Direct3D

Plane Equation

A plane is represented by its normal and distance along it. In your example, the normal is the (x, y, z) component (which is (0, 0, 1) - meaning it faces towards +z), and the distance from the origin to it is 0.

A plane is often a normal and a distance from the origin. Your plane has a normal along positive Z, and is at the origin.

Thanks guys and what about the fourth component of D3DXVECTOR4 (w component)?

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Original post by Asesh Thanks guys and what about the fourth component of D3DXVECTOR4 (w component)?

That's the distance from the origin.

Quote:

Original post by Evil Steve Quote: Original post by Asesh Thanks guys and what about the fourth component of D3DXVECTOR4 (w component)? That's the distance from the origin.

If you consider the content of D3DXPLANE is represented by a D3DXVECTOR4 struct, so yes.

But D3DXVECTOR4 is just a 4D vector that could be used to store numeric values, colors data and other things that could be nice to represent with 4 components.

Considering model transformations, a 4D vector is mainly defined for providing a homogenisation on the transformation calculations. In other words, rotation and scaling transformations can be represented by 3x3 matrices, but a translation transformation don't. However, you can describe all the transformations as 4x4 matrices, in order to allow the product of different transformation matrices. And in this case, a vector transformation (by a 4x4 matrix) requires it is 4D. In general, the fourth value is 1.

It is interesting notice that many D3DX math functions transform 3D vectors (D3DXVECTOR3) by using 4x4 matrices (D3DXMATRIX). In true, the 3D vector is internally transformed in a 4D vector to provide the math operation.