Blador vs. Spike

While I was checking collisions/interactions were still working fine after introducing the G_FIGHT group, I noted something not so right about the dumblador. Something I don't think I've ever blogged although it was available since the anniversary level: throw a dumblador into pencil spikes and it will snap to the spike it lands on, turning itself into an additional safe platform.

But with the current engine, you may end up with the blador "waking up" and start walking within spikes. You may also see it stopping completely misaligned and almost everytime, it would be too low compared to where it used to stop.

I first tried to tune collision areas, but that did not seem to help. I checked some values in the DDD debugger, but it's a bit of a lottery: you can't really tell in advance whether you'll find yourself in an interesting case. Note to future self: there are save states in desmume! (In such a case, I should have saved the emulator state before throwing the blador, save again when the breakpoint triggers, fast-forward to see whether the condition will happen and only then go back in time to either review the step-by-step behaviour or change a little bit the initial conditions and try another throw).

But I had not came back from the future to leave myself a note yet, so instead, I started adding coordinates of colliding entities in the "gobscript expression debugger" so I could have something that is stepping faster than DDD, and present precisely the information I needed (although I could have used it in base 10 :P).

And there I realised that when the blador ended up misaligned, it was colliding with a spike whose position was a mere multiple of 8 rather than a multiple of 16 ...

Back in SchoolRush times, it was mandatory to be a 16x16 pixels block if you wanted to have special behaviour such as hurting the player. But it changed with the tiled engine revision where each individual 8x8 tile can be of any 64 special type (or any of the other 192 "normal" types).

Larger blocks are still possible thanks to "refer too" special tiles that point towards the top-left corner tile of the block. When loading an older map, the conversion is automatic, but when I created the "school teleporter" room for the 3-rooms-demo, I just added 1-tile spikes instead. With a small change to the Level Editor, you can now press A to reveal the redirecting arrows (default behaviour is to mirror the pink tile instead). That should make such errors easier to spot in the future, if I ever make them again.

So the script for the dumblador now looks like

$THROWN :anim3 {
  using gravity(24,1536)
  testpoint off (8,18)
  test 0 (0,0)-(8,12) ${F_BAD|G_FIGHT|F_WEAPON} //# weapon against other monsters.
  test 1 (0,15)-(16,16) ${F_BAD|F_PLATFORM};
  area 0 (0,0)-(16,12) ${F_ISINK} //# deleted-by-ink
  area 1 (0,0)-(16,8) ${G_FIGHT|F_HURT} // # stand-on-spike
}

$THROWN->$STUNSTAND on hit1 (0 :1 0 :0 Lc $vPlatform(2));
$STUNFALL->$STUNSTAND on hit1 (0 :1 0 :0 Lc $vPlatform(2));

and the script for the pencil spike looks like

 block 21 {
   is spike "0101030307070f0f"
   area (7,0)-(8,16) 10010010 # hurts
   on hit [0] (t)
 }

 Together, they allow to get a functional blador-align-on-spike (aligning is performed by the Lc opcode), but there's still one thing to fix if I don't want to see dumblador waking up and start walking on pencils: duplicate the $STUNSTAND state into something like $SPIKED, while removing the "get feet" area. But well, a remaining glitch makes some more fun for ScreenshotSaturday ;-)