Log In  1  So I'm relatively new to coding, so I thought Pico-8 would be good to fiddle around with.
So after playing a few games and messing with a few of the demo's code, I found a problem.
Sometimes, in the bounce demo which I modified, when you bounce the velocity y of the ball
would suddenly stay at 0 mid-air. I don't know why can anyone help? ```-- bouncy ball demo -- by zep -- modified by help_plz size = 10 ballx = 64 bally = 80 floor_y = 100 bounce_per_sec = 0 -- starting velocity velx =0 vely =0 frame=0 lag=0 offset=3 bounce=false collision=false function _draw() cls(1) map(0,0,0,100,16,1) print("press ❎ to bump", 32,10, 6) --rectfill(0,floor_y,2227,127,8) --circfill(ballx,bally,size,clr) if vely < 5.5 and vely > -4 then lag=vely end spr(1,ballx-offset-velx, bally-4-lag) spr(17,ballx-10,bally-10,2.75,2.75) print("x:"..ballx, 20,26) print("y:"..bally, 20,32) print("b_p/s"..bounce_per_sec, 20,38) print("vx:"..velx, 20,44) print("vy:"..vely, 20,50) print("col:"..(collision and 'true' or 'false'),20,56) --print("cx:"..camerax, 20+ballx,56,1) --print("cy:"..cameray, 20+ballx,62) end function _update60() offset=4 collision=false if bally < 0 then cameray=flr(bally)-64-flr(vely) end if bally > 10 then cameray=0 end camera(camerax, cameray) frame+=1 if frame==60 then bounce_per_sec = 0 end if frame==60 then frame = 0 end if ballx+velx < 0+size or ballx+velx > 128-size then -- bounce on side! sfx(1) velx *= -0.8 else ballx += velx end --==================-- -- move ball up/down if bally+vely >= floor_y-size then -- bounce on floor bounce_per_sec+=1 vely = vely * -0.8 collision = true sfx(0) else bally += vely end --so the ball doesn't bounce forever, and instead stops if bounce_per_sec >= 5.5 then vely = 0 end -- gravity if vely > 0 or vely < 0 then vely += 0.2 end --====================-- if btn(0) then offset=8 end if btn(1) then offset=-1 end if (btnp(5)) then vely = 5 sfx(2) if btn(0) then velx=-4 end if btn(1) then velx=4 end end end ```
P#57026 2018-09-24 00:31 ( Edited 2018-09-24 06:56)

:: Davbo  ``` --so the ball doesn't bounce forever, and instead stops if bounce_per_sec >= 5.5 then vely = 0 end -- gravity if vely > 0 or vely < 0 then vely += 0.2 end```

Your gravity check misses out 0, so if vely is 0 gravity is not applied. So I'd guess you want to check for a while number in bounces_per_sec instead of a decimal since it does look like in that gif the ball does bounce five and a half times before stopping.
When I do gravity I use an 'on_ground' Boolean to control if gravity is applied or not, I would recommend doing that instead of 0 having odd behaviour

P#57027 2018-09-24 02:33 ( Edited 2018-09-24 06:33)
:: Davbo  So yeah I'd have something like

• apply gravity only if on_ground is false.
• start with on_ground as true, then when the bouncing starts set it to false
• have some kind of 'bounces_till_stop' variable and every time the ball hits the ground reduce it by 1
• when the ball hits the ground and 'bounces_till_stop' is 0, set on_ground to true again.

It'll need a little tweaking but something like that. You probably want some terminal velocity as well.

P#57028 2018-09-24 02:56 ( Edited 2018-09-24 06:56)