aselimov/zigsdof
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

Add matrix inverse calculation

Browse source
This commit is contained in:
Alex Selimov 2026-08-10 19:44:56 -04:00
parent 923574ec48
commit 6e805b45bb
1 changed files with 73 additions and 0 deletions
Download patch file Download diff file Expand all files Collapse all files

73
src/vec3.zig
View file

@ -32,6 +32,10 @@ pub fn vec3Dot(a: Vec3F64, b: Vec3F64) f64 {
return @reduce(.Add, a.data * b.data);
}
pub fn vec3MulScalar(a: Vec3F64, b: f64) Vec3F64 {
return .init(a.x() * b, a.y() * b, a.z() * b);
}
pub fn vec3Cross(a: Vec3F64, b: Vec3F64) Vec3F64 {
const x_component = a.y() * b.z() - a.z() * b.y();
const y_component = a.z() * b.x() - a.x() * b.z();
@ -83,6 +87,45 @@ pub fn mat3Mul(a: Mat3F64, b: Mat3F64) Mat3F64 {
return .{ .row1 = c_row1, .row2 = c_row2, .row3 = c_row3 };
}
pub fn mat3Det(a: Mat3F64) f64 {
return a.row1.x() * (a.row2.y() * a.row3.z() - a.row2.z() * a.row3.y()) -
a.row1.y() * (a.row2.x() * a.row3.z() - a.row2.z() * a.row3.x()) +
a.row1.y() * (a.row2.x() * a.row3.y() - a.row2.y() * a.row3.x());
}
pub fn mat3Inv(a: Mat3F64) Mat3F64 {
const inv_det = 1.0 / mat3Det(a);
const row1 = vec3MulScalar(
.init(
a.row2.y() * a.row3.z() - a.row2.z() * a.row3.y(),
a.row1.z() * a.row3.y() - a.row1.y() * a.row3.z(),
a.row1.y() * a.row2.z() - a.row1.z() * a.row2.y(),
),
inv_det,
);
const row2 = vec3MulScalar(
.init(
a.row2.z() * a.row3.x() + a.row2.x() * a.row3.z(),
a.row1.x() * a.row3.z() - a.row1.z() * a.row3.x(),
a.row1.z() * a.row2.x() - a.row1.x() * a.row2.z(),
),
inv_det,
);
const row3 = vec3MulScalar(
.init(
a.row2.x() * a.row3.y() + a.row2.y() * a.row3.x(),
a.row1.y() * a.row3.x() - a.row1.x() * a.row3.y(),
a.row1.x() * a.row2.y() - a.row1.y() * a.row2.x(),
),
inv_det,
);
return .{
.row1 = row1,
.row2 = row2,
.row3 = row3,
};
}
pub fn vec3MulMat3(a: Mat3F64, b: Vec3F64) Vec3F64 {
return .init(
vec3Dot(a.row1, b),
@ -267,6 +310,36 @@ test "Mat3 mul works" {
try std.testing.expect(c.row3.z() == 9);
}
test "mat determinant works" {
const a: Mat3F64 = .{
.row1 = Vec3F64.init(1, 2, 3),
.row2 = Vec3F64.init(0, 1, 5),
.row3 = Vec3F64.init(0, 0, 9),
};
try std.testing.expectApproxEqAbs(9, mat3Det(a), 1e-12);
}
test "mat inverse works" {
const a: Mat3F64 = .{
.row1 = Vec3F64.init(1, 2, 3),
.row2 = Vec3F64.init(0, 1, 5),
.row3 = Vec3F64.init(0, 0, 9),
};
const ainv = mat3Inv(a);
std.debug.print("{}", .{ainv});
std.debug.print("{}", .{ainv.row2.z()});
try std.testing.expectApproxEqAbs(1, ainv.row1.x(), 1e-12);
try std.testing.expectApproxEqAbs(-2, ainv.row1.y(), 1e-12);
try std.testing.expectApproxEqAbs(7.0 / 9.0, ainv.row1.z(), 1e-12);
try std.testing.expectApproxEqAbs(0, ainv.row2.x(), 1e-12);
try std.testing.expectApproxEqAbs(1, ainv.row2.y(), 1e-12);
try std.testing.expectApproxEqAbs(-5.0 / 9.0, ainv.row2.z(), 1e-12);
try std.testing.expectApproxEqAbs(0, ainv.row3.x(), 1e-12);
try std.testing.expectApproxEqAbs(0, ainv.row3.y(), 1e-12);
try std.testing.expectApproxEqAbs(1.0 / 9.0, ainv.row3.z(), 1e-12);
}
test "vec3 mul mat3 works" {
const b: Mat3F64 = .{
.row1 = Vec3F64.init(0, 1, 0),