Re: [stella] Color & drawing limitations questions

Subject: Re: [stella] Color & drawing limitations questions
From: slapdash@xxxxxxxxxxxx (Russ Perry Jr)
Date: Sat, 20 Mar 1999 00:04:03 -0600
Eckhard Stolberg wrote:
>[I] wrote:
>>[many questions!]
>The background has a colour register of it's own. Player0 & missile0,
>player1 & missile1 and the ball & playfield share their colour registers.

So there are four independent colors without using any trickery?

>The TIA uses the graphics and colour values that are in the TIA registers
>when it's time to draw an object. So if you manage to change the colour
>and/or the graphics between two copies of a sprite, the TIA will display
>two different looking sprites in that scanline.

If you choose to make a 'XXX' copy, is there enough time to change each
so there are three different colored sprites?

>>And what is the exact resolution of the screen in low-res and high-res

>There is no low-res or high-res screen mode. Depending on your TV set
>the TIA can display about 200 scanlines on a NTSC TV. The movable
>objects have a horizontal resolution of 160 pixels and the playfield
>is 2*20 pixels per scanline.

What is the difference between single-line and double-line "mode" then?
I thought there was a higher resolution (like Vanguard compared to
Outlaw); I understand it's probably a software choice...

>>How many "sprites" can you put on the screen at once?

>If you mean independently moving objects, then there are only the
>two player graphics, the two missiles and the ball. The player
>graphics can display two or three copies with various spacings,
>but then their missiles will also display two or three copies.

That I didn't know...  That could definitely affect their potential
use in adjusting the way a sprite looks...

>If you mean sprites with fixed positions and spacings, you can trick
>the TIA to display up to nine copies of each player graphics per
>scanline. But during this trick you don't have enough time to change
>the graphics or colours during display, so that all copies will share
>the same colour and shape in that scanline.

So where does it break over?  Can you do 7 with a reasonable amount of
changes to the registers?

>>If you want to summarize all this mess into one simple question, here it
>>is: "what would you have to keep in mind if you wanted to make a fake
>>screen shot that might theoretically be possible?".  :-)

>Cycle counting! You can change all the TIA registers at any time,
>but the 6507 isn't fast enough to change all of them in one scanline.
>There are 76 cycles per scanline with three pixels per cycle. Reading
>a value into the 6507 takes at least two cycles and writing a value
>to the TIA takes at least three cycles. And there are only three
>registers inside the 6507 to read a value into, which means that you
>can store only three different values in a short time into the TIA.

And that assumes no game logic, I imagine, but that's fine for this

Is there ANY way to change a color in the MIDDLE of a sprite, due to
issues of timing (i.e. the time the register has been changed coincides
with the time 4 of 8 pixels have been drawn of a sprite)?

>If you are unsure about your picture you can always send it to the
>list and we'll tell you why it wouldn't work. You still have some
>days left before it has to be finished, right? ;-)

True, but I'm asking the question for someone else, who'd like to know
ahead of time so he can get it right.  And don't worry, this image isn't
being made up to advertise vapor on eBay. :-)

||  Russ Perry Jr   2175 S Tonne Dr #105   Arlington Hts IL 60005  ||
||  847-952-9729    slapdash@xxxxxxxxxxxx    VIDEOGAME COLLECTOR!  ||

Archives (includes files) at
Unsub & more at

Current Thread