how to add item QComboBox with QVideoFrame::PixelFormat?

pauledd · 7 Sept 2016, 06:51

Hi there,
I want to fill a QComboBox with all supported pixelformats of a given QCamera. I load the camera and I fill the QListQVideoFrame::PixelFormat Object "suppPixFmt" with camera->supportedViewfinderPixelFormats(). This works so far an I can print one single format with qDebug() << suppPixFmt->at(1);
Now I want to fill a QComboBox with the formats list but my fist attempt ended in:

no known conversion for argument 1 from 'const QVideoFrame::PixelFormat' to 'const QString&'

My next thought was to use static_cast to convert it to QString but then the QComboBox is filled with stange Unicode? text:

Does someone know what's going wrong here?
Thats the code:
mainwindow.cpp

#include "mainwindow.h"
#include <QDebug>
MainWindow::MainWindow(QWidget *parent) : QWidget(parent)
{
	setFixedSize(800,600);
	move(600,250);

	comboBoxFormats = new QComboBox(this);
	camera = new QCamera(this);
	suppPixFmt = new QList<QVideoFrame::PixelFormat>;	
	connect(camera, &QCamera::statusChanged, this, &MainWindow::updatedStatus);
	camera->load();
}

MainWindow::~MainWindow()
{
}

void MainWindow::updatedStatus(){
	
	qDebug() << camera->status();
	
	if(camera->status() == QCamera::LoadedStatus)
	{
		qDebug()<< "loaded & filling supported formats";
		
		foreach (QVideoFrame::PixelFormat fmt, camera->supportedViewfinderPixelFormats()) {
			suppPixFmt->append(fmt);
		}
		for (int i = 0;i < suppPixFmt->size();i++){
			comboBoxFormats->addItem(static_cast<QString>(suppPixFmt->at(i)));
		}
	}
}

raven-worx · 9 Jul 2016, 06:51

@pauledd said in how to add item QComboBox with QVideoFrame::PixelFormat?:

Does someone know what's going wrong here?

yes, its impossible to convert a enum to a string. Converting it by casting will make QString interpret it as unicode as you already noticed.

In Qt you could use QMetaObject to traverse a class' (registered) enum and use it to fill the combobox.
But QVideoFrame unfortunately doesn't inherit from QObject nor its a Q_GADGET, so it doesn't have a meta object.

So you will have to fill the combobox with the string values yourself.

pauledd · 7 Sept 2016, 10:21

Ok, thank you for enlightening me :)

I created a struct that contains the Format QString and the corresponding number int. I created a QVector with that struct and filled it with a for loop - switch statement. I think it is awkward but it seems to work, my QComboBox gets filled with available pixelformats.

structs.h

#ifndef STRUCTS_H
#define STRUCTS_H
#include <QString>
struct PixFmt{
	unsigned int i;
	QString format;
};

#endif // STRUCTS_H

mainwindow.cpp

#include "mainwindow.h"
#include <QDebug>
#include "structs.h"
MainWindow::MainWindow(QWidget *parent) : QWidget(parent)
{
	setFixedSize(800,600);
	move(600,250);
	comboBoxFormats = new QComboBox(this);
	vl = new QVBoxLayout(this);
	camera = new QCamera(this);
	suppPixFmt = new QList<QVideoFrame::PixelFormat>;	
	connect(camera, &QCamera::statusChanged, this, &MainWindow::updatedStatus);
	camera->load();
}

MainWindow::~MainWindow()
{
	
}

void MainWindow::updatedStatus(){

	PixFmt pfmt;
	QVector<PixFmt> vPixFmt;
	
	if(camera->status() == QCamera::LoadedStatus)
	{
		qDebug()<< "loaded & filling supported formats";
		foreach (QVideoFrame::PixelFormat fmt, camera->supportedViewfinderPixelFormats())
		{
			suppPixFmt->append(fmt);
		}
		
