QSGGeometry Class

The QSGGeometry class provides low-level storage for graphics primitives in the Qt Quick Scene Graph. More...

Header: #include <QSGGeometry>
qmake: QT += quick

Public Types

class Attribute
class AttributeSet
class ColoredPoint2D
class Point2D
class TexturedPoint2D
enum AttributeType { UnknownAttribute, PositionAttribute, ColorAttribute, TexCoordAttribute, TexCoord1Attribute, TexCoord2Attribute }
enum DataPattern { AlwaysUploadPattern, DynamicPattern, StaticPattern, StreamPattern }
enum DrawingMode { DrawPoints, DrawLines, DrawLineLoop, DrawLineStrip, ..., DrawTriangleFan }
enum Type { ByteType, UnsignedByteType, ShortType, UnsignedShortType, ..., FloatType }

Public Functions

QSGGeometry(const QSGGeometry::AttributeSet &attributes, int vertexCount, int indexCount = 0, int indexType = UnsignedShortType)
virtual ~QSGGeometry()
void allocate(int vertexCount, int indexCount = 0)
int attributeCount() const
const Attribute *attributes() const
unsigned int drawingMode() const
int indexCount() const
void *indexData()
const void *indexData() const
uint *indexDataAsUInt()
const uint *indexDataAsUInt() const
quint16 *indexDataAsUShort()
const quint16 *indexDataAsUShort() const
DataPattern indexDataPattern() const
int indexType() const
float lineWidth() const
void markIndexDataDirty()
void markVertexDataDirty()
void setDrawingMode(unsigned int mode)
void setIndexDataPattern(DataPattern p)
void setLineWidth(float width)
void setVertexDataPattern(DataPattern p)
int sizeOfIndex() const
int sizeOfVertex() const
int vertexCount() const
void *vertexData()
const void *vertexData() const
ColoredPoint2D *vertexDataAsColoredPoint2D()
const ColoredPoint2D *vertexDataAsColoredPoint2D() const
Point2D *vertexDataAsPoint2D()
const Point2D *vertexDataAsPoint2D() const
TexturedPoint2D *vertexDataAsTexturedPoint2D()
const TexturedPoint2D *vertexDataAsTexturedPoint2D() const
DataPattern vertexDataPattern() const

Static Public Members

const AttributeSet &defaultAttributes_ColoredPoint2D()
const AttributeSet &defaultAttributes_Point2D()
const AttributeSet &defaultAttributes_TexturedPoint2D()
void updateColoredRectGeometry(QSGGeometry *g, const QRectF &rect)
void updateRectGeometry(QSGGeometry *g, const QRectF &rect)
void updateTexturedRectGeometry(QSGGeometry *g, const QRectF &rect, const QRectF &textureRect)

Detailed Description

The QSGGeometry class provides low-level storage for graphics primitives in the Qt Quick Scene Graph.

The QSGGeometry class stores the geometry of the primitives rendered with the scene graph. It contains vertex data and optionally index data. The mode used to draw the geometry is specified with setDrawingMode(), which maps directly to the graphics API's drawing mode, such as GL_TRIANGLE_STRIP, GL_TRIANGLES, or GL_POINTS in case of OpenGL.

Vertices can be as simple as points defined by x and y values or can be more complex where each vertex contains a normal, texture coordinates and a 3D position. The QSGGeometry::AttributeSet is used to describe how the vertex data is built up. The attribute set can only be specified on construction. The QSGGeometry class provides a few convenience attributes and attribute sets by default. The defaultAttributes_Point2D() function returns an attribute set to be used in normal solid color rectangles, while the defaultAttributes_TexturedPoint2D function returns attributes to be used for textured 2D geometry. The vertex data is internally stored as a void * and is accessible with the vertexData() function. Convenience accessors for the common attribute sets are available with vertexDataAsPoint2D() and vertexDataAsTexturedPoint2D(). Vertex data is allocated by passing a vertex count to the constructor or by calling allocate() later.

The QSGGeometry can optionally contain indices of either unsigned 32-bit, unsigned 16-bit, or unsigned 8-bit integers. The index type must be specified during construction and cannot be changed.

