/// <summary>
/// Checks our movement vector against all the planes of the brush
/// </summary>
private void CheckBrush(QBrush pBrush, Vector3 vStart, Vector3 vEnd)
{
float startRatio = -1.0f; // Like in BrushCollision.htm, start a ratio at -1
float endRatio = 1.0f; // Set the end ratio to 1
bool startsOut = false; // This tells us if we starting outside the brush
// This function actually does the collision detection between our movement
// vector and the brushes in the world data. We will go through all of the
// brush sides and check our start and end ratio against the planes to see if
// they pass each other. We start the startRatio at -1 and the endRatio at
// 1, but as we set the ratios to their intersection points (ratios), then
// they slowly move toward each other. If they pass each other, then there
// is definitely not a collision.
// Go through all of the brush sides and check collision against each plane
for (int i = 0; i < pBrush.numSides; i++)
{
// Here we grab the current brush side and plane in this brush
QBrushSide pBrushSide = bspMap.Data.brushSides[pBrush.firstSide + i];
QPlane pPlane = bspMap.Data.planes[pBrushSide.planeNum];
// Let's store a variable for the offset (like for sphere collision)
float offset = 0.0f;
// If we are testing sphere collision we need to add the sphere radius
if (traceType == TYPE_SPHERE)
{
offset = traceRadius;
}
// Test the start and end points against the current plane of the brush side.
// Notice that we add an offset to the distance from the origin, which makes
// our sphere collision work.
float startDistance = Vector3.Dot(vStart, pPlane.normal) - (pPlane.dist + offset);
float endDistance = Vector3.Dot(vEnd, pPlane.normal) - (pPlane.dist + offset);
// This is the last beefy part of code in this tutorial. In this
// section we need to do a few special checks to see which extents
// we should use. We do this by checking the x,y,z of the normal.
// If the vNormal.x is less than zero, we want to use the Max.x
// value, otherwise use the Min.x value. We do these checks because
// we want the corner of the bounding box that is closest to the plane to
// test for collision. Write it down on paper and see how this works.
// We want to grab the closest corner (x, y, or z value that is...) so we
// dont go through the wall. This works because the bounding box is axis aligned.
// Store the offset that we will check against the plane
// If we are using AABB collision
if (traceType == TYPE_BOX)
{
Vector3 vOffset = new Vector3();
// Grab the closest corner (x, y, or z value) that is closest to the plane
vOffset.X = (pPlane.normal.X < 0) ? vTraceMaxs.X : vTraceMins.X;
vOffset.Y = (pPlane.normal.Y < 0) ? vTraceMaxs.Y : vTraceMins.Y;
vOffset.Z = (pPlane.normal.Z < 0) ? vTraceMaxs.Z : vTraceMins.Z;
// Use the plane equation to grab the distance our start position is from the plane.
// We need to add the offset to this to see if the box collides with the plane,
// even if the position doesn't.
startDistance = Vector3.Dot(vStart + vOffset, pPlane.normal) - pPlane.dist;
// Get the distance our end position is from this current brush plane
endDistance = Vector3.Dot(vEnd + vOffset, pPlane.normal) - pPlane.dist;
}
// Make sure we start outside of the brush's volume
if (startDistance > 0)
{
startsOut = true;
}
// Stop checking since both the start and end position are in front of the plane
if (startDistance > 0 && endDistance > 0)
{
return;
}
// Continue on to the next brush side if both points are behind or on the plane
if (startDistance <= 0 && endDistance <= 0)
{
continue;
}
// If the distance of the start point is greater than the end point, we have a collision!
if (startDistance > endDistance)
{
// This gets a ratio from our starting point to the approximate collision spot
float Ratio1 = (startDistance - kEpsilon) / (startDistance - endDistance);
// If this is the first time coming here, then this will always be true,
// since startRatio starts at -1.0f. We want to find the closest collision,
// so we still continue to check all of the brushes before quitting.
if (Ratio1 > startRatio)
{
// Set the startRatio (currently the closest collision distance from start)
startRatio = Ratio1;
bCollided = true; // Let us know we collided!
vCollisionNormal = pPlane.normal;
if (vCollisionNormal.Y >= 0.2f)
{
onGround = true;
}
// This checks first tests if we actually moved along the x or z-axis,
// meaning that we went in a direction somewhere. The next check makes
// sure that we don't always check to step every time we collide. If
// the normal of the plane has a Y value of 1, that means it's just the
// flat ground and we don't need to check if we can step over it, it's flat!
if ((vStart.X != vEnd.X || vStart.Z != vEnd.Z) && pPlane.normal.Y != 1)
{
// We can try and step over the wall we collided with
bTryStep = true;
}
}
}
else
{
// Get the ratio of the current brush side for the endRatio
float Ratio = (startDistance + kEpsilon) / (startDistance - endDistance);
// If the ratio is less than the current endRatio, assign a new endRatio.
