- Qt 5.15
- Qt 3D
- C++ Classes
- QParameter
- Qt 5.15.11 Reference Documentation

# QParameter Class

class Qt3DRender::QParameter

Provides storage for a name and value pair. This maps to a shader uniform. More...

Header: | #include <Qt3DRender/QParameter>
qmake: | QT += 3drender
Instantiated By: | Parameter
Inherits: | Qt3DCore::QNode

- List of all members, including inherited members

## Properties

- name : QString
- value : QVariant

## Public Functions

| QParameter(Qt3DCore::QNode *parent = nullptr)
QString | name() const
QVariant | value() const

## Public Slots

void | setName(const QString &name)
void | setValue(const QVariant &dv)

## Signals

void | nameChanged(const QString &name)
void | valueChanged(const QVariant &value)

## Detailed Description

A QParameter can be referenced by a QRenderPass, QTechnique, QEffect, QMaterial, QTechniqueFilter, QRenderPassFilter. At runtime, depending on which shader is selected for a given step of the rendering, the value contained in a QParameter will be converted and uploaded if the shader contains a uniform with a name matching that of the QParameter.

     QParameter *param = new QParameter();
     param->setName(QStringLiteral("diffuseColor"));
     param->setValue(QColor::fromRgbF(0.0f, 0.0f, 1.0f, 1.0f));

     // Alternatively you can create and set a QParameter this way
     QParameter *param2 = new QParameter(QStringLiteral("diffuseColor"), QColor::fromRgbF(0.0f, 0.0f, 1.0f, 1.0f));

     // Such QParameters will work with the following GLSL uniform shader declarations
     // uniform vec4 diffuseColor;
     // uniform vec3 diffuseColor;
     // uniform vec2 diffuseColor;
     // uniform float diffuseColor;

Note: some care must be taken to ensure the value wrapped by a QParameter can actually be converted to what the real uniform expect. Giving a value stored as an int where the actual shader uniform is of type float could result in undefined behaviors.

Note: when the targeted uniform is an array, the name should be the name of the uniform with [0] appended to it.

Note: QParameter node can not be disabled.

     QParameter *param = new QParameter();
     QVariantList values = QVariantList() << 0.0f << 1.0f << 2.0f << 3.0f << 4.0f << 883.0f << 1340.0f << 1584.0f;

     param->setName(QStringLiteral("diffuseValues[0]"));
     param->setValue(values);

     // Matching GLSL shader uniform  declaration
     // uniform float diffuseValues[8];

When it comes to texture support, the QParameter value should be set to the appropriate QAbstractTexture subclass that matches the sampler type of the shader uniform.

     QTexture2D *texture = new QTexture2D();
     ...
     QParameter *param = new QParameter();
     param->setName(QStringLiteral("diffuseTexture"));
     param->setValue(QVariant::fromValue(texture));

     // Works with the following GLSL uniform shader declaration
     // uniform sampler2D diffuseTexture

See also QAbstractTexture.

## Property Documentation

### name : QString

Specifies the name of the parameter

Access functions:

QString | name() const
void | setName(const QString &name)

Notifier signal:

void | nameChanged(const QString &name)

### value : QVariant

Specifies the value of the parameter

Access functions:

QVariant | value() const
void | setValue(const QVariant &dv)

Notifier signal:

void | valueChanged(const QVariant &value)

## Member Function Documentation

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

Constructs a new QParameter with the specified parent.