Mouse co-ordinate detection (Air Hockey)

[richcash]

Not every movement of the mouse can be detected by the computer especially when you move the mouse really fast. This is a problem considering that I have a mouse-controlled paddle in the Air Hockey game I am making. Are there any suggestions on how I can work around this. Here's my code so far.

code:

setscreen ("graphics:700;max,position:center;center,nobuttonbar,offscreenonly") var x, y, button, paddlex, paddley, lastballx, lastbally := 100 var ballx, bally : real := 100 var power := 5 var dx, dy : real := 1 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     drawfilloval (round (ballx), round (bally), 15, 15, 7)     %paddle     drawfilloval (paddlex, paddley, 35, 35, 12)     View.Update     cls end drawscreen proc detection     if ballx > maxx or ballx < 0 then         dx *= -1     end if     if bally > maxy or bally < 0 then         dy *= -1     end if     if abs (sqrt ((ballx - paddlex) ** 2 + (bally - paddley) ** 2)) < 35 then         dx := (ballx - paddlex) / 10         dy := (bally - paddley) / 10     end if end detection loop     mousewhere (x, y, button)     if y > maxy div 2 then         paddley := maxy div 2     else         paddley := y     end if     if x > maxx then         paddlex := maxx     elsif x < 0 then         paddlex := 0     else         paddlex := x     end if     ballx += dx     bally += dy     detection     if abs (ballx - lastballx) > power or abs (bally - lastbally) > power then         lastballx := round (ballx)         lastbally := round (bally)         drawscreen     end if end loop

**As of now, when you move the mouse too fast, the collision detection is incorrect between puck and paddle or it might not even pick up the collision at all. Thanks for any help!

[TheOneTrueGod]

Well, since code moves linearly, the mouse's position will only be recorded at the *instant* that you use the command "mousewhere". Therefore, the only way to increase the mouse's accuracy is to put it right before the collision detection part, or to have multiple "mousewhere"s.

The second option might get kinda laggy if you have too many, or if you have them in a for loop, but its your choice. Either way, there is only a maximum degree of accuracy that you are going to get because of linear code.

[Cervantes]

This is a common problem, though more often found in detecting collisions between two fast moving objects, such as a bullet and a car, for instance.

One solution is to do some math to determine whether there is a collision. You know the start and end points of two shapes. If you do a little bit of math, you can determine whether there was a collision. This is harder than just determining whether the line segments that represent the motion of the two shapes intersect. It's not that easy because there is the element of time in question. By the time shape A has moved almost to its end point, shape B coould cross the path that shape A was on, but there is no collision because shape A is long gone.

You should read the "Circle-Circle Collisions - Clipping problem" thread.

[richcash]

Thanks for the help. I guess I can never get it perfectly accurate, but I will use some trig to identify the probable first point of collision (assuming that consecutive points of the mouse picked up by the computer that are not side-by-side are linearly connected).

[[Gandalf]]

Another approach you can take is to add the factor of realism into your game. When you are moving really fast from one point to another the paddle must be on the table in order for there to be a collision. If it's not on the table, you can assume no collision occured, but in your game the paddle is always on the table. Anyway, getting to the point, there is a limitation to how fast someone can drag the paddle on the table in reality, so you can incorporate this into your game. Instead of having the paddle pop to the new location on the screen, you can make it move there at whatever you choose to be the maximum velocity. This will allow you to easily keep track of the paddle at all times, and also have some realistic paddle movement.