// This will usually always be true when starting out.
if (Ratio < endRatio)
{
endRatio = Ratio;
}
}
}
// If we didn't start outside of the brush we don't want to count this collision - return;
if (startsOut == false)
{
return;
}
// If our startRatio is less than the endRatio there was a collision!!!
if (startRatio < endRatio)
{
// Make sure the startRatio moved from the start and check if the collision
// ratio we just got is less than the current ratio stored in m_traceRatio.
// We want the closest collision to our original starting position.
if (startRatio > -1 && startRatio < traceRatio)
{
// If the startRatio is less than 0, just set it to 0
if (startRatio < 0)
{
startRatio = 0;
}
// Store the new ratio in our member variable for later
traceRatio = startRatio;
}
}
}
/// <summary>
/// Checks our movement vector against all the planes of the brush
/// </summary>
private void CheckBrush(QBrush pBrush, Vector3 vStart, Vector3 vEnd)
{
float startRatio = -1.0f; // Like in BrushCollision.htm, start a ratio at -1
float endRatio = 1.0f; // Set the end ratio to 1
bool startsOut = false; // This tells us if we starting outside the brush
// This function actually does the collision detection between our movement
// vector and the brushes in the world data. We will go through all of the
// brush sides and check our start and end ratio against the planes to see if
// they pass each other. We start the startRatio at -1 and the endRatio at
// 1, but as we set the ratios to their intersection points (ratios), then
// they slowly move toward each other. If they pass each other, then there
// is definitely not a collision.
// Go through all of the brush sides and check collision against each plane
for (int i = 0; i < pBrush.numSides; i++)
{
// Here we grab the current brush side and plane in this brush
QBrushSide pBrushSide = bspMap.Data.brushSides[pBrush.firstSide + i];
QPlane pPlane = bspMap.Data.planes[pBrushSide.planeNum];
// Let's store a variable for the offset (like for sphere collision)
float offset = 0.0f;
// If we are testing sphere collision we need to add the sphere radius
if (traceType == TYPE_SPHERE)
offset = traceRadius;
// Test the start and end points against the current plane of the brush side.
// Notice that we add an offset to the distance from the origin, which makes
// our sphere collision work.
float startDistance = Vector3.Dot(vStart, pPlane.normal) - (pPlane.dist + offset);
float endDistance = Vector3.Dot(vEnd, pPlane.normal) - (pPlane.dist + offset);
// This is the last beefy part of code in this tutorial. In this
// section we need to do a few special checks to see which extents
// we should use. We do this by checking the x,y,z of the normal.
// If the vNormal.x is less than zero, we want to use the Max.x
// value, otherwise use the Min.x value. We do these checks because
// we want the corner of the bounding box that is closest to the plane to
// test for collision. Write it down on paper and see how this works.
// We want to grab the closest corner (x, y, or z value that is...) so we
// dont go through the wall. This works because the bounding box is axis aligned.
// Store the offset that we will check against the plane
// If we are using AABB collision
if (traceType == TYPE_BOX)
{
Vector3 vOffset = new Vector3();
// Grab the closest corner (x, y, or z value) that is closest to the plane
vOffset.X = (pPlane.normal.X < 0) ? vTraceMaxs.X : vTraceMins.X;
vOffset.Y = (pPlane.normal.Y < 0) ? vTraceMaxs.Y : vTraceMins.Y;
vOffset.Z = (pPlane.normal.Z < 0) ? vTraceMaxs.Z : vTraceMins.Z;
// Use the plane equation to grab the distance our start position is from the plane.
// We need to add the offset to this to see if the box collides with the plane,
// even if the position doesn't.
startDistance = Vector3.Dot(vStart + vOffset, pPlane.normal) - pPlane.dist;
// Get the distance our end position is from this current brush plane
endDistance = Vector3.Dot(vEnd + vOffset, pPlane.normal) - pPlane.dist;
}
// Make sure we start outside of the brush's volume
if (startDistance > 0) startsOut = true;
// Stop checking since both the start and end position are in front of the plane
if (startDistance > 0 && endDistance > 0)
return;
// Continue on to the next brush side if both points are behind or on the plane
if (startDistance <= 0 && endDistance <= 0)
continue;
// If the distance of the start point is greater than the end point, we have a collision!
if (startDistance > endDistance)
{
// This gets a ratio from our starting point to the approximate collision spot
float Ratio1 = (startDistance - kEpsilon) / (startDistance - endDistance);
// If this is the first time coming here, then this will always be true,
// since startRatio starts at -1.0f. We want to find the closest collision,
// so we still continue to check all of the brushes before quitting.
