public static void AlignWithTexture(this Texture tex, Plane currentPlane, Plane alignToPlane, Texture alignToTexture)
{
// Get reference values for the axes
var refU = alignToTexture.UAxis;
var refV = alignToTexture.VAxis;
// Reference points in the texture plane to use for shifting later on
var refX = alignToTexture.UAxis * alignToTexture.XShift * alignToTexture.XScale;
var refY = alignToTexture.VAxis * alignToTexture.YShift * alignToTexture.YScale;
// Two non-parallel planes intersect at an edge. We want the textures on this face
// to line up with the textures on the provided face. To do this, we rotate the texture
// normal on the provided face around the intersection edge to get the new texture axes.
// Then we rotate the texture reference point around this edge as well to get the new shift values.
// The scale values on both faces will always end up being the same value.
// Find the intersection edge vector
var intersectionEdge = alignToPlane.Normal.Cross(currentPlane.Normal);
// If the planes are parallel, the texture doesn't need any rotation - just different shift values.
if (Math.Abs(intersectionEdge.Length()) > 0.01f)
{
// Create a plane using the intersection edge as the normal
var intersectionPlane = new Plane(intersectionEdge, 0);
var intersect = Plane.Intersect(alignToPlane, currentPlane, intersectionPlane);
if (intersect != null)
{
// Since the intersection plane is perpendicular to both face planes, we can find the angle
// between the two planes (the align plane and the plane of this face) by projecting
// the normals of the planes onto the perpendicular plane and taking the cross product.
// Project the two normals onto the perpendicular plane
var apNormal = intersectionPlane.Project(alignToPlane.Normal).Normalise();
var cpNormal = intersectionPlane.Project(currentPlane.Normal).Normalise();
// Get the angle between the projected normals
var dot = Math.Round(apNormal.Dot(cpNormal), 4);
var angle = (float)Math.Acos(dot); // A.B = cos(angle)
// Rotate the texture axis by the angle around the intersection edge
var transform = Matrix4x4.CreateFromAxisAngle(intersectionEdge.Normalise(), angle);
refU = transform.Transform(refU);
refV = transform.Transform(refV);
// Rotate the texture reference points as well, but around the intersection line, not the origin
refX = transform.Transform(refX + intersect.Value) - intersect.Value;
refY = transform.Transform(refY + intersect.Value) - intersect.Value;
}
}
// Convert the reference points back to get the final values
tex.Rotation = 0;
tex.UAxis = refU;
tex.VAxis = refV;
tex.XShift = refU.Dot(refX) / alignToTexture.XScale;
tex.YShift = refV.Dot(refY) / alignToTexture.YScale;
tex.XScale = alignToTexture.XScale;
tex.YScale = alignToTexture.YScale;
}
