Breaking Ice?

https://zdoom.org/wiki/A_CheckFloor

Edit: Should have also mentioned that you will need to set up a decal and DECALDEF for the floor ice cracks as the engine doesn't apply decals to floor or ceiling flats. These are the states from a projectile that one of my enemies throw, when it hits the floor or ceiling it spawns a decal named "ink splat"

States
	{
		Spawn:
			BALL A 1;
			BALL A 1 ThrustThingZ (0, 6, 0, 1);
			Goto Flight;
		Flight:
			BALL A 1;
			Loop;
		Death:
			TNT1 A 1 A_CheckFloor ("FloorDeath");
			TNT1 A 1 A_CheckCeiling ("FloorDeath");
			Stop;
		FloorDeath:
			TNT1 A 1 A_SpawnItemEx ("InkSplat", 0.0, 0.0, 0.0);
			Stop;
		XDeath:
			TNT1 A 5;
			Stop;
		Crash:
			TNT1 A 1;
			Stop;
	}

You can use UDB to create models to use as "sprites" in floors and ceilings.

Make the crack an actor and spawn it on the explosion

No no no, I think you got me wrong. I want the decal to be spawned but ONLY on the ice, not in any other texture than ICE

If you only want it to spawn on your ice texture you could set up that texture as a specific terrain type and use GetFloorTerrain() in the grenades death state to check for what type of terrain it is on. If it's on ice you would spawn the crack decal/model/sprite, if not they you could spawn a scorch mark.

Edit: I'm assuming you are using Zscript for your mod?

14 hours ago, HorseJockey said:

If you only want it to spawn on your ice texture you could set up that texture as a specific terrain type and use GetFloorTerrain() in the grenades death state to check for what type of terrain it is on. If it's on ice you would spawn the crack decal/model/sprite, if not they you could spawn a scorch mark.

 

Edit: I'm assuming you are using Zscript for your mod?

DECORATE.

What source port are you making this for? 

18 hours ago, HorseJockey said:

What source port are you making this for? 

GZDoom

Ok, so you can use Zscript which is going to be the easiest way. Otherwise I think you would have to use a combination of ACS CheckFloortexture and Decorate. Can you post your grenade's decorate code? You can either make a function that checks floor terrain on projectile death or you can make an annonymous function something like this 

Death:
	TNT1 A 1 A_CheckFloor ("FloorDeath");
	TNT1 A 1 A_CheckCeiling ("FloorDeath");
	Stop;
FloorDeath:
	TNT1 A 0
	{
		if (GetFloorTerrain() == "YourIceTerrain")
		{
			SpawnItemEx()//you would fill this in with the postition you want to decal to spawn and decal
		}
		else
		{
			//do something else on differnt terrain
		}
	}
	Stop;

GetFloorTerrain() info

A_CheckFloor info

TERRAIN info

41 minutes ago, HorseJockey said:

Ok, so you can use Zscript which is going to be the easiest way. Otherwise I think you would have to use a combination of ACS CheckFloortexture and Decorate. Can you post your grenade's decorate code? You can either make a function that checks floor terrain on projectile death or you can make an annonymous function something like this 

Death:
	TNT1 A 1 A_CheckFloor ("FloorDeath");
	TNT1 A 1 A_CheckCeiling ("FloorDeath");
	Stop;
FloorDeath:
	TNT1 A 0
	{
		if (GetFloorTerrain() == "YourIceTerrain")
		{
			SpawnItemEx()//you would fill this in with the postition you want to decal to spawn and decal
		}
		else
		{
			//do something else on differnt terrain
		}
	}
	Stop;

GetFloorTerrain() info

A_CheckFloor info

TERRAIN info

Hmm, I'm not so happy about the use of ZScript, i prefer working in Decorate. I will think of it, then I will post the code if i will need it

Good luck. Maybe someone else has an elegant solution utilizing ACS and Decorate that can post a solution. I'm just not familiar with any functions that would allow you to check floor texture or terrain in Decorate.