Subject: Re: [stella] Color & drawing limitations questions From: Eckhard Stolberg <Eckhard_Stolberg@xxxxxxxxxxxxxxxxxxxxx> Date: Sat, 20 Mar 1999 16:14:54 +0100 |
At 00:04 20.03.99 -0600, you wrote: >So there are four independent colors without using any trickery? Correct. >If you choose to make a 'XXX' copy, is there enough time to change each >so there are three different colored sprites? The closest spacing between two copies of a sprite is eight pixels. So you can only do 'X_X_X'. You can preset the colour for the first copy during the horizontal blank and preload two processor registers with the other two colours. Then you can change the colours during the eight pixel gaps. If you set player0 to two copies with an eight pixel gap and place one copy of player1 between them, you can preset the colours for the first and the second sprite during the HBLANK and change the colour for the third sprite, while the second one is displayed. >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... The TIA has only enough memory to store data for one scanline. It will keep displaying this data in every scanline until the registers are changed. You can update the registers only every couple of scanlines. You will loose some vertical resolution, but gain some more processor time to calculate new graphics data etc. The TIA has the possibility to update the player graphics only when you write data in the other player graphics register. That way you can update the graphics for both players in alternating scanlines, while the change will take effect for both players in the same line. >So where does it break over? Can you do 7 with a reasonable amount of >changes to the registers? The trick requires you to constantly trigger the positioning registers to get another set of sprites. There is no processor time inbetween. If you don't use both player graphics to get 18 sprites per scanline, but restrict yourself to using only one player for nine sprites, you have three cycles between two sprites to change it's colour or shape. If you preset the data during HBLANK and preload all three processor registers, you can have four colours or shapes for the nine sprites. If you go with the more irregular spacing between sprites like in EXTRA18.BIN, you have five out of every eleven cycles to change the sprites' look. >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)? In such a case you will get four pixels with one colour and four with the other colour. That is for normal pixels. For double or quadruple width sprites or the playfield the change can happen while one of those big pixels is still beeing displayed, but the change will take effect from the next pixel on. >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. :-) Glad to hear that. So the deadline for the picture is not something like very early next month? ;-) Ciao, Eckhard Stolberg -- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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