internal bool IsInsideClipBoundary(FrustumFace face)
{
switch (face)
{
case FrustumFace.Left: return(IsInsideLeftClipBoundary);
case FrustumFace.Right: return(IsInsideRightClipBoundary);
case FrustumFace.Bottom: return(IsInsideBottomClipBoundary);
case FrustumFace.Top: return(IsInsideTopClipBoundary);
case FrustumFace.Near: return(IsInsideNearClipBoundary);
case FrustumFace.Far: return(IsInsideFarClipBoundary);
default:
return(false);
}
}
//Clip the edge with a face
private static UnitProperty ClipEdge(UnitProperty start, UnitProperty end, FrustumFace faceIndex)
{
float t = 0;
//vector = end - start
var vector = end - start;
// result = start + (end - start) * t
switch (faceIndex)
{
case FrustumFace.Left:
// (start.x + vector.x * t) / (start.w + vector.w * t) = -1
// t = -(start.x + start.w) / (vector.x + vector.w)
// and (vector.x + vector.w) != 0
// because there is most one vertex on the face(x = -w), so (vector.x + vector.w) = (end.x - start.x + end.w - start.w) != 0
t = -(start.PositionTransformed.X + start.PositionTransformed.W) /
(vector.PositionTransformed.X + vector.PositionTransformed.W);
break;
case FrustumFace.Right:
// (start.x + vector.x * t) / (start.w + vector.w * t) = 1
// t = (start.w - start.x) / (vector.x - vector.w)
// and (vector.x - vector.w) != 0
// because there is most one vertex on the face(x = w), so (vector.x - vector.w) = (end.x - start.x - end.w + start.w) != 0
t = (start.PositionTransformed.W - start.PositionTransformed.X) /
(vector.PositionTransformed.X - vector.PositionTransformed.W);
break;
case FrustumFace.Bottom:
// (start.y + vector.y * t) / (start.w + vector.w * t) = -1
// t = (start.y + start.w) / (vector.y + vector.w)
// and (vector.y + vector.w) != 0
// because there is most one vertex on the face(y = -w), so (vector.y + vector.w) = (end.y - start.y + end.w - start.w) != 0
t = -(start.PositionTransformed.Y + start.PositionTransformed.W) /
(vector.PositionTransformed.Y + vector.PositionTransformed.W);
break;
case FrustumFace.Top:
// (start.y + vector.y * t) / (start.w + vector.w * t) = 1
// t = (start.w - start.y) / (vector.y - vector.w)
// and (vector.y - vector.w) != 0
// because there is most one vertex on the face(y = w), so (vector.y - vector.w) = (end.y - start.y - end.w + start.w) != 0
t = (start.PositionTransformed.W - start.PositionTransformed.Y) /
(vector.PositionTransformed.Y - vector.PositionTransformed.W);
break;
case FrustumFace.Near:
// (start.z + vector.z * t) / (start.w + vector.w * t) = 0
// t = - (start.z / vector.z)
// and vector.z != 0
// because there is most one vertex on the face(z = 0), so vector.z = (end.z - start.z) != 0
t = -(start.PositionTransformed.Z / vector.PositionTransformed.Z);
break;
case FrustumFace.Far:
// (start.z + vector.z * t) / (start.w + vector.w * t) = 1
// t = (start.w - start.z) / (vector.z - vector.w)
// and (vector.z - vector.w) != 0
// because there is most one vertex on the face(z = w), so (vector.z - vector.w) = (end.z - start.z - end.w + start.w) != 0
t = (start.PositionTransformed.W - start.PositionTransformed.Z) /
(vector.PositionTransformed.Z - vector.PositionTransformed.W);
break;
default:
break;
}
var result = start + vector * t;
//divide for the new vertex
result.PositionAfterDivide = result.PositionTransformed / result.PositionTransformed.W;
return(result);
}
//Sutherland-Hodgeman algorithm
private void ClipPrimitives(ref DrawCall drawCall)
{
//we enum all primitives in the draw call
for (int i = 0; i < drawCall.Primitives.Length; i++)
{
//create a temp for calculating
var result = new Primitive(drawCall.Primitives[i].Vertics);
//for all face of frustum
for (FrustumFace face = FrustumFace.Left; face <= FrustumFace.Far; face++)
{
var verticesList = new List <UnitProperty>();
//enum all edge in edge primitive
for (int vertexIndex = 0; vertexIndex < result.Vertics.Length; vertexIndex++)
{
var currentVertex = result.Vertics[vertexIndex];
var nextVertex = result.Vertics[0];
//the last edge
if (vertexIndex + 1 != result.Vertics.Length)
{
nextVertex = result.Vertics[vertexIndex + 1];
}
//the edge is not inside the clip boundary, so we do not add the vertex to result
if (currentVertex.IsInsideClipBoundary(face) is false &&
nextVertex.IsInsideClipBoundary(face) is false)
{
continue;
}
//the edge is inside the clip boundary, so we add the vertex to result
if (currentVertex.IsInsideClipBoundary(face) is true &&
nextVertex.IsInsideClipBoundary(face) is true)
{
//we only add the start vertex
verticesList.Add(currentVertex);
continue;
}
//the start is not insided but the end is insided.
if (currentVertex.IsInsideClipBoundary(face) is false)
{
verticesList.Add(ClipEdge(currentVertex, nextVertex, face));
continue;
}
//the start is insided but the end is not insided
if (nextVertex.IsInsideClipBoundary(face) is false)
{
verticesList.Add(currentVertex);
verticesList.Add(ClipEdge(currentVertex, nextVertex, face));
continue;
}
}
//update the primitive
result = new Primitive(verticesList.ToArray());
}
//get result
drawCall.Primitives[i] = result;
}
}