if (Ratio1 > startRatio)
{
// Set the startRatio (currently the closest collision distance from start)
startRatio = Ratio1;
bCollided = true; // Let us know we collided!
vCollisionNormal = pPlane.normal;
if (vCollisionNormal.Y >= 0.2f)
onGround = true;
// This checks first tests if we actually moved along the x or z-axis,
// meaning that we went in a direction somewhere. The next check makes
// sure that we don't always check to step every time we collide. If
// the normal of the plane has a Y value of 1, that means it's just the
// flat ground and we don't need to check if we can step over it, it's flat!
if ((vStart.X != vEnd.X || vStart.Z != vEnd.Z) && pPlane.normal.Y != 1)
{
// We can try and step over the wall we collided with
bTryStep = true;
}
}
}
else
{
// Get the ratio of the current brush side for the endRatio
float Ratio = (startDistance + kEpsilon) / (startDistance - endDistance);
// If the ratio is less than the current endRatio, assign a new endRatio.
// This will usually always be true when starting out.
if (Ratio < endRatio)
endRatio = Ratio;
}
}
// If we didn't start outside of the brush we don't want to count this collision - return;
if (startsOut == false)
{
return;
}
// If our startRatio is less than the endRatio there was a collision!!!
if (startRatio < endRatio)
{
// Make sure the startRatio moved from the start and check if the collision
// ratio we just got is less than the current ratio stored in m_traceRatio.
// We want the closest collision to our original starting position.
if (startRatio > -1 && startRatio < traceRatio)
{
// If the startRatio is less than 0, just set it to 0
if (startRatio < 0)
startRatio = 0;
// Store the new ratio in our member variable for later
traceRatio = startRatio;
}
}
}
/// <summary>
/// Traverses the BSP to find the brushes closest to our position
/// </summary>
private void CheckNode(int nodeIndex, float startRatio, float endRatio, Vector3 vStart, Vector3 vEnd)
{
// Remember, the nodeIndices are stored as negative numbers when we get to a leaf, so we
// check if the current node is a leaf, which holds brushes. If the nodeIndex is negative,
// the next index is a leaf (note the: nodeIndex + 1)
if (nodeIndex < 0)
{
// If this node in the BSP is a leaf, we need to negate and add 1 to offset
// the real node index into the m_pLeafs[] array. You could also do [~nodeIndex].
QLeaf pLeaf = bspMap.Data.leafs[~nodeIndex];
// We have a leaf, so let's go through all of the brushes for that leaf
for (int i = 0; i < pLeaf.numLeafBrushes; i++)
{
// Get the current brush that we going to check
QBrush pBrush = bspMap.Data.brushes[bspMap.Data.leafbrushes[pLeaf.firstLeafBrush + i]];
// This is kind of an important line. First, we check if there is actually
// and brush sides (which store indices to the normal and plane data for the brush).
// If not, then go to the next one. Otherwise, we also check to see if the brush
// is something that we want to collide with. For instance, there are brushes for
// water, lava, bushes, misc. sprites, etc... We don't want to collide with water
// and other things like bushes, so we check the texture type to see if it's a solid.
// If the textureType can be binary-anded (&) and still be 1, then it's solid,
// otherwise it's something that can be walked through. That's how Quake chose to
// do it.
// Check if we have brush sides and the current brush is solid and collidable
if ((pBrush.numSides > 0) && (bspMap.Data.shaders[pBrush.shaderNum].contentFlags & 1) > 0)
{
// Now we delve into the dark depths of the real calculations for collision.
// We can now check the movement vector against our brush planes.
CheckBrush(pBrush, vStart, vEnd);
}
}
// Since we found the brushes, we can go back up and stop recursing at this level
return;
}
// If we haven't found a leaf in the node, then we need to keep doing some dirty work
// until we find the leafs which store the brush information for collision detection.
// Grad the next node to work with and grab this node's plane data
QNode pNode = bspMap.Data.nodes[nodeIndex];
QPlane pPlane = bspMap.Data.planes[pNode.planeNum];
// Now we do some quick tests to see which side we fall on of the node in the BSP
// Here we use the plane equation to find out where our initial start position is
// according the the node that we are checking. We then grab the same info for the end pos.
float startDistance = Vector3.Dot(vStart, pPlane.normal) - pPlane.dist;
float endDistance = Vector3.Dot(vEnd, pPlane.normal) - pPlane.dist;
float offset = 0.0f;
// If we are doing any type of collision detection besides a ray, we need to change
// the offset for which we are testing collision against the brushes. If we are testing
// a sphere against the brushes, we need to add the sphere's offset when we do the plane
// equation for testing our movement vector (start and end position). * More Info * For
// more info on sphere collision, check out our tutorials on this subject.
