261 lines
6.5 KiB
ReStructuredText
261 lines
6.5 KiB
ReStructuredText
.. _doc_particle_systems_2d:
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Particle Systems (2D)
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=====================
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Intro
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-----
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A simple (but flexible enough for most uses) particle system is
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provided. Particle systems are used to simulate complex physical effects
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such as sparks, fire, magic particles, smoke, mist, magic, etc.
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The idea is that a "particle" is emitted at a fixed interval and with a
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fixed lifetime. During his lifetime, every particle will have the same
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base behavior. What makes every particle different and provides a more
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organic look is the "randomness" associated to each parameter. In
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essence, creating a particle system means setting base physics
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parameters and then adding randomness to them.
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Particles2D
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~~~~~~~~~~~
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Particle systems are added to the scene via the
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:ref:`Particles2D <class_Particles2D>`
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node. They are enabled by default and start emitting white points
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downwards (as affected by the gravity). This provides a reasonable
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starting point to start adapting it to our needs.
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.. image:: /img/particles1.png
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Texture
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~~~~~~~
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A particle system uses a single texture (in the future this might be
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extended to animated textures via spritesheet). The texture is set via
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the relevant texture property:
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.. image:: /img/particles2.png
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Physics variables
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-----------------
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Before taking a look at the global parameters for the particle system,
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let's first see what happens when the physics variables are tweaked.
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Direction
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---------
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This is the base angle at which particles emit. Default is 0 (down):
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.. image:: /img/paranim1.gif
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Changing it will change the emissor direction, but gravity will still
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affect them:
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.. image:: /img/paranim2.gif
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This parameter is useful because, by rotating the node, gravity will
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also be rotated. Changing direction keeps them separate.
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Spread
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------
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Spread is the angle at which particles will randomly be emitted.
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Increasing the spread will increase the angle. A spread of 180 will emit
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in all directions.
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.. image:: /img/paranim3.gif
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Linear velocity
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---------------
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Linear velocity is the speed at which particles will be emitted (in
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pixels/sec). Speed might later be modified by gravity or other
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accelerations (as described further below).
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.. image:: /img/paranim4.gif
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Spin velocity
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-------------
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Spin velocity is the speed at which particles turn around their center
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(in degrees/sec).
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.. image:: /img/paranim5.gif
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Orbit velocity
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--------------
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Orbit velocity is used to make particles turn around their center.
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.. image:: /img/paranim6.gif
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Gravity direction & strength
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----------------------------
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Gravity can be modified as in direction and strength. Gravity affects
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every particle currently alive.
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.. image:: /img/paranim7.gif
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Radial acceleration
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-------------------
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If this acceleration is positive, particles are accelerated away from
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the center. If negative, they are absorbed towards it.
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.. image:: /img/paranim8.gif
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Tangential acceleration
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-----------------------
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This acceleration will use the tangent vector to the center. Combining
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with radial acceleration can do nice effects.
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.. image:: /img/paranim9.gif
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Damping
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-------
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Damping applies friction to the particles, forcing them to stop. It is
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specially useful for sparks or explosions, which usually begin with a
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high linear velocity and then stop as they fade.
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.. image:: /img/paranim10.gif
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Initial angle
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-------------
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Determines the initial angle of the particle (in degress). This parameter
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is mostly useful randomized.
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.. image:: /img/paranim11.gif
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Initial & final size
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--------------------
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Determines the initial and final scales of the particle.
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.. image:: /img/paranim12.gif
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Color phases
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------------
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Particles can use up to 4 color phases. Each color phase can include
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transparency.
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Phases must provide an offset value from 0 to 1, and always in
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ascending order. For example, a color will begin at offset 0 and end
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in offset 1, but 4 colors might use different offsets, such as 0, 0.2,
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0.8 and 1.0 for the different phases:
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.. image:: /img/particlecolorphases.png
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Will result in:
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.. image:: /img/paranim13.gif
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Global parameters
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-----------------
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These parameters affect the behavior of the entire system.
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Lifetime
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--------
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The time in seconds that every particle will stay alive. When lifetime
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ends, a new particle is created to replace it.
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Lifetime: 0.5
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.. image:: /img/paranim14.gif
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Lifetime: 4.0
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.. image:: /img/paranim15.gif
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Timescale
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---------
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It happens often that the effect achieved is perfect, except too fast or
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too slow. Timescale helps adjust the overall speed.
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Timescale everything 2x:
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.. image:: /img/paranim16.gif
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Preprocess
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----------
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Particle systems begin with 0 particles emitted, then start emitting.
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This can be an inconvenience when just loading a scene and systems like
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a torch, mist, etc begin emitting the moment you enter. Preprocess is
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used to let the system process a given amount of seconds before it is
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actually shown the first time.
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Emit timeout
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------------
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This variable will switch emission off after given amount of seconds
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being on. When zero, itś disabled.
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Offset
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------
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Allows to move the emission center away from the center
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Half extents
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------------
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Makes the center (by default 1 pixel) wider, to the size in pixels
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desired. Particles will emit randomly inside this area.
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.. image:: /img/paranim17.gif
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It is also possible to set an emission mask by using this value. Check
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the "Particles" menu on the 2D scene editor viewport and select your
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favorite texture. Opaque pixels will be used as potential emission
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location, while transparent ones will be ignored:
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.. image:: /img/paranim19.gif
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Local space
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-----------
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By default this option is on, and it means that the space that particles
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are emitted to is contained within the node. If the node is moved, all
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particles are moved with it:
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.. image:: /img/paranim20.gif
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If disabled, particles will emit to global space, meaning that if the
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node is moved, the emissor is moved too:
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.. image:: /img/paranim21.gif
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Explosiveness
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-------------
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If lifetime is 1 and there are 10 particles, it means every particle
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will be emitted every 0.1 seconds. The explosiveness parameter changes
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this, and forces particles to be emitted all together. Ranges are:
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- 0: Emit all particles together.
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- 1: Emit particles at equal interval.
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Values in the middle are also allowed. This feature is useful for
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creating explosions or sudden bursts of particles:
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.. image:: /img/paranim18.gif
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Randomness
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----------
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All physics parameters can be randomized. Random variables go from 0 to
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1. the formula to randomize a parameter is:
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::
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initial_value = param_value + param_value*randomness
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