Below is a snippet illustrating how a geometry composed of position and color vertices can be built.

struct MyPoint2D {
    float x;
    float y;
    float r;
    float g;
    float b;
    float a;

    void set(float x_, float y_, float r_, float g_, float b_, float a_) {
        x = x_;
        y = y_;
        r = r_;
        g = g_;
        b = b_;
        a = a_;
    }
};

QSGGeometry::Attribute MyPoint2D_Attributes[] = {
    QSGGeometry::Attribute::create(0, 2, GL_FLOAT, true),
    QSGGeometry::Attribute::create(1, 4, GL_FLOAT, false)
};

QSGGeometry::AttributeSet MyPoint2D_AttributeSet = {
    2,
    sizeof(MyPoint2D),
    MyPoint2D_Attributes
};

...

geometry = new QSGGeometry(MyPoint2D_AttributeSet, 2);
geometry->setDrawingMode(GL_LINES);

MyPoint2D *vertices = static_cast<MyPoint2D *>(geometry->vertexData());
vertices[0].set(0, 0, 1, 0, 0, 1);
vertices[1].set(width(), height(), 0, 0, 1, 1);

The QSGGeometry is a software buffer and client-side in terms of OpenGL rendering, as the buffers used in 2D graphics typically consist of many small buffers that change every frame and do not benefit from being uploaded to graphics memory. However, the QSGGeometry supports hinting to the renderer that a buffer should be uploaded using the setVertexDataPattern() and setIndexDataPattern() functions. Whether this hint is respected or not is implementation specific.

Note: All classes with QSG prefix should be used solely on the scene graph's rendering thread. See Scene Graph and Rendering for more information.

See also QSGGeometryNode and Scene Graph - Custom Geometry.

Member Type Documentation

enum QSGGeometry::AttributeType

enum QSGGeometry::DataPattern

The DataPattern enum is used to specify the use pattern for the vertex and index data in a geometry object.

ConstantValueDescription
QSGGeometry::AlwaysUploadPattern0The data is always uploaded. This means that the user does not need to explicitly mark index and vertex data as dirty after changing it. This is the default.
QSGGeometry::DynamicPattern2The data is modified repeatedly and drawn many times. This is a hint that may provide better performance. When set the user must make sure to mark the data as dirty after changing it.
QSGGeometry::StaticPattern3The data is modified once and drawn many times. This is a hint that may provide better performance. When set the user must make sure to mark the data as dirty after changing it.
QSGGeometry::StreamPattern1The data is modified for almost every time it is drawn. This is a hint that may provide better performance. When set, the user must make sure to mark the data as dirty after changing it.

enum QSGGeometry::DrawingMode

The values correspond to OpenGL enum values like GL_POINTS, GL_LINES, etc. QSGGeometry provies its own type in order to be able to provide the same API with non-OpenGL backends as well.

ConstantValue
QSGGeometry::DrawPoints0x0000
QSGGeometry::DrawLines0x0001
QSGGeometry::DrawLineLoop0x0002
QSGGeometry::DrawLineStrip0x0003
QSGGeometry::DrawTriangles0x0004
QSGGeometry::DrawTriangleStrip0x0005
QSGGeometry::DrawTriangleFan0x0006

enum QSGGeometry::Type

The values correspond to OpenGL type constants like GL_BYTE, GL_UNSIGNED_BYTE, etc. QSGGeometry provies its own type in order to be able to provide the same API with non-OpenGL backends as well.

ConstantValue
QSGGeometry::ByteType0x1400
QSGGeometry::UnsignedByteType0x1401
QSGGeometry::ShortType0x1402
QSGGeometry::UnsignedShortType0x1403
QSGGeometry::IntType0x1404
QSGGeometry::UnsignedIntType0x1405
QSGGeometry::FloatType0x1406

Member Function Documentation

QSGGeometry::QSGGeometry(const QSGGeometry::AttributeSet &attributes, int vertexCount, int indexCount = 0, int indexType = UnsignedShortType)

Constructs a geometry object based on attributes.

The object allocate space for vertexCount vertices based on the accumulated size in attributes and for indexCount.

The indexType maps to the OpenGL index type and can be GL_UNSIGNED_SHORT and GL_UNSIGNED_BYTE. On OpenGL implementations that support it, such as desktop OpenGL, GL_UNSIGNED_INT can also be used.

