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Initialize a 4x4 matrix i.e. sdf.M44 #69

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Megidd opened this issue May 8, 2023 · 9 comments · Fixed by #70
Closed

Initialize a 4x4 matrix i.e. sdf.M44 #69

Megidd opened this issue May 8, 2023 · 9 comments · Fixed by #70

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@Megidd
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Megidd commented May 8, 2023 •
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Problem

There is no public method to declare a new instance of sdf.M44 with the initialization of its values.

The fields of the sdf.M44 are all private:

// M44 is a 4x4 matrix.
type M44 struct {
	x00, x01, x02, x03 float64
	x10, x11, x12, x13 float64
	x20, x21, x22, x23 float64
	x30, x31, x32, x33 float64
}

Why

The reason that I'm running into this problem is that I need to create a Quaternion type:

import (
	"math"

	"github.com/deadsy/sdfx/sdf"
	v3 "github.com/deadsy/sdfx/vec/v3"
)

// Quaternion represents a quaternion.
type Quaternion struct {
	W, X, Y, Z float64
}

// FromVectors creates a quaternion representing the rotation from vector a to vector b.
func FromVectors(a, b v3.Vec) Quaternion {
	v := a.Cross(b)
	w := math.Sqrt(a.Length2()*b.Length2())   a.Dot(b)
	q := Quaternion{W: w, X: v.X, Y: v.Y, Z: v.Z}
	return q.Normalize()
}

// Normalize normalizes the quaternion.
func (q Quaternion) Normalize() Quaternion {
	length := math.Sqrt(q.W*q.W   q.X*q.X   q.Y*q.Y   q.Z*q.Z)
	return Quaternion{W: q.W / length, X: q.X / length, Y: q.Y / length, Z: q.Z / length}
}

// ToMatrix converts the quaternion to a 4x4 matrix.
func (q Quaternion) ToMatrix() sdf.M44 {
	xx := q.X * q.X
	yy := q.Y * q.Y
	zz := q.Z * q.Z
	xy := q.X * q.Y
	xz := q.X * q.Z
	yz := q.Y * q.Z
	wx := q.W * q.X
	wy := q.W * q.Y
	wz := q.W * q.Z

	return sdf.M44{
		1 - 2*(yy zz), 2 * (xy - wz), 2 * (xz   wy), 0,
		2 * (xy   wz), 1 - 2*(xx zz), 2 * (yz - wx), 0,
		2 * (xz - wy), 2 * (yz   wx), 1 - 2*(xx yy), 0,
		0, 0, 0, 1,
	}
}

But, the last statement cannot be done, I mean:

	return sdf.M44{
		1 - 2*(yy zz), 2 * (xy - wz), 2 * (xz   wy), 0,
		2 * (xy   wz), 1 - 2*(xx zz), 2 * (yz - wx), 0,
		2 * (xz - wy), 2 * (yz   wx), 1 - 2*(xx yy), 0,
		0, 0, 0, 1,
	}

There is no way to initialize a sdf.M44, as far as I understand. Am I right? 🙄
@Megidd Megidd mentioned this issue May 8, 2023
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@deadsy
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deadsy commented May 8, 2023

What about just making "Quaternion" an object within the sdf package itself? ie- it would have access to private members within M44.

A couple of other points...

  • Doing m[i][j] = k is probably nicer than doing m.Set(i,j,k)
  • What about M22 and M33?
  • The Get/Set for the vector types were about wanting to access the vector by component index rather than by name. Not so much a private/public thing.

@deadsy
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deadsy commented May 8, 2023

btw - looking at M22/33/44 references I think the argument could be made to split off matrix operations into their own package. Maybe Quaternions could join them there.

@Megidd
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Megidd commented May 9, 2023

What about just making "Quaternion" an object within the sdf package itself?

... Maybe Quaternions could join them there.

Eventually, I ended up using the Quaternion provided by this Go pkg rather than my own custom Quaternion logic:

https://github.com/go-gl/mathgl

https://github.com/go-gl/mathgl/blob/e426c0894fa41bc41ac04704eef3ac4011b19ecf/mgl32/quat.go#L32

Data types need to be converted of course 🙂

@Megidd
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Megidd commented May 9, 2023 •
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  • Doing m[i][j] = k is probably nicer than doing m.Set(i,j,k)

btw - looking at M22/33/44 references I think the argument could be made to split off matrix operations into their own package...

I guess to do the above points, heavy modifications are needed. Probably affecting many other things. Maybe a heavy restructuring needs rigorous testing. A bit risky maybe 🤔

  • What about M22 and M33?

I'm going to modify I modified the PR so that the same Get and Set methods are provided for M22 and M33 too ✔️ Just a simple way to have access to matrix values for now.

@deadsy
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deadsy commented May 9, 2023

So are you doing 16 set's to initialise the M44 for your quaternion stuff?
Not very efficient...
What about:

func NewM44(x []float64) M44

which initialises based on up to 16 values out of x

E.g.

m := sdf.NewM33([]float64{
0,1,2,
3,4,5,
6,7,8,
})

@deadsy
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deadsy commented May 9, 2023

I'd be curious to benchmark differences between type built with arrays vs type built with named elements.

E.g.

M44 as [16]float64
M44 as struct{x00,x01,x02..... float64}

I guess they should be the same.

The former representation makes any sort of indexed access very simple.
The latter representations is good for 2d/3d vectors where you can do v.X, v.Y, v.Z

But for a matrix maybe I should convert the representation to a x[i] form internally.

@Megidd
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Megidd commented May 10, 2023 •
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So are you doing 16 set's to initialise the M44 for your quaternion stuff? Not very efficient... What about:

func NewM44(x []float64) M44

which initialises based on up to 16 values out of x

E.g.

m := sdf.NewM33([]float64{ 0,1,2, 3,4,5, 6,7,8, })

Makes sense. I'm going to modify I modified the PR accordingly 👍

@Megidd
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Megidd commented May 10, 2023

I'd be curious to benchmark differences between type built with arrays vs type built with named elements.

E.g.

M44 as [16]float64 M44 as struct{x00,x01,x02..... float64}

I guess they should be the same.

The former representation makes any sort of indexed access very simple. The latter representations is good for 2d/3d vectors where you can do v.X, v.Y, v.Z

But for a matrix maybe I should convert the representation to a x[i] form internally.

https://poe.com/s/GArFor42nHhIhRKhvBVb 🤖

@deadsy
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deadsy commented May 10, 2023

Funny. TIL: ChatGPTs opinion is worth about as much as the opinion of any rando on the internet, in fact it's probably an amalgam of the opinion of said randos.

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More public methods for matrix Megidd/sdfx
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@deadsy @Megidd