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mode7: Update doc

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Vince Weaver 2018-04-06 01:43:34 -04:00
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mode7_demo/docs/mode7_demo.tex
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@ -2,7 +2,7 @@
\usepackage{graphicx}
\usepackage{url}
\usepackage{hyperref}
\usepackage{fancyvrb}
\begin{document}
@ -105,6 +105,7 @@ systems were common.
While the demo itself fits in 8k, it decompresses to a larger size and uses
a full 48k of RAM;
this would have been very expensive in 1977.
See Figure~\ref{fig:map} for a diagram of the memory map.
Also in 1977 you would probably be loading this from cassette tape.
It would be another year before Woz's single-sided
@ -208,6 +209,49 @@ the actual Apple II (an Apple IIe platinum edition).
% http://www.deater.net/weave/vmwprod/mode7_demo/
\begin{figure}[tb]
\begin{center}
\includegraphics[width=2in]{figures/hidden_vmw.png}
\end{center}
\caption{VMW logo hidden in the executable data.\label{fig:vmw}}
\end{figure}
\begin{figure}[tb]
\begin{center}
\includegraphics[width=\columnwidth]{figures/mode7_demo_title.png}
\end{center}
\caption{The title screen.\label{fig:title}}
\end{figure}
\begin{figure}[tb]
\begin{center}
\includegraphics[width=\columnwidth]{figures/m7_screen1.jpg}
\caption{Bouncing ball on infinite checkerboard.\label{fig:ball}}
\end{center}
\end{figure}
\begin{figure}[tb]
\begin{center}
\includegraphics[width=\columnwidth]{figures/m7_screen4.jpg}
\caption{Spaceship flying over an island.\label{fig:tb1}}
\end{center}
\end{figure}
\begin{figure}[tb]
\begin{center}
\includegraphics[width=\columnwidth]{figures/m7_screen3.jpg}
\end{center}
\caption{Spaceship with starfield.\label{fig:stars}}
\end{figure}
\begin{figure}[tb]
\begin{center}
\includegraphics[width=\columnwidth]{figures/m7_screen2.jpg}
\end{center}
\caption{Rasterbars, stars, and credits. Stealth Susie was a particularly
well-traveled guinea pig.
\label{fig:credits}}
\end{figure}
\section{The Demo}
@ -230,13 +274,6 @@ Upon loading, execution starts at address \$2000
\subsection{DECOMPRESSER}
\begin{figure}[tb]
\begin{center}
\includegraphics[width=2in]{figures/hidden_vmw.png}
\end{center}
\caption{VMW logo hidden in the executable data.\label{fig:vmw}}
\end{figure}
The binary is encoded with the LZ4 algorithm.
We flip to hi-res Page 2 and decompress there so the user continues to get
a show of random noise.
@ -274,12 +311,6 @@ copy in the faded versions on the fly.
\subsection{TITLE SCREEN}
\begin{figure}[tb]
\begin{center}
\includegraphics[width=\columnwidth]{figures/mode7_demo_title.png}
\end{center}
\caption{The title screen.\label{fig:title}}
\end{figure}
Once decompression is done, execution continues at address \$4000.
We switch to low-res mode for the rest of the demo.
@ -450,13 +481,6 @@ We managed to take this algorithm and speed it up in the following ways:
\subsection{BOUNCING BALL ON CHECKERBOARD}
\begin{figure}
\begin{center}
\includegraphics[width=\columnwidth]{figures/m7_screen1.jpg}
\caption{Bouncing ball on infinite checkerboard.\label{fig:ball}}
\end{center}
\end{figure}
The first scence starts out viewing an infinite checkerboard.
Any demo would be incomplete without some sort of bouncing geometric solid,
in our case a pink sphere.
@ -472,90 +496,72 @@ This gives some sound for those viewing the demo without a Mockingboard.
\subsection{TFV SPACESHIP FLYING}
\begin{figure}[tb]
\begin{center}
\includegraphics[width=\columnwidth]{figures/m7_screen4.jpg}
\end{center}
\caption{Spaceship flying over an island.\label{fig:tb1}}
\end{figure}
This next scene has a spaceship flying over an island.
The spaceship, water splash, and shadows are all sprites.
They are all drawn in software as the Apple II has no sprite hardware.
This is the TFV game engine flying-spaceship code, with the keyboard
routines replaced to read from memory instead (sort of like a script
of what to do when).
The path the ship takes is pre-recorded; this is adapted from the
Talbot Fantasy~7 game engine with the keyboard code replaced by a hard-coded
script of actions to take.