Geometry objects are constructed with GL_TRIANGLE_STRIP as default drawing mode.

The attribute structure is assumed to be POD and the geometry object assumes this will not go away. There is no memory management involved.

[virtual] QSGGeometry::~QSGGeometry()

Destroys the geometry object and the vertex and index data it has allocated.

void QSGGeometry::allocate(int vertexCount, int indexCount = 0)

Resizes the vertex and index data of this geometry object to fit vertexCount vertices and indexCount indices.

Vertex and index data will be invalidated after this call and the caller must mark the associated geometry node as dirty, by calling node->markDirty(QSGNode::DirtyGeometry) to ensure that the renderer has a chance to update internal buffers.

int QSGGeometry::attributeCount() const

Returns the number of attributes in the attrbute set used by this geometry.

const Attribute *QSGGeometry::attributes() const

Returns an array with the attributes of this geometry. The size of the array is given with attributeCount().

[static] const AttributeSet &QSGGeometry::defaultAttributes_ColoredPoint2D()

Convenience function which returns attributes to be used for per vertex colored 2D drawing.

[static] const AttributeSet &QSGGeometry::defaultAttributes_Point2D()

Convenience function which returns attributes to be used for 2D solid color drawing.

[static] const AttributeSet &QSGGeometry::defaultAttributes_TexturedPoint2D()

Convenience function which returns attributes to be used for textured 2D drawing.

unsigned int QSGGeometry::drawingMode() const

Returns the drawing mode of this geometry.

The default value is GL_TRIANGLE_STRIP.

See also setDrawingMode().

int QSGGeometry::indexCount() const

Returns the number of indices in this geometry object.

void *QSGGeometry::indexData()

Returns a pointer to the raw index data of this geometry object.

See also indexDataAsUShort() and indexDataAsUInt().

const void *QSGGeometry::indexData() const

Returns a pointer to the raw index data of this geometry object.

See also indexDataAsUShort() and indexDataAsUInt().

uint *QSGGeometry::indexDataAsUInt()

Convenience function to access the index data as a mutable array of 32-bit unsigned integers.

const uint *QSGGeometry::indexDataAsUInt() const

Convenience function to access the index data as an immutable array of 32-bit unsigned integers.

quint16 *QSGGeometry::indexDataAsUShort()

Convenience function to access the index data as a mutable array of 16-bit unsigned integers.

const quint16 *QSGGeometry::indexDataAsUShort() const

Convenience function to access the index data as an immutable array of 16-bit unsigned integers.

DataPattern QSGGeometry::indexDataPattern() const

Returns the usage pattern for indices in this geometry. The default pattern is AlwaysUploadPattern.

See also setIndexDataPattern().

int QSGGeometry::indexType() const

Returns the primitive type used for indices in this geometry object.

float QSGGeometry::lineWidth() const

Gets the current line or point width or to be used for this geometry. This property only applies to line width when the drawingMode is DrawLines, DarwLineStrip, or DrawLineLoop. For desktop OpenGL, it also applies to point size when the drawingMode is DrawPoints.

The default value is 1.0

Note: When not using OpenGL, support for point and line drawing may be limited. For example, some APIs do not support point sprites and so setting a size other than 1 is not possible. Some backends may be able implement support via geometry shaders, but this is not guaranteed to be always available.

See also setLineWidth() and drawingMode().

void QSGGeometry::markIndexDataDirty()

Mark that the vertices in this geometry has changed and must be uploaded again.

This function only has an effect when the usage pattern for vertices is StaticData and the renderer that renders this geometry uploads the geometry into Vertex Buffer Objects (VBOs).

void QSGGeometry::markVertexDataDirty()

Mark that the vertices in this geometry has changed and must be uploaded again.

This function only has an effect when the usage pattern for vertices is StaticData and the renderer that renders this geometry uploads the geometry into Vertex Buffer Objects (VBOs).

void QSGGeometry::setDrawingMode(unsigned int mode)

Sets the mode to be used for drawing this geometry.

The default value is QSGGeometry::DrawTriangleStrip.

