Vec3 * Mat4x4

[Meanz]

I am a newbie at matrices.
So my question is simple, how would I go about doing the following multiplication ?

Vec3 * Mat4x4

[ClickerMonkey]

Very carefully..

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public void transform(Matrix4x4 m, Vec3 in, Vec3i out) {   out.x = (in.x * m.e00) + (in.y * m.e01) + (in.z * m.e02) + m.e03;   out.y = (in.x * m.e10) + (in.y * m.e11) + (in.z * m.e12) + m.e13;   out.z = (in.x * m.e20) + (in.y * m.e21) + (in.z * m.e22) + m.e23; }

[Meanz]

Thanks a lot, that finally finished my skinning process!

I really need to take some time to sit down and learn more of them matrices.

Games published by our own members! Check 'em out!

[Roquen]

My opinion here is that you'd be better off understanding vectors and coordinate frames first.  Linear algebra is 'just' folding a couple of operations into a logically single one for affine transforms.

[Meanz]

"coordinate frames" ?

[Spasi]

The linear algebra course on Khan Academy is pretty good.

[sproingie]

Just to elaborate on ClickerMonkey's perfectly correct answer:

You can't generally multiply a vector of 3 components with a 4x4 matrix, but the standard geometric interpretation of a 4x4 matrix is of an affine transform in homogeneous coordinate space.  A vector in 3d Cartesian space (x,y,z) is a vector in homogeneous space (x,y,z,w) where w=1.  So long story short, you turn your vec3(x,y,z) into a vec4(x,y,z,1) and then do normal matrix multiplication with it. 

[ClickerMonkey]

Just to elaborate on ClickerMonkey's perfectly correct answer:

You can't generally multiply a vector of 3 components with a 4x4 matrix, but the standard geometric interpretation of a 4x4 matrix is of an affine transform in homogeneous coordinate space.  A vector in 3d Cartesian space (x,y,z) is a vector in homogeneous space (x,y,z,w) where w=1.  So long story short, you turn your vec3(x,y,z) into a vec4(x,y,z,1) and then do normal matrix multiplication with it.  

Agreed! Transforming vectors need a w value of 0 and transforming points need a value of 1!

w is this neat part of a vector, if you set it to the square root of a point, the point is interpreted by OpenGL or a Matrix as a normalized vector.

1	v.w = (float)Math.sqrt(v.x * v.x + v.y * v.y + v.z * v.z);

Point/Vector is now normalized!

Full transform method with Vec4

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out.x = (in.x * e00) + (in.y * e01) + (in.z * e02) + (in.w * e03); out.y = (in.x * e10) + (in.y * e11) + (in.z * e12) + (in.w * e13); out.z = (in.x * e20) + (in.y * e21) + (in.z * e22) + (in.w * e23); out.w = (in.x * e30) + (in.y * e31) + (in.z * e32) + (in.w * e33);