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Did anyone 'fix' Air Raid?


cosmosiss

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  • 2 weeks later...

Don't bother...it still needs fixing. The original game begins with a scanline count of 290...and alternates between 291 and 292 scanlines during gameplay (returning to 290 once the game is over or game reset is used). The above hack begins with 274 scanlines and alternates between 275 and 276 scanlines during gameplay...but hits 292 scanlines when reset is pressed. To insure against rolling, an NTSC game should never run above 262 or (at the very least) be at a constant number of scanlines.

 

The fact that the original game bounces around consistantly raise doubts that it is a official "PAL" release...frames with an odd number of scanlines would lose all color (and of course, the blue sky would be purple using the PAL color set).

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Thanks for that.

 

The hack attempted to lower the scanline count by setting a lower timer value @F03D. While the timer was still within an acceptable delay...this change would not affect the count when the game reset switch was used (see below). Seems safe enough to use, so I adopted the hack's value.

 

I corrected the game reset scanline glitch. This was due to the game clearing ram down into the hardware register range @F06D (addresses $4E upward...even the original game did this, so I dunno what stretch of ram they had in mind - a little guesswork done here). Bumping the number of scanlines used for the green ground area @F593 got it into a more acceptable range. It still bounces around a bit when missiles reach the upper or lower boundries...but it -might- keep the set from rolling (AFAIK, it should be no worse than a quick jitter...but I dunno). Missile boundries still need correcting to fix that.

Air_Raid.zip

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