		for (int i=0;i<suppPixFmt->size();i++)
		{
			switch (suppPixFmt->at(i)) {
			case 0: pfmt.i = 0;pfmt.format = "Invalid"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 1: pfmt.i = 1;pfmt.format = "ARGB32"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 2: pfmt.i = 2;pfmt.format = "ARGB32_Premultiplied"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 3: pfmt.i = 3;pfmt.format = "RGB32"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 4: pfmt.i = 4;pfmt.format = "RGB24"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 5: pfmt.i = 5;pfmt.format = "RGB565"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 6: pfmt.i = 6;pfmt.format = "RGB555"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 7: pfmt.i = 7;pfmt.format = "ARGB8565_Premultiplied"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 8: pfmt.i = 8;pfmt.format = "BGRA32"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 9: pfmt.i = 9;pfmt.format = "BGRA32_Premultiplied"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 10: pfmt.i = 10;pfmt.format = "BGR32"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 11: pfmt.i = 11;pfmt.format = "BGR24"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 12: pfmt.i = 12;pfmt.format = "BGR565"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 13: pfmt.i = 13;pfmt.format = "BGR555"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 14: pfmt.i = 14;pfmt.format = "BGRA5658_Premultiplied"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 15: pfmt.i = 15;pfmt.format = "AYUV444"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 16: pfmt.i = 16;pfmt.format = "AYUV444_Premultiplied"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 17: pfmt.i = 17;pfmt.format = "YUV444"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 18: pfmt.i = 18;pfmt.format = "YUV420P"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 19: pfmt.i = 19;pfmt.format = "YV12"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 20: pfmt.i = 20;pfmt.format = "UYVY"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 21: pfmt.i = 21;pfmt.format = "YUYV"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 22: pfmt.i = 22;pfmt.format = "NV12"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 23: pfmt.i = 23;pfmt.format = "NV21"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 24: pfmt.i = 24;pfmt.format = "IMC1"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 25: pfmt.i = 25;pfmt.format = "IMC2"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 26: pfmt.i = 26;pfmt.format = "IMC3"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 27: pfmt.i = 27;pfmt.format = "IMC4"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 28: pfmt.i = 28;pfmt.format = "Y8"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 29: pfmt.i = 29;pfmt.format = "Y16"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 30: pfmt.i = 30;pfmt.format = "Jpeg"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 31: pfmt.i = 31;pfmt.format = "CameraRaw"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 32: pfmt.i = 32;pfmt.format = "AdobeDng"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			case 33: pfmt.i = 33;pfmt.format = "User"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			default: pfmt.i = 0;pfmt.format = "unknown Pixelformat"; vPixFmt.push_back(PixFmt(pfmt));
				break;
			}
		}
	}
	for (int i=0;i<vPixFmt.size();i++)
	{
		comboBoxFormats->addItem(vPixFmt[i].format);
	}
}

raven-worx · 9 Jul 2016, 10:32

@pauledd
yes, thats the only way to achieve what you want.
But i recommend that you use the actual enum values instead the int values like you do now.
Also this code can be dramatically improved (regarding performance):

QString pixelFormatToString( QVideoFrame::PixelFormat f )
{
     switch( f ) {
           default:
           case QVideoFrame::Format_Invalid:          return QLatin1String("Invalid");
           case QVideoFrame::Format_ARGB32:       return QLatin1String("ARGB32");
           ...
     }
}

void MainWindow::updatedStatus(){

	if(camera->status() == QCamera::LoadedStatus)
	{
		qDebug()<< "loaded & filling supported formats";
		foreach (QVideoFrame::PixelFormat fmt, camera->supportedViewfinderPixelFormats())
		{
			comboBoxFormats->addItem( pixelFormatToString(fmt), QVariant::fromValue<int>(fmt));  //store it to the user data so you can retrieve it again with QComboBox::itemData() upon selection change
		}
	}
}

pauledd · 7 Sept 2016, 11:12

@raven-worx said in how to add item QComboBox with QVideoFrame::PixelFormat?:

QVariant::fromValue<int>(fmt));

What does this? Is it returning the format corresponding int number from the pixelformat enum?

raven-worx · wrote on 7 Sept 2016, 11:12

@pauledd
it stores the (int explicitly in this case) value of the enum inside a QVariant.
This is just for convenience, to store the value along with the combobox item.
As i said check QCombobox::itemData(), if you want to retrieve the value (and cast it back to a QVideoFrame::PixelFormat enum type) when the selection changes in the combobox.

pauledd · wrote on 7 Sept 2016, 11:14

Ok, thanks a lot! Marked as solved!