Perihelion tutorial 7 - Revision history

>Wongck at 03:33, 19 February 2012

2012-02-19T03:33:30Z

← Older revision		Revision as of 23:33, 18 February 2012
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	Last edited 2002-06-14		Last edited 2002-06-14
			<br/><br/>
			Go back to [[Perihelion tutorial 6]]<br/>
			Proceed to [[Perihelion tutorial 8]]

	[[Category: Perihelions Atari ST M68000 tutorial]]		[[Category: Perihelions Atari ST M68000 tutorial]]

>Wongck at 14:34, 12 October 2011

2011-10-12T14:34:13Z

← Older revision		Revision as of 10:34, 12 October 2011
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	Last edited 2002-06-14		Last edited 2002-06-14
	[[Category:~~Category~~ Perihelions Atari ST M68000 tutorial]]		[[Category: Perihelions Atari ST M68000 tutorial]]
	~~[[Category:Programming]]~~
	~~[[Category:Assembly Language~~]]

>Wongck at 10:07, 30 August 2011

2011-08-30T10:07:23Z

Show changes

>Silver Surfer: clean up

2009-05-03T15:38:45Z

clean up

← Older revision		Revision as of 11:38, 3 May 2009
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	[[Category:Category Perihelions Atari ST M68000 tutorial]]		[[Category:Category Perihelions Atari ST M68000 tutorial]]
	[[Category:Programming]]		[[Category:Programming]]
			[[Category:Assembly Language]]

>Silver Surfer: clean up

2009-05-03T15:33:48Z

clean up

← Older revision		Revision as of 11:33, 3 May 2009
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	~~[[Category:Category Perihelions Atari ST M68000 tutorial]]~~

	The Atari ST M68000 tutorial part 7 â€“ on scrollers		The Atari ST M68000 tutorial part 7 â€“ on scrollers

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	Last edited 2002-06-14		Last edited 2002-06-14
			[[Category:Category Perihelions Atari ST M68000 tutorial]]
			[[Category:Programming]]

>Muguk at 16:37, 2 February 2006

2006-02-02T16:37:42Z

← Older revision		Revision as of 12:37, 2 February 2006
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	add.l #1,a1 put a1 8 pixels ahead of a0		add.l #1,a1 put a1 8 pixels ahead of a0
	move.l #159,d0 scroll a line		move.l #159,d0 scroll a line
	loop		loop
	move.b (a1)+,(a0)+		move.b (a1)+,(a0)+

	For each loop we take the byte one byte ahead, and move it one byte to the left. This should move 8 pixels each loop, right? Wrong! Totally wrong! The screen is made of 16 pixel clusters, each cluster being 8 bytes long. So when you just barge in and move single bytes like that, youâ€™ll misalign the whole shit. Not only will the colours be misaligned, the pixels will be as well. Consider this memory configuration.		For each loop we take the byte one byte ahead, and move it one byte to the left. This should move 8 pixels each loop, right? Wrong! Totally wrong! The screen is made of 16 pixel clusters, each cluster being 8 bytes long. So when you just barge in and move single bytes like that, youâ€™ll misalign the whole shit. Not only will the colours be misaligned, the pixels will be as well. Consider this memory configuration.


	First byte Second byte		First byte Second byte
	%11000000 %00000000 first word		%11000000 %00000000 first word
	%11000000 %00000101 second word		%11000000 %00000101 second word
	%01000000 %00000110 third word		%01000000 %00000110 third word
	%01100000 %00000000 fourth word		%01100000 %00000000 fourth word
	%00000000		%00000000


	...		...


	fifth word		fifth word


	$3F800000 $00000642 pixels		$3F800000 $00000642 pixels

>Muguk at 16:36, 2 February 2006

2006-02-02T16:36:34Z

>Muguk at 16:35, 2 February 2006

2006-02-02T16:35:26Z

← Older revision		Revision as of 12:35, 2 February 2006
Line 22:		Line 22:
	Does this seem right? Letâ€™s try. We want letter â€˜Câ€™, at 3,5. Thus we should increment by 332160 + 5*16 = 15440 bytes. â€˜Câ€™ is about the middle of the screen and 15440 is about half of 32000, so it seems safe to assume that the formula above is working. Question is, how do we get the X and Y coordinates? We had a value for C, right, that was 35. The first digit seems to be the Y coordinate, and the second the X coordinate. If we divide 35 by 10 we get 3.5. 3 is the quotient and 5 the remainder. The instruction divu (DIVide Unsigned) puts the quotient in the lower word of a data register, and the remainder in the higher word. Swap is an instruction that swaps the low and high word in a data register. Great! We now have what wee need. The code looks like this:		Does this seem right? Letâ€™s try. We want letter â€˜Câ€™, at 3,5. Thus we should increment by 332160 + 5*16 = 15440 bytes. â€˜Câ€™ is about the middle of the screen and 15440 is about half of 32000, so it seems safe to assume that the formula above is working. Question is, how do we get the X and Y coordinates? We had a value for C, right, that was 35. The first digit seems to be the Y coordinate, and the second the X coordinate. If we divide 35 by 10 we get 3.5. 3 is the quotient and 5 the remainder. The instruction divu (DIVide Unsigned) puts the quotient in the lower word of a data register, and the remainder in the higher word. Swap is an instruction that swaps the low and high word in a data register. Great! We now have what wee need. The code looks like this:

	~~<p>~~
	move.l #character,a0 points to character		move.l #character,a0 points to character
	move.l #font+34,a1 points to pixel start		move.l #font+34,a1 points to pixel start
Line 40:		Line 40:
	section data		section data
	font incbin font.pi1		font incbin font.pi1
	character dc.b â€œCâ€ ~~</p>~~		character dc.b â€œCâ€

>Muguk at 16:35, 2 February 2006

2006-02-02T16:35:00Z

>Muguk at 13:35, 2 February 2006

2006-02-02T13:35:32Z

Show changes

← Older revision		Revision as of 12:36, 2 February 2006
Line 23:		Line 23:


	move.l #character,a0 points to character		move.l #character,a0 points to character
	move.l #font+34,a1 points to pixel start		move.l #font+34,a1 points to pixel start
	move.b (a0),d0 put letter ascii value in d0		move.b (a0),d0 put letter ascii value in d0
	add.b #-$20,d0 align asciin with font number		add.b #-$20,d0 align asciin with font number
	divu #10,d0 10 letters per row		divu #10,d0 10 letters per row
	move.w d0,d1 d1 contains y value		move.w d0,d1 d1 contains y value
	swap d0		swap d0
	move.w d0,d2 d2 contains x value		move.w d0,d2 d2 contains x value
	mulu #16,d2 16 bytes for each letter		mulu #16,d2 16 bytes for each letter
	mulu #32,d1 32 lines per row		mulu #32,d1 32 lines per row
	mulu #160,d1 160 bytes per row		mulu #160,d1 160 bytes per row
	move.l #font+34,a0 put font screen start in a0		move.l #font+34,a0 put font screen start in a0
	add.l d2,d1 add x and y value together		add.l d2,d1 add x and y value together
	add.l d1,a0 a0 points to correct letter		add.l d1,a0 a0 points to correct letter

	section data		section data
	font incbin font.pi1
	character dc.b â€œCâ€		font incbin font.pi1
			character dc.b â€œCâ€