Game Engine Bread

Step 0. Let's make an oil puddle that can be burned with fire.  If you want simple one(single actor with static mesh, limited shape), don't need to use physics material or multiple fire actors.  In this time, we will make more flexible system. Unlimited shape, and perhaps it will work with dynamic decal if you change a bit more. Related post :  Surface reaction character Step 1. These are final assets. The fire particle is from Unreal Engine 4 sample. Open 'Project settings'. Add Physical surface properties. Step 2. Create new PhysicalMaterial and select surface type. Step 3. Create a oil material and change Phys Material. Make planes with the material. Step 4.  This is the oil fire actor blueprint. If you look at the function name, you'll see what it does. Use overlapping actors array and avoid line-trace function calls. Step 5.  Fire with LMB. More... ...

Step 0. Let's make a surface reaction character on Unreal engine 4. We can make it with trigger box(volume). But character with physical material is more accurate and easier to setup. Step 1. These are final assets. Maybe you don't need 'mud' things. Open 'Project settings'. Add Physical surface properties. Step 2. Create new PhysicalMaterial and select surface type. Step 3. Create a material and change Phys Material. Step 4.  This is the character blueprint.  How to find a slope vector from normal : https://stackoverflow.com/questions/4372120/how-do-i-calculate-the-downward-slope-vector-of-a-3d-polygon More...  In most cases, we do not need to do check surface on every tick.