2 replies to this topic

[Allan]

This is really for anybody to answer.

In Dan's 7800 sprite demo, what exactly is this bit of code doing in relation to the Display List?

;********************** reset DL ends ******************
	
	ldx 	#$0C
	lda	#$00
dlclearloop
	dex
	sta	dlend,x
	bne	dlclearloop
	

Is this erasing the previous drawing of the 'sprite', a.k.a. erasing the one (or two zones) the graphics are drawn in?

Thanks,
Allan

[DanBoris]

The dlend table is used to store the index of the next available spot in each DL where you can write a DL entry. The piece of code below simple resets all these indexes to 0. When I write to a DL entry this index is added to the starting address of the DL to get the address to write the entry into.

Dan

Allan, on Tue Dec 19, 2006 10:50 AM, said:

This is really for anybody to answer.

In Dan's 7800 sprite demo, what exactly is this bit of code doing in relation to the Display List?

;********************** reset DL ends ******************
	
	ldx 	#$0C
	lda	#$00
dlclearloop
	dex
	sta	dlend,x
	bne	dlclearloop
	

Is this erasing the previous drawing of the 'sprite', a.k.a. erasing the one (or two zones) the graphics are drawn in?

Thanks,
Allan

[Allan]

DanBoris, on Tue Dec 19, 2006 2:42 PM, said:

The dlend table is used to store the index of the next available spot in each DL where you can write a DL entry. The piece of code below simple resets all these indexes to 0. When I write to a DL entry this index is added to the starting address of the DL to get the address to write the entry into.

Dan

Allan, on Tue Dec 19, 2006 10:50 AM, said:

This is really for anybody to answer.

In Dan's 7800 sprite demo, what exactly is this bit of code doing in relation to the Display List?

;********************** reset DL ends ******************
	
	ldx 	#$0C
I get it now. 	lda	#$00
dlclearloop
	dex
	sta	dlend,x
	bne	dlclearloop
	

Is this erasing the previous drawing of the 'sprite', a.k.a. erasing the one (or two zones) the graphics are drawn in?

Thanks,
Allan

I get now. Thanks Dan for the explanation. And thanks for writing the demo to begin with. It's helped a lot in understanding the 7800.

Allan