Direct drawing on UI

Mikl

Hi

And it is fast enough?

I mean it will not take my RGB, convert it to Image, when to Pixmap, when use slow OS methods to display,....

The reason i asking, similar way in .NET is terribly slow.

Update:
Some more questions:
-Can i pass my image (RGB data in a memory) to paintEvent(QPaintEvent *)?
-Can it be inside of QPaintEvent?
-How to pass it? Something like this: videoFrame->update(RGBPointer)?
-Pass image using global variable?

mrjj

@Mikl
hi
sorry just saw the question about painting outside of event.
You should use opengl :) The sample to draw on pixmap will have way to much overhead.

-Can i pass my image (RGB data in a memory) to paintEvent(QPaintEvent *)?
No, it has fixed signature so u cant change it. (adding the param)

-Can it be inside of QPaintEvent?
yes. should not be an issue

-How to pass it? Something like this: videoFrame->update(RGBPointer)?
Really depends on what format you get from camera.

-Pass image using global variable?
nope. never really a reason to use globals.
since you might create your own widget , you can just add a function
to assign/share the data from the source.

Mikl

Hi

-I like the way to draw on opengl. Should be 'fast'. But will i meet capability problem? it will run on Win AND Linux?
Can you point me to the example, please?

-Pass image using global variable?
never was thinking about it. just looking for solution

-Can i pass my image (RGB data in a memory) to paintEvent(QPaintEvent *)?
-Can it be inside of QPaintEvent?
-How to pass it? Something like this: videoFrame->update(RGBPointer)?
From camera i have raw 24bit RGB data.
If it is not possible to pass my data to paintEvent(QPaintEvent *) how can i get it? Even if it is inside of QPaintEvent. Not really see how to do it. I will start something. Correct/add me please.

main()
{
char* RGBData = new char[frame size];//data from camera

videoFrame = new VideoFrameWidget();
videoFrame->update(RGBData);
}

class VideoFrameWidget : public QWidget
{
	Q_OBJECT
public:
	VideoFrameWidget(QWidget *parent);
	virtual void paintEvent(QPaintEvent *);
};

void VideoFrameWidget::paintEvent(QPaintEvent *data)
{
//use opengl to draw image from data
}

mrjj

hi
why cant RGBData just live in VideoFrameWidget ?
so you dont need to give it from main. ?

but else u just use functions to give it to the widget.

Mikl

@mrjj

It can, but i found it not logic. it is coming from the camera.
It was simplification of main. In a reality it will be a loop.

If i understood you correctly, you propose to do it like this:

main()
{
 char* RGBData;//data from camera
 VideoFrameWidget videoFrame = new VideoFrameWidget();
 CameraDevice videoSource = new CameraDevice ();

 for(;;)
 {
  RGBData = videoSource->getFrame();
  videoFrame->setFrame(RGBData);
  videoFrame->update();
 }
}

class VideoFrameWidget : public QWidget
{
    Q_OBJECT
public:
    VideoFrameWidget(QWidget *parent);
    virtual void paintEvent(QPaintEvent *);
    void setFrame(char* newFrameData);
private:
 char* frameData;
};

void VideoFrameWidget::paintEvent(QPaintEvent*)
{
//use opengl to draw image from frameData 
}

 void VideoFrameWidget::setFrame(char* newFrameData)
{
 frameData = newFrameData;
}

mrjj

yes exactly and then u can use
char* frameData;
in paintEvent

Mikl

@mrjj

But i still have a question of realization of paintEvent :)

Can you give me a hand, please

mrjj

@Mikl
hii . super :)
im not good with opengl so better ask @Wieland
or anyone using it often. :)

Mikl

@mrjj
Thank you for helping

@Wieland
Can i ask for help with my problem please?
I need to display raw RGB on a screen in a fastest way.

mrjj

@Mikl
note, this is user run forum.
so he might first be on in the evening.
:)

Mikl

@mrjj
Ok. Thanks.

For me it is looks strange, but reading this example
http://doc.qt.io/qt-5/qtopengl-2dpainting-example.html
i found, what the only different is using GLWidget as base class.
All painting is done by the same QPainter.

Am i right?

If it is so, task can be really simple.
Maybe you know the fastest way to paint from RGB raw data on widget: draw line by line, pixel by pixel, memcopy,....

mrjj

@Mikl
Yes as far as i know its VERY similar to
normal widget drawing even when opengl.
(when 2d)

well, the sample i have seen , used something like
uchar* data = getDataFromSomewhere();
QImage img(data, width, height, QImage::Format_ARGB32);
and then convert ot pixmap and draw.
or directly into pixmap with
http://doc.qt.io/qt-4.8/qpixmap.html#loadFromData

? Offline

@Mikl said:

For me it is looks strange, but reading this example
http://doc.qt.io/qt-5/qtopengl-2dpainting-example.html
i found, what the only different is using GLWidget as base class.
All painting is done by the same QPainter.

Am i right?

Hi! Yes, getting 2D hardware acceleration for QPainter is really easy :)