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Rotate A Quad Along Axis To Face Camera
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Garold, in Math and Physics
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Garold 118
Thanks Rob.
I found a solution within the library, after learning some basic math.
Orientation3D.SetUpDirection(ref cparticle.Orientation, Vector3.Cross(cparticle.Velocity, CameraPosition  cparticle.Position));
I'll try to see if I can use your method to edit the vertices directly, but it looks a little like the function it calls is doing as you suggest anyway.
public static Quaternion GetRotationTo(Vector3 CurrentDirection, Vector3 DesiredDirection, Vector3 sFallbackAxis) { Quaternion quaternion = new Quaternion(); Vector3 vector = CurrentDirection; Vector3 vector2 = DesiredDirection; vector.Normalize(); vector2.Normalize(); float num = Vector3.Dot(vector, vector2); if (num >= 1f) { return Quaternion.Identity; } if (num <= 0.999999f) { if (sFallbackAxis != Vector3.Zero) { sFallbackAxis.Normalize(); return Quaternion.CreateFromAxisAngle(sFallbackAxis, 3.141593f); } Vector3 axis = Vector3.Cross(Vector3.UnitX, vector); if (axis.LengthSquared() < 0.999998f) { axis = Vector3.Cross(Vector3.UnitY, vector); } axis.Normalize(); return Quaternion.CreateFromAxisAngle(axis, 3.141593f); } Vector3 vector4 = Vector3.Cross(vector, vector2); double num2 = Math.Sqrt((double) ((1f + num) * 2f)); double num3 = 1.0 / num2; quaternion.X = (float) (vector4.X * num3); quaternion.Y = (float) (vector4.Y * num3); quaternion.Z = (float) (vector4.Z * num3); quaternion.W = (float) (num2 * 0.5); quaternion.Normalize(); return quaternion; }
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Garold 118
Your method seems way simpler :)
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Basically, stop rotating it! :)
Get the transform matrix of your camera:
X = [ a b c 0 ]
Y = [ d e f 0 ]
Z = [ g h i 0 ]
The camera *looks* down Z, and the X/Y axes are left/right and up/down respectively. Given the width & height of your quad, you can compute the points directly:
P0 = X * (width/2) + Y * (height/2)
P1 = X * (width/2) + Y * (height/2)
P2 = X * (width/2)  Y * (height/2)
P3 = X * (width/2)  Y * (height/2)
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