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Cart #movement_2d-0 | 2020-04-22 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

I have been experimenting with player movement for a top-down 2D game. At the moment, I have "fixed" diagonal movement to be 0.7x the speed of straight-line movement, and also added friction so the character sprite slows down gradually.

The next step however is acceleration.

I'm wondering how a slow ramp into movement (acceleration) might be achieved using the lerping algorithm as introduced here: https://demoman.net/?a=animation-code-part-1

Does anyone have tips or a tutorial on how I could achieve this acceleration/deceleration??

Code for movement:

if (btn(➡️) and btn(⬆️)) then
        p.dx=p.speed*.707
        p.dy=0-(p.speed*.707)
    elseif (btn(➡️) and btn(⬇️)) then
        p.dx=p.speed*.707
        p.dy=p.speed*.707
    elseif (btn(⬅️) and btn(⬇️)) then
        p.dx=0-(p.speed*.707)
        p.dy=p.speed*.707
    elseif (btn(⬅️) and btn(⬆️)) then
        p.dx=0-(p.speed*.707)
        p.dy=0-(p.speed*.707)
    elseif (btn(⬆️)) then
        p.dy=0-p.speed
    elseif (btn(➡️)) then
        p.dx=p.speed
    elseif (btn(⬇️)) then
        p.dy=p.speed
    elseif (btn(⬅️)) then
        p.dx=0-p.speed
    end

 if not btnp(⬆️) and not btnp(⬇️) then
  p.dy*=friction
  if p.dy<0.01 and p.dy>-0.01 then
    p.dy=0
    end
 end
 if not btnp(➡️) and not btnp(⬅️) then
  p.dx*=friction
  if p.dx<0.01 and p.dx>-0.01 then
   p.dx=0
  end
 end

 p.x+=p.dx
 p.y+=p.dy
 p.x=mid(0,p.x,124) 
 p.y=mid(0,p.y,124) 
P#75146 2020-04-22 01:40

2

Hello,

you were actually most of the way there, all you need to change in your current code to have acceleration is to add or subtract a value to the speed instead of reassigning it each frame. I wrote up some example code that accomplishes that while streamlining things, and also resets the speed to zero if you hit a screen edge. You'll probably need to tweak some values like friction, as I don't know the values you're using at present.

pdx=0 pdy=0

b=btn()%16 --outputs bit values for directional buttons(5,6,9,or 10 means diagonals)
accel=.1
friction=.94
if (b==5 or b==6 or b==9 or b==10) accel=.0707
if (btn(⬅️)) pdx-=accel
if (btn(➡️)) pdx+=accel
if (btn(⬆️)) pdy-=accel
if (btn(⬇️)) pdy+=accel
if (not btn(⬅️) and not btn(➡️)) pdx*=friction
if (not btn(⬆️) and not btn(⬇️)) pdy*=friction
if (abs(pdx)<.07) pdx=0
if (abs(pdy)<.07) pdy=0
px+=pdx
py+=pdy
if (px>122) px=122 pdx=0
if (px<0) px=0 pdx=0
if (py>122) py=122 pdy=0
if (py<0) py=0 pdy=0
P#75160 2020-04-22 13:28 ( Edited 2020-04-22 15:36)

Thanks for replying! I really appreciate it.

b=btn()%16 --outputs bit values for directional buttons(5,6,9,or 10 means diagonals) accel=.1 friction=.94 if (b==5 or b==6 or b==9 or b==10) accel=.0707

Oh my goodness what is this magic?!?! So many tokens saved <3 Thank you for showing me this!

I have changed my code and it works!

Cart #movement_2d-1 | 2020-04-22 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

Next: I'll try and implement a "quick turn" style movement so the player can turn back quickly (like smash bros when you let go of the stick before moving in the opposite direction 😉 )

Again, I'm so very grateful or you help here. 🙇

James/Cheapshot

P#75178 2020-04-22 22:51
1

Glad I could help. I learned about the btn() feature and how it outputs button bit values if no arguments are entered from reading about optimization strategies for Tweetcarts. There are definitely some cool optimization strategies available if you dig into the system memory a little bit instead of always going with the standard functions.

Oh, one other thing I thought of, if you're noticing the character gets moving too fast, you might want to limit its maximum speed, using something like this.

max=3
if (abs(pdx)>max) pdx=mid(-max,pdx,max)
if (abs(pdy)>max) pdy=mid(-max,pdy,max)

James/JadeLombax =)

P#75189 2020-04-23 00:29 ( Edited 2020-04-23 00:43)

Yes! I implemented that straight away, too actually. (Great minds eh? ;) )

P#75190 2020-04-23 00:42

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