf (m_fSplitFarZ / m_fSplitNearZ, fStep);

vsFloat32 fLinearSplit = m_fSplitNearZ + (m_fSplitFarZ - m_fSplitNearZ) * fStep;

// linearly interpolate between the linear and logarithmic split values
m_fSplitPositions [iSplit] = fLogSplit * m_fLogSplitWeight + fLinearSplit * (1.0f - m_fLogSplitWeight);
}

// ensure the border split values are accurate
m_fSplitPositions [0] = m_fSplitNearZ;

```

So now I have my frustum splits.....

I use these splits to calculate the corners of the cascade frustum that is being considered. So if I am going to update the first cascade shadow map I use the first and second frustum split positions. ie. m_fSplitPositions [0] and m_fSplitPositions [1].

So now I have 8 view space corners for the split frustum in view space. I generate the bounding box of these points and get the center. Again this is in View space. I take the max AABB point, subtract from the centroid I calculated and get it's length. This is what I use as the radius of the sphere that encloses this split frustum.

I then multiply the View Space frustum center by the inverse view to get the center in world space. I do the above for all FOUR cascade frustums when I am done I have FOUR spheres in TOTAL. One for each split sub frustum. Since I have 4 cascades I have 4 spheres.

```CalculateCascadeBoundingSphere (void)
{
// find the minimum enclosing sphere for the split frustum, this is done in
// local space to avoid precision variation between frames

ICamera *pcCurrentCamera = getCurrentCamera ();
vsAssert (pcCurrentCamera != NULL);

vsFloat32 fTanHalfFOVY = pcCurrentCamera->getTanHalfFOVY ();
vsFloat32 fTanHalfFOVX = fTanHalfFOVY * pcCurrentCamera->getAspectRatio ();

vsFloat32 fNearX = fTanHalfFOVX * m_fCurrentNearSplit;
vsFloat32 fNearY = fTanHalfFOVY * m_fCurrentNearSplit;
vsFloat32 fNearZ = m_fCurrentNearSplit;

vsFloat32 fFarX = fTanHalfFOVX  * m_fCurrentFarSplit;
vsFloat32 fFarY = fTanHalfFOVY * m_fCurrentFarSplit;
vsFloat32 fFarZ = m_fCurrentFarSplit;

// calculate the frustum AABB in view space
CAABB cFrustumAABB;

cFrustumAABB.m_cMin.setVector (FLT_MAX, FLT_MAX, FLT_MAX);
cFrustumAABB.m_cMax.setVector (-FLT_MAX, -FLT_MAX, -FLT_MAX);

cCenter.MulScalar (0.5f);

}
```

These spheres I use to generate FOUR light view and FOUR light view projection matrices. I do that as follows:

Remember I do this FOUR times, so at the end I have FOUR light view matrices and FOUR light projection matrices:

```CalculateCascadeViewMatrix (vsUInt32 iCascade)
{
vsAssert (m_pcDirectionalLightEditorObject != NULL);

// calculate the cascade view matrix

const CVector3 &rcLightDirection = m_pcDirectionalLightEditorObject->getDirection ();

CVector3 cEye, cTarget;

// target is center of view split frustum in world space

// scale the light direction based on the shadow range
CVector3 cScaledLightDirection (rcLightDirection);

// eye = target - (light_direction * shadow_range)
cEye.Sub (cTarget, cScaledLightDirection);

// generate the light view look at matrix
}

LookAt (CMatrix4 &rcViewMatrix, const CVector3 &rcEye, const CVector3 &rcTarget)
{
CVector3 cZAxis;

// we look down -z axis this is why vector is reversed
cZAxis.Sub (rcEye, rcTarget);
cZAxis.Normalize ();

CVector3 cYAxis (CVector3::Y_AXIS);

// check it's not coincident with direction
if (CMath::FAbs (cYAxis.DotProduct (cZAxis)) >= 1.0f)
{
// use camera up
cYAxis.setVector (CVector3::Z_AXIS);
}

// cross twice to rederive, only direction is unaltered
CVector3 cXAxis;

cXAxis.CrossProduct (cYAxis, cZAxis);
cXAxis.Normalize ();

cYAxis.CrossProduct (cZAxis, cXAxis);
cYAxis.Normalize ();

// setup the light view matrix (this places objects in light view space)
rcViewMatrix.m [m00] = cXAxis.x;
rcViewMatrix.m [m01] = cXAxis.y;
rcViewMatrix.m [m02] = cXAxis.z;
rcViewMatrix.m [m03] = -cXAxis.DotProduct (rcEye);

rcViewMatrix.m [m10] = cYAxis.x;
rcViewMatrix.m [m11] = cYAxis.y;
rcViewMatrix.m [m12] = cYAxis.z;
rcViewMatrix.m [m13] = -cYAxis.DotProduct (rcEye);

rcViewMatrix.m [m20] = cZAxis.x;
rcViewMatrix.m [m21] = cZAxis.y;
rcViewMatrix.m [m22] = cZAxis.z;
rcViewMatrix.m [m23] = -cZAxis.DotProduct (rcEye);

rcViewMatrix.m [m30] = 0.0f;
rcViewMatrix.m [m31] = 0.0f;
rcViewMatrix.m [m32] = 0.0f;
rcViewMatrix.m [m33] = 1.0f;
}
```

Ok now I generate FOUR orthographic projection matrices, using the radius values of the four frustum split bounding spheres I generated up above:

