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Add mat3.determinant and use it in inverse().

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treeform 2021-10-04 12:44:27 -07:00
parent ec9940810d
commit 47891e35d2
1 changed files with 10 additions and 7 deletions
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17
src/vmath.nim
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@ -1098,6 +1098,14 @@ proc transpose*[T](a: GMat4[T]): GMat4[T] =
a[0, 3], a[1, 3], a[2, 3], a[3, 3]
)
proc determinant*[T](a: GMat3[T]): T =
## Compute a determinant of the matrix.
(
a[0, 0] * (a[1, 1] * a[2, 2] - a[2, 1] * a[1, 2]) -
a[0, 1] * (a[1, 0] * a[2, 2] - a[1, 2] * a[2, 0]) +
a[0, 2] * (a[1, 0] * a[2, 1] - a[1, 1] * a[2, 0])
)
proc determinant*[T](a: GMat4[T]): T =
## Compute a determinant of the matrix.
let
@ -1129,12 +1137,7 @@ proc determinant*[T](a: GMat4[T]): T =
proc inverse*[T](a: GMat3[T]): GMat3[T] =
## Return an inverse of the matrix.
let
determinant = (
a[0, 0] * (a[1, 1] * a[2, 2] - a[2, 1] * a[1, 2]) -
a[0, 1] * (a[1, 0] * a[2, 2] - a[1, 2] * a[2, 0]) +
a[0, 2] * (a[1, 0] * a[2, 1] - a[1, 1] * a[2, 0])
)
invDet = 1 / determinant
invDet = 1 / a.determinant
result[0, 0] = +(a[1, 1] * a[2, 2] - a[2, 1] * a[1, 2]) * invDet
result[0, 1] = -(a[0, 1] * a[2, 2] - a[0, 2] * a[2, 1]) * invDet
@ -1183,7 +1186,7 @@ proc inverse*[T](a: GMat4[T]): GMat4[T] =
b11 = a22 * a33 - a23 * a32
# Calculate the inverse determinant.
let invDet = T(1.0)/(b00*b11 - b01*b10 + b02*b09 + b03*b08 - b04*b07 + b05*b06)
let invDet = 1 / a.determinant
result[0, 0] = (+a11 * b11 - a12 * b10 + a13 * b09) * invDet
result[0, 1] = (-a01 * b11 + a02 * b10 - a03 * b09) * invDet