Nested Model Matrices (Metal Part 12)

Source Code

See Project in GitHub 👩‍💻

References

• Metal Render Pipeline tutorial series by Rick Twohy

Table of Content

• Implementation
• Result

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Implementation

The model matrix is now located in the transform level, and every lateUpdate, the transform updates its model matrix.

Each transform will check if it has a parent, and will multiply the parent model matrix by its model matrix, making a new model matrix that takes into account the transformations of the parent.

1class Transform {
2    ...
3
4    public var modelMatrix: float4x4 = matrix_identity_float4x4
5
6    private var _parent: Transform?
7    public var parent: Transform? {
8        return _parent
9    }
10
11    public func setParent(_ parent: Transform){
12        _parent = parent
13    }
14
15    private func updateModelMatrix() {
16        var result: float4x4 = matrix_identity_float4x4
17
18        result.translate(position: position)
19        result.scale(scale: scale)
20
21        result.rotateX(angle: rotation.x)
22        result.rotateY(angle: rotation.y)
23        result.rotateZ(angle: rotation.z)
24
25        if(_parent != nil){
26            modelMatrix = _parent!.modelMatrix * result
27        } else {
28            modelMatrix = result
29        }
30    }
31
32    // https://docs.unity3d.com/ScriptReference/MonoBehaviour.LateUpdate.html
33    // LateUpdate is called after all Update functions have been called
34    public func lateUpdate(){
35        if let updatableSelf = self as? LateUpdatable {
36            updatableSelf.doLateUpdate()
37        }
38
39        updateModelMatrix()
40
41        for child in _children {
42            child.lateUpdate()
43        }
44    }
45}

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Result

Now the cube moves along the parent quad.