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package main
import "math"
// In a real application, use a dedicated math library like 'gonum/mat' or 'go-gl/mathgl'
type vec3 struct{ x, y, z float32 }
type mat4 [16]float32
func identity() mat4 {
return mat4{
1, 0, 0, 0,
0, 1, 0, 0,
0, 0, 1, 0,
0, 0, 0, 1,
}
}
func perspective(fovY, aspect, near, far float32) mat4 {
f := float32(1.0 / math.Tan(float64(fovY*(math.Pi/180.0))/2.0))
return mat4{
f / aspect, 0, 0, 0,
0, f, 0, 0,
0, 0, (far + near) / (near - far), -1,
0, 0, (2 * far * near) / (near - far), 0,
}
}
func lookAt(eye, center, up vec3) mat4 {
f := normalize(sub(center, eye))
s := normalize(cross(f, up))
u := cross(s, f)
return mat4{
s.x, u.x, -f.x, 0,
s.y, u.y, -f.y, 0,
s.z, u.z, -f.z, 0,
-dot(s, eye), -dot(u, eye), dot(f, eye), 1,
}
}
func rotate(m mat4, angle float32, axis vec3) mat4 {
c := float32(math.Cos(float64(angle * (math.Pi / 180.0))))
s := float32(math.Sin(float64(angle * (math.Pi / 180.0))))
t := 1 - c
x, y, z := axis.x, axis.y, axis.z
// Normalize axis
lenSq := x*x + y*y + z*z
if lenSq > 0 && (lenSq < 0.9999 || lenSq > 1.0001) { // Check if not already normalized
invLen := 1.0 / float32(math.Sqrt(float64(lenSq)))
x *= invLen
y *= invLen
z *= invLen
}
rot := mat4{
t*x*x + c, t*x*y - s*z, t*x*z + s*y, 0,
t*x*y + s*z, t*y*y + c, t*y*z - s*x, 0,
t*x*z - s*y, t*y*z + s*x, t*z*z + c, 0,
0, 0, 0, 1,
}
return multiply(m, rot) // Apply rotation to existing model matrix
}
func sub(a, b vec3) vec3 { return vec3{a.x - b.x, a.y - b.y, a.z - b.z} }
func cross(a, b vec3) vec3 {
return vec3{a.y*b.z - a.z*b.y, a.z*b.x - a.x*b.z, a.x*b.y - a.y*b.x}
}
func dot(a, b vec3) float32 { return a.x*b.x + a.y*b.y + a.z*b.z }
func length(v vec3) float32 { return float32(math.Sqrt(float64(dot(v, v)))) }
func normalize(v vec3) vec3 {
l := length(v)
if l == 0 {
return vec3{0, 0, 0}
}
return vec3{v.x / l, v.y / l, v.z / l}
}
func multiply(a, b mat4) mat4 {
var out mat4
for i := 0; i < 4; i++ {
for j := 0; j < 4; j++ {
sum := float32(0.0)
for k := 0; k < 4; k++ {
sum += a[i*4+k] * b[k*4+j]
}
out[i*4+j] = sum
}
}
return out
}
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