在 QML 插件的 QGLWidget 上渲染 QImage

2022-01-19 00:00:00 opengl qt4 qt qml c++

我正在尝试编写一个 QML 插件，它从视频中读取帧(使用自定义小部件来完成该任务，而不是 QtMultimedia/Phonon)，并且每个帧都转换为 QImage RGB888，然后显示在 QGLWidget 上(出于性能原因).现在什么都没有画到屏幕上，屏幕一直保持白色.

I'm trying to write a QML plugin that reads frames from a video (using a custom widget to do that task, NOT QtMultimedia/Phonon), and each frame is converted to a QImage RGB888, and then displayed on a QGLWidget (for performance reasons). Right now nothing is draw to the screen and the screen stays white all the time.

重要的是要说明我已经在没有 QGLWidget 的情况下完成了所有这些工作，所以我知道问题在于设置和绘制 QGLWidget.

It's important to state that I already have all of this working without QGLWidget, so I know the issue is setting up and drawing on QGLWidget.

插件正在注册:

qmlRegisterType<Video>(uri,1,0,"Video");

所以 Video 是插件的主类.在它的构造函数上，我们有:

so Video is the main class of the plugin. On it's constructor we have:

Video::Video(QDeclarativeItem* parent)
: QDeclarativeItem(parent), d_ptr(new VideoPrivate(this))
{    
    setFlag(QGraphicsItem::ItemHasNoContents, false);            

    Q_D(Video);
    QDeclarativeView* view = new QDeclarativeView;
    view->setViewport(&d->canvas()); // canvas() returns a reference to my custom OpenGL Widget
}

在我跳转到 canvas 对象之前，让我说我重载了 Video::paint() 所以它调用了 canvas.paint() 在传递 QImage 作为参数时，我不知道这是否是正确的方法，所以我想对此提出一些建议:

Before I jump to the canvas object, let me say that I overloaded Video::paint() so it calls canvas.paint() while passing QImage as parameter, I don't know if this is the right way to do it so I would like some advice on this:

void Video::paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QWidget* widget)
{
    Q_UNUSED(painter);
    Q_UNUSED(widget);
    Q_UNUSED(option);

    Q_D(Video);
    // I know for sure at this point "d->image()" is valid, but I'm hiding the code for clarity
    d->canvas().paint(painter, option, d->image());
}

canvas对象声明为GLWidget canvas;，该类的头部定义为:

The canvas object is declared as GLWidget canvas; and the header of this class is defined as:

class GLWidget : public QGLWidget
{
    Q_OBJECT
public:        
    explicit GLWidget(QWidget* parent = NULL);
    ~GLWidget();

    void paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QImage* image);
};

看起来很简单.现在，QGLWidget的实现如下:

Seems pretty simple. Now, the implementation of QGLWidget is the following:

GLWidget::GLWidget(QWidget* parent)
: QGLWidget(QGLFormat(QGL::SampleBuffers), parent)
{
   // Should I do something here?
   // Maybe setAutoFillBackground(false); ???
}

GLWidget::~GLWidget()
{
}

最后:

void GLWidget::paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QImage* image)
{
   // I ignore painter because it comes from Video, so I create a new one:
   QPainter gl_painter(this);


   // Perform drawing as Qt::KeepAspectRatio

   gl_painter.fillRect(QRectF(QPoint(0, 0), QSize(this->width(), this->height())), Qt::black);

   QImage scaled_img = image->scaled(QSize(this->width(), this->height()), _ar, Qt::FastTransformation);

   gl_painter.drawImage(qRound(this->width()/2)  - qRound(scaled_img.size().width()/2),
                        qRound(this->height()/2) - qRound(scaled_img.size().height()/2),
                        scaled_img); 
}

我错过了什么?

我最初在 Qt 论坛上问 这个问题，但没有得到任何答复.

I originally asked this question on Qt Forum but got no replies.

推荐答案

已解决.问题是当我应该从加载它的应用程序中检索 GL 上下文时，我试图在我的插件中创建一个新的 GL 上下文.

Solved. The problem was that I was trying to create a new GL context within my plugin when I should be retrieving the GL context from the application that loaded it.

此代码是非常有帮助了解如何做到这一点.

This code was very helpful to understand how to accomplish that.

顺便说一句，我发现这些东西是在 view 中绘制的.只是我需要执行 view->show()，但这会创建另一个窗口，这不是我想要的.我上面分享的链接有答案.

By the way, I discovered that the stuff was being draw inside view. It's just that I needed to execute view->show(), but that created another window which was not what I was looking for. The link I shared above has the answer.

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