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Overview

Material effects expose the way a surface material reacts to other materials. For example, a metal material will react to bullet impacts differently (i.e. by generating sparks) than a grass material does (i.e. by generating dirt or dust).

Because hard-coding these effects in code would be impossible to keep updated, these effects are exposed through a small number of asset files.

Required Files

  • The SurfaceTypes, defined in Game/Libs/MaterialEffects/SurfaceTypes.xml defines the physical properties of all the available material types. It can be edited with any text editor.
  • The MaterialEffects, which usually resides in Game/Libs/MaterialEffects/MaterialEffects.xml, define the interaction of 2 materials, i.e. what effect to generate on an interactive event between 2 surface types. For example, it defines that when a bullet collides with the soil surface, a dirt particle effect is spawned. This file has to be read and edited with Microsoft Excel.
  • The Effect libraries, found in Game/Libs/MaterialEffects/FXLibs, contain the associated effects. The ammo files in Game/Scripts/Entities/Items/Ammo define what material a bullet is made from.

Creating a New Material Effect

Adding a Surface type to SurfaceTypes.xml

A surface type is defined by the XML element SurfaceType. Its attribute name is the one that can be selected in the Sandbox.

Surface types defined here will appear as options in the drop down list of the Material Editor. The other attribute type is optional. It can be used in other processes by game code. The physical parameters are defined by the Physics element.

Physics block

Parameter

Description

friction

A material's friction (friction is the average of contacting materials). A recommended default is 0.8. Internally it's clamped to 0.1 if it's below that.

elasticity

Also known as Bounciness. It's averaged from 2 materials. Clamped to 0 as the elasticity can't be negative. Recommended default is 0, unless you specifically want something bouncy.

breakable_id

Procedural breakability index; a corresponding boolean cutter shape should be registered in the physics.lua.

pierceability

Integer from 0-15, with 0 being the least pierceable. For each ray, a hit is pierceable if ray's pierceability is less than the material's pierceability.

break_energy

Energy= (mass*velocity^2/2) and it refers to the colliding object that triggers breaking (typically should be tweaked based on bullets' parameters).

hit_points

Each collision above break_energy takes round_to_int(collision_energy/break_energy) hitpoints; real breaking only happens when hit points are depleted.

hit_maxdmg

Max amount of hitpoints a single hit can take.

hit_radius

Hitpoints can be localized with this radius (i.e. it'll require that all hits are within this radius from each other); 0 disables.

hit_lifetime

Lifetime for localized hits info, it expires after that (note that it's just a hint; it can expire earlier if there are too many newer hit infos, or later if there's no concurrency).

hole_size

Characteristic size for boolean carving; shape registered in physics.lua is scaled by this size / shape's characteristic size (specified in physics.lua).

hole_size_explosion

Same as above, but for explosions (first one is for collisions with bullets and general physicalized objects).

breakable_2d

If set, uses 2D breakability instead of 3D boolean carving.

vehicle_only_collisions

Entire node will only collide with vehicle (even if material with this flag is only applied to some triangles of it).

<SurfaceType name="mat_new_material">
 <Physics friction="0.5" elasticity="1"  pierceability="3" can_shatter="1"  />
</SurfaceType>

The breakable parameters are defined by the breakable_2d element.

breakable_2d block

Parameter

Description

blast_radius

Procedural hole size (note that when an object hits the surface, it will use the colliding area's size instead – unless it's smaller than this).

blast_radius_first

Same as above, but for the first hit that breaks the object.

vert_size_spread

Vertical hole size = blast_radius * (1+random(0..vert_size_spread)).

rigid_body

Broken pieces will be physicalized as rigid bodies (otherwise as physical particles).

lifetime

Pieces will expire after that (currently it'll only happen when the player looks away, but that might change).

cell_size

Cell size for the breakage grid (default 0.1).

max_patch_tris

Governs the number of grid triangles in each shard (triangles are taken from the breakage grid, around the hit point and within blast_radius); default is 6.

filter_angle

Filters the hole's edges with this angle to avoid the 'saw tooth' look; default 0 (disabled), but 75 seems to look good in most cases.

shard_density

Used to calculate shards' masses and buoyancy (float/sink) properties; default 1200.

max_fracture

Triggers full fracture when the object is damaged beyond this (0..1); default 1.

particle_effect

Name of the effect to generate along the broken edges.

fracture_fx

Single effect for each breakage.

full_fracture_fx

Effect to play when a full fracture condition is triggered.

no_procedural_full_fracture

In case of full fracture, doesn't generate broken pieces procedurally, relies only on full_fracture_fx.

use_edge_alpha

Sets alpha of vertices along the broken edges to 0 (should be used if there's a special shader that expects that).

crack_decal_mtl

Puts a decal with this material whenever a break occurs.

crack_decal_scale

Sets the decal size wrt the hole size (0 disables crack decals).

Besides the <Physics> element, the optional <BreakageParticles> defines the type of particle that will be spawned on breakage. Its attribute type defines the break event and can take one of the following values:

  • breakage
  • joint_break
  • joint_shatter
  • destroy

The effect attribute points to the particle effect that will be spawned on breakage, along with the attributes count_per_unit, count_scale and scale defining respectively the number of particle systems to be spawned, and their scale. Normally, their value should be 1.

