Displayscroll!

[Havie]

So - how do I use Displayscroll to move a section of the screen right or left. I get that it offsets each time but I can't seem to workout how to undo the offset to make the section move as one. Help!

[Havie]

So I worked this out. Basically, when you run your for next loop to change the values for the display scroll, you need to go to the value before the one you changed and subtract whatever you just added. This must reset the Copper to the correct place?

  For loop.q=50 To 100
        xpos.q(loop)+ax1 :xpos.q(loop-1)-ax1                                                                                                                 
  Next

Notice how it is loop-1!

So to set up three independent scrolling areas for simple non-overlapping parallax, I do this:

  For loop.q=50 To 100
        xpos.q(loop)+ax1 :xpos.q(loop-1)-ax1                                                                                                                    
  Next

  For loop.q=101 To 150
        xpos.q(loop)+2*ax1 :xpos.q(loop-1)-2*ax1
  Next

  For loop.q=151 To 255
        xpos.q(loop)+3*ax1 :xpos.q(loop-1)-3*ax1
  Next

And then you just run DisplayScroll 0,&xpos.q(0),&xpos.q(0)

Changing the numbers in the Displayscroll creates different effects and I have no idea why yet.

I'll put together a small demo and upload it later so you can see all the code in action and play with it yourself.

Seems fast!

[Havie]

P.S. Looks like I'm on my annual game program!

[Havie]

So here is a simple demo - three levels of parallax but using Displayscroll you could probably do 200!!!

WBStartup

;use a screen high sprite to hide screen corruption
LoadShape 1,"Graphics/hide": GetaSprite 0,1
LoadShape 2,"Graphics/backgroundtest"

;set up 32 lores screen 320x200
InitCopList 0,44,200,$5+$400,8,32,-4
;DisplayControls 0,0,$1c00,$0023


LoadPalette  0,"Palette/pal1.col"

Dim xpos.q(200); array for displayscroll


BLITZ

;make the image 640 pixels long to be a bit more interesting!
BitMap 0,640,200,5
BitMap 1,640,200,5

CreateDisplay 0
DisplayPalette 0,0

;Two bitmaps for double buffering
Use BitMap 0:Block 2,0,0:
Use BitMap 1:Block 2,0,0

DisplaySprite 0,0,0,0,0; displays the screen high sprite

db=0

While Joyb(0)=0


  ax1.q=Joyx(1)*-1; joystick left/right controls scroll


If RawStatus(1)=1 Then Stop

;three sections of the screen scrolling at different speeds
  For loop.q=28 To 89
     xpos.q(loop)+ax1 :xpos.q(loop-1)-ax1
  Next

  For loop.q=90 To 112
     xpos.q(loop)+2*ax1 :xpos.q(loop-1)-2*ax1
  Next

  For loop.q=113 To 196
     xpos.q(loop)+3*ax1 :xpos.q(loop-1)-3*ax1
  Next

; note - reset previous copper value in array (loop-1) stops the offset


VWait
DisplayBitMap db,0,0,0
DisplayScroll 0,&xpos.q(10),&xpos.q(10); this one command scrolls the whole display using the copper.  Amazing!

db=-db


Wend

I have also uploaded an LHA file with simple graphics etc. to the Zone if you just want to have a look. UnLHA it and the load into Blitz!

https://eab.abime.net/zone/Displayscrolldemo.lha

I hope this is helpful for someone.

Any comments,suggestions or errors pointed out are most welcome.