Les portes ... prochain vrai objectif

C'est ce qu'on pouvait lire en mars sur une de mes pages d'agenda et en avril sur mastodon. Et c'est toujours d'actualité, bien que j'envisage de faire d'abord un essai des éléments de base de leur implémentation sur un le bonus qui rend des points de vie ... Si vous avez un peu essayé la dernière démo, vous avez sans doute été surpris par un brusque changement de niveau dès que vous vous approchez un peu trop d'un truc en forme d'ouverture. C'est clairement quelque-chose que je voudrais améliorer.

La bonne nouvelle, c'est qu'en fait, j'ai déjà la moitié du travail: enregistrer la position actuelle dans des variables. Et voici la deuxième partie: se diriger vers les coordonnées enregistrées.

Bilou's Adventure maps have doors... you know, the kind that are located at some point on the map and will near-instant put you somewhere else on the map. So I'd like "Bilou Dreamland" to have doors as well... That will require a bit more effort in the GEDS environment that can't simply do ROOM=12 : xbilou=100 : ybilou=100. So i've got this nice tree stump sketch in my agenda since at least March'25, and I've been twisting my mind around the issue of how to make it work with state machines and collisions and linked game objects.

Now, my Basic games typically struggled to extend beyond one level. At best, I'd chain-load the next level which would happen to look a lot like the previous one (or not) by sharing lot of code thanks to copy-pasta... And entering a door would typically freeze everything as the game had entered a dedicated micro-script that ignored everything but entering the door. 

L'idée générale, c'est donc d'avoir deux "personnages" pour une porte, l'un représentant le point d'entrée et l'autre le point de sortie. Le mécanisme d'attache qui permet à Spongebop de rester pendue à son clou peut aussi servir pour lier les portes. Bilou, lui, se liera à la porte "entrée", et la suit de la même façon que dumblador suit Bilou quand il le transporte.

The overall idea is to have two game objects involved in a door-to-door transit: one being the incoming door, and the other being the target location. There will be a one-way link between them in the level script. As part of the 'entering' trigger, Bilou would attach to the input door, which is itself attached to a target GOB. Using that to transport Bilou to the destination should work quite nicely: it's been years that tracking the attached object works nicely. The question is "how do I send back the door once Bilou has left?"

I cannot just "track an object left at the original position", because so far, the engine only track *one* object at a time. But I could record the position before leaving, and -- with the help of a new controller -- track that position. In fact, I already have such "record position" behaviour as part of the "grid" controller used by bouncy branch and furblock.

Coding directly such a multi-step mechanics didn't sound a wise move to me, but I had an animation for the health power-up that made it circle around ... and a notebook entry suggesting to do that with lines of code rather than lines of pixels. I'll save the introduction of an invisible permanent object to circle around if I inject "reccoords" and "track(recorded)" in that health pick-up ... which has just been completed today. 

Voilà donc un premier pas franchi: ce petit point bleu volant a enregistré sa position d'origine comme l'aurait fait une porte et est en train de se servir du nouveau contrôleur pour s'orienter et graviter autour. 

Bon, et se faire transporter ne sera pas tout: je voudrais aussi qu'on ait l'impression que Bilou *rentre* dans la porte avant le transport. Quelque-chose de plus convaincant que le simple décalage vers le noir de la version BASIC où appuyer sur "haut" un peu trop à gauche ou à droite nous enverrait à travers le chambranle, la main devenue noire de Bilou ressemblant à un trou de trop dans le mur :P  

And I must admit I injected significant time in thinking how Bilou would *enter* the door. I know it isn't required to see him walk into the door like Bubsy did, and likely the spin at the start isn't strictly required either, but I intend to use it as the excuse to align Bilou with the door such that I can later fade him to black without having a Bilou-shaped hole dug into the wall (QBilou.bas did that ^^) nor require pixel-precise location to activate the door (Super Princess Peach did that >_<)

edit: If I give the engine one extra opcode to "attach to the object that object is attached to", then all those extra steps about the "door" acting as a flying carpet that takes you to a given destination and then goes back to its anchor location becomes useless...