PointAngles.bas

#include "fbgfx.bi"

type coord
    x as integer
    y as integer
end type

function dotProduct(u as coord, v as coord) as double
    return (u.x * v.x) + (u.y * v.y)
end function

function norm(u as coord) as double
    return sqr((u.x*u.x) + (u.y*u.y))
end function

dim as coord a = type(260, 50)
dim as coord b = type(160, 100)

screenres 640, 480, 8

dim as coord c = type(1, 0) ' C is the unit vector pointing left

' Make b into a vector where the origin is at 'a', not (0, 0)
b.x = a.x-b.x
b.y = a.y-b.y

' Find the angle between b and c
dim as double angle = acos(dotProduct(c, b)/(norm(c)*norm(b)))

const PI = atn(1)/45
#define RadToAng( _R ) (_R)/PI
do
    if multikey(fb.SC_LEFT) then
        b.x -= 1
    end if
    if multikey(fb.SC_RIGHT) then
        b.x += 1
    end if
    if multikey(fb.SC_UP) then
        b.y -= 1
    end if
    if multikey(fb.SC_DOWN) then
        b.y += 1
    end if

    screenlock

    cls
    angle = acos(dotProduct(c, b)/(norm(c)*norm(b)))
    locate(0, 0)
    print "a = (";a.x;",";a.y;")"
    print "b = (";b.x;",";b.y;")"
    print "c = (";c.x;",";c.y;")"
    print "angle =";RadToAng(angle);" degrees"

    ' Line from origin pointing to other point
    if b.y > 0 then
        line(a.x, a.y)-step(10*cos(angle), 10*sin(angle)), &H8
    else
        line(a.x, a.y)-step(10*cos(angle), -10*sin(angle)), &H8
    end if

    pset(a.x, a.y), &HF         ' Origin (where we rotate from)
    pset(a.x+b.x, a.y+b.y), &HE ' Point we're pointing to

    screenunlock

    sleep 10,1
loop until multikey(1)


sleep