ShaderCamera.swift

class Camera {
    private var _zoom: Float = 45.0    
    var position: SIMD3<Float> = .init(0, 0, 3)
    var rotation: SIMD3<Float> = .init(repeating: 0)
    var scale: SIMD3<Float> = .init(repeating: 1)
    
    var projectionMatrix: matrix_float4x4 {
        return Matrix.perspective(fov: Angle(degrees: Double(self._zoom)),
                                  aspectRatio: Renderer.aspectRatio,
                                  near: 0.1,
                                  far: 1000)
    }
    
    var viewMatrix: matrix_float4x4 {
        matrix_identity_float4x4
        * Matrix.rotation(angle: .degrees(Double(rotation.x)), axis: Axis.x.simd)
        * Matrix.rotation(angle: .degrees(Double(rotation.y)), axis: Axis.y.simd)
        * Matrix.rotation(angle: .degrees(Double(rotation.z)), axis: Axis.z.simd)
        * Matrix.translation(direction: -position)
    }
}

extension Matrix {
  static func perspective(fov: Angle, aspectRatio: Float, near: Float, far: Float) -> matrix_float4x4 {
      let fov = Float(fov.radians)

      let t: Float = tan(fov / 2)

      let x: Float = 1 / (aspectRatio * t)
      let y: Float = 1 / t
      let z: Float = -((far + near) / (far - near))
      let w: Float = -((2 * far * near) / (far - near))

      var result = matrix_identity_float4x4
      result.columns = (
          SIMD4<Float>(x,  0,  0,   0),
          SIMD4<Float>(0,  y,  0,   0),
          SIMD4<Float>(0,  0,  z,  -1),
          SIMD4<Float>(0,  0,  w,   0)
      )
      return result
  }
}