Implement explosion damage for missile based weapon

[danilko]

As a player, I want missile type weapon to have explosion effect to impact blast area

Similar effect as describe in
https://www.youtube.com/watch?v=xPk9cxHrPrU

[danilko]

After experimentation, move way from initial raycast based explosion
https://www.youtube.com/watch?v=xPk9cxHrPrU

To a simpler area2D explosion

The reason is the performance can drop to 10 FPS under certain cases when there are 5 - 10 missile explosion happen once.

If reducing the raycast number to lower number, it seem the explosion effect is not that realistic (i.e 60 rays as oppose to 200 rays).

Utilize area2D seem to be much perform as the FPS remain around 60 even with 5 - 10 missile explosions. The tradeoff is less accuracy but overall seem good enough in some degree.

Also utilize deferred method to dynamically adjust raycast parameters

During missle explosion, utilize deffered to avoid warning Recommend to use deffered (reference from here godotengine/godot#33766)

In Missile.cs

    public override void Explode()
    {
        base.Explode();

        CallDeferred("createExplosion");

        QueueFree();
    }

    private void createExplosion()
    {
        ExplosionBlast explosionBlast = (ExplosionBlast)((PackedScene)GD.Load("res://projectiles/ExplosionBlast.tscn")).Instance();
        GameWorld.AddChild(explosionBlast);
        explosionBlast.Initialize(Source, SourceTeam,  GameWorld, DamageRayRadius, Damage, GlobalPosition);
    }

Also in ExplosionBlast.cs

    public void Initialize(Node2D source, Team sourceTeam, GameWorld gameWorld, float raidus, float damage, Vector2 position)
    {
        CollisionShape2D detectRadius = (CollisionShape2D)GetNode("CollisionShape2D");

        // Use SetDeferred to change the pyhsic world when it is ready
        // reference from here https://github.com/godotengine/godot/issues/33766
        ((CircleShape2D)(detectRadius.Shape)).SetDeferred("radius", raidus);

        Source = source;
        SourceTeam = sourceTeam;
        Damage = damage;

        // Set the parent to gameworld
        if (!IsConnected(nameof(ExplosionBlastDamageSignal), gameWorld, "_onDamageCalculation"))
        {
            Connect(nameof(ExplosionBlastDamageSignal), gameWorld, "_onDamageCalculation");
        }

        GlobalPosition = position;

        AgentExplosionParticle agentExplosionParticle = (AgentExplosionParticle)GetNode("AgentExplosionParticle");
        agentExplosionParticle.SetTrigger(true);

        IsInitialize = true;
    }

[danilko]

Also change overall projectile from raycast + area2D to pure Area2D again.

As it seem with godot 3.3.4, the Physics for Area2D are much more accurate alone.

This allows better performance for browser based export.

[danilko]

Close the issue with current implementation