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Initial PART doc
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(Initial PART doc)
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{{research|3|We don't know anything about this format.}}
{{research|1|Key descriptions are subject to corrections}}


The '''PART format''' controls particles. The format is nearly entirely unknown.
The '''PART''' [[effect script]] format is used to configure ''particle effects''.
 
Particles are the most widely-used effect in ''Metroid Prime'', with approximately
3,500 unique scripts across the [[PAK_(Metroid_Prime)|PAK archives]]. Each script configures a complete ''particle system''
that may draw into the scene.
 
The particle system is configurable to generate many visual effects:
 
* Flames and smoke
* Floating embers
* Water splashes/drips
* Dust and dirt in windy conditions
* Volumetric light "shimmers"
* Energy/plasma discharges
* Many others
 
The concept behind the particle system is quite simple: lots of
view-aligned (camera-facing) quadrilaterals (rectangles) with a texture-image
are emitted, positioned, rotated, sized, colored, etc... according to the
parameters in the particle script.
 
== Particle Instance ==
 
Using the ''power-in-numbers'' principle, sophisticated visual effects
may be assembled from a large number of individual ''particles''.  
The effect runtime manages the state of all
active particles and their visual properties.
 
For each frame, each particle does the following primary tasks:
 
* Integrates all velocity sources, applies time-scale and advances position 1/60th of a second
* Evaluates local transforms
** Scale
** View-aligned rotation
** View-aligned offset
* Evaluates particle color (shader-multiplied with texture-image)
 
There are other operational steps activated and controlled by the script
 
== Emitter ==
 
Each particle-system employs a single ''emitter'' (<code>EMTR</code>) context.
The emitter generates a specified number of particles each frame; determining
the initial position and velocity-vector for each. It also evaluates a lifetime
(frame count) for each particle to be in the scene.
 
Emitters are represented by multiple node-classes:
 
=== Point Emitter (<code>SEMR</code> and <code>SETR</code>) ===
 
Both nodes receive position and velocity vector parameters.
All particle instances are constructed using the parameters directly.
 
The differences between <code>SEMR</code> and <code>SETR</code> are presently unknown.
 
=== Sphere Emitter (<code>SPHE</code>) ===
 
The *sphere emitter* randomly evaluates a point on a sphere of specified
offset-vector and radius. The velocity vector is computed from the sphere's
normal and scaled by a specified amount.
 
=== Partial-Sphere Emitter (<code>ASPH</code>) ===
 
Same as the sphere emitter; with additional angular constraints
to randomly evaluate within. Therefore, only a sphere-section is emitted from.
 
== PART Keys ==
 
'''Scope''' is one of (''Constant'', ''System'', ''Particle'')
 
* ''Constant'' parameters are evaluated once initially and retained within the system.
* ''System'' parameters are evaluated per-system, per-frame.
* ''Particle'' parameters are evaluated per-system, per-frame, per-particle-instance.
 
