GraphMath unit / LineEndPoint

[BubikolRamios]

Is this expected, or  ?

{------------------------------------------------------------------------------
  Method:   LineEndPoint
  Params:   StartPoint, Angle, Length
  Returns:  TPoint

  Use LineEndPoint to get the End-Point of a line of ANY given Length at
  any given angle with any given Start-Point. It is primarily for use in
  other routines such as RadialPoint. The angle is in 1/16th of a degree.
  For example, a full circle equals 5760 (16*360).  Zero degrees is at the
  3'o clock position.

------------------------------------------------------------------------------}

1.Test LineEndPoint.
See image 1
From center, find end point at 0 degrees, and 100 distance. Find end points from there under +/-90 angle,distance 100,  connect, --> draw tangent.
2. let me see tangent  for all 360 degrees, step 10
see image 2

Code: Pascal  [Select][+][-]

1. // some not needed declarations, delete them
2.   var
3.    arr: TFloatPointArray;
4.    t,t1,t2: TfloatPoint;
5.    str:string;
6.    toCanvasCenterX,toCanvasCenterY: integer;
7.    alpha: integer;
8. begin
9.  
10.   //arr := getLineEndPointsMC(FloatPoint(0,0),degtorad(0),200);
11.  
12.   str := '';
13.  
14.  
15.   toCanvasCenterX := round(PaintBox1.width/2);
16.   toCanvasCenterY := round(PaintBox1.Height/2);
17.  
18.   PaintBox1.Canvas.Brush.Color := clWhite;
19.   PaintBox1.Canvas.EllipseC(0+ toCanvasCenterX,toCanvasCenterY - 0,100,100);
20.  
21.   alpha := 0;
22.   while  alpha < 360 do
23.   begin
24.  
25.  
26.   t := LineEndPoint(FloatPoint(0,0),alpha*16,100);
27.  
28.   PaintBox1.Canvas.Pen.Color := clBlack;
29.   PaintBox1.Canvas.Line(round(FloatPoint(0,0).x+ toCanvasCenterX),round(toCanvasCenterY -FloatPoint(0,0).Y),round(t.x+ toCanvasCenterX),round(toCanvasCenterY -t.y));
30.  
31.   PaintBox1.Canvas.Pen.Color := clRed;
32.   PaintBox1.Canvas.Ellipse(Rect(Round(t.X-2+ toCanvasCenterX),
33.                                       Round(toCanvasCenterY - t.Y-2),
34.                                       Round(t.X+2+ toCanvasCenterX),
35.                                       Round(toCanvasCenterY - t.Y+2)));
36.  
37.   t1 := LineEndPoint(t,(alpha+90)*16,100);
38.   PaintBox1.Canvas.Pen.Color := clBlue;
39.   PaintBox1.Canvas.Ellipse(Rect(Round(t1.X-2+ toCanvasCenterX),
40.                                       Round(toCanvasCenterY - t1.Y-2),
41.                                       Round(t1.X+2+ toCanvasCenterX),
42.                                       Round(toCanvasCenterY - t1.Y+2)));
43.  
44.   t2 := LineEndPoint(t,(alpha-90)*16,100);
45.   PaintBox1.Canvas.Pen.Color := clBlue;
46.   PaintBox1.Canvas.Ellipse(Rect(Round(t2.X-2+ toCanvasCenterX),
47.                                       Round(toCanvasCenterY - t2.Y-2),
48.                                       Round(t2.X+2+ toCanvasCenterX),
49.                                       Round(toCanvasCenterY - t2.Y+2)));
50.  
51.   PaintBox1.Canvas.Line(round(t1.x+ toCanvasCenterX),round(toCanvasCenterY -t1.Y),round(t2.x+    toCanvasCenterX),round(toCanvasCenterY -t2.y));
52.  
53.   alpha := alpha +10;
54.  
55.   end;
56. end;
57.  

[tetrastes]

Code: Pascal  [Select][+][-]

1.   //t1 := LineEndPoint(t,(alpha+90)*16,100);
2.   a2 := alpha + 90;
3.   if a2 > 359 then a2 := a2 - 360;
4.   t1 := LineEndPoint(t,a2*16,100);
5.  

[BubikolRamios]

Code: Pascal  [Select][+][-]

1.  if a2 > 359 then a2 := a2 - 360;

probably this should be handled inside LineEndPoint, right ?

extracted, and all I did removed '16', and now returns FloatPoint insead of Point

Code: Pascal  [Select][+][-]

1. var
2.   sinAngle, cosAngle: Extended;
3. begin
4.   if angleDegrees > 360 then
5.     angleDegrees := Frac(angleDegrees / 360) * 360;
6.  
7.   if angleDegrees < 0 then
8.     angleDegrees := 360 - abs(angleDegrees);
9.  
10.   SinCos(DegToRad(angleDegrees), sinAngle, cosAngle);
11.   Result.Y := StartPoint.Y - Round(Length*sinAngle);
12.   Result.X := StartPoint.X + Round(Length*cosAngle);
13. end;    
14.  

and all works OK, one can do

Code: Pascal  [Select][+][-]

1. while  alpha < num greater than 360 do

and it works.

[tetrastes]

Yes, you are right. There is error in graphmath.pp:

Code: Pascal  [Select][+][-]

1.   if Angle > 360*16 then
2.     Angle := Frac(Angle / 360*16) * 360*16;
3.  

must be

Code: Pascal  [Select][+][-]

1.   if Angle > 360*16 then
2.     Angle := Frac(Angle / (360*16)) * 360*16;
3.  

[BubikolRamios]

Have no clue where to file bug report ... I hope you will do it.

[tetrastes]

Done.
https://gitlab.com/freepascal.org/lazarus/lazarus/-/issues/41400

[wp]

Bug fixed along with the same one in PolyBezierArcPoints. Fix back-ported to Fixes_4 and Fixed_3 (i.e. fix will be in Laz 4.0 and 3.10 (if that will ever be released)).