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SIDWAVE
Account closed
Registered: Apr 2002
Posts: 2238 |
Negative sprite X-position ?
Hehe I kinda know it isnt doable, but still, i would ask what to do..
An expanded sprite goes to X-pos 0, and then half of it is visible on the screen.
So, when scrolling left, it suddenly disappears when it hits X-pos 0.
This looks ugly :D
If i set D010 at this point, its still not possible to give it a position, so it is hiding under the left border.
So what can i do ?
I have thought about the insane work, to, when X-pos=0, to start a left scrolling of the sprite data. This isnt very appealing to have to code.. :D
Also, dont we get the same problem if the whole sideborder is gone ? when sprite at pos 0 = it suddenly vanishes from there, because you set d010 and give it another position ?
I dont know what to do.
Ofcourse NOT using expanded sprites solves the problem, and my flying sprites can look nice.. but i WANT them expanded.
Anyone ? |
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chatGPZ
Registered: Dec 2001
Posts: 11293 |
there is a "gap" in the sprite coordinates on the left side of the screen... to display a sprite further left than regular position 0, set MSB in $d010 and substract 8 extra pixels. (this is for pal, its different on ntsc) |
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SIDWAVE
Account closed
Registered: Apr 2002
Posts: 2238 |
How is it possible to subtract 8 from 0 ?
poke d000,0
poke d010,0 = visible sprite in left
poke d000,0
poke d010,1 = visible sprites on pos $100
once on pos 0, and d010=0 - i have no way to subtract 8 from 0!!
sorry, i dont get it :D
i just tried all.. |
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chatGPZ
Registered: Dec 2001
Posts: 11293 |
$00 - $08 == $f8 |
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assiduous
Account closed
Registered: Jun 2007
Posts: 343 |
actually you should do:-
$00 - $09 == $f7 |
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SIDWAVE
Account closed
Registered: Apr 2002
Posts: 2238 |
mhhh. oh, but it needs to be 224 before the sprite is hidden away completely.
mmmm so any trick here ?
it is visible from 247 down to 225
at 224 its hidden
when d010=x1
so... scrolling left from 255, when it hits 0:
switch d010, put x to 247
do until x=224
auuu.. now i have to THINK when i code this :D
Thanks for your input! |
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Stryyker
Registered: Dec 2001
Posts: 466 |
Grab the Vic Article. It has some notes about sprite positions. It is how those lovely side border scrollers managed to make it look nice on the left and the right of the screen. |
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SIDWAVE
Account closed
Registered: Apr 2002
Posts: 2238 |
I have grab on it, but my flags to say where i am are a bit messed up :D
I take a break now, hehe. |
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JackAsser
Registered: Jun 2002
Posts: 2014 |
I usually do this:
1) Have all sprite x-positions as signed 16-bit values.
2) If x<0 then x-=8.
3) If hibyte(x)!=0 then set corresponding $d010-bit else clear the corresponding $d010-bit.
4) poke lobyte(x) into the corresponding sprx-register.
This is not 100% general but covers most cases. One should really disable the sprite completly if it's outside the screen, with my method it will eventually wrap and show again if it's some 100 pixels or so outside the screen.
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SIDWAVE
Account closed
Registered: Apr 2002
Posts: 2238 |
Jackasser: i asked how to hide an expanded sprite behind the left border, completely - and got it working with help from Groepaz.
d010=x1
d000=224 ;it is now completely hidden
so thats all.
Thanks for your input! |
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JackAsser
Registered: Jun 2002
Posts: 2014 |
Quote: Jackasser: i asked how to hide an expanded sprite behind the left border, completely - and got it working with help from Groepaz.
d010=x1
d000=224 ;it is now completely hidden
so thats all.
Thanks for your input!
And I answered in a general way trying to give some hints but ok... :)
Border ends at 24. An expanded sprite is 48. To hide it you must place it at 24-48 = -24. But since -24 < 0 we must subtract by 8 => -24-8 = -32 ($e0 = 224).
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SIDWAVE
Account closed
Registered: Apr 2002
Posts: 2238 |
Quote: And I answered in a general way trying to give some hints but ok... :)
Border ends at 24. An expanded sprite is 48. To hide it you must place it at 24-48 = -24. But since -24 < 0 we must subtract by 8 => -24-8 = -32 ($e0 = 224).
You keep telling me stuff I already know :D
The sprites use 3 bytes for x-pos; the 3rd is for the d010 gap in left side (pos 224-247). |
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The Human Code Machine
Registered: Sep 2005
Posts: 110 |
Quote: You keep telling me stuff I already know :D
The sprites use 3 bytes for x-pos; the 3rd is for the d010 gap in left side (pos 224-247).
Why does a sprite need 3 bytes for x-pos? I always thought only 9 bits are needed for the x-pos? |
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SIDWAVE
Account closed
Registered: Apr 2002
Posts: 2238 |
Well, yes, but actually it is 3 seperate counters, so i decided to use a byte for it, instead of using 1 byte for 2 different things.
0-255 | d010,0
0-159 | d010,1
224,247 | d010,1
So to make the code easier, i use 3 bytes.. |
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JackAsser
Registered: Jun 2002
Posts: 2014 |
Quote: Well, yes, but actually it is 3 seperate counters, so i decided to use a byte for it, instead of using 1 byte for 2 different things.
0-255 | d010,0
0-159 | d010,1
224,247 | d010,1
So to make the code easier, i use 3 bytes..
To make the code even easier you can use two bytes per sprite that represents -32768..32767. :P
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WVL
Registered: Mar 2002
Posts: 889 |
Quote: Well, yes, but actually it is 3 seperate counters, so i decided to use a byte for it, instead of using 1 byte for 2 different things.
0-255 | d010,0
0-159 | d010,1
224,247 | d010,1
So to make the code easier, i use 3 bytes..
Easy?
Like Jackasser said : just use a 16-bit coordinate system.
You can improve it a bit further with some small checks :
5. position >$180? then position is $180
6. position <-$c0? then position is -$c0
This fixes the 'wraparounds' |
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HCL
Registered: Feb 2003
Posts: 727 |
Heh. :D. I'd better not make a comment on this.. |
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WVL
Registered: Mar 2002
Posts: 889 |
Quote: Heh. :D. I'd better not make a comment on this..
Let me guess : you have an ever easier system using 5 bytes? ;) |
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Jetboy
Registered: Jul 2006
Posts: 268 |
Why limit yourself to only using 5 bytes where there is so many of them available? :) |
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SIDWAVE
Account closed
Registered: Apr 2002
Posts: 2238 |
Jackasser: yes I see now.... :D
I must have been blind.. |