See also drawingMode() and DrawingMode.

void QSGGeometry::setIndexDataPattern(DataPattern p)

Sets the usage pattern for indices to p.

The default is AlwaysUploadPattern. When set to anything other than the default, the user must call markIndexDataDirty() after changing the index data, in addition to calling QSGNode::markDirty() with QSGNode::DirtyGeometry.

See also indexDataPattern().

void QSGGeometry::setLineWidth(float width)

Sets the line or point width to be used for this geometry to width. This property only applies to line width when the drawingMode is DrawLines, DrawLineStrip, or DrawLineLoop. For Desktop OpenGL, it also applies to point size when the drawingMode is DrawPoints.

Note: How line width and point size are treated is implementation dependent: The application should not rely on these, but rather create triangles or similar to draw areas. On OpenGL ES, line width support is limited and point size is unsupported.

See also lineWidth() and drawingMode().

void QSGGeometry::setVertexDataPattern(DataPattern p)

Sets the usage pattern for vertices to p.

The default is AlwaysUploadPattern. When set to anything other than the default, the user must call markVertexDataDirty() after changing the vertex data, in addition to calling QSGNode::markDirty() with QSGNode::DirtyGeometry.

See also vertexDataPattern().

int QSGGeometry::sizeOfIndex() const

Returns the byte size of the index type.

This value is either 1 when index type is GL_UNSIGNED_BYTE or 2 when index type is GL_UNSIGNED_SHORT. For Desktop OpenGL, GL_UNSIGNED_INT with the value 4 is also supported.

int QSGGeometry::sizeOfVertex() const

Returns the size in bytes of one vertex.

This value comes from the attributes.

[static] void QSGGeometry::updateColoredRectGeometry(QSGGeometry *g, const QRectF &rect)

Updates the geometry g with the coordinates in rect.

The function assumes the geometry object contains a single triangle strip of QSGGeometry::ColoredPoint2D vertices

[static] void QSGGeometry::updateRectGeometry(QSGGeometry *g, const QRectF &rect)

Updates the geometry g with the coordinates in rect.

The function assumes the geometry object contains a single triangle strip of QSGGeometry::Point2D vertices

[static] void QSGGeometry::updateTexturedRectGeometry(QSGGeometry *g, const QRectF &rect, const QRectF &textureRect)

Updates the geometry g with the coordinates in rect and texture coordinates from textureRect.

textureRect should be in normalized coordinates.

g is assumed to be a triangle strip of four vertices of type QSGGeometry::TexturedPoint2D.

int QSGGeometry::vertexCount() const

Returns the number of vertices in this geometry object.

void *QSGGeometry::vertexData()

Returns a pointer to the raw vertex data of this geometry object.

See also vertexDataAsPoint2D() and vertexDataAsTexturedPoint2D().

const void *QSGGeometry::vertexData() const

Returns a pointer to the raw vertex data of this geometry object.

See also vertexDataAsPoint2D() and vertexDataAsTexturedPoint2D().

ColoredPoint2D *QSGGeometry::vertexDataAsColoredPoint2D()

Convenience function to access the vertex data as a mutable array of QSGGeometry::ColoredPoint2D.

const ColoredPoint2D *QSGGeometry::vertexDataAsColoredPoint2D() const

Convenience function to access the vertex data as an immutable array of QSGGeometry::ColoredPoint2D.

Point2D *QSGGeometry::vertexDataAsPoint2D()

Convenience function to access the vertex data as a mutable array of QSGGeometry::Point2D.

const Point2D *QSGGeometry::vertexDataAsPoint2D() const

Convenience function to access the vertex data as an immutable array of QSGGeometry::Point2D.

TexturedPoint2D *QSGGeometry::vertexDataAsTexturedPoint2D()

Convenience function to access the vertex data as a mutable array of QSGGeometry::TexturedPoint2D.

const TexturedPoint2D *QSGGeometry::vertexDataAsTexturedPoint2D() const

Convenience function to access the vertex data as an immutable array of QSGGeometry::TexturedPoint2D.

DataPattern QSGGeometry::vertexDataPattern() const

Returns the usage pattern for vertices in this geometry. The default pattern is AlwaysUploadPattern.

See also setVertexDataPattern().

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