Impossible Mission for the 800

Rybags · November 18, 2005

I've been contemplating a conversion for over 3 years. So far all I've done is some theoretical planning, and ripped/converted the player sprite animations.

Sample video (just open the .AVI inside the zip file):

IM_Vid1.zip

The animation and movement is a bit jerky because it just uses a BASIC program to control paramaters that the VBI uses to create the sprite. I did a quick&dirty rip of the player sprites by vid-capping in WinVICe and just doing run/jumps against a wall, then using VitrualDub to output each frame into a .BMP file.

The problem with using PMGs for the player sprite is that to be faithful to the original, all 4 players would have to be used.

That would mean that software sprites would need to be used for the robots and floating ball, and the missiles could be used for the robot's energy rays.

An alternative would be to do the player as a software sprite, although with around 25 sprite definitions for the player running or jumping in each direction it would be fairly memory hungry. The advantage of doing so would be that the 4 players would be free to render the robots in multicolor PMG mode (there are only 2 rooms where 2 robots appear at the same vertical location, and the robot sprites are only 7 pixels wide).

For the background graphics, multicolor mode 4 (40x25 5 colors) would probably be the best bet. DLIs would allow reusing the 2 colors that the floors use for the furniture and other objects.

Collision detection would have to be done in software. Since the robots have basically the same shape in each animation frame, it makes it a lot easier.

With some tight coding the game should easily fit into 48K. Small memory machines would have to miss out on the digitized sound effects, and possibly have extra disk accesses.

Cybergoth · November 18, 2005

Hi there!

If it helps, I have the original source code for the Apple 2 version of Impossible Mission 2 on my homepage.

Greetings,

Manuel

vdub_bobby · November 18, 2005

You know, this brings up a question I have about the A8s:

How feasible is it to change player color registers line-by-line? How frequently is this done?

For example, in Keystone Kapers (for the 2600), they use one player, it's color changed just about every line, to display the escaped prisoner sprite seen in this screenshot:

If you were converting this game to the A8 (and it probably has been converted, for all I know), would you use one player and change it's color every line, or would you use 2+ players to create the same effect?

EDIT: Ok, I looked at the A8 conversion and it looks like they used the same technique.

Edited November 18, 2005 by vdub_bobby

Rybags · November 18, 2005

It won't be feasible to have too much DLI action happening. At best, several playfield color changes for the whole screen. Rendering up to 4 robot playfield sprites against static background objects will use up most of the machine cycles available.

Due to the fact that the player does sommersault jumps, changing the colors of it is not possible.

I just had an idea for the collision detection. The missiles could be used as P4. They could then be cycled between laser bolts and underlayed on the robot closest to the player. Flickering would occur but with the laser bolts it would not be a problem.

Edited November 18, 2005 by Rybags