\subsection{STARFIELD}
\begin{figure}[tb]
\begin{center}
\includegraphics[width=\columnwidth]{figures/m7_screen3.jpg}
\end{center}
\caption{Spaceship with starfield.\label{fig:stars}}
\end{figure}
The spaceship takes to the stars.
This is typical starfield code.
Only 16 stars are modeled, and the movement code re-uses the
same fast-multiply routine described previously.
The starfield is your typical starfield code. Only 16 stars are modeled.
It re-uses the fast-multiply code from the mode7 graphics.
Random number generation is not fast on the 6502, so we cheat.
Originally we had a 256-byte blob of "random" values generated earlier.
This wasted space, so now instead we just treat the executable code
at \$5000 as if it were a block of random numbers. This was arbitrarily
chosen, I tried different areas of memory until I got one where the
stars seemed to move in a pleasing pattern.
A simple state machine controls if the stars move or not, whether the
background is cleared or not (the streak effect) and what color the
background is (for the blue flash).
The ship moving to the distance is just done with different sized sprites.
The star positions require random number generation, but this is not
fast on the 6502.
Originally we had a 256-byte blob of pre-generated ``random'' values
included in the code.
This wasted space, so now instead we just use our code at address
at \$5000 as if it were a block of random numbers.
This was arbitrarily chosen, and it is not as random as it could be
as seen when the ship enters hyperspace the lower right quadrant has fewer
starts than one could desire.
A simple state machine controls star speed, ship movement, hyperspace,
background color (for the blue flash) and the eventual sequence of sprites
as the ship vanishes into the distance.
\subsection{RASTERBARS/CREDITS}
\begin{figure}[tb]
\begin{center}
\includegraphics[width=\columnwidth]{figures/m7_screen2.jpg}
\end{center}
\caption{Rasterbars, stars, and credits.\label{fig:credits}}
\end{figure}
Once the ship has departed, it is time for the credits as the stars
continue to run.
The text is written to the bottom 4 lines of the screen and appears
to be surrounded by low-res graphics blocks.
Mixed graphics/text would generally not be possible on the Apple II, although
with careful cycle counting and mode switching groups such as FrenchTouch
have achieved this effect.
I was lazy and instead used inverse-mode space characters which appear the same
as white graphics blocks.
The credits happen with the starfield continuing to run.
The rasterbar effect is not really rasterbars, it's just a colorful assortment
of horizontal lines drawn at a location determined with a sine lookup table.
Horizontal lines can take a surprising amount of time to draw, so this
was optimized using inlining and a few other methods.
The text is written in the bottom 4 lines of the screen. Some inverse-mode
space characters are used to try to make it look like graphics are surrounding
the text. It's actually possible with careful cycle counting to switch
modes fast enough to have actual mixed graphics/text (See the FrenchTouch
demos) but I was too lazy to attempt that here.
The rasterbar effect isn't really rasterbars, it's just a rainbow assortment
of lines being drawn with a SINEWAVE lookup table.
It's the same rasterbar code from my chiptune player demo. I ended up
optimizing it a lot via inlining and a few other ways because it turned
out just drawing a horizontal line can take a very long time.
The rotating text is just taking the output string and rapidly rotating the
character values through the ASCII table.
The annoying clicking noise is the same speaker effect caused by hitting
\$C030.
Choosing who to thank ended up being extremely critical to fitting in 8kB,
as unique text strings do not compress well. I'm also still not satisfied
with how the centering looks.
The rotating text is done by just rapidly rotating the output string through
the ASCII table, with the clicking effect again by hitting the speaker
at address \$C030.
The list of people to thank ended up being extremely critical to fitting in 8kB,
as unique text strings do not compress well.
I apologize to everyone whose moniker got compressed beyond recognition,
and I am still not totally happy with the centering of the text.
\section{Obtaining the Code}
More details, disk image, and full source can be found at the website:
\url{http://www.deater.net/weave/vmwprod/mode7_demo/}
\begin{table}
\begin{center}
\begin{verbatim}
%\section{Appendix: Memory Map}
\begin{figure}
\begin{center}
\begin{scriptsize}
\begin{BVerbatim}
------------- $ffff
| ROM/IO |
------------- $c000
@ -587,10 +593,12 @@ More details, disk image, and full source can be found at the website:
------------- $0100
| zero pg |
------------- $0000
\end{verbatim}
\end{BVerbatim}
\end{scriptsize}
\end{center}
\caption{Memory Map (not to scale)}
\end{table}
\caption{Memory Map (not to scale)\label{fig:map}}
\end{figure}
\end{document}