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278 lines
6.9 KiB
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.. _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 its 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. However, after creating that node you will notice that only a white dot was created,
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and that there is a warning icon next to your Particles2D node in the inspector. This
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is because the node needs a ParticlesMaterial to function.
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ParticlesMaterial
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~~~~~~~~~~~~~~~~~
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To add a process material to your particles node, go to Process Material in
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your inspector panel. Click on the box next to material, and from the dropdown
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menu select New Particles Material.
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.. image:: img/particles_material.png
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Your Particles2D node should now be emitting
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white points downward.
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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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Time Parameters
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---------------
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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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One Shot
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~~~~~~~~
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When enabled, a Particles2D node will emit all of its particles once
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and then never again.
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Preprocess
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~~~~~~~~~~
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Particle systems begin with zero particles emitted, then start emitting.
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This can be an inconvenience when 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 number of seconds before it is
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actually drawn the first time.
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Speed Scale
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~~~~~~~~~~~
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The speed scale has a default value of ``1`` and is used to adjust the
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speed of a particle system. Lowering the value will make the particles
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slower while increasing the value will make the particles much faster.
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Explosiveness
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~~~~~~~~~~~~~
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If lifetime is ``1`` and there are 10 particles, it means a 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 particles at regular intervals (default value).
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- 1: Emit all particles simultaneously.
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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 values range 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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Fixed FPS
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~~~~~~~~~
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This setting can be used to set the particle system to render at a fixed
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FPS. For instance, changing the value to ``2`` will make the particles render
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at 2 frames per second. Note this does not slow down the particle system itself.
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Fract Delta
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~~~~~~~~~~~
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This can be used to turn Fract Delta on or off.
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Drawing Parameters
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------------------
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Visibility Rect
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~~~~~~~~~~~~~~~
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The ``W`` and ``H`` values control width and height of the visibility
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rectangle. The ``X`` and ``Y`` values control the position of the upper-left
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corner of the visibility rectangle relative to the particle emitter.
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Local Coords
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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 relative to 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, already emitted particles are not affected:
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.. image:: img/paranim21.gif
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Draw Order
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~~~~~~~~~~
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This controls the order in which individual particles are drawn. ``Index``
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means particles are drawn according to their emission order (default).
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``Lifetime`` means they are drawn in order of remaining lifetime.
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ParticlesMaterial settings
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--------------------------
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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 allows them to be separated.
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Spread
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~~~~~~
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This parameter is the angle in degrees which will be randomly added in
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either direction to the base ``Direction``. A spread of ``180`` will emit
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in all directions (+/- 180).
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.. image:: img/paranim3.gif
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Gravity
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~~~~~~~
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The gravity applied to every particle.
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.. image:: img/paranim7.gif
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Initial 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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Angular Velocity
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~~~~~~~~~~~~~~~~
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Angular velocity is the initial angular velocity applied to particles.
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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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Linear Acceleration
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~~~~~~~~~~~~~~~~~~~
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The linear acceleration applied to each particle.
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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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especially 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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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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Scale
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~~~~~
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Determines the initial scale of the particles.
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.. image:: img/paranim12.gif
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Color
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~~~~~
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Used to change the color of the particles being emitted.
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Hue variation
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~~~~~~~~~~~~~
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The Variation value sets the initial hue variation applied to each
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particle. The Variation Rand value controls the hue variation
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randomness ratio.
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