Collision Detection with distance from point to line segment

[PhOtO!]

Me and my partner are working on this air hockey game for our final project (Air Hockey). We're almost done our program but we have problems with our collision detection (which is using distance between 2 circles) when users move thier paddle too fast. This is because the computer can not pick up on all of the movements of the mouse.
So, we are going to make a variable for the previous mouse position and a variable for the current mouse position. Then we are going to make an imaginary line from those two points (y = mx + b). Now, we want to see if the distance from our ball (another circle) to the closest point on our imaginary line segment is less than 50 (then the mouse has gone through the ball). However, we don't know the formula for the distance from a point to a line segment. Also, could you tell us if this will work or if there are much more efficent ways.

If you need the source code, just tell me.

Thanks for any help

[PhOtO!]

Actually, here is the source code :

code:

setscreen ("graphics:700;max,position:center;center,nobuttonbar,offscreenonly") var x, y, button, paddlex, paddley := 100 var cpux, cpuy := maxx div 2 % x and y value of paddle var ballx, bally : real := 100 % x and y value of ball var dx, dy : real := 0 % difference in x and y value for ball var cpuxd, cpuyd := 1 % difference in x and y value for comp paddle var maxspeed := 3 % maximum speed for comp paddle var numofhits : int := 0 var maxballspeed : int := 3 var a, b : int := 0 var paddler : int := 35 var ballr : int := 30 cpuy := maxy - 100 ballx := maxx div 2 bally := maxy div 2 proc drawscreen     drawfillbox (0, 0, maxx, maxy, red) % Border     drawfillbox (20, 20, maxx - 20, maxy - 20, 1) %Background     drawfillbox (20, maxy div 2 - 150, maxx - 20, maxy div 2 - 155, red) % bottom line from center     drawfillbox (20, maxy div 2 + 150, maxx - 20, maxy div 2 + 155, red) % top line from center     drawfillbox (20, 20, maxx - 20, 30, grey) % bottom     drawfillbox (maxx div 2 - 70, 20, maxx div 2 + 70, 40, black) % net     drawfillbox (20, maxy - 20, maxx - 20, maxy - 30, grey) % top     drawfillbox (maxx div 2 - 70, maxy - 20, maxx div 2 + 70, maxy - 40, black) % net     drawfillbox (20, maxy div 2, maxx - 20, maxy div 2 + 5, grey) %center line     %Center Circle     drawfilloval (maxx div 2, maxy div 2, 80, 80, grey)     drawfilloval (maxx div 2, maxy div 2, 70, 70, 1)     drawfilloval (maxx div 2, maxy div 2, 10, 10, grey)     % Left top circle     drawfilloval (maxx div 2 - 200, maxy div 2 + 250, 70, 70, grey)     drawfilloval (maxx div 2 - 200, maxy div 2 + 250, 60, 60, 1)     % Right top circle     drawfilloval (maxx div 2 + 200, maxy div 2 + 250, 70, 70, grey)     drawfilloval (maxx div 2 + 200, maxy div 2 + 250, 60, 60, 1)     % Right bottom     drawfilloval (maxx div 2 + 200, maxy div 2 - 250, 70, 70, grey)     drawfilloval (maxx div 2 + 200, maxy div 2 - 250, 60, 60, 1)     % Left bottom     drawfilloval (maxx div 2 - 200, maxy div 2 - 250, 70, 70, grey)     drawfilloval (maxx div 2 - 200, maxy div 2 - 250, 60, 60, 1)     %ball     if ballx > 35 and ballx < maxx - 35 and bally > 35 and bally < maxy - 35 then         drawfilloval (round (ballx), round (bally), ballr, ballr, black)     end if     %paddle     drawfilloval (paddlex, paddley, paddler, paddler, 12)     drawfilloval (cpux, cpuy, paddler, paddler, 12)     locate (1, 1)     put "Computer score:", a     locate (1, 30)     put "Player score:", b     View.Update end drawscreen proc detection     %if the ball hits either end then make it go in the opposite direction     if ballx > maxx - 35 then         dx := abs (dx) * -1     elsif ballx < 35 then         dx := abs (dx)     end if     %if the ball hits either side then make it go in the opposite direction     if bally > maxy - 35 then         dy := abs (dy) * -1     elsif bally < 35 then         dy := abs (dy)     end if         %if the distance between the ball and the paddle is less than 50 (touching) then change direction     if abs (sqrt ((ballx - paddlex) ** 2 + (bally - paddley) ** 2)) < 50 then         dx := (ballx - paddlex) / 10    %the ball will go back in the same direction at the same         dy := (bally - paddley) / 10    %angle at which it came into the paddle     end if     if (sqrt ((ballx - cpux) ** 2 + (bally - cpuy) ** 2)) < paddler + ballr then         dx := (ballx - cpux) / 10         dy := (bally - cpuy) / 10         numofhits := numofhits + 1     end if end detection loop     if bally < maxy - 75 then         numofhits := 0     end if     if numofhits > 3 then         cpux := maxx div 2     end if     %USER PADDLE     mousewhere (x, y, button)     if y + paddler > maxy div 2 then  %if the mouse is above the center line, the paddle stays at center line         paddley := maxy div 2 - paddler     elsif y < paddler + 20 then         paddley := paddler + 20     else         paddley := y     end if     if x > maxx - paddler + 20 then    %if the mouse is off the screen to the right then make the paddle be at the         paddlex := maxx - (paddler + 20) %furthest point horizontally on the screen (maxx)     elsif x < paddler + 20 then     %**same as above but for the left side**         paddlex := paddler + 20     else         paddlex := x     end if     %BALL MOVEMENT     ballx += dx %make the ball move     bally += dy %""     %COMPUTER PADDLE     cpux := cpux + cpuxd % makes comp paddle move     if cpux > ballx then % checks if cpu x coordinate is greater than ball x coordinate         cpuxd := cpuxd - 1 % comp paddle x value moves negative direction     elsif             cpux < ballx then % checks if cpu x coordinate is less than ball x coordinate         cpuxd := cpuxd + 1 % comp paddle x value moves positive direction     end if     % Computer paddle speed doesn't go past assigned maximum speed     if cpuxd > maxspeed then %         cpuxd := maxspeed     elsif cpuxd < maxspeed * -1 then         cpuxd := maxspeed * -1     end if     % Keeps computer paddle inside the table     if cpux > maxx - 100 then         cpux := maxx - 100     elsif             cpux < 100 then         cpux := 100     end if     detection     if ballx > maxx div 2 - 70 and ballx < maxx div 2 + 70 and bally < 35 then         a := a + 1         ballx := maxx div 2         bally := maxy div 2         delay (500)     elsif ballx > maxx div 2 - 70 and ballx < maxx div 2 + 70 and bally > maxy - 35 then         b := b + 1         ballx := maxx div 2         bally := maxy div 2         delay (500)     end if     drawscreen end loop

