Scroll speed?

MrGuppy · 16 October 2020, 15:25

Hi!

I'm trying to learn about scrolling.

Have made a horizontal scroll in one plane with 4 colors.

Works fine but the speed is way to fast. I'm not sure how to attack the problem.

Should I delay the blitter in some way? Put some time delays somewhere?

..::MrGuppy

ross · 16 October 2020, 16:21

Quote:

Originally Posted by MrGuppy

Have made a horizontal scroll in one plane with 4 colors.

You probably meant one playfield and two bitplanes (or you need to explain me how to do it

)

Quote:

Works fine but the speed is way to fast. I'm not sure how to attack the problem.

Should I delay the blitter in some way? Put some time delays somewhere?

You simply need to sync you scroll with the video vertical frequency (or sub-multiples).

There are many ways to do this, it depends on how you wrote your code.

MrGuppy · 16 October 2020, 16:43

Yes, one playfield and two bitplanes!

What's "sub-multiples", new word for me?

mcgeezer · 16 October 2020, 18:37

To move at 1/2 speed...

Code:

	add.l	#$8000,xPos
	move.w	xPos,Scrolling_Position...
	
xPos:	dc.l	0

To move at 1/4 speed...

Code:

	add.l	#$4000,xPos
	move.w	xPos,Scrolling_Position...
	
xPos:	dc.l	0

To move at 1/8 speed...

Code:

	add.l	#$2000,xPos
	move.w	xPos,Scrolling_Position...
	
xPos:	dc.l	0

and so on...

phx · 16 October 2020, 19:17

Quote:

Originally Posted by MrGuppy

What's "sub-multiples", new word for me?

I think he means syncing to multiples of one 50Hz frame, i.e. running the game in 25Hz or 12.5Hz.

ross · 16 October 2020, 19:59

Quote:

Originally Posted by phx

I think he means syncing to multiples of one 50Hz frame, i.e. running the game in 25Hz or 12.5Hz.

Or 16.67Hz

MrGuppy · 18 October 2020, 21:12

Thanks for the help!

I'll try both approaches and see what will be best for me!

..::Mr Guppy

defor · 18 October 2020, 22:31

Or have hires screen for horizontal scroll, image of 2x width and enjoy "subpixel" scrolling :-) (same for vertical with interlace)

MrGuppy · 26 October 2020, 18:04

Finally got the solution!

Probably there are several solutions for this problem but in this case I have set the speed for the blitter in reg. BLTCON0($dff040).

You can set the speed from $1 to $f.

Below I have set the speed to $1, the slowest.

bsr.w BlitWait ; First, check if Blitter is busy?
move.l #$19f00002,$dff040 ; $dff040 = BLTCON0, Blitter control reg 0
; #$1xxxxxxx -> Speed, 1 to f(15)
; #$x9f0xxxx -> A source and D destination are set, B and C ignored
; #$xxxxxxx2 -> Descending mode, scrolling from right to left
; #$xxxxxxx0 -> Ascending mode, scrolling from left to right

16 October 2020, 15:25	#1
MrGuppy Registered User Join Date: May 2019 Location: Stenungsund/Sweden Posts: 22	Scroll speed? Hi! I'm trying to learn about scrolling. Have made a horizontal scroll in one plane with 4 colors. Works fine but the speed is way to fast. I'm not sure how to attack the problem. Should I delay the blitter in some way? Put some time delays somewhere? ..::MrGuppy

16 October 2020, 18:37	#4
mcgeezer Registered User Join Date: Oct 2017 Location: Sunderland, England Posts: 2,702	To move at 1/2 speed... Code: add.l #$8000,xPos move.w xPos,Scrolling_Position... xPos: dc.l 0 To move at 1/4 speed... Code: add.l #$4000,xPos move.w xPos,Scrolling_Position... xPos: dc.l 0 To move at 1/8 speed... Code: add.l #$2000,xPos move.w xPos,Scrolling_Position... xPos: dc.l 0 and so on...

26 October 2020, 18:04	#9
MrGuppy Registered User Join Date: May 2019 Location: Stenungsund/Sweden Posts: 22	Finally got the solution! Probably there are several solutions for this problem but in this case I have set the speed for the blitter in reg. BLTCON0($dff040). You can set the speed from $1 to $f. Below I have set the speed to $1, the slowest. bsr.w BlitWait ; First, check if Blitter is busy? move.l #$19f00002,$dff040 ; $dff040 = BLTCON0, Blitter control reg 0 ; #$1xxxxxxx -> Speed, 1 to f(15) ; #$x9f0xxxx -> A source and D destination are set, B and C ignored ; #$xxxxxxx2 -> Descending mode, scrolling from right to left ; #$xxxxxxx0 -> Ascending mode, scrolling from left to right Last edited by MrGuppy; 26 October 2020 at 19:41.

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16 October 2020, 16:43	#3
MrGuppy Registered User Join Date: May 2019 Location: Stenungsund/Sweden Posts: 22	Yes, one playfield and two bitplanes! What's "sub-multiples", new word for me?

18 October 2020, 21:12	#7
MrGuppy Registered User Join Date: May 2019 Location: Stenungsund/Sweden Posts: 22	Thanks for the help! I'll try both approaches and see what will be best for me! ..::Mr Guppy

18 October 2020, 22:31	#8
defor Registered User Join Date: Jun 2020 Location: Brno Posts: 90	Or have hires screen for horizontal scroll, image of 2x width and enjoy "subpixel" scrolling :-) (same for vertical with interlace)

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