BuGS/BUGS.md

BUGS

This is a list of the software bugs (as opposed to the bugs in the game that you shoot) that still need attention:

• On the latest build (0136579125) on real HW, I can play a game and finish that game. But when I try to start a second game, I crash. The stack looks corrupted and execution is way off in the weeds somewhere. This isn't happening on either emulator.
  • I am thinking this is the same crash as the one which follows. I tried to reproduce this on real HW again with that debug in place but could not.
• I reproduced a crash on GSPlus after dying and starting a new game. From the stack, it was clear it was trying to draw a body segment but the jump instruction was set to garbage. I am hoping this is the same crash as the one saw on real HW.
  • I have added some debug code to detect this. I am validating that the offset into the draw table for head and body segments is "sane" and if not brk.
  • I reproduced it and ended up at brk $4 with y set to $2270 which is much larger than the max of 156. Also odd is that X is 1 but I think it needs to be an even number.
  • In order to get the wrong value in Y, I noticed that the segmentSpriteOffset was overwritten with the pattern 70 02 70 02, etc.
  • Something is trashing memory.
• A spider moving left to right went off screen and left garbage on the RHS as it exited. I have only seen this once. I think it coincided with the player dying.
  • I have just seen it again. I think the problem happens when the player dies on the extreme RHS of the screen (perhaps the LHS also but I have seen it on the RHS). I think the non game tile just beyond the bounds gets marked as dirty but is not put on the dirty non-game tiles list. So, it remains "dirty" forever and is never cleaned up. Once that happens, then if a spider traverses the tile, it leaves behind junk.
• I have seen some mushrooms appear suddenly. Sometimes, if I am shooting, the shot "hits" an invisible mushroom which then becomes visible. My guess is that there is something wrong with the code which turns a centipede segment into a mushroom when shot and the tile isn't correctly marked dirty all the time.
  • In theory, there shouldn't be a collision with an invisible mushroom but what happens is that when the shot overlaps with the tile, it becomes dirty. At that point, the mushroom will appear on the next frame and a collision can then occur.
• I am still seeing shots go through almost gone mushrooms sometimes. I checked more rows of pixels for collisions even though the shot doesn't draw there but it still seems to be possible. If the height of the shot is equal to the amount it moves in one frame, it shouldn't be possible so that is worth checking.
• It is possible to shoot between two segments of a centipede. The problem is that there are black pixels between the segments and if things are timed just right (or just wrong), the shot can slot in at those black pixels and end up missing both segments.
  • I am not sure how much can be done about this given how collisions are detected.

FIXED

• Sometimes at the end of the flea sound, there is a short high pitched tone.
• Sometimes when the player dies, the "you can shoot" indicator is left behind as garbage on-screen.
• Sometimes when you die, a spider may enter and the spider sound will start playing. Because audio is stopped by player death and it has already happened, the spider sound ends up going on even though the spider is not moving.
• Sometimes the spider doesn't seem to freeze when the player dies. This may be related to the sound problem also. If the per-frame spider update code isn't handling player death correctly, that could explain both.
• When a centipede segment is added on the right, if there is a mushroom either right at the edge or maybe on tile from the edge (not sure which), the segment seems to turn around and travel up along the edge of the screen. Not sure if this can happen on the left side also. This is likely a problem with the mushroom collision detection and a segment which is mostly off-screen should probably ignore blocking mushrooms until on-screen.
• A shot is able to pass through an almost gone mushroom if lined up just right. Best to change the sprite code for the shot to scan the two pixels below for a collision.
• I have seen a couple of crashes. I think an off-screen centipede segment is getting "shot" at the beginning of a level leading to a crash. Almost definitely related to collision and shot handling.
• I am seeing other crashes where the PC ends up in bank 22 or so. Need to dig into the stack to figure out where it is coming from.
  • I have confirmed that we are jumping to band 22 from segmentBodyJump_jumpInst. Not sure how a bad address is ending up in the jump table here.
  • Seems to happen pretty reliably if I die from the last segment and progress to the next level.
  • Caused by both gamePlayer.s and level.s calling start level when the last segment is the one which kills the player. The player code now defers to the level code to handle starting the level after the player dies that way.
• Sometimes centipede segments seem to be stacked one on top of another. You think there is just one left but you shoot it and there is one underneath it. This should not happen.
  • Caused by the lack of head segment collision detection in the slow segment code paths. I had thought that slow head segments would never collide. But once you split a slow centipede into two separate segments, you now have slow heads that can collide.
• If you die holding the mouse button down, your next game will start shooting without pressing the mouse button.
  • I was reproducing this reliably on real HW but I don't see it from either emulator. Need to try to reproduce it again on real HW.
  • The problem is that the game should ignore the first poll from the mouse when starting a new level. The mouse HW/ADB has put some info in about the state of the mouse and we don't poll it for quite some time. Even if the mouse changes state, the last state is still there and becomes stale. The solution I implemented was to throw away the first mouse poll at the start of every level.