(Vic) Avenger large screen hack

[Victragic]

This is a modification of the original Avenger cartridge ROM to increase the number of rows on the screen from 22 to 28.

avengerhack.zip

(6.01 KiB) Downloaded 190 times

(Updated 8/1/2019)

Avenger was a very faithful Space Invaders clone. It was the first cartridge I owned, and I remember thinking back in 1982(?) how much better it looked than Atari Space Invaders, despite the lack of game variations. However, I've always thought the gameplay was quite brutal. It feels like the invaders are on top of you, raining down a barrage of missiles the second you begin. From about the third wave, it becomes almost impossible.

..or, maybe I just plain sucked at this game.

Anyway, the main reason for this increased difficulty was the dimensions of the screen. The Vic screen size adopted was 23 columns wide, however the number of rows was only 22. On my PAL TV, it looked quite ridiculous, as there was so much empty space at the bottom of the screen.

I have wondered how difficult it would be to change the screen size for quite some time, to make it a little closer to the original 'vertical' game, and a little more enjoyable.

While not as simple a change as I would have hoped, it wasn't too difficult. I had to move the display from $1e00 to $1000, and move the graphics from $1000 to $1400. After changing these references, it was just a matter of modifying various values to increase the number of rows.

An odd thing in looking through the original code - the table for screen row lookups in the cart has 25 lines, not 22. Which suggests to me that the game may have been converted from another machine to the Vic, or that the programmers intended it to have 25 rows originally. Why this didn't happen is a mystery. I am aware this was perhaps the first cartridge game out for the Vic in 1981, perhaps it was developed in a hurry without a great deal of knowledge of the target machine?

I've recompiled the game to load and run on any Vic with at least an 8K memory expansion. If there's anyone else in the known universe wishing to play space invaders clones in 2019, this is for you

[beamrider]

Excellent - looks good with the bigger screen. Have you compared the starting distance and rate of advance against the arcade, just asking as maybe it's now a bit too easy?

Good job relocating the cartridge too.

[eslapion]

An odd thing in looking through the original code - the table for screen row lookups in the cart has 25 lines, not 22. Which suggests to me that the game may have been converted from another machine to the Vic, or that the programmers intended it to have 25 rows originally. Why this didn't happen is a mystery. I am aware this was perhaps the first cartridge game out for the Vic in 1981, perhaps it was developed in a hurry without a great deal of knowledge of the target machine?

NTSC ?

I assume the programmers noticed 22 rows wasn't quite enough but on the NTSC version of the VIC-20, if you have too many rows then the top/bottom ones may not show at all.

[tokra]

What a nice idea! I'm always fond of using a larger screen-area on the VIC, especially on the PAL-version. There are a few games that make use of it. As a child I loved to play "Fire Galaxy" by Kingsoft, see here: https://www.youtube.com/watch?v=kCDJySQKXJ4

[Victragic]

Excellent - looks good with the bigger screen. Have you compared the starting distance and rate of advance against the arcade, just asking as maybe it's now a bit too easy?

Good job relocating the cartridge too.

Thanks. You mean it's too easy? Darn - I thought I was just brilliant - haha.

The original arcade appears to use a 224 x 256 display (28 x 32 chars), with 11 columns in the phalanx. There are two extra lines at the top of the screen and two at the bottom, which would suggest 28 rows is correct.

I would put the difference to the speed the enemy missiles fall, seems noticeably faster on the arcade machine. The player and enemies seem to move about the same speed.

Re NTSC - while 28 might be a stretch, would 25 rows also have been problematic?

[Victragic]

What a nice idea! I'm always fond of using a larger screen-area on the VIC, especially on the PAL-version. There are a few games that make use of it. As a child I loved to play "Fire Galaxy" by Kingsoft, see here: https://www.youtube.com/watch?v=kCDJySQKXJ4

Yes there were quite a few - ACE, Wunda Walter. Come to think of it even Jelly Monsters used a large screen.

Kingsoft did some nice work on the Vic, from memory they also did also Tom Thumb. Never saw these games in the day though.

[beamrider]

If you scale the screen so that the bases and score line up, I would say that the Vic version is starting about two rows too high?

[Victragic]

(Edit: You'd probably have to line up the Vic score with the arcade score line two lines lower for it to be a closer comparison)

Interesting, the original Avenger is closer to the arcade than I thought.

I'm tempted to implement a difficulty setting like in the 64 version.

[orion70]

A difficulty setting would be just great.. I'd use the easiest of course

[Victragic]

I've created three difficulty settings - easy, normal and hard. The difficulty affects the height of the invaders, and the speed of their missiles. I've set the default to 'easy', as that's likely the only mode I'd play as well

Press F3 while on the title screen to select the difficulty mode.

avengerhack.zip

(6.01 KiB) Downloaded 203 times

[beamrider]

:thumbs up

[vicist]

Brilliant!!

Thanks

[orion70]

Thanks so much!