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Qt--windows平台上如何获取qml中Camera的数据

来源：程序员人生发布时间：2016-12-20 16:29:57 阅读次数：3212次

曾写了1个博客：
我们为何不习惯使用qml？最后有1个悬念，到底如何在C++代码中获得qml中camera的数据呢？

QAbstractVideoFilter
The QAbstractVideoFilter class represents a filter that is applied to the video frames received by a VideoOutput type.
https://doc-snapshots.qt.io/qt5-dev/qabstractvideofilter.html#details

QVideoFilterRunnable
The QVideoFilterRunnable class represents the implementation of a filter that owns all graphics and computational resources, and performs the actual filtering or calculations.

上面两个类自己去看官方文档吧，翻译不好。

开始撸代码!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

写1个自己的类叫CameraFilter吧：

camerafilter.h

#ifndef CAMERAFILTER
#define CAMERAFILTER
#include <QVideoFilterRunnable>

class CameraFilter : public QAbstractVideoFilter
{
    Q_OBJECT
public:
    CameraFilter();
    ~CameraFilter();
    QVideoFilterRunnable *createFilterRunnable();
private:
signals:
    void finished(QObject *result);
    void cameraFrameSignal(QVideoFrame);
public slots:

};

class CameraFilterRunnable : public QVideoFilterRunnable
{
public:
    CameraFilterRunnable(CameraFilter* filter = NULL);
    ~CameraFilterRunnable();
    QVideoFrame run(QVideoFrame *input, const QVideoSurfaceFormat &surfaceFormat, RunFlags flags);

private:
    CameraFilter *m_filter;
};

#endif // CAMERAFILTER

camerafilter.cc

#include "camerafilter.h"
#include "qdebug.h"

CameraFilter::CameraFilter()
{

}

CameraFilter::~CameraFilter()
{

}

QVideoFilterRunnable *CameraFilter::createFilterRunnable()
{
    return new CameraFilterRunnable(this);
}

CameraFilterRunnable::CameraFilterRunnable(CameraFilter* filter)
{
    m_filter = filter;
}

CameraFilterRunnable::~CameraFilterRunnable()
{

}

QVideoFrame CameraFilterRunnable::run(QVideoFrame *input, const QVideoSurfaceFormat &surfaceFormat, RunFlags flags)
{
    QVideoFrame cloneFrame(*input);

    emit m_filter->cameraFrameSignal(cloneFrame);

    return cloneFrame;
}

不要骂娘，上面的代码很简单的，其实官方的文档中也有类似的代码片断，不懂的自己看奥。
是通过：

emit m_filter->cameraFrameSignal(cloneFrame);

我们自己写1个slot，然后对Frame进行相应的处理！

接下来才是高潮！！！！

第1步、让qml中理解我们自己的类CameraFilter(Defining QML Types from C++) ：

在C++中注册：

qmlRegisterType<CameraFilter>("CameraFilter", 1, 0, "CameraFilter");

在qml中导入：

import CameraFilter 1.0

第2步、在qml中干点大事儿：

          Camera {
                objectName: "CameraObject"
                id: camera
                imageProcessing.whiteBalanceMode: CameraImageProcessing.WhiteBalanceFlash
                exposure {
                    exposureCompensation: -1.0
                    exposureMode: Camera.ExposurePortrait
                }
                captureMode: Camera.CaptureVideo
                flash.mode: Camera.FlashRedEyeReduction
            }

            VideoOutput {
                width: 160
                height: 90
                id: video_output
                objectName: "VidelOutputObject"
                source: camera
                anchors.fill: parent
                focus : visible // to receive focus and capture key events when visible
                visible: false
                filters: [filter]
                fillMode: VideoOutput.PreserveAspectFit
            }

            CameraFilter {
                objectName: "cameraFilterObject"
                id: filter
            }

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