Contrails and bugfixes

Bug fixes

I fixed a bug where the border wasn’t being set on the loader screen. I also removed the scr_set_ink function and replaced it with a function that writes the palette entries directly into the ASIC, which saves time and bytes.

When I replaced the landing carrier with a hardware sprite and scrolled it onto the screen, I forgot to check to see if the player had blown it up at the start! So it definitely won’t appear now if that is the case.

I fixed a bug in the border flash routine for when the player crashes their plane. The function I made was expecting DE to be an RGB word, but instead the code was still passing a pen number between 0 and 15 as the argument. So it flashes a bit more now.

Hopefully fixed a bug relating to the paging in and out of the ASIC. Sometimes when an interrupt is called during the updating of the instrument panel, the ASIC has been paged out. I suspect that the interrupt sometimes misses paging it in, and the palette values for the split screen are occasionally being pasted into the instrument panel memory area, corrupting the screen. Instead of setting a byte when I page in the ASIC and checking it in the interrupt, I read the memory area occupied by the instrument panel. If it is &0f, I know the ASIC hasn’t been paged in. Hopefully this method will be a bit more reliable than the previous one.

Changing the range of the missiles helped me track down another bug. When the player’s missile destroyed an enemy plane, the hardware sprite was hidden but it remained in the object tilemap, so the player could still crash into it.

Contrails

I decided to make it possible for the player to change the range of the rockets. The default range is set to 10 squares. This means the player has to get right up close to the enemy plane in order to take it out. Having a longer range makes it easier to target the enemy aircraft, as you can ‘fire and forget’. The missile will strike the target long before the enemy aircraft gets into range to fire his missiles. Having the option to display contrails also adds a little more realism to the game graphics.