Note

Ammo surface types do not need to be added to the SurfaceTypes.xml file.

Adding Events to MaterialEffects.xml

New surface types have to be added both as a row and as a column, and have to be kept in the same order. The cross reference between 2 surface types defines the type of event that will happen on interaction.

Surface types that are only called by code are required to only have rows and must be added at the bottom, below the surface types defined in SurfaceTypes.xml (the exception is when it is needed to be used on materials through the Material Editor).

Obsolete:

It should be noted that Objects which need to use Alpha Test for Collision (railings, etc) should have a surface type with the suffix _RayProxy. This is also used to allow characters to see through glass objects and such as part of the perception system.

Adding Material Effect Events

Material effect (MFX) events are those events that occur at interactions between 2 surface types, as defined in MaterialEffects.xml. They are named according to the following schema:

<MFX_lib_name>:<MFX_name>

For instance, bulletimpacts:hit_mat_soil points to the event (and XML element) hit_mat_soil defined in Game/Libs/MaterialEffects/FXLibs/bulletimpacts.xml.

This event is defined as follows in the old library-based PFX1 system as well as the new Particle Effect system:

<Effect name="hit_mat_soil" delay="0.05">
       <Sound>
              <Name>sounds/physics:bullets/impacts:grass</Name>
       </Sound>
       <RandEffect>
              <Decal minscale="0.03" maxscale="0.07">
                    <Filename>textures/decals/metal.dds</Filename>
                    <Material>materials/decals/terrain_soil</Material>
              </Decal>
       </RandEffect>
       <RandEffect>
              <Particle>
                    <Name minscale="0.6" maxscale="1.2" maxscaledist="80">bullet.hit_soil.a</Name>
<Direction>Normal</Direction>
              </Particle>
              <Particle>
                    <Name minscale="0.6" maxscale="1.2" maxscaledist="80">bullet.hit_soil.b</Name>
<Direction>Ricochet</Direction>
              </Particle>
              <Particle>
                    <Name minscale="0.6" maxscale="1.2" maxscaledist="80">bullet.hit_soil.c</Name>
<Direction>Reverse</Direction>
              </Particle>
       </RandEffect>
       <FlowGraph name="dirt_bullet_hit" maxdist="2"/>
</Effect>

Modifying Attributes That Were Set in the Particle Editor

With the new Particle Editor system, it is possible to modify attributes in the bulletimpacts.xml file as well. This can be done as follows:

<RandEffect>
	<Particle>
		<Name minscale="0.6" maxscale="1.2" maxscaledist="80">particles/collisions/bullet_soil_dir.pfx
		<Attribute name="strength" type="float" value="0.5"/>
		<Attribute name="debris" type="bool" value="0"/>
		</Name> 
		<Direction>Normal</Direction>
	</Particle>
</RandEffect>

Each effect Name can have the following optional additional attributes:

Attribute

Description

Direction

Effect spawn direction:

  • Normal(default) surface normal.
  • Ricochetreflection of hit source direction off surface normal.
  • ProjectileDirAllows to inherit directions from the projectile source for material effects. It is recommended to use this attribute over Normal or Ricochet
  • Reverse: reverse of hit source direction.

Minscale / Maxscale

Scale to apply to effect when it's near / far from camera.

Maxscaledist

Distance at which maxscale applies.

Maxdist

Max distance to show effect.

Adding an Ammo Surface Type

The surface type for ammunition is the attribute name of the XML element ammo in an ammo file. Its value is required to be the same as the value in the MFX table.

Debugging

A couple of console variables exist to debug the Material Effects in the Sandbox or the Game Launcher:

  • mfx_Debug0 (Disabled) / 1 (Collisions) / 2 (Breakage) / 3 (Both)

    [MFX] Running effect for:
          : Mat0=mat_metal_shell
          : Mat1=mat_concrete
    impact-speed=5.756900 fx-threshold=2.000000 mass=0.018203 speed=0.147297
    
  • mfx_DebugVisual0 (Disabled) / 1 (Basic visual debugging) / 2 (Enhanced visual debugging):
  • mfx_DebugVisualFilter0 (Disabled) / Name (Only show visual debug information for this Material Effect).
  • mfx_DebugFlowGraphFX0 (Disabled) / 1 (Show debug information for triggered Material Effect flowgraphs)
Material FlowGraphFX manager: Effect Test1 was triggered.
Material FlowGraphFX manager: Effect 'Test1' .Dynamic parameter 'BlendOutTime' set to value 0.056

Note

Non visual debug information will be shown in the console.

Reloading

To reload all Material Effects from the MaterialEffect.xml file it is possible to use the console command mfx_reload.

Note

Because it is necessary to have matching rows and columns in the MaterialEffects.xml file it is possible to set mfx_debug to 1/2/3 for an automatic check before reloading the Material Effects. Any warnings are outputted to the console.

Known issues

The MFX table is prone to breakage and unexpected behavior when the order in rows and columns is different from the expected one, e.g. after using find-replace and/or inserting cells.

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