Any support for Perpendicular Lines

[SandyG]

Looked around but didn't see (might have missed it) Perpendicular lines from 2 points on another line, with one of the points being used for the end of the perpendicular line and then I can draw a polygon in the right angle/orientation around an arc of the gauge.

Before I do more math, was checking to see if it exists.

My fallback is to calc the slope of the line, - and inverse to get the perpendicular slope, then come up with the y=mx+b stuff. This does have some problems with lines that are vertical and such, but can work that out.

Trying to draw a triangle marker that indicates the Max (or Min) of the pointer on the gauge. The example is just a line but would like to draw the line as a upside down right triangle of sorts.

Sandy

[circular]

Hi SandyG,

If you have a segment defined by two points A and B, then you can compute a vector u from A to B. Then from that you can build a vector v that is perpendicular. By adding this vector to a point, you will get the end of the new segment.

Code: Pascal  [Select][+][-]

1. uses BGRABitmapTypes;
2. var
3.   A,B,C : TPointF;
4.   u,v : TPointF;
5. begin
6.   // given segment AB
7.   A := PointF(5, 5);
8.   B := PointF(10, 5);
9.   // vector from A to B
10.   u := B - A; // = (5, 0)
11.   // build the perpendicular vector
12.   // (clockwise in screen coordinates while the opposite would be counter clockwise)
13.   v := PointF(-u.y, u.x); // = (0, 5)
14.   // you can scale it to set the new segment length
15.   v := v * (10 / VectLen(v)); // = (0, 10)
16.   C := B + v; // = (10, 15)
17. end;
18.  

Alternatively, you can rotate a vector by any angle by using an affine matrix.

Code: Pascal  [Select][+][-]

1. uses BGRATransform;
2. begin
3.   ...
4.   v := AffineMatrixRotationDeg(90) * u;
5.   ...
6. end;
7.  

Regards

[SandyG]

Awesome!!

I will give the Vector version a try, looks pretty straight forward.

Trying to get the last of the features into the gauge then to clean up the range and related scaling as right now it's only good for 0-100. Slowly getting it done 

Thanks again, this will keep it moving forward!

Sandy

[circular]

I am glad I could help