[source] circle - line segment collision detection

[zylum]

this is something I recently started working on. it still needs work with collisions at the vertices but that shouldnt be too hard to take care of. this could be useful if you want to make a pinball game.

code:

View.Set ("offscreenonly,graphics:600;600,nobuttonbar") type Point :     record         x, y : real     end record fcn closestPoint (p1, p2, p3 : Point) : Point     var ret : Point     var u : real := ((p3.x - p1.x) * (p2.x - p1.x) + (p3.y - p1.y) * (p2.y - p1.y)) / Math.Distance (p1.x, p1.y, p2.x, p2.y) ** 2     ret.x := p1.x + u * (p2.x - p1.x)     ret.y := p1.y + u * (p2.y - p1.y)     if ret.x < min (p1.x, p2.x) then         if p1.x < p2.x then             ret := p1         else             ret := p2         end if     elsif ret.x > max (p1.x, p2.x) then         if p1.x > p2.x then             ret := p1         else             ret := p2         end if     end if     result ret end closestPoint fcn dist (p1, p2 : Point) : real     result Math.Distance (p1.x, p1.y, p2.x, p2.y) end dist fcn whatAngle (x1, y1, x2, y2 : real) : real     var dx, dy, ratio, angle : real     dx := x2 - x1     dy := y2 - y1     if dx not= 0 then         ratio := dy / dx     else         ratio := dy / 0.00001     end if     angle := arctand (abs (ratio))     if dx < 0 then         angle := 180 - angle     end if     if dy < 0 then         angle := 360 - angle     end if     result round (angle) end whatAngle proc drawLine (p1, p2 : Point)     Draw.Line (round (p1.x), round (p1.y), round (p2.x), round (p2.y), black)     Draw.FillOval (round (p1.x), round (p1.y), 3, 3, white)     Draw.Oval (round (p1.x), round (p1.y), 3, 3, black)     Draw.FillOval (round (p2.x), round (p2.y), 3, 3, white)     Draw.Oval (round (p2.x), round (p2.y), 3, 3, black) end drawLine const POINTS := 8 const RADIUS := 20 const GRAVITY := 0.001 var points : array 1 .. POINTS of Point for i : 1 .. POINTS     %points (i).y := Rand.Int (maxy div 2 - 10, maxy div 2 + 10) - 100     %points (i).x := (maxx / (POINTS - 1)) * (i - 1)     points (i).x := cosd ((-i + 1) * (180 / (POINTS - 1))) * (maxx div 2) + maxx div 2     points (i).y := sind ((-i + 1) * (180 / (POINTS - 1))) * (maxx div 2) + maxy div 2 end for var p, d, V, P, Z : Point var vx, vy, angle, mag, s : real := 0 p.x := maxx p.y := maxy div 2 + 50 Z.x := 0 Z.y := 0 vx := -0.3 loop     for i : 1 .. POINTS - 1         drawLine (points (i), points (i + 1))         Draw.Oval (round (p.x), round (p.y), RADIUS, RADIUS, black)         d := closestPoint (points (i), points (i + 1), p)         if dist (p, d) <= RADIUS then             s := Math.Distance (0, 0, vx, vy)             angle := whatAngle (0, 0, -vx, -vy) - (whatAngle (points (i + 1).x, points (i + 1).y, points (i).x, points (i).y) + 90)             angle := (whatAngle (points (i + 1).x, points (i + 1).y, points (i).x, points (i).y) + 90) - angle             vx := cosd (angle) * s             vy := sind (angle) * s         end if         %drawLine (p, closestPoint (points (i), points (i + 1), p))     end for     if p.x <= RADIUS| p.x >= maxx - RADIUS then         p.x := max (RADIUS, min (maxx - RADIUS, p.x))         vx *= -1     elsif p.y >= maxy - RADIUS then         p.x := maxy - RADIUS         vy *= -1     end if     p.x += vx     p.y += vy     vy -= GRAVITY     locate (1, 1)     put "X: ", p.x, " Y: ", p.y     put "VX: ", vx, " VY: ", vy     put angle     View.Update     cls end loop

[[Gandalf]]

Very nice! What else is there to say... No gaping bugs that I can see.

Just one thing... And I may be being completely ignorant to say this since I have not taken the time to understand your code, but... Could not such a collision be detected via Math.DistancePointLine()?

Here is the code for that function (inside the Math module) just in case:

code:

%     % Calculate the distance between a point and a line segment     %     function DistancePointLine (px, py, x1, y1, x2, y2 : real) : real         var lineSize : real := Distance (x1, y1, x2, y2)         if lineSize = 0 then             result Distance (px, py, x1, y1)         end if         var u : real := ((px - x1) * (x2 - x1) +             (py - y1) * (y2 - y1)) / (lineSize * lineSize)         if u < 0.0 then             result Distance (px, py, x1, y1)         elsif u > 1.0 then             result Distance (px, py, x2, y2)         else             var ix : real := x1 + u * (x2 - x1)             var iy : real := y1 + u * (y2 - y1)             result Distance (px, py, ix, iy)         end if     end DistancePointLine

[jamonathin]

This is very cool. I too haven't taken too much time in trying to figure it out (maybe you could comment a little ). From this model you could almost make a pinball game, except for the simple fact that this model represents a perfect machine and never seems to die down. As a matter of fact, lets speed things up and go:

vy -= GRAVITY * 100

It's . . more than perfect!!! AMAZING!! lol

Very well done zylum.

[zylum]

hmm... i didnt know that function exists . but wow, they use the exact same method that i use, the only difference is that i return the point that is closest to the ball.. this helps me with the collision reaction. also, they uses a slightly different method than me to check whether the point is on the line segment..