// Copyright (C) 2017 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only

/*!
    \qmlmodule QtQuick.Particles
    \title Qt Quick Particles QML Types
    \ingroup qmlmodules
    \brief Provides QML types for particle effects

  This QML module contains a particle system for Qt Quick. To use these types, import the module with the following line:

  \qml
  import QtQuick.Particles
  \endqml

  For a simple overview of how the system can be used, see \l{Using the Qt Quick Particle System}.

  For details on the performance characteristics see \l{qtquick-particles-performance.html}{Qt Quick Particle System Performance}.

*/

/*!
    \page qtquick-effects-particles.html
    \title Using the Qt Quick Particle System

    Documentation for all Particle System types can be found on the \l QtQuick.Particles module page.

    To use the types from the particles module, import the module with the following line:

    \qml
    import QtQuick.Particles
    \endqml

    \section1 The ParticleSystem
    This particle system contains four main types of QML types: ParticleSystem, Painters, Emitters and Affectors.

    The ParticleSystem type ties all the other types together, and manages the shared timeline. Painters, Emitters
    and Affectors must all have the same ParticleSystem to be able to interact with each other.

    You may have as many ParticleSystems as you want subject to this constraint, so the logical separation is to have
    one ParticleSystem for all the types that you want to interact, or just one if the number of types is small
    and they are easily kept under control..

    \section1 Logical Particles
    All the particle system types act on "logical particles". Every particle has a logical representation inside
    the particle system, and this is what the types act upon. Not every logical particle needs to be visualized,
    and some logical particles could lead to multiple visual particles being drawn on screen.

    \section1 Particle Groups
    Every logical particle is a member of a particle group, and each group is identified by a name. If no other
    group has been specified, a logical particle belongs to the group with the name "" (the empty string), which
    acts the same as any other group. Groups are used for two purposes, for controlling particles and because they
    can have stochastic state transitions.

    Groups control particles because you can never access an individual particle with any of the particle system
    types. All types act on groups as a whole, and so any particles that need to behave differently from each
    other (aside from the usual stochastic parameter variation) will need to be in different groups.

    Particles can also change groups dynamically. When this happens the particles trajectory is unaltered, but it
    can be acted upon by different ParticlePainters or Affectors. Particles can either have their group changed by
    an Affector, or stochastic state transitions can be defined in a ParticleGroup type.

    Generally, groups should only be defined in a ParticleGroup if they require stochastic state transitions. Otherwise,
    it is sufficient to have the groups be defined simply by the strings used in the particle/particles properties
    of the types.

    \section1 Emitters
    Emitters emit logical particles into the system. These particles have a trajectory and lifespan, but no visualization.
    These particles are emitted from the location of the Emitter.

    TrailEmitters are a special type of emitter which emits particles from the location of other logicial particles. Any logical
    particle of the followed type within the bounds of a TrailEmitter will cause particle emission from its location, as if there
    were an Emitter on it with the same properties as the TrailEmitter.

    \sa {Qt Quick Particles Examples - Emitters}

    \section1 ParticlePainters
    Painters are the types that visualize logical particles. For each logical particle in the groups assigned to it,
    which are within its bounds (or outside, if you do not set the clip property on the type) it will be visualized
    in a manner dependent on the type of ParticlePainter.  The base type of ParticlePainter does not draw anything.
    ImageParticle renders an image at the particle location. ItemParticle allows you to visualize logical particles
    using arbitrary QML delegates. ModelParticle is similar, but coordinates model data amongst the delegates in a
    similar manner to the view classes.

    As the ParticlePainter is the QML type visualizing the particles in the scene, it is its Z value which is important
    when trying to place particles above or below other types visually.

    \section1 Affectors
    Affectors are an optional component of a particle system. They can perform a variety of manipulations to the simulation,
    such as altering the trajectory of particles or prematurely ending their life in the simulation. For performance reasons,
    it is recommended not to use Affectors in high-volume particle systems.

    \sa {Qt Quick Particles Examples - Affectors}{Examples Affectors},
        {Qt Quick Particles Examples - Image Particles}{Examples Image Particles},
        {Qt Quick Particles Examples - System}{Example Affectors - System}

    \section1 Stochastic Parameters
    As particle systems benefit from stochastic control of parameters across a large number of instances, several stochastic
    helper types are used by the particle system. If you do not wish to have any stochastic variation in these parameters,
    then do not specify any variation in these types.

    \section2 Directions
    Directions can be specified by angle and magnitude, or by x and y components. While any direction can be specified with
    either method, there is a significant difference between varying the x and y components and varying the angle and magnitude.
    Varying the x and y components will lead to a rectangular area around the specified point, while varying the angle will lead
    to an arc centered on the specified point.

    \section2 Shapes
    The particle system contains several types which represent shapes. These types do not visualize shapes, and are used
    for the purpose of selecting a random point within the shape. If you want a specific point with no randomness, use a 0 width
    and 0 height shape (which is the default). Otherwise you can use the shape types to specify an area, so that the
    result can use a random point selected from that area.
*/

/*!
    \page qtquick-particles-performance.html
    \title Particle System Performance Guide

    The performance of the particle system scales with the number of particles it is maintaining. After prototyping the desired
    effect, performance can be improved by lowering the particle count. Conversely, if performance is well within the acceptable
    bounds, you can increase the number of particles until you hit that point (should that improve the effect).

    Note that particle count is often estimated by the particle system, and in some cases explicitly providing hints as to how
    many particles will be needed will improve performance. You can do this by setting maximumEmitted on an Emitter, and it is
    generally useful for Emitters which do not continuously emit particles.

    Like ShaderEffect, the performance of the particle system is largely dependent on the graphics hardware it is running on.
    The exception to this is Affectors. For systems not including Affectors, the majority of the performance cost of particles
    will be on the GPU. Since the GPU is better at parallelizing large numbers of operations more particles can be drawn at 60FPS
    when Affectors are not used.

    Affectors, particularly if modifying the particles in javascript, can be relatively slow as well as increasing the CPU cost
    of using particles. Avoid using them in high-volume systems where possible. Some easy cases where Affectors can be avoided
    are using timed ParticleGroup transitions instead of time-triggered Affectors, or setting acceleration due to gravity in the
    acceleration property of the Emitter instead of with a Gravity Affector.
*/
