[A86] Re: The f'n 86 screen

To: "Notbynow@aol.com" <assembly-86@lists.ticalc.org>
Subject: [A86] Re: The f'n 86 screen
From: Aaron <acurti1@umbc.edu>
Date: Sat, 29 Sep 2001 21:28:43 -0400
In-Reply-To: <99.1b6589ff.28e7aac7@aol.com>
Organization: The Coalition for World Domination
References: <99.1b6589ff.28e7aac7@aol.com>
Reply-To: assembly-86@lists.ticalc.org

If you're writing directly to video mem, there could problems when you
erase sprites and then redraw them.  What might be happening is that
your sprites are only actually in video memory for a fraction of the
time it takes to complete a loop, so sometimes when the screen
refreshes it shows the graphic and other times it doesn't.  If you did
something like this....

main_loop:
        ;draw sprites directly to video mem
        ;take inputs, calculate stuff
        ;erase sprites

The reason the top of the screen looks different from the bottom would
be because the screen refreshes from top to bottom, and it takes a
certain amount of time to do it.  So by the time the screen refresh is
halfway done, a bunch of code will have been executed...

Anyway a good way to fix this is to draw all your graphics somewhere
else in memory, then periodically copy them in video memory.  For
example if you play Sqrxz, the sprites will look dim and flickery,
until you turn on the "virtual screen" option.

Increasing the relative time the graphics are around before they're
erased will also help, but it'll probably always flicker a little...

On Saturday, September 29, 2001, Notbynow wrote:
>        I have been having many problems with the screen of the Ti-86.  In 
> several of my programs, the sprites that I draw (like bullets going 
> vertically up the screen) get very dim, no matter what the contrast.  Also, 
> the little sprite at the bottom of the screen that doesn't move gets a little 
> hole in the middle of it where the line of bullet sprites are above it.  When 
> I used halts to slow down the cycles of the program, the dimness will flip 
> between the top half of the screen to the bottom half of the screen every few 
> seconds.  If I disable interrupts and loop a large number of loops to slow 
> down the program, the graphics get all choppy and the problem with the 
> dimness affects about half the screen, but scrolls vertically down and 
> restarts at the top of the screen.  I also have this exact problem in my 
> 3-level grayscale routine.  If you know what this is or know how to fix it, 
> please let me know, because I kinda have no clue.

> Thanks,
> Marc McG

-- 
Aaron was here.
acurti1@umbc.edu

References:

[A86] The f'n 86 screen

From: Notbynow@aol.com