QLevelOfDetail Class | Qt 3D 5.9

Qt 5.9 | Qt 3D | C++ Classes | QLevelOfDetail

Qt 5.9.9 Reference Documentation

# QLevelOfDetail Class

(Qt3DRender::QLevelOfDetail)

The QLevelOfDetail class provides a way of controlling the complexity of rendered entities based on their size on the screen. More...

Header: | #include <QLevelOfDetail>
qmake: | QT += 3drender
Since: | Qt 5.9
Instantiated By: | LevelOfDetail
Inherits: | Qt3DCore::QComponent
Inherited By: | Qt3DRender::QLevelOfDetailSwitch

- List of all members, including inherited members

## Public Types

enum | ThresholdType { DistanceToCameraThreshold, ProjectedScreenPixelSizeThreshold }

## Properties

- camera : Qt3DRender::QCamera *
- currentIndex : int
- thresholdType : ThresholdType

- thresholds : QVector<qreal>
- volumeOverride : Qt3DRender::QLevelOfDetailBoundingSphere

- 1 property inherited from Qt3DCore::QComponent
- 3 properties inherited from Qt3DCore::QNode
- 1 property inherited from QObject

## Public Functions

| QLevelOfDetail(Qt3DCore::QNode *parent = nullptr)
QCamera * | camera() const
QLevelOfDetailBoundingSphere | createBoundingSphere(const QVector3D &center, float radius)
int | currentIndex() const
ThresholdType | thresholdType() const
QVector<qreal> | thresholds() const
QLevelOfDetailBoundingSphere | volumeOverride() const

- 2 public functions inherited from Qt3DCore::QComponent
- 11 public functions inherited from Qt3DCore::QNode
- 32 public functions inherited from QObject

## Public Slots

void | setCamera(QCamera *camera)
void | setCurrentIndex(int currentIndex)
void | setThresholdType(ThresholdType thresholdType)
void | setThresholds(const QVector<qreal> &thresholds)
void | setVolumeOverride(const QLevelOfDetailBoundingSphere &volumeOverride)

- 1 public slot inherited from Qt3DCore::QComponent
- 3 public slots inherited from Qt3DCore::QNode
- 1 public slot inherited from QObject

## Signals

void | cameraChanged(QCamera *camera)
void | currentIndexChanged(int currentIndex)
void | thresholdTypeChanged(ThresholdType thresholdType)
void | thresholdsChanged(const QVector<qreal> &thresholds)
void | volumeOverrideChanged(const QLevelOfDetailBoundingSphere &volumeOverride)

- 3 signals inherited from Qt3DCore::QComponent
- 4 signals inherited from Qt3DCore::QNode
- 2 signals inherited from QObject

## Protected Functions

| QLevelOfDetail(QLevelOfDetailPrivate &dd, Qt3DCore::QNode *parent = nullptr)

- 2 protected functions inherited from Qt3DCore::QNode
- 9 protected functions inherited from QObject

### Additional Inherited Members

- 1 public variable inherited from QObject
- 10 static public members inherited from QObject
- 2 protected variables inherited from QObject

## Detailed Description

The QLevelOfDetail class provides a way of controlling the complexity of rendered entities based on their size on the screen.

QLevelOfDetail can be used to control the representation of an entity based on distance from the observer or size on the screen.

In order to improve rendering performance, objects that are very small can be rendered using far fewer details, in geometry or texture.

The component is controlled by specifying thresholds of values which are interpreted as either distances from the camera or screen size.

As the point of view changes, the currentIndex property will change to reflect matching value in the range array.

The currentIndex property can then be used, for example, to enable or disable entities, change material, etc.

The LevelOfDetail component is not shareable between multiple entities.

       #include <Qt3DCore/QEntity>
       #include <Qt3DRender/QGeometryRenderer>
       #include <Qt3DRender/QLevelOfDetail>

      // Scene
      Qt3DCore::QEntity *rootEntity = new Qt3DCore::Qt3DCore::QEntity;

      Qt3DCore::QEntity *renderableEntity = new Qt3DCore::QEntity(rootEntity);
      Qt3DRender::QGeometryRenderer *geometryRenderer = new Qt3DCore::QGeometryRenderer(renderableEntity);
      renderableEntity->addComponent(geometryRenderer);
      Qt3DRender::QLevelOfDetail* lod = new Qt3Render::QLevelOfDetail(renderableEntity);
      QVector<qreal> thresholds = {20, 35, 50, 65};
      lod->setThresholds(thresholds);
      lod->setCamera(mainCamera);
      renderableEntity->addComponent(lod);

      // connect to QLevelOfDetail::currentIndexChanged to toggle rendering
      ...

