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Author Topic: Why screen size varies across games?  (Read 2681 times)

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Offline pkupcikTopic starter

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Why screen size varies across games?
« on: June 24, 2010, 09:18:12 PM »
Can anyone enlighten me why some Amiga games are displayed in full screen, some games take up about 3/4 of the screen and some games some other weird portion of the screen? Is it to accelerate games when they use less of the screen? I've also noticed that AGA games are more likely to run full screen than not. Why? Is there a way to force games to use full screen?
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Offline Karlos

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Re: Why screen size varies across games?
« Reply #1 on: June 24, 2010, 09:28:35 PM »
Quote from: pkupcik;567032
Can anyone enlighten me why some Amiga games are displayed in full screen, some games take up about 3/4 of the screen and some games some other weird portion of the screen? Is it to accelerate games when they use less of the screen? I've also noticed that AGA games are more likely to run full screen than not. Why? Is there a way to force games to use full screen?


Assuming you have a PAL amiga, the games that appear to be vertically short are those that were designed for NTSC, which has a somewhat lower vertical resolution than PAL.
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Offline Speelgoedmannetje

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Re: Why screen size varies across games?
« Reply #2 on: June 24, 2010, 09:33:49 PM »
I guess you're European?
The Amiga PAL resolution is 320x256, while the American resolution is 320x200.
Also, AtariST and PC games were back in those days at the 320x200 resolution. It saves a hell of a lot of coding keeping a game at just one resolution when having to port it to multiple systems.
But some games, like Lionheart, I think is kept at a lower resolution to maintain speed.
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Offline pkupcikTopic starter

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Re: Why screen size varies across games?
« Reply #3 on: June 24, 2010, 09:55:34 PM »
I have PAL A1200 and tried using it with composite output on PAL TV or RGB PAL to VGA NTSC converter on computer monitor - both with the same result. Most of the games are too short, e.g. Lotus, Lemings, Street Fighter, Chuckie Egg, Test Drive, etc. Some seem to be just a little bit short, say 1/5 of a screen which would probably explain the PAL vs NTSC optimization, but some are way short, like 1/3 of the screen, eg. Lotus 2. Most of the AGA games I have seem to be either full screen or just 1/5 too short.
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Offline KThunder

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Re: Why screen size varies across games?
« Reply #4 on: June 24, 2010, 09:57:28 PM »
Amiga applications can also be coded to use overscan. This increases the resolution slightly and allows them to display full screen.

standard 320x200 uses a border around the displayed area. The overscan settings put that higher at something like 356x220 putting the area all the way to the edges to the screen.

There are different settings for some apps like dpaint with normal, overscan and maximum overscan. Games can do this too.
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Offline pkupcikTopic starter

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Re: Why screen size varies across games?
« Reply #5 on: June 24, 2010, 10:29:42 PM »
I looked at Lotus 2 again and it looks like the screen is only about 1/5 short which would be the missing pixels from 256 PAL resolution compared to 200 in NTSC. And because the game has extra black border around the whole screen, the bottom gap looks extra tall (when you add both gaps together) - I guess I was visually tricked thinking the gap is larger than that.
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Offline KThunder

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Re: Why screen size varies across games?
« Reply #6 on: June 24, 2010, 10:42:02 PM »
so you are using a pal amiga, what are the games? are they pal or ntsc? I think overscan is more likely a reason for the varying size of screens. Overscan uses more memory so many games dont use it.

I have only ever had ntsc amigas and games and the screens on many were different.
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Offline pkupcikTopic starter

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Re: Why screen size varies across games?
« Reply #7 on: June 24, 2010, 11:47:17 PM »
Quote from: KThunder;567056
so you are using a pal amiga, what are the games? are they pal or ntsc? I think overscan is more likely a reason for the varying size of screens. Overscan uses more memory so many games dont use it.

I have only ever had ntsc amigas and games and the screens on many were different.

Yes I'm using PAL A1200 and I'm in USA, but I do also own PAL/NTSC TV. The games I tried I believe are PAL, e.g. Lotus 2, 3, Lemmings, Indiana Jones, etc.

I just did another test though with Lotus 2. I booted Amiga in NTSC mode by holding the mouse buttons on reboot and when I played Lotus 2 the screen was nicely stretched all the way to the bottom. I guess I will need to try playing games in NTSC mode to have the picture stretched across the full screen. Does anyone know how to force NTSC boot by default?
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Offline pkupcikTopic starter

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Re: Why screen size varies across games?
« Reply #8 on: June 25, 2010, 12:04:35 AM »
Now I've read somewhere that there's a way to configure WHDLoad to force either PAL or NTSC for each game. Does anyone know how to do that? That would be great if I could pre-configure that on game by game basis.
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Offline pkupcikTopic starter

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Re: Why screen size varies across games?
« Reply #9 on: June 25, 2010, 12:32:07 AM »
OK, I figured it out, I can use TOOLTYPE to configure each game to use PAL or NTSC, that way I configure each game individually depending on whether it looks and works better in PAL vs. NTSC.
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Offline platon42

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Re: Why screen size varies across games?
« Reply #10 on: June 27, 2010, 01:08:13 AM »
Two issues not mentioned yet: if you start the display at the normal left border AND want to use the horizontal hardware scrolling feature, you will lose the 8th sprite (for each 16 pixels further left you will lose two more sprites each due to overlap with screen dma). Thats why e.g. Turrican has a slightly smaller screen to the left.

Also screen DMA (and copperlists) will take away cycles for blitter and generic chipram access, so turning off the display at an earlier vertical position will leave more cycles for blitting (with complex source combinations) and cpu chipmem access (usually starts happening with 5 bitplanes at ocs/ecs.
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Offline Daedalus

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Re: Why screen size varies across games?
« Reply #11 on: June 27, 2010, 02:58:33 AM »
@platon42

Yes, this is the reason for having the black borders on the left and right of the screen in Super Skidmarks - if you want all those sprites on screen at once, you need to reduce the screen width to prevent the overlap.
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