Let the Invasion Commence [Part 6]

From Richard's C64 blog!

5th September – 10th September 2016

Quite a lot of hard work has been done with Let’s Invade during the week or so. Most of this week, I have been concentrating on getting the rest of the levels in place into the game code, and finally got that finished. I was very pleased with the result, but some more work needs to be done on the invaders.

The invaders were not being able to use the full screen to move across during each level. If 5 rows of aliens were shot at either end, the other aliens would NOT stop moving to the end. So I made loads of macros to get the aliens to move how the Space Invaders would have moved in the first place. Once they got to a certain stopping position. The invaders move down 4 pixels. Unfortunately, there were loads of flickers over the aliens, due to sprites being called inside a raster split. I then move the sprites up each raster about 20 pixels. That was much better. Although there were still flickering aliens.

Next I generated some macros for the collision for each alien sprite. An alien should get shot according to which position the player’s bullet is located, and the raster beam of where the alien sits. It resulted quite nicely, but after so much code had been produced. While I was still tweaking bits of the code, an unknown bug had occurred. Sadly the player sprite and the bullets no longer use the ASL ROR $D010 sprite expansion. I couldn’t work out why this happened, when the synchronized loop in the game code calls for Sprite0, 1 and 2 to expand its MSB X position. The aliens MSB expanded okay. Maybe one day I may find the solution. If not, then I’ll have to just go back to the previous backup of the code, and just work on the power ups instead, and leave the invader’s movement to how it was before. We’ll just have to wait and see.

Sadly not a good result 🙁

Original URL: https://tnd64.blogspot.com/2016/09/let-invasion-commence-part-5_10.html