Better gravity projectile launching?

[Major Cooke]

Replicating the Doom 2016 imp's gravity fireballs is a tad bit more difficult than I thought it would be. I'm trying to properly calculate the throwing distance and how high the projectile needs to be launched in order to hit the target. For right now I'm just pretending there's no obstructions like low ceilings or anything like that, though I will eventually turn my focus to it if possible.

[Matt]

It's far from perfect but here's what I've been doing with the marines' grenade launchers in HD:

Code: Select all

    void A_DropAdjust(class<actor> missiletype,double dist=0,bool userocket=false){
        double dist=max(1,(target?distance2d(target):0));
        double spd=getdefaultbytype(missiletype).speed;
        if(getdefaultbytype(missiletype).gravity&&dist>spd){
            if(userocket&&missiletype is "GyroGrenade")spd*=6.4; //used only for the gyrorockets
            int ticstotake=dist/spd;
            int dropamt=0;
            for(int i=1;i<=ticstotake;i++){
                dropamt+=i;
            }
            pitch-=min(atan(dropamt/dist),30);
        }

        //because we don't shoot from height 32 but 42
        if(dist>0)pitch+=atan(10/dist);
    }

(That cap on the pitch change should probably be omitted along with the additional adjustment for shooting height)

EDIT: Dropamt should also be multiplied by the projectile's actual gravity - I've gotten away with assuming 1 for everything since that's all that the HD marines will ever shoot.

[Major Cooke]

This is called just once, right before actually doing A_SpawnProjectile for example, right?

[Matt]

Yeah.

You could change the last line to have it return a pitch value instead of directly changing the caller's pitch if you want to do more adjustments (or you need the shooter facing a different pitch for whatever reason).

[Major Cooke]

Hmm, do you think this could also apply to monster leaping?

Bearing in mind I may also need to slow down the speed based on distance... not quite sure what I should do there.

[Matt]

I see no reason why it would not! (and thanks for the reminder too...)

The angle calculation should work at any distance for the same speed (and at least the same elevation), though the leaping monster might think it's a good idea not to leap as hard in case it misses and overshoots. I would have it determine the ideal speed and save that variable somewhere to be called in the drop compensation function.