Tutorial: Basic POOL and realistic collision

[Tendulkar]

this is great! excellent work thoughtful

[gamer]

helo thoughtful btw GREAT JOB on this pool program, u see im kind of new to program so my question is, do you think u can explain to me how the collision part of the program works?? i understand the fact that u applied trig but how exactly did you do it?

[gamer]

heloo??

thoughtful can ya reply?

or anyone else who knows please tell me, i reli gota understand
thnx

[gamer]

still no reply??? omg

[Paul]

Thoughtful is not on Compsci very often, and don't triple post lol, Asian Sensation would be angry at you. Im sure whenever he gets on, he'll try and reply. You could always send him a PM.

[Tony]

you find the angle
you break it up into vector components (x and y)
you find total energy transfer from the collision
you use vector components as ratios to redestribute the energy after collision.

[gamer]

thnx

[evildaddy911]

i dont have gr11 math till next semester, can you explain what you mean by vector components?

[Raknarg]

It's actually physics... lets say you have a line. This line goes up by 3 and across by 4. Those woule be the x and y vector components: The change in x and the change in y.

Correect me if I'm wrong.

[evildaddy911]

so its like finding slope, but not actually finding the slope, cuz slope is change in y divided by change in x, but you dont do the dividing

[Raknarg]

Its basically trigonometry. Usually when you're working with vectors, you are given a bunch of distances with directions (ex. 35m[E25oS], or 25 meters, East 25 degrees to the South) and from that you calculate the overall displacement and the overall angle (compared from your starting point to your finishing point).

Of course, this is a really bad explaination. You should look it up:
http://zonalandeducation.com/mstm/physics/mechanics/vectors/introduction/introductionVectors.html
That seems promising.

[evildaddy911]

okay, so the vectors are really just horizontal/vertical distances.... and i puzzled out a quick screensaver-like program...
im not sure what you mean by displacement, but i think i could figure out the angle...
anyways, voila:

Turing:

var x, y, xv, yv : int var change_time : int := 10000 var last_change : int := -change_time x := Rand.Int (10, maxx - 10) y := Rand.Int (10, maxy - 10) xv := Rand.Int ((-5), 5) yv := Rand.Int ((-5), 5) loop     var now := Time.Elapsed     if now - last_change >= change_time then         xv := Rand.Int ((-5), 5)         yv := Rand.Int ((-5), 5)         last_change := now     end if     drawfilloval (x, y, 10, 10, white)     x := xv + x     y := y + yv     if x <= 10 or x >= maxx - 10 then         xv := xv * (-1)     end if     if y >= maxy - 10 or y <= 10 then         yv := yv * (-1)     end if     drawfilloval (x, y, 10, 10, black)     drawfilloval (x - 2, y, 1, 2, brightgreen)     drawfilloval (x + 2, y, 1, 2, brightgreen)     drawline (x - 3, y - 4, x + 3, y - 4, brightred)     delay (20) end loop

it draws a smiley face ball bouncing off the walls, and every 10 seconds it randomly changes the x and y vectors

[Raknarg]

That would work. You could even use angles:

Turing:

View.Set ("offscreenonly, graphics:700;700") const xPos := 350 const yPos := 350 var x, y, b : int := 0 % variables for the Mouse.Where var t : real % Theta, or the angle var bltx, blty, bltvx, bltvy : real := 0 % the bullet positions, and the amount the x and y changes var bltd : boolean := true % whether or not the bullet is live or dead loop     Mouse.Where (x, y, b)     if x = xPos and y > yPos then         t := 270     elsif x < xPos and y = yPos then         t := 0     elsif x = xPos and y < yPos then         t := 90     elsif x > xPos and y = yPos then         t := 180     elsif x = xPos and y = yPos then         t := 0     elsif x > xPos then         t := arctand ((y - yPos) / (x - xPos)) + 180     else         t := arctand ((y - yPos) / (x - xPos))     end if     % This thing here calculates your angle. It'll make sense if you've ever done vectors before. It uses the function tan-1. The ones before it are for mathematical correctness; you cannot divide anything by zero.         if b = 1 and bltd = true then % Only shoots when the bullet is dead and the button is clicked.         bltd := false         bltx := xPos - (40 * cosd (t)) % setting the position of the bullet         blty := yPos - (40 * sind (t)) % same         bltvx := -5 * cosd (t) % setting the change in x         bltvy := -5 * sind (t) % setting the change in y     end if         Draw.FillOval (xPos, yPos, 20, 20, blue)     Draw.ThickLine (xPos, yPos, xPos - round (40 * cosd (t)), yPos - round (40 * sind (t)), 4, 7) % This is important for drawing shapes according to an angle. You add onto the original postion. In the case of x, its the radius * cos(angle). For y it's radius * sin (angle)     if bltd = false then         Draw.FillOval (round (bltx), round (blty), 4, 4, brightred)         Draw.FillOval (round (bltx), round (blty), 2, 2, 7)         bltx += bltvx % Changes the bullet x position relative to the change in x         blty += bltvy % Changes the bullet y position relative to the change in y         if bltx > maxx or bltx < 0 or blty > maxy or blty < 0 then % If the bullet hits the edge, it dies             bltd := true         end if     end if     View.Update     cls end loop