Emulation/A7800DS
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Added section on screen tweaking.

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README.md
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@ -108,7 +108,7 @@ Controls :
I want to do as the game runs... so you must do it... the high scores will also
auto-save if you quit the emulator or select a new game.
Configuration :
Configuration :
----------
Generally you would use this to select a bankswitching scheme if the proper type wasn't auto-detected.
The following schemes are supported:
@ -127,15 +127,6 @@ The following schemes are supported:
* ABSOLETE Only for the F-18 Hornet game by Absolete Entertainment
* FRACTALUS Only for the Rescue on Fractalus prototype (not a complete game but neat to see). This is EXRAM/A8.
The X/Y screen settings can be tweaked to position the 7800 emulated screen on the DS screen as best you can. Unfortunately
the 7800 screen resolution isn't a perfect match for the DS 256x192 so you'll have to stretch and offset a bit. Most
games have defaults that look good enough. Some games will cut off a few pixel lines at the top and bottom - but they will
still be perfectly playalbe. Such is life with only 192 vertical pixels to play with on the DS!
Recent versions of the emulator have a magnifying glass icon that will zoom and center the display to 1:1 of the actual 7800 output.
This will crop some pixels off the sides and top/bottom but is useful to temporarily zoom up to enter things like high scores
where the text may be hard to read when shrunk down.
Frame Skipping can be OFF (show all frames), Moderate (Show 3/4 frames) or Agressive (only show 1/2 frames). The latter is
only really needed for the DS-Lite/Phat where the faster DSi CPU isn't available.
@ -143,6 +134,43 @@ Don't touch the DMA Cycle Adjustment unless you understand them... and most peop
Press START to save off your configuration - if you made changes you should re-load the game to ensure all settings are applied.
Of Mice, Men and Screen Resolutions :
----------
The DS/DSi has a native screen resolution of 256x192. This is not ideal for the Atari 7800 where many of the games are 320
pixels across and often more than 192 scanlines. The original Atari NTSC spec called for 192 vertical scanlines and a few
of the early games (Asteroids, Ms. Pac-Man, etc.) did stick to that but most later games utilize more vertical scanlines.
A typical NTSC TV can handle 230+ scanlines fairly well and so many of the Atari 7800 games utilize some number of extra
scanlines to pack as much awesome gameplay as possible onto the screen.
This is a problem for our hero, the DS/DSi. Fortunately the DS has the ability to scale/stretch as needed. But when doing
so, there will be missing scanlines. For example, if the game utilizes 200 scalines but the DS can only show 192, there are
8 scanlines that must go missing... if scaled down to 192 pixels to fit the screen, these extra scalines might be in the
middle of the playfield which is not great. If you scale the screen up (using Configuration options or the L/R shoulder
buttons in conjunction with the D-PAD to shift/scale the sceren), then some of the pixels (left or right, up or down) will
be cropped off the screen. This might not be a big deal - sometimes the very top and bottom of a game are just clouds or
ground that can be safely cropped without any loss in gameplay. For many games, the top 16 pixels are the score / lives
remaining.
Most games have scaling defaults that look good enough. Some games will cut off a few pixel lines at the top and bottom - but
they will still be perfectly playalbe. However there are some thigns you can (and should!) do to help.
Recent versions of the emulator have a magnifying glass icon that will zoom and center the display to 1:1 of the actual 7800 output.
This will crop some pixels off the sides and top/bottom but is useful to temporarily zoom up to enter things like high scores
where the text may be hard to read when shrunk down.
More importantly, you can utilize the X and Y buttons as a pan down/up. This is massively useful for games that have a score at
the top of the display (Galaxian, Space Invaders, Popeye, bonQ, etc). Here you can stretch up the screen in the Y direction so
that it is nearly 1:1 and shift the score off the top of the screen. Then, during gameplay, you can tap the X button to temporarily
pan the display down so the score comes into view briefly... and it will magically shift back up after a half second. You can do
this while you are playing - usually when you lose a life you can tap the X button to quickly glace at your score. This gives
more useable scanlines for actual gameplay. Think of this like you're at the arcade and you have to glance up to see your
score when focused on the field of play. It takes a little getting used to but this mechanism really helps map the more complicated
game graphics onto the small sceren. Of course youc an always scale the screen down to it's totally visible - but there will be
some loss of scanline information. Experiment and determine what works best for you.
And remember - once you get your screen settings the way you want, be sure to go into the GEAR icon and hit START to save out
your current configuration (which includes your screen offset/scaling tweaks on a per-game basis).
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Credits:
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