[[Gandalf]]

Check out the Math.DistancePointLine() function in the Turing help files. Also, here are two topics/posts you may want to read:
this and
this

[PhOtO!]

I have version 4.01 so I don't have this funtion. Can you please post up the actual function?

[[Gandalf]]

Sure thing.

code:

function MathDistance (x1, y1, x2, y2 : real) : real     var dx : real := x1 - x2     var dy : real := y1 - y2     result sqrt (dx * dx + dy * dy) end MathDistance function MathDistancePointLine (px, py, x1, y1, x2, y2 : real) : real     var lineSize : real := MathDistance (x1, y1, x2, y2)     if lineSize = 0 then         result MathDistance (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 MathDistance (px, py, x1, y1)     elsif u > 1.0 then         result MathDistance (px, py, x2, y2)     else         var ix : real := x1 + u * (x2 - x1)         var iy : real := y1 + u * (y2 - y1)         result MathDistance (px, py, ix, iy)     end if end MathDistancePointLine

You will also need MathDistance because MathDistancePointLine makes use of it.

[PhOtO!]

Thanks alot Gandalf

We decided that we're gonna finish a simple space frogger game for the final project since we have many more glitches with the air hockey program.

But we'll continue working on that and post it up soon.

[upthescale]

how wud the space frogger werk? anyway awsome game

[PhOtO!]

It's just a simple frogger version. We didnt' add alot of things we planned to add. We'll probably post it up tommorow.