```CalculateCascadeProjectionMatrix (vsUInt32 iCascade)
{

// calculate the cascade orthographic projection matrix
m_cProjectionMatrix [iCascade].m [m00] = 2.0f / fWidth;
m_cProjectionMatrix [iCascade].m [m11] = 2.0f / fHeight;

m_cProjectionMatrix [iCascade].m [m22] = -2.0f / (m_fProjectionFarZ - m_fProjectionNearZ);
m_cProjectionMatrix [iCascade].m [m23] = -(m_fProjectionFarZ + m_fProjectionNearZ) / (m_fProjectionFarZ - m_fProjectionNearZ);

// engine specific projection matrix with render system depth range
}
```

I also generate a rounding matrix to prevent the shadow map cascades from shimmering as the camera translates:

```CalculateCascadeRoundMatrix (vsUInt32 iCascade)
{
CVector3 cOrigin (0.0f, 0.0f, 0.0f);

// transform origin to light view projection space

// convert clip space to texture coordinates

// round to the nearest whole texel
vsFloat32 fTexCoordRoundedX = CMath::Round (fTexCoordX);
vsFloat32 fTexCoordRoundedY = CMath::Round (fTexCoordY);

/*
the difference between the rounded and actual tex coordinate is the
amount by which we need to translate the shadow matrix in order to
cancel sub-texel movement
*/
vsFloat32 fDX = fTexCoordRoundedX - fTexCoordX;
vsFloat32 fDY = fTexCoordRoundedY - fTexCoordY;

// transform fDX, fDY back to homogenous light space

// set the rounding matrix
}
```

So now I have CMatrix4x4 m_cLightViewMatrix [4],  CMatrix4x4 m_cLightProjectionMatrix [4] and m_cRoundMatrix [4];

I loop like so and generate the shadow matrix:

{

}

I use m_cShadowMatrix [4] to generate the shadow maps in my shadow atlas..... So In the shader I generate the vertices of the shadow caster into word space and then multiply like so:

In the pixel shader I save out the z value.

Is my algortihm sound? Or perhaps I missed something in my understanding of the algorithm. I would appreciate any help anyone can give me as to where I could be going wrong. Also if anyone knows of any demos with source that I could run to test this algorithm I would be ever so greatful.

Many thanks to anyone who can help me!

### Blending in Pain animations is a pain in the...

14 October 2008 - 02:08 PM

Ok so I have my engine up and running and I am able to blend in and blend out animations. However I cannot seem to get around the idea of how to get pain animations working with the current state of the engine. Currently the AI goes through some scripted behavior threads. Where the character periodically reloads his gun and then fires, then ducks and fires, stands up and fires, reloads etc. etc. Now my question is if the said character gets hit by a players bullet I want him to respond by playing a pain animation, but then still have him do whatever it was that he was doing in his scripted AI thread, ie. reloading, firing after the pain animation is done. Is there some way I could have this work automatically? Perhaps I should fade in a pain animation and when the pain animation is done playing, I gradually fade it out. This way whatever animations are still playing in the character will continue after the pain animation is done. Thanks for anyone's thoughts and opinions.

### colliding a moving AABB against a triangle

19 August 2008 - 07:32 PM

Hi, I am having a devil of a time figuring out when a moving AABB collides with a triangle. I can't seem to figure this out. I think that this would be an extension of my ray triangle code but alas the way to relate a moving AABB to ray collision escapes me. Is there a kind soul that could point me in the right direction? either through relevant links (I was unable to find any) or pseudo code as to how one might go about this? Many thanks in advance to anyone who can help me. Thanks!

### Detecting Vsync...

31 March 2008 - 09:34 AM

Hello, I need to be able to detect when the card is in vertical sync. I am working under windows and using DirectX. I know that you can set that the swap effect is locked to vertical sync. But I need to actually detect when vertical sync actually happens. The reason for this is that I am developing an arcade game and I need to flash the screen white when a gun trigger is pressed. This needs to happen on a vertical sync. Thanks for anyones help.

### Attaching projectile to a mesh

28 February 2008 - 12:04 PM

Hello I have a question in regards to projectiles. In several games you are able to fire a projectile and have it hit an enemy and stick to the enemy at the point of impact. Then as the enemy plays it's death animation the spike or projectile follows the animation at the location where it hit the mesh. Does anyone know how this is done? Or could point me to any information that might be helpful? Many thanks in advance for any help you anyone can give me. Thanks

PARTNERS