What would that do to cities anyway? Was there ever any discussions how houses would be placed there? Or are we just expected that MagicPerson that creates diagonal roads also redraws and recodes every house GRF? ^^;
This is something I've thought about too. Obviously the answer is no. Existing house sets won't be recoded/drawn. I expect they would line the road at the same angle they would if the road was orthogonal - that is, if they even worked at all.
The solution could be add-on sets of diagonal houses. They would need to be coded so that they only line diagonal roads, and normal houses would need to be prevented from doing so without breaking existing sets.
There's something else to think about too. If you made a grid of diagonal roads the illusion of 3D would be lost. As an experiment, try making a grid of diagonal rails, you'll see what I mean. Diagonal houses would look "flat", also ruining the illusion.
I think that if diagonal roads were ever implemented, then they should only be able to be built by a player - that is leave the game to create roads and towns normally. Perhaps diagonal houses could be placed by the player, and even in that case only as objects (you would have to swap out to the scenario editor to place actual houses manually, also requiring another patch). Thinking about this further, you wouldn'be able to place a diagonal house (or object) directly next to a diagonal road as sections of road and house would have to occupy the same tile, so that's another problem that would need to be overcome. Personally, I could live with the "glitch" of having orthogonal houses along a diagonal road, but then I'd only build short sections anyway, to get rid of those stretches where you have to use a zigzag (which I think looks ridiculous), or as on/off ramps to a motorway (that would be really cool!)
Another thing. Lets say you built a stretch of diagonal road to extend a town, and then continued with orthogonal roads. Would the town recognize this and continue building houses on the orthogonal roads? Would the town continue building orthogonal roads after a diagonal section? Towns do recognize player built roads and continue building houses (and road), even after a long tunnel, for example. At first glance it seems like that could be one possible solution - treat diagonal roads as a "wormhole" like bridges or tunnels, but then you couldn't have junctions on the diagonal sections, so the wormhole idea is probably not viable or practical.
Speaking of diagonal wormholes - as in bridges and tunnels, would these also be coded (and drawn, in the case of bridges)? It'd be really cool if the answer is yes. Maybe that could be applied to rail as well if they were.
How about bus and truck stops? Would we get diagonal versions of those too. Could that lead to diagonal railway stations? Diagonal runways at airports? While we're at it, why not diagonal rivers and canals? Diagonal aqueducts?
"Couldn't you reuse the same code?"
Maybe. A bit. Kind of.
Diagonal roads would be really cool, and I'd love to be able to use them, but I doubt it's going to happen anytime soon, if ever. Even with my (very) limited knowledge of OTTD coding I'm aware of the sheer magnitude of the task. It just isn't that simple, and probably much harder (and time consuming) than I can imagine.
As far as roads are concerned I'd much rather see developers efforts concentrated on NRT (I hope that project hasn't stalled, and wish the devs of that patch every success).