{| class="wikitable"
!FourCC
!Scope
!Data Type
!Description
!Notes
|-
|<code>EMTR</code>
|System
|<code>SEMR</code>, <code>SETR</code>, <code>SPHE</code>, <code>ASPH</code>
|Emitter attachment
|References the object responsible for positioning and setting the initial velocity of new particles
|-
|<code>MAXP</code>
|Constant
|<code>int</code>
|Maximum particle count
|The maximum number of particle instances that may exist simultaneously. The emitter will suspend emissions when this count is reached.
|-
|<code>GRTE</code>
|System
|<code>float</code>
|Generation rate
|An accumulated floating-point value that specifies how many particles to generate each frame. A value of 1.0 will generate one particle each frame. A value of 2.0 will generate two particles per frame. A value of 0.5 will generate one particle every other frame.
|-
|<code>LTME</code>
|System
|<code>int</code>
|Particle lifetime
|Count of frames for generated particles to exist in the scene
|-
|<code>PSLT</code>
|Constant
|<code>int</code>
|Particle-system lifetime
|Count of frames for emitter to generate particles. Default behavior is infinite if <code>PSLT</code> not specified.
|-
|<code>PSTS</code>
|Constant
|<code>float</code>
|Particle-system time-scale
|Factor to multiply with time-differentials (velocities, gen-rates and lifetimes).
|-
|<code>ICTS</code>
|Constant
|<code>int</code> (data ref)
|Concurrent particle-system
|Specifies an external particle script to construct into a parallel system that shares time and space.
|-
|<code>IDTS</code>
|Constant
|<code>int</code> (data ref)
|Deferred particle-system
|Specifies an external particle script to construct a particle system that shares space, but doesn’t start emitting until this system’s emitter stops.
|-
|<code>KSSM</code>
|Constant
|Compound
|Child effect tree
|A tree structure that constructs an arbitrary set of external particle effects and starts them emitting after specified frame-counts.
|-
|<code>SIZE</code>
|Particle
|<code>float</code>
|Particle size
|Proportional scale (against normalized device coordinates) of the particle instance
|-
|<code>ROTA</code>
|Particle
|<code>float</code>
|View-aligned rotation angle
|Angle (in degrees) to rotate the particle counter-clockwise around the view-axis.
|-
|<code>POFS</code>
|Particle
|<code>float3</code>
|View-aligned particle offset
|Vector to translate particle instance after view-alignment
|-
|<code>COLR</code>
|Particle
|<code>float4</code>
|Particle color
|RGBA vector specifying a color to multiply the particle instance’s texture with.
|-
|<code>AAPH</code>
|Constant
|<code>bool</code>
|Additive blending
|Particle instances are drawn with graphics pipeline configured to add particle’s color with existing framebuffer color.
|-
|<code>TEXR</code>
|Constant
|<code>int</code> (data ref)
|Texture attachment
|Specifies the texture resource to map to each particle instance’s surface.
|-
|<code>TIND</code>
|Constant
|<code>int</code> (data ref)
|Indirect texture attachment
|Certain particle effects are drawn after the main scene against the player’s ‘visor’. Effects that simulate visor water-droplet refraction use an indirect texture to warp texture coordinates when sampling the underlying scene.
|-
|<code>ORNT</code>
|Constant
|<code>bool</code>
|Oriented particle mode
|The X-axis of generated particles will extend towards the particle’s emitter. The Y and Z axis are computed via up-vector and cross product. In this mode, <code>ROTA</code> specifies the particle’s aspect ratio instead of rotation. Commonly used to implement radial light-beams.
|-
|<code>MBLR</code>
|Constant
|<code>bool</code>
|Motion blur mode
|Each particle instance is over-drawn a specified number of times along the velocity-vector.
|-
|<code>MBSP</code>
|Constant
|<code>int</code>
|Motion blur sample count
|Number of times to draw motion-blur particle instances.
|-
|<code>LINE</code>
|Constant
|<code>bool</code>
|Line rendering mode
|Instead of the view-aligned appearance, particle instances are drawn as a line with a trailing, specified length
|-
|<code>WIDT</code>
|Particle
|<code>float</code>
|Line width
|In line mode, specifies the projected line width (in 480p pixels)
|-
|<code>LENG</code>
|Particle
|<code>float</code>
|Line length
|In line mode, specifies the line length (as a multiple of each frame's velocity magnitude)
|-
|<code>PMUS</code>
|Constant
|<code>bool</code>
|Non-view-aligned quad mode
|In addition to the view-aligned appearance, particle instances transform a normalized, non-view-aligned quadrilateral in the XZ plane. All ‘particle model’ parameters (<code>PMAB</code>, <code>PMSC</code>, <code>PMCL</code>, etc…) affect this quad.
|-
|<code>PMSC</code>
|Particle
|<code>float3</code>
|Particle-model scale
|Local particle model scale vector
|-
|<code>PMRT</code>
|Particle
|<code>float3</code>
|Particle-model rotation
|XYZ-euler particle model rotation
|-
|<code>PMOP</code>
|Particle
|<code>float3</code>
|Particle-model offset
|Local particle model offset (after scale and rotation)
|-
|<code>PMAB</code>
|Constant
|<code>bool</code>
|Particle-model additive blending
|<code>AAPH</code> for particle models
|-
|<code>VELn</code>
|Particle
|<code>WIND</code>, <code>GRAV</code>, <code>SWRL</code>, <code>BNCE</code>, <code>EXPL</code>, <code>IMPL</code>, <code>EMPL</code>, <code>LMPL</code>
|Velocity attachments (1-4)
|In addition to the initial velocity provided by the emitter, other simulated forces may be attached as velocity sources.
|-
|<code>SORT</code>
|Constant
|<code>bool</code>
|Particle depth sort
|Particle instances are sorted from back-to-front in view (for proper alpha-blending)
|-
|<code>ZBUF</code>
|Constant
|<code>bool</code>
|Particle z-buffer write
|Particle instances modify the z-buffer if set
|-
|<code>LTYP</code>
|Constant
|<code>int</code>
|Lamp type enumeration
|Particle emitter is also a dynamic area lamp when non zero (0:off, 1:point, 2:spot)
|-
|<code>LOFF</code>
|System
|<code>float3</code>
|Lamp offset vector
|Local offset from emitter to position lamp
|-
|<code>LDIR</code>
|System
|<code>float3</code>
|Lamp direction vector
|Local direction to cast spot lamps
|-
|<code>LFOT</code>
|Constant
|<code>int</code>
|Lamp falloff type
|Affects how quadratic falloff coefficients are assigned in the lighting shader (0:constant, 1:inverse-linear, 2:inverse-quadratic)
|-
|<code>LFOR</code>
|System
|<code>float</code>
|Lamp falloff radius
|Radius from emitter that lamp casts light
|-
|<code>LCLR</code>
|System
|<code>float4</code>
|Lamp color
|RGBA vector of lamp’s color
|-
|<code>LINT</code>
|System
|<code>float</code>
|Lamp intensity
|Multiplied with lamp color to affect lamp’s energy
|}
 
== PART Nodes ==
 
{{main|Effect Script}}
 
PART scripts share [[Effect Script#Script Nodes|effect nodes]] with other effect script formats.
 
Some nodes are exclusive to PART:
 
* <code>SETR</code>
* <code>SEMR</code>
* <code>SPHE</code>
* <code>ASPH</code>
* <code>SPOS</code>
* <code>PLCO</code>
* <code>PLOC</code>


[[Category:File Formats]]
[[Category:File Formats]]
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