QML/Qt3D GeometryRenderer 使用基本示例 [英] QML/Qt3D Basic example of GeometryRenderer use
问题描述
我正在寻找如何在 QML 中使用 GeometryRenderer 设置实体的基本示例.
I'm looking for a basic example of how to set up an Entity with a GeometryRenderer in QML.
我现在使用的代码如下所示.如果我将 geometryRenderer
替换为 CuboidMesh
,则会显示一个空白立方体.目标是显示一个简单的三角形.我的 GeometryRenderer 声明是否正确?
The code I'm using right now is shown below. If I replace geometryRenderer
by a CuboidMesh
then a blank cube is shown. The goal is to display a simple triangle. Is my GeometryRenderer declaration correct ?
Entity{
Material{
id: simpleMaterial
effect: SimpleEffect{}
}
GeometryRenderer{
id: geometryRenderer
instanceCount: 1
primitiveType: GeometryRenderer.Triangles
geometry: Geometry{
Attribute{
attributeType: Attribute.VertexAttribute
vertexBaseType: Attribute.Float
vertexSize: 3
byteOffset: 0
byteStride: 3 * 4
count: 3
buffer : Buffer{
id: vertexBuffer
type: Buffer.VertexBuffer
data: [ 0.0, 0.0, 0.0,
0.0, 10.0, 0.0,
10.0, 10.0, 0.0]
}
}
}
}
components: [simpleMaterial, geometryRenderer]
}
推荐答案
问题如下:Buffer 对象的 data
属性实际上需要一个 QByteArray.但是,QByteArray 不是 QML 类型,仅将顶点写入列表是行不通的.
The problem was the following: the data
property of the Buffer object actually expects a QByteArray. However, QByteArray is not a QML type and simply writing the vertices in a list won't do the trick.
解决方案是编写一个 C++ 包装器,然后 提供到 QML.这个包装器应该至少为 QBuffer 或直接为 QByteArray 提供可读属性.
The solution is to write a C++ wrapper which is then made available to QML. This wrapper should offer at least a readable property to a QBuffer or directly a QByteArray.
然后可以使用 C++ 或 QML 设置包装器的数据(提供一些写入功能,看这里).
It is then possible to set the wrapper's data using either C++ or QML (provided some write function, see here).
以下代码是一个基本示例,我改编自 this answer 其中它在功能方面更加完善.
The following code is a basic example, I adapted it from this answer where it is more complete in terms of functionality.
Entity{
property DrawData drawData
Material{
id: material
...
}
GeometryRenderer{
id: geometryRenderer
instanceCount: drawData.count
primitiveType: GeometryRenderer.TriangleStrip
geometry: Geometry{
Attribute{
name: "vertexPosition" // Name of attribute in the shader
attributeType: Attribute.VertexAttribute
vertexBaseType: Attribute.Float
vertexSize: 3
byteOffset: 0 // See OpenGL doc for details about these properties
byteStride: 3 * 4
count: drawData.count
buffer : drawData.buffer // The actual QBuffer which holds the vertex data
}
}
}
components: [material, geometryRenderer]
}
其中DrawData
定义如下:
/*
* This struct is not strictly necessary, it is just convenient in case more
* vertex attributes are needed. If so, it is necessary to change the ByteStride
* in the geometry attribute.
*/
struct DrawVBOData {
QVector3D position;
};
class DrawData : public Qt3DCore::QNode {
Q_OBJECT
// Make properties available in QML
Q_PROPERTY(Qt3DRender::QBuffer *buffer READ buffer CONSTANT)
Q_PROPERTY(int count READ count NOTIFY countChanged)
public:
explicit DrawData (Qt3DCore::QNode *parent = 0);
Qt3DRender::QBuffer *buffer();
void setData(const QVector<QVector3D> &positions);
int count() const;
signals:
void countChanged(int count);
public slots:
private:
QScopedPointer<Qt3DRender::QBuffer> m_buffer;
int m_count = 0;
};
最后,实现:
DrawData::DrawData(Qt3DCore::QNode *parent)
: Qt3DCore::QNode(parent), m_buffer(new QBuffer(QBuffer::VertexBuffer, this)){}
Qt3DRender::QBuffer *DrawData::buffer() { return m_buffer.data();}
void DrawData::setData(const QVector<QVector3D> &positions) {
QByteArray ba;
ba.resize(positions.size() * sizeof(DrawVBOData));
DrawVBOData *vboData = reinterpret_cast<DrawVBOData *>(ba.data());
for (int i = 0; i < positions.size(); i++) {
DrawVBOData &vbo = vboData[i];
vbo.position = positions[i];
}
m_buffer->setData(ba);
m_count = positions.count();
emit countChanged(m_count);
}
int DrawData::count() const { return m_count; }
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