Destructable Terrain

Next we’ll add destructible terrain. This is a fairly simple trick, but it’s definitely worth applying, as it’s yet another detail that makes your world feel more real

Burnable Grass

Since we have missiles and flames in our game, I figured we’d do breakable objects a little differently and make them burnable instead. I think you can do it. Use sGrass as the sprite, and then make it toggle to frame 1 when it get’s hit by missiles or flames

// oGrass Create
image_speed = 0;

// oMissile Step Event
//// MOVEMENT
//// DEATH
//// HURT PLAYER
//// HURT GRASS
{
	if(place_meeting(x, y, oGrass)){
		with(instance_place(x, y, oGrass)){
			image_index = 1;
		}
	}
}

// oSpark Step Event
//// MOVEMENT
//// DEATH
//// HURT PLAYER
//// HURT GRASS
{
	if(place_meeting(x, y, oGrass)){
		with(instance_place(x, y, oGrass)){
			image_index = 1;
		}
	}
}

This should be pretty straight forward, the projectile changes the grass’s frame to 1 when collisions happen

instance_place: If you need a refresher on this, be sure to refer back to “Platformer Turrets Missile Turrets

parenting: This current scenario also highlights the case for parenting. oMissile and oSpark have the same behaviour, so it could be worth moving some of that shared code to a oEnemyBullet object

Now when we test it out we should have burnable grass! Now the world feels a little more dynamic, and the turrets feel a little more mean 😿

Curable Terrain

But what about the player bullets? Well, I didn’t want the player to be just another source of destruction, to let’s give the player’s bullets a green thumb. Can you make the player bullets heal (unburn), they collide?

// oBullet Step
//// TURRET COLLISION
//// WALL COLLISION
//// APPLY MOVEMENT
//// GRASS COLLISION
{
	if(place_meeting(x, y, oGrass)){
		with(instance_place(x, y, oGrass)){
			image_index = 0;
		}
	}
}

Same code as before 😉

Now the grass can be healed as well as burned 😍 (I guess we have aloe bullets?)

More Burnables

No need to settle with grass. Let’s make more burnable things! This is actually a great opportunity for parenting and polymorphism. Let’s add a bush and then generalize the 2 burnables into a oBurnable object

// oBurnable Create
image_speed = 0;

// oGrass Create
//// delete code and let it inherit from oBurnable

// oBush Create
//// this should also inherit from oBurnable

// oBullet Step
//// TURRET COLLISION
//// WALL COLLISION
//// APPLY MOVEMENT
//// BURN BURNABLES
{
	if(place_meeting(x, y, oBurnable)){
		with(instance_place(x, y, oBurnable)){
			image_index = 0;
		}
	}
}

// oMissile Step Event
//// MOVEMENT
//// DEATH
//// HURT PLAYER
//// BURN BURNABLES
{
	if(place_meeting(x, y, oBurnable)){
		with(instance_place(x, y, oBurnable)){
			image_index = 1;
		}
	}
}

// oSpark Step Event
//// MOVEMENT
//// DEATH
//// HURT PLAYER
//// BURN BURNABLES
{
	if(place_meeting(x, y, oBurnable)){
		with(instance_place(x, y, oBurnable)){
			image_index = 1;
		}
	}
}

Here I’ve created a generic oBurnable object, assigned it to be the parent of both oGrass and oBush

We get some code sharing benefit since we don’t need to write out image_speed twice, but the bigger benefit is the polymorphism. Now oPlayer, oMissile, and oSpark only need to handle collisions with oBurnable then it get’s both oGrass and oBush collisions for free 😎

I still see a lot of duplicate code, the burnable collision, looks very similar the player collision: Correct 🤓! In the polymorphism section I mentioned that we could, in theory, lump oPlayer, and oTurret under a super generic oTargetable parent. We could try lumping oBurnable into that mold as well. It would just have a max hp of 1. If we did that the bullet’s would only need to handle collisions w/ oTargetable 😲. Proceed w/ caution though, each targetable has slightly different behaviours when the collisions happen, so you’ll need to be careful accounting for that in the generic parent

Burnable bushes and grass ✅

Further Inspiration

Destructable terrain comes up in a lot of games, but I was specifically inspired by this vlaambeer talk. He goes over a bunch of easy tricks you can apply to make your game more polished, so it’s definitely worth checking out

Also, if we look at the way hollow knight does destructible terrain, you can see that a bunch of pieces fly out

Feel free to try adding that as a side exercize, I’ve got a video here on exploding coins that can be used as a starting point