QSGGeometry

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

Inheritance diagram of PySide2.QtQuick.QSGGeometry

Synopsis

Functions

Detailed Description

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 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 Scene Graph - Custom Geometry

class QSGGeometry(attribs, vertexCount[, indexCount=0[, indexType=UnsignedShortType]])
param attribs

AttributeSet

param vertexCount

int

param indexCount

int

param indexType

int

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.

PySide2.QtQuick.QSGGeometry.AttributeType

This enum identifies several attribute types.

Constant

Description

QSGGeometry.UnknownAttribute

Don’t care

QSGGeometry.PositionAttribute

Position

QSGGeometry.ColorAttribute

Color

QSGGeometry.TexCoordAttribute

Texture coordinate

QSGGeometry.TexCoord1Attribute

Texture coordinate 1

QSGGeometry.TexCoord2Attribute

Texture coordinate 2

New in version 5.8.

PySide2.QtQuick.QSGGeometry.DataPattern

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

Constant

Description

QSGGeometry.AlwaysUploadPattern

The 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.DynamicPattern

The 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.StaticPattern

The 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.StreamPattern

The 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.

PySide2.QtQuick.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.

Constant

Description

QSGGeometry.DrawPoints

QSGGeometry.DrawLines

QSGGeometry.DrawLineLoop

QSGGeometry.DrawLineStrip

QSGGeometry.DrawTriangles

QSGGeometry.DrawTriangleStrip

QSGGeometry.DrawTriangleFan

New in version 5.8.

PySide2.QtQuick.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.

Constant

Description

QSGGeometry.ByteType

QSGGeometry.UnsignedByteType

QSGGeometry.ShortType

QSGGeometry.UnsignedShortType

QSGGeometry.IntType

QSGGeometry.UnsignedIntType

QSGGeometry.FloatType

New in version 5.8.

PySide2.QtQuick.QSGGeometry.allocate(vertexCount[, indexCount=0])
Parameters
  • vertexCountint

  • indexCountint

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( DirtyGeometry ) to ensure that the renderer has a chance to update internal buffers.

PySide2.QtQuick.QSGGeometry.attributeCount()
Return type

int

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

PySide2.QtQuick.QSGGeometry.attributes()
Return type

Attribute

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

static PySide2.QtQuick.QSGGeometry.defaultAttributes_ColoredPoint2D()
Return type

AttributeSet

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

static PySide2.QtQuick.QSGGeometry.defaultAttributes_Point2D()
Return type

AttributeSet

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

static PySide2.QtQuick.QSGGeometry.defaultAttributes_TexturedPoint2D()
Return type

AttributeSet

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

PySide2.QtQuick.QSGGeometry.drawingMode()
Return type

long

Returns the drawing mode of this geometry.

The default value is GL_TRIANGLE_STRIP .

See also

setDrawingMode()

PySide2.QtQuick.QSGGeometry.indexCount()
Return type

int

Returns the number of indices in this geometry object.

PySide2.QtQuick.QSGGeometry.indexData()
Return type

void

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

PySide2.QtQuick.QSGGeometry.indexDataAsUInt()
Return type

uint

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

PySide2.QtQuick.QSGGeometry.indexDataAsUShort()
Return type

quint16

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

PySide2.QtQuick.QSGGeometry.indexDataPattern()
Return type

DataPattern

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

PySide2.QtQuick.QSGGeometry.indexType()
Return type

int

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

PySide2.QtQuick.QSGGeometry.lineWidth()
Return type

float

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.

PySide2.QtQuick.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).

PySide2.QtQuick.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).

PySide2.QtQuick.QSGGeometry.setDrawingMode(mode)
Parameters

mode – long

Sets the mode to be used for drawing this geometry.

The default value is DrawTriangleStrip .

See also

drawingMode() DrawingMode

PySide2.QtQuick.QSGGeometry.setIndexDataPattern(p)
Parameters

pDataPattern

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 markDirty() with DirtyGeometry .

PySide2.QtQuick.QSGGeometry.setLineWidth(w)
Parameters

wfloat

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.

PySide2.QtQuick.QSGGeometry.setVertexDataPattern(p)
Parameters

pDataPattern

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 markDirty() with DirtyGeometry .

PySide2.QtQuick.QSGGeometry.sizeOfIndex()
Return type

int

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.

PySide2.QtQuick.QSGGeometry.sizeOfVertex()
Return type

int

Returns the size in bytes of one vertex.

This value comes from the attributes.

static PySide2.QtQuick.QSGGeometry.updateColoredRectGeometry(g, rect)
Parameters

Updates the geometry g with the coordinates in rect .

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

static PySide2.QtQuick.QSGGeometry.updateRectGeometry(g, rect)
Parameters

Updates the geometry g with the coordinates in rect .

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

static PySide2.QtQuick.QSGGeometry.updateTexturedRectGeometry(g, rect, sourceRect)
Parameters
  • gQSGGeometry

  • rectQRectF

  • sourceRectQRectF

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 TexturedPoint2D .

PySide2.QtQuick.QSGGeometry.vertexCount()
Return type

int

Returns the number of vertices in this geometry object.

PySide2.QtQuick.QSGGeometry.vertexData()
Return type

void

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

PySide2.QtQuick.QSGGeometry.vertexDataAsColoredPoint2D()
Return type

ColoredPoint2D

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

PySide2.QtQuick.QSGGeometry.vertexDataAsPoint2D()
Return type

Point2D

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

PySide2.QtQuick.QSGGeometry.vertexDataAsTexturedPoint2D()
Return type

TexturedPoint2D

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

PySide2.QtQuick.QSGGeometry.vertexDataPattern()
Return type

DataPattern

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