Subject: Re: [stella] Repositioning Proof Of Concept From: Manuel Polik <cybergoth@xxxxxxxx> Date: Sun, 17 Mar 2002 20:38:52 +0100 |
Hi Piero! >>It repositions _both_ sprites in the same scannline! >How do you do that? It works pretty straightforward. Basically, as one would expect, I just do STA RESP0 STA RESP1 in one scannline. With the second RESP, I loose one pixel, so using the same HMOV values for both sprites would produce a one pixel gap. You lose 15 cycles every iteration in the timing loop before the RESPs, but you have 16 different HMOV values, i.e. a one pixel shift is just possible! So I worked out two tables, that are shifted by one pixel. Here's a little example code: LDA movetab1,X sta HMP0 LDA movetab2,X sta HMP1 AND #$0F TAY RespLoop dey bpl RespLoop sta RESP0 sta RESP1 The tables look like this: movetab1 .byte $6X,$5X,$4X,$3X,$2X,$1X,$0X,$FX .byte $EX,$DX,$CX,$BX,$AX,$9X,$8X repeat with X+1; repeat with X+2; ... movetab2 .byte $7X,$6X,$5X,$4X,$3X,$2X,$1X,$0X .byte $FX,$EX,$DX,$CX,$BX,$AX,$9X repeat with X+1; repeat with X+2; ... >Are there any restrictions? Well, there's some troubles at the left/right edges. I have yet to determine the maximum range where the big ships can be freely moved. And I've yet to find out the ranges where RESPX is working properly. (I think there's a table somewhere in the archive :-)) Another restriction is, that all you can do with this technique is gaps with 0-2 pixels between both sprites. This is working perfect for my game, but if your intention would be total free positioning of both sprites, the solution would be... uhm... complex. I think it is possible, but... Greetings, Manuel ---------------------------------------------------------------------------------------------- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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