// If we are doing sphere collision, include an offset for our collision tests below
if (traceType == TYPE_SPHERE)
{
offset = traceRadius;
}
else if (traceType == TYPE_BOX)
{
// This equation does a dot product to see how far our
// AABB is away from the current plane we are checking.
// Since this is a distance, we need to make it an absolute
// value, which calls for the fabs() function (abs() for floats).
// Get the distance our AABB is from the current splitter plane
offset = Math.Abs(vExtents.X * pPlane.normal.X) +
Math.Abs(vExtents.Y * pPlane.normal.Y) +
Math.Abs(vExtents.Z * pPlane.normal.Z);
}
// Below we just do a basic traversal down the BSP tree. If the points are in
// front of the current splitter plane, then only check the nodes in front of
// that splitter plane. Otherwise, if both are behind, check the nodes that are
// behind the current splitter plane. The next case is that the movement vector
// is on both sides of the splitter plane, which makes it a bit more tricky because we now
// need to check both the front and the back and split up the movement vector for both sides.
// Here we check to see if the start and end point are both in front of the current node.
// If so, we want to check all of the nodes in front of this current splitter plane.
if (startDistance >= offset && endDistance >= offset)
{
// Traverse the BSP tree on all the nodes in front of this current splitter plane
CheckNode(pNode.children[0], startDistance, endDistance, vStart, vEnd);
}
// If both points are behind the current splitter plane, traverse down the back nodes
else if (startDistance < -offset && endDistance < -offset)
{
// Traverse the BSP tree on all the nodes in back of this current splitter plane
CheckNode(pNode.children[1], startDistance, endDistance, vStart, vEnd);
}
else
{
// If we get here, then our ray needs to be split in half to check the nodes
// on both sides of the current splitter plane. Thus we create 2 ratios.
float Ratio1 = 1.0f, Ratio2 = 0.0f, middleRatio = 0.0f;
Vector3 vMiddle; // This stores the middle point for our split ray
// Start of the side as the front side to check
int side = pNode.children[0];
// Here we check to see if the start point is in back of the plane (negative)
if (startDistance < endDistance)
{
// Since the start position is in back, let's check the back nodes
side = pNode.children[1];
// Here we create 2 ratios that hold a distance from the start to the
// extent closest to the start (take into account a sphere and epsilon).
// We use epsilon like Quake does to compensate for float errors. The second
// ratio holds a distance from the other size of the extents on the other side
// of the plane. This essential splits the ray for both sides of the splitter plane.
float inverseDistance = 1.0f / (startDistance - endDistance);
Ratio1 = (startDistance - offset - kEpsilon) * inverseDistance;
Ratio2 = (startDistance + offset + kEpsilon) * inverseDistance;
}
// Check if the starting point is greater than the end point (positive)
else if (startDistance > endDistance)
{
// This means that we are going to recurse down the front nodes first.
// We do the same thing as above and get 2 ratios for split ray.
// Ratio 1 and 2 are switched in contrast to the last if statement.
// This is because the start is starting in the front of the splitter plane.
float inverseDistance = 1.0f / (startDistance - endDistance);
Ratio1 = (startDistance + offset + kEpsilon) * inverseDistance;
Ratio2 = (startDistance - offset - kEpsilon) * inverseDistance;
}
// Make sure that we have valid numbers and not some weird float problems.
// This ensures that we have a value from 0 to 1 as a good ratio should be :)
if (Ratio1 < 0.0f)
{
Ratio1 = 0.0f;
}
else if (Ratio1 > 1.0f)
{
Ratio1 = 1.0f;
}
if (Ratio2 < 0.0f)
{
Ratio2 = 0.0f;
}
else if (Ratio2 > 1.0f)
{
Ratio2 = 1.0f;
}
// Just like we do in the Trace() function, we find the desired middle
// point on the ray, but instead of a point we get a middleRatio percentage.
// This isn't the true middle point since we are using offset's and the epsilon value.
// We also grab the middle point to go with the ratio.
middleRatio = startRatio + ((endRatio - startRatio) * Ratio1);
vMiddle = vStart + ((vEnd - vStart) * Ratio1);
// Now we recurse on the current side with only the first half of the ray
CheckNode(side, startRatio, middleRatio, vStart, vMiddle);
// Now we need to make a middle point and ratio for the other side of the node
middleRatio = startRatio + ((endRatio - startRatio) * Ratio2);
vMiddle = vStart + ((vEnd - vStart) * Ratio2);
// Depending on which side should go last, traverse the bsp with the
// other side of the split ray (movement vector).
if (side == pNode.children[1])
{
CheckNode(pNode.children[0], middleRatio, endRatio, vMiddle, vEnd);
}
else
{
CheckNode(pNode.children[1], middleRatio, endRatio, vMiddle, vEnd);
}
}
}
