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Slower horizontal scrolling?

Retro Lord

By Retro Lord
in batari Basic

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Retro Lord Moonsweeper

Retro Lord

Posted
Posted

Fiddling with a sideproject, a homage of Adventure Island for the NES and I was wondering, how do I slow down the horizontal scrolling?

   set kernel_options player1colors playercolors pfcolors

   dim rand16 = z

   pfhline 8 5 23 on

   COLUPF = $CE



 playfield:
 ................................
 ................................
 .......X...X.............X...X..
 ......X.XXX.X...........X.XXX.X.
 .........X.................X....
 .........X.................X....
 .........X.................X....
 .........X.................X....
 .........X.................X....
 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
end





  rem POSSIBLY INEFFICIENT CODE, SEPARATE COLOR INFO FOR EACH FRAME...


   player0color:
    $3E
    $3E
    $3E
    $D8
    $3E
    $3E
    $3E
    $3E
    $3E
    $3E
    $3E
    $3E
    $3E
    $0E
    $0E
    $0E
end


   player1:
   %00000000
   %00000011
   %11111001
   %00011111
   %10011111
   %11111111
   %00000011
   %00000011
   %00000011
   %11000011
   %11111111
   %10011111
   %11111111
end
   player1x = 255 : player1y = 255

__Main_Loop


  f=f+1

  if f = 10 then player0:
        %00011100
        %00011000
        %00011000
        %00011100
        %00000100
        %00110110
        %01110110
        %01101100
        %01111000
        %00111100
        %00111000
        %00111110
        %00110100
        %00111111
        %00111100
        %00111100
end
   player0x = 40 : player0y = 72

  if f = 20 then player0:
        %01000011
        %01100110
        %00111100
        %00000100
        %00110100
        %00110100
        %01101110
        %01101110
        %01111000
        %00111100
        %00111000
        %00111110
        %00110100
        %00111111
        %00111100
        %00111100
end

 if f=20 then f=0

   pfcolors:
   $D6
   $D6
   $D6
   $D6
   $FC
   $FC
   $FC
   $FC
   $FC
   $D6
   $FC
end

   if joy0up then player0y=player0y-1
   if joy0down then player0y=player0y+1
   if joy0right then pfscroll left


   drawscreen

   goto __Main_Loop

DEMO - default.bas.bin

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Random Terrain Quadrunner

+Random Terrain

Posted
Posted

Here's one way to do it:

   set kernel_options player1colors playercolors pfcolors

   dim _Scroll_Control = a.b
   dim rand16 = z


   COLUPF = $CE



 playfield:
 ................................
 ................................
 .......X...X.............X...X..
 ......X.XXX.X...........X.XXX.X.
 .........X.................X....
 .........X.................X....
 .........X.................X....
 .........X.................X....
 .........X.................X....
 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
end





  rem POSSIBLY INEFFICIENT CODE, SEPARATE COLOR INFO FOR EACH FRAME...


   player0color:
    $3E
    $3E
    $3E
    $D8
    $3E
    $3E
    $3E
    $3E
    $3E
    $3E
    $3E
    $3E
    $3E
    $0E
    $0E
    $0E
end


   player1:
   %00000000
   %00000011
   %11111001
   %00011111
   %10011111
   %11111111
   %00000011
   %00000011
   %00000011
   %11000011
   %11111111
   %10011111
   %11111111
end
   player1x = 255 : player1y = 255

__Main_Loop


  f=f+1

  if f = 10 then player0:
        %00011100
        %00011000
        %00011000
        %00011100
        %00000100
        %00110110
        %01110110
        %01101100
        %01111000
        %00111100
        %00111000
        %00111110
        %00110100
        %00111111
        %00111100
        %00111100
end
   player0x = 40 : player0y = 72

  if f = 20 then player0:
        %01000011
        %01100110
        %00111100
        %00000100
        %00110100
        %00110100
        %01101110
        %01101110
        %01111000
        %00111100
        %00111000
        %00111110
        %00110100
        %00111111
        %00111100
        %00111100
end

 if f=20 then f=0

   pfcolors:
   $D6
   $D6
   $D6
   $D6
   $FC
   $FC
   $FC
   $FC
   $FC
   $D6
   $FC
end

   if joy0up then player0y=player0y-1
   if joy0down then player0y=player0y+1
   if !joy0right then goto __Skip_JR
   _Scroll_Control = _Scroll_Control + 0.45
   if _Scroll_Control > 1 then pfscroll left : _Scroll_Control = 0
__Skip_JR

   drawscreen

   goto __Main_Loop

_

Right now it is scrolling at 0.45. If you want it to scroll faster, use a larger number such as 0.56 or 0.62 or 0.70 or whatever (I just picked some random numbers). If you want it even slower, use a smaller number such as 0.30 or 0.28 or 0.15 or whatever (I just picked some random numbers).

