The Material ID operator can be used to assign a material ID to particles.
Operation: the material ID operation.
Bake into particle meshes: instead of being a post-process particle override, the override will be baked into the existing particle mesh and then cleared.
“Keep existing” mode is only useful when “bake into particle meshes” is enabled, since it will leave material ID override values unchanged.
Static mode sets material IDs to a static value.
Random mode chooses a random material ID from a range of possible IDs.
Frequency mode controls the random frequency of specified material IDs.
Cycle mode assigns material IDs to particles each frame, cycling over a range of values as time progresses.
Range: the range of material ID values to cycle over.
Change/frame: the amount to progress the cycle each frame.
Ping-pong: values will cycle from max to min at the same rate they cycled from min to max.
Change Current mode clamps current material IDs to a range of values.
Clamp: clamps the current material ID value to the range using a min/max operation.
Loop: loops the current material ID value, to the range using a modulus operator.
Min/Max: the desired range of values.
In clamp mode, an ID of 7 clamped to a min/max of 1 and 5 will be set to 5: min(7, 5) = 5.
In loop mode, an ID of 7 looped to a min/max of 1 and 5 will be set to 2: 7 % 5 = 2.
3ds Max displays material IDs in a 1-based fashion, but stores them in a 0-based fashion. This becomes slightly confusing when assigning material IDs directly, from other values. For example, a UI value of 1 is actually a stored value of 0 - so assigning a particle birth ID value of 0 to a particle’s material ID channel is effectively the same as assigning a UI value of 1. In other words, whatever birth ID value you assign as the material ID, will be interpreted as a UI value of [birth ID + 1] anywhere else in 3ds Max where material IDs are used (example: Multi-Sub Material).
Velocity mode derives material IDs from particle velocities, by using the ratio between particle velocity magnitudes and a range of target velocity values (which is normalized to a value between 0 and 1). That ratio is then converted to a material ID value between ID min and ID max.
Velocity Min: the minimum velocity used to construct the target value range.
Velocity Min: the minimum velocity used to construct the target value range.
ID Min: the minimum resulting material ID.
ID Max: the maximum resulting material ID.
Input object list: the input objects whose surfaces material IDs will be taken from.
Sample type: controls which sampler will be used to determine closest-object proximities for particles.