## Member Type Documentation

### enum QLevelOfDetail::ThresholdType

Specifies how the values in the thresholds are interpreted

Constant | Value | Description
--- | --- | ---
`Qt3DRender::QLevelOfDetail::DistanceToCameraThreshold` | `0` | Distance from the entity to the selected camera
`Qt3DRender::QLevelOfDetail::ProjectedScreenPixelSizeThreshold` | `1` | Size of the entity when projected on the screen as seen from the selected camera, expressed in number of pixels on the side of the bounding square in screen space.

## Property Documentation

### camera : Qt3DRender::QCamera *

Holds the id of the camera that is used to compute the actual distance or the screen size.

Access functions:

QCamera * | camera() const
void | setCamera(QCamera *camera)

Notifier signal:

void | cameraChanged(QCamera *camera)

### currentIndex : int

The index in the range array which matches the current distance to the camera or screen size.

Access functions:

int | currentIndex() const
void | setCurrentIndex(int currentIndex)

Notifier signal:

void | currentIndexChanged(int currentIndex)

### thresholdType : ThresholdType

Specifies how range values are interpreted.

Access functions:

ThresholdType | thresholdType() const
void | setThresholdType(ThresholdType thresholdType)

Notifier signal:

void | thresholdTypeChanged(ThresholdType thresholdType)

See also Qt3DRender::QLevelOfDetail::ThresholdType.

### thresholds : QVector<qreal>

Array of range values as float point numbers. The value for the most detailed representation should be specified first.

If Qt3DRender::QLevelOfDetail::thresholdType is set to Qt3DRender::QLevelOfDetail::DistanceToCameraThreshold, values should be specified in ascending order, in camera space coordinates

If Qt3DRender::QLevelOfDetail::thresholdType is set to Qt3DRender::QLevelOfDetail::ProjectedScreenPixelSizeThreshold, values should be specified in descending order, in screen space pixels.

Access functions:

QVector<qreal> | thresholds() const
void | setThresholds(const QVector<qreal> &thresholds)

Notifier signal:

void | thresholdsChanged(const QVector<qreal> &thresholds)

See also Qt3DRender::QLevelOfDetail::ThresholdType.

### volumeOverride : Qt3DRender::QLevelOfDetailBoundingSphere

The default is a sphere of radius 1 and centered at the local origin of the entity. This proxy volume is used to compute the distance to the camera or the size of the screen projection.

If this value to nullptr, the bounding volume of the entity is used. Care must be taken that this bounding volume never becomes invalid.

Access functions:

QLevelOfDetailBoundingSphere | volumeOverride() const
void | setVolumeOverride(const QLevelOfDetailBoundingSphere &volumeOverride)

Notifier signal:

void | volumeOverrideChanged(const QLevelOfDetailBoundingSphere &volumeOverride)

See also Qt3DRender::QLevelOfDetailBoundingSphere.

## Member Function Documentation

### QLevelOfDetail::QLevelOfDetail(Qt3DCore::QNode *parent = nullptr)

Constructs a new QLevelOfDetail with the specified parent.

### `[protected]` QLevelOfDetail::QLevelOfDetail(QLevelOfDetailPrivate &dd, Qt3DCore::QNode *parent = nullptr)

Copy constructor.

### QLevelOfDetailBoundingSphere QLevelOfDetail::createBoundingSphere(const QVector3D &center, float radius)

### `[slot]` void QLevelOfDetail::setCamera(QCamera *camera)

Sets the camera relative to which distance and size are computed.

Note: Setter function for property camera.

See also camera().

### `[slot]` void QLevelOfDetail::setCurrentIndex(int currentIndex)

Sets the currentIndex.

Note: This should not normally be set by the user.

However, if the component is disabled, then changing the current index is a simple way of switching between multiple representations.

Note: Setter function for property currentIndex.

See also currentIndex().

### `[slot]` void QLevelOfDetail::setThresholdType(ThresholdType thresholdType)

Sets the way thresholds values are interpreted with parameter thresholdType

Note: Setter function for property thresholdType.

See also thresholdType() and Qt3DRender::QLevelOfDetail::ThresholdType.

### `[slot]` void QLevelOfDetail::setThresholds(const QVector<qreal> &thresholds)

Sets the range values in thresholds.

Note: Setter function for property thresholds.

See also thresholds() and Qt3DRender::QLevelOfDetail::thresholdType.