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SpiceWare Quadrunner

+SpiceWare

Posted
Posted (edited)

This doesn't look quite right:

 

   _Scroll_Control = _Scroll_Control + 0.45
   if _Scroll_Control > 1 then pfscroll left : _Scroll_Control = 0
it should be

   _Scroll_Control = _Scroll_Control + 0.45
   if _Scroll_Control >= 1 then pfscroll left : _Scroll_Control = _Scroll_Control - 1.0
With the original routine the scrolling would always happen every 3rd frame if the scroll value was between 0.3333 and 0.5, and every 2nd frame if the value was 0.50 thru 1.0. Edited by SpiceWare
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Random Terrain Quadrunner

+Random Terrain

Posted
Posted

This doesn't look quite right:

 

   _Scroll_Control = _Scroll_Control + 0.45
   if _Scroll_Control > 1 then pfscroll left : _Scroll_Control = 0
it should be

   _Scroll_Control = _Scroll_Control + 0.45
   if _Scroll_Control >= 1 then pfscroll left : _Scroll_Control = _Scroll_Control - 1.0
With the original routine the scrolling would always happen every 3rd frame if the scroll value was between 0.3333 and 0.5, and every 2nd frame if the value was 0.50 thru 1.0.

 

 

Thanks.

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Random Terrain Quadrunner

+Random Terrain

Posted
Posted

I don't know why I decided to waste a variable, though. I guess it's because I was just working with fixed point variables. This is probably a better way to do it:

_

   set kernel_options player1colors playercolors pfcolors

   dim _Scroll_Control = a
   dim rand16 = z


   COLUPF = $CE



 playfield:
 ................................
 ................................
 .......X...X.............X...X..
 ......X.XXX.X...........X.XXX.X.
 .........X.................X....
 .........X.................X....
 .........X.................X....
 .........X.................X....
 .........X.................X....
 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
end





  rem POSSIBLY INEFFICIENT CODE, SEPARATE COLOR INFO FOR EACH FRAME...


   player0color:
    $3E
    $3E
    $3E
    $D8
    $3E
    $3E
    $3E
    $3E
    $3E
    $3E
    $3E
    $3E
    $3E
    $0E
    $0E
    $0E
end


   player1:
   %00000000
   %00000011
   %11111001
   %00011111
   %10011111
   %11111111
   %00000011
   %00000011
   %00000011
   %11000011
   %11111111
   %10011111
   %11111111
end
   player1x = 255 : player1y = 255

__Main_Loop


  f=f+1

  if f = 10 then player0:
        %00011100
        %00011000
        %00011000
        %00011100
        %00000100
        %00110110
        %01110110
        %01101100
        %01111000
        %00111100
        %00111000
        %00111110
        %00110100
        %00111111
        %00111100
        %00111100
end
   player0x = 40 : player0y = 72

  if f = 20 then player0:
        %01000011
        %01100110
        %00111100
        %00000100
        %00110100
        %00110100
        %01101110
        %01101110
        %01111000
        %00111100
        %00111000
        %00111110
        %00110100
        %00111111
        %00111100
        %00111100
end

 if f=20 then f=0

   pfcolors:
   $D6
   $D6
   $D6
   $D6
   $FC
   $FC
   $FC
   $FC
   $FC
   $D6
   $FC
end

   if joy0up then player0y=player0y-1
   if joy0down then player0y=player0y+1
   if !joy0right then goto __Skip_JR
   if _Scroll_Control = 4 then pfscroll left : _Scroll_Control = 0 : goto __Skip_JR
   _Scroll_Control = _Scroll_Control + 1
__Skip_JR

   drawscreen

   goto __Main_Loop

_

Just change "if _Scroll_Control = 4" to a lower or higher number to change the speed.

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SpiceWare Quadrunner

+SpiceWare

Posted
Posted

I think this is a great approach if the speed will be constant. If the speed will be changed at runtime there might be a more linear way to do it with a single variable.

Using assembly, I'd do something like this for a constant speed:

 

SPEED = $64

ScrollCheck:
    clc
    lda #SPEED
    adc ScrollControl ; RAM variable
    sta ScrollControl
    bcc NoScroll
    ; Carry flag was set so we need to scroll
    ; scroll logic goes here
NoScroll:

If I wanted the speed to be variable I'd do this:

ScrollCheck:
    clc
    lda CurrentSpeed ; RAM variable
    adc ScrollControl ; RAM variable
    sta ScrollControl
    bcc NoScroll
    ; Carry flag was set so we need to scroll
    ; scroll logic goes here
NoScroll:
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bogax Dragonstomper

bogax

Posted
Posted

Nice. Just wrap it in an asm statement and you've got linear scrolling speed control with a single variable in bB.

 

 

or you could just do it in bB

 

 

 temp1 = scroll_distance
 scroll_distance = scroll_distance + scroll_speed
 if scroll_distance < temp1 then scroll

 

 

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