Echo BASIC - Icon routines 2 of 2 1/2

 BBS: Inland Empire Archive
Date: 07-02-92 (22:21)             Number: 230
From: MATT PRITCHARD @ 930/21      Refer#: NONE
  To: MIKE THAYER                   Recvd: NO  
Subj: Icon routines 2 of 2  1/2      Conf: (2) Quik_Bas

___Cont from previous message---

MT>   Drawing a straight line is easy. Just find the two end points and
MT>call for the

MT>        LINE(x1,y1)-(x2,y2),13

MT>That's easy. But what if you want to draw a zig-zag between those two
MT>points? Straight lines were not always used in Heraldry. There are so
MT>many different line patterns they used. If I could get at least two
MT>different line patterns I would be a happy camper.

MT>        I played with the DRAW statement,

Hmm, I think you'll find that lacking in capability.

MT>        But I didn't know how to compute the angle. I've received
MT> three postings so far on that problem. One illumanited the inherent
MT> short falls of using that method with SCREEN 9.

MT>        For the past week I've been playing using LINE but in short
MT> steps. Getting a dashed line a certain length was easy, but trying
MT> to draw another line underneath that is perplexing.


MT>I'm trying to figure
MT>a way to rotate all points from the first set 90 degrees so that no matter
MT>the angle, the lines always form right angles. As an
MT>example, if points x1,y
MT>and x2,y2 draw a horizontal line then all I need to do is drop down an
MT>increment (let's say 5) on both ends forming x3,y3 and x4,y4 and draw the
MT>line:
MT>     x1,y1                            x2,y2

MT>       .--------------------------------.
MT>     5                                      5
MT>       .--------------------------------.
MT>     x3,y3                            x4,y4

MT>      All lines meet at right angles.

MT>     So far, so good. Now if one end of the orginal line drops farther than
MT>the other, i.e. x2,y2 drop 10 units further, than x3,y3
MT>should move to match
MT>(x4,y4 are assumed to have moved as well), ensuring all
MT>lines drawn continue
MT>to be made at right angles.

MT>     Any suggestions?


Hell yes!   8)

You need to be thinking vectors.  You need to be thinking
relative coordinates.  You need to be thinking real
numbers...  I am dropping into impromtu mode...
Wheeeeeee...    (Eddie Van Halen guitar starts in
background...)

40 seconds and a couple scribbles on a graph paper pad later...

Ah yes, it is all clear to me now!

Oh?  Say what?   You'd like it to be clear for you... ok.. sure!

A line between point (X1,Y1) and point (X2,Y2) is a vector.  The vector we'll
represent as (Vx,Vy) where Vx = X2-X1 and Vy = Y2-Y1.

To make a sqaure pattern out of the line, (or other shaped
line patterns), we break the vector up into N little
vectors.  N is how many squares or repeating patterns we
want to make.  Instead of drawing a normal, straight, mini-
vector we'll get to the end point by way of other points
that a relative to the starting point.

Let me do a quick bit of code:

        SCREEN 9

        X1 = 10 : Y1 = 10      ' Line that slants sharply down.
        X2 = 40 : Y2 = 100     ' and to the right.


        '     +---->+---->  ... each "+---->" is one mini-vector
        '
        'Draw +--+  +--+  +-->
        '        |  |  |  |     Pattern
        '        +--+  +--+

        Vx = X2 - X1 : Vy = Y2 - Y1
        N = 10        ' Number of patterns to appear.

        Vx1! = Vx / N  'size of vector for one pattern
        Vy1! = Vy / N

        Sx! = X1 : Sy! = Y1    ' Starting coordinates.

        'Make sub vectors that make up pattern

        Vx2! = Vx1! / 2        ' 1/2 len, parallel to vector
        Vy2! = Vy1! / 2

        Vx3! = -Vy2!           ' 1/2 len, 270 deg to vector
        Vy3! = Vx2!

        Vx4! = Vy2!            ' 1/2 len, 90 deg to vector
        Vy4! = -Vx2!           '

        FOR Z = 1 TO N         ' # of patterns to make

          'Follow direct line to point B
          CALL MOVE.VECTOR( Sx!, Sy!, Vx2!, Vy2!, 7 )

          'Hook it 90 deg to right (270 deg)
          CALL MOVE.VECTOR( Sx!, Sy!, Vx3!, Vy3!, 7 )

          'Now follow parallel to direct line
          CALL MOVE.VECTOR( Sx!, Sy!, Vx2!, Vy2!, 7 )

          'Hook it 90 deg to left, getting back origional line
          CALL MOVE.VECTOR( Sx!, Sy!, Vx4!, Vy4!, 7 )

        NEXT Z

        DO
        LOOP WHILE LEN(INKEY$) = 0

        'Sub to move and draw our vector

SUB MOVE.VECTOR( Px!, Py!, Vx!, Vy!, Colour% ) STATIC


      Px = INT( Px! + 0.49 )
      Py = INT( Py! + 0.49 )

      Px! = Px! + Vx!
      Py! = Py! + Vy!

      Dx = INT( Px! + 0.49 )
      Dy = INT( Py! + 0.49 )

      LINE (Px,Py)-(Dx,Dy),Colour%

END SUB

>>> Continued to next message
===
 * SLMR 2.1a * On a clear disk you can seek forever