Files
linear_math_note/transform/RotateSingle.pas
2025-07-10 15:58:14 +08:00

79 lines
1.5 KiB
ObjectPascal

program RotateSingle;
uses
Math;
function LinearTrans(arr: array of array of Real; x: array of Real): array of Real;
var
result: array[0..1] of Real;
i, j: Integer;
begin
result[0] := x[0]*arr[0][0] + x[1]*arr[0][1];
result[1] := x[0]*arr[1][0] + x[1]*arr[1][1];
LinearTrans := result;
end;
function RotateLine(line: array of Real; p: array of Real; dgr: Real): array of Real;
var
k, b: Real;
arr: array[0..1, 0..1] of Real;
kvec, rkvec: array[0..1] of Real;
rk: Real;
p1: array[0..1] of Real;
pvec, rpvec: array[0..1] of Real;
rp1: array[0..1] of Real;
result: array[0..1] of Real;
begin
{
Rotate y=kx+b with p for dgr.
dgr measured in radians.
line: [k, b] => y = kx + b
}
k := line[0];
b := line[1];
arr[0][0] := Cos(dgr);
arr[0][1] := -Sin(dgr);
arr[1][0] := Sin(dgr);
arr[1][1] := Cos(dgr);
kvec[0] := 1;
kvec[1] := k;
rkvec := LinearTrans(arr, kvec);
rk := rkvec[1] / rkvec[0]; // (a,b) => (1,b/a)
p1[0] := 0;
p1[1] := b;
pvec[0] := p1[0] - p[0];
pvec[1] := p1[1] - p[1];
rpvec := LinearTrans(arr, pvec);
rp1[0] := p[0] + rpvec[0];
rp1[1] := p[1] + rpvec[1];
result[0] := rk;
result[1] := rp1[1] - rk * rp1[0];
RotateLine := result;
end;
var
line, p, result: array[0..1] of Real;
dgr: Real;
begin
line[0] := 3;
line[1] := 4;
p[0] := 2;
p[1] := 1;
dgr := Pi / 4;
result := RotateLine(line, p, dgr);
WriteLn('Rotated line: k=', result[0]:0:6, ', b=', result[1]:0:6);
end.