使用原始 OpenGL 调用绘制 Qml 项目的问题

Question

我想使用原始 OpenGL 调用在 QtQuick 场景中绘制单个项目。我决定采用 .

中建议的方法

我创建了一个派生自 QQuickFramebufferObject 的 Qt Quick 项，并将其作为 Renderer 暴露给 QML：（代码基于 Qt 示例：Scene Graph - Rendering FBOs）

class FboInSGRenderer : public QQuickFramebufferObject {
    Q_OBJECT
public:
    Renderer *createRenderer() const;
};

源文件：

class LogoInFboRenderer : public QQuickFramebufferObject::Renderer {
    public:
        LogoInFboRenderer() { }

        void render() {
            int width = 1, height = 1;
            glEnable(GL_BLEND);
            glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
            glColor4f(0.0, 1.0, 0.0, 0.8);
            glBegin(GL_QUADS);
            glVertex2f(0, 0);
            glVertex2f(width, 0);
            glVertex2f(width, height);
            glVertex2f(0, height);
            glEnd();

            glLineWidth(2.5);
            glColor4f(0.0, 0.0, 0.0, 1.0);
            glBegin(GL_LINES);
            glVertex2f(0, 0);
            glVertex2f(width, height);
            glVertex2f(width, 0);
            glVertex2f(0, height);
            glEnd();

            update();
        }

        QOpenGLFramebufferObject *createFramebufferObject(const QSize &size) {
            QOpenGLFramebufferObjectFormat format;
            format.setAttachment(QOpenGLFramebufferObject::CombinedDepthStencil);
            format.setSamples(4);
            return new QOpenGLFramebufferObject(size, format);
        }
};

QQuickFramebufferObject::Renderer *FboInSGRenderer::createRenderer() const {
    return new LogoInFboRenderer();
}

在Qml中我是这样使用的：

import QtQuick 2.4
import SceneGraphRendering 1.0

Rectangle {
    width: 400
    height: 400
    color: "purple"
    Renderer {
        id: renderer
        anchors.fill: parent
    }
}

我期待看到渲染的 "X" 将填满整个场景，但我得到的结果如下所示：

其他实验似乎证实绘制的形状始终是其大小 (width/height) 除以 2。

我还检查了 createFramebufferObject 中的 size 参数值是否正确。

查看文档让我在 QQuickFramebufferObject class 中找到了属性 textureFollowsItemSize 但它默认设置为 true.

我是不是做错了什么或者我应该将此行为视为 Qt 错误？

Answer 1

正如 Qt 文档所说："Warning: It is crucial that OpenGL operations and interaction with the scene graph happens exclusively on the rendering thread, primarily during the updatePaintNode() call. The best rule of thumb is to only use classes with the "QSG" prefix inside the QQuickItem::updatePaintNode() function." 我是这样做的：

*.h

class MyQuickItem : public QQuickItem
{
    Q_OBJECT
public:
    MyQuickItem();
    ~MyQuickItem();

protected:
    QSGNode *updatePaintNode(QSGNode * oldNode, UpdatePaintNodeData * updatePaintNodeData);
    QSGNode *addNode(QSGGeometry *geometry, const QColor &color);
};

*.cpp

MyQuickItem::MyQuickItem()
{
    setFlag(QQuickItem::ItemHasContents,true);
}

MyQuickItem::~MyQuickItem()
{

}

QSGNode *MyQuickItem::updatePaintNode(QSGNode *oldNode, QQuickItem::UpdatePaintNodeData *updatePaintNodeData)
{
    Q_UNUSED(updatePaintNodeData)

    QSGTransformNode *root = static_cast<QSGTransformNode *>(oldNode);
    if(!root) root = new QSGTransformNode;
    QSGNode *node;
    QSGGeometry *geometry;

    QSGSimpleRectNode *rect = new QSGSimpleRectNode();
    rect->setColor(Qt::green);
    rect->setRect(boundingRect());
    root->appendChildNode(rect);

    geometry = new QSGGeometry(QSGGeometry::defaultAttributes_Point2D(), 2);
    geometry->setDrawingMode(GL_LINES);
    geometry->setLineWidth(5.0);
    geometry->vertexDataAsPoint2D()[0].set(x(), y());
    geometry->vertexDataAsPoint2D()[1].set(width(), height());
    node = addNode(geometry,Qt::blue);
    root->appendChildNode(node);

    geometry = new QSGGeometry(QSGGeometry::defaultAttributes_Point2D(), 2);
    geometry->setDrawingMode(GL_LINES);
    geometry->setLineWidth(5.0);
    geometry->vertexDataAsPoint2D()[0].set(width(), y());
    geometry->vertexDataAsPoint2D()[1].set(x(), height());
    node = addNode(geometry,Qt::blue);
    root->appendChildNode(node);

    return root;
}

QSGNode *MyQuickItem::addNode(QSGGeometry *geometry, const QColor &color)
{
    QSGFlatColorMaterial *material = new QSGFlatColorMaterial;
    material->setColor(color);
    QSGGeometryNode *node = new QSGGeometryNode;
    node->setGeometry(geometry);
    node->setFlag(QSGNode::OwnsGeometry);
    node->setMaterial(material);
    node->setFlag(QSGNode::OwnsMaterial);
    return node;
}

在main.cpp

qmlRegisterType<MyQuickItem>("MyObjects", 1, 0, "MyObject");

和用法：

import QtQuick 2.3
import QtQuick.Window 2.2
import MyObjects 1.0    

Window {
    visible: true
    width: 360
    height: 360

    MyObject {
        anchors.fill: parent
    }
}

Answer 2

绘制的矩形是您预期大小的一半，因为默认坐标范围是 [-1, 1]，而不是代码假定的 [0, 1]。如果要使用[0, 1] scale，那么应该适当设置投影矩阵：

glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0.0, 1.0, 0.0, 1.0, -1.0, 1.0);

使用原始 OpenGL 调用绘制 Qml 项目的问题

Issue with drawing an Qml Item with raw OpenGL calls

opengl

qt

qml

qt-quick

qtquick2