How to create my own QPixmap Or QImage

[sagirahmed]

Hi,

I want create my own QPixmap or QImage using my own data. so that I able to set this QPixmap to QLabel instead of drawing the same content again and again in paintEvent()

Thanks & Regards

[nish]

QPixmap pix;
QPainter p(&pix);
p.drawXYZ();
 
lablel->setPixmap(pix);

QPixmap pix;
QPainter p(&pix);
p.drawXYZ();

lablel->setPixmap(pix);

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[aamer4yu]

QPixmap pix;
QPainter p(&pix);
p.drawXYZ();
 
lablel->setPixmap(pix);

QPixmap pix;
QPainter p(&pix);
p.drawXYZ();

lablel->setPixmap(pix);

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One mistake.. always specify a size for the pixmap / image while creating it.
Something like - QPixmap pix(600,480);
You cannot paint on null pixmap !!

[sagirahmed]

Hi,

I have tried this code but it is not working.

---

Added after 55 minutes:

Hi,

Again i tried but it doesn't work. Can you give me small code so that I can get help from it.

[Lykurg]

What have you tried? Show us your code.

[sagirahmed]

void DrawImage()
{
      QPixmap pix(700,700);
      QPainter painter(&pix); 
      painter.drawText(QPoint(0 ,0),"text");	
      painter.save();
      labelPixmap->setPixmap(pix);
}

void DrawImage()
{
      QPixmap pix(700,700);
      QPainter painter(&pix); 
      painter.drawText(QPoint(0 ,0),"text");	
      painter.save();
      labelPixmap->setPixmap(pix);
}

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This is my code that I have written. It show some garbage color on Label. Not showing the text

[Lykurg]

First we have [CODE]-tags. Second

painter.save();

painter.save();

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is nonsense here! Third read the documentation about QPainter::drawText() especially what the point is defining. And forth: You might want to fill the pixmap with a color first because it is initialized with no specific value.

[nish]

One mistake..

That was not a mistake. That was left as an exercise for the reader.

always specify a size for the pixmap / image while creating it.
Something like - QPixmap pix(600,480);
You cannot paint on null pixmap !!

You PASSED!!

[sagirahmed]

Hi,

Thanks I am successfully drawn the image using QPainter and set this image to Qlabel.

Thanks & Regards

[sagirahmed]

Hi,

I want to create a large QPixmap. The size of QPixmap pix(741,2000000). It cause crashing when we execute the code is

QPixmap pix(741,2000000);
QPainter painter(&pix);
QColor clrbg(144,204,114);
pix.fill(clrbg); /// it crash at this point

So help me for creating very large pixmap

[Lykurg]

If you are not using the [CODE] tags I won't help you!

[sagirahmed]

Hi,

I want to create a large QPixmap. The size of QPixmap pix(741,2000000). It cause crashing when we execute the code is

QPixmap pix(741,2000000);
QPainter painter(&pix);
QColor clrbg(144,204,114);
pix.fill(clrbg); /// it crash at this point
So help me for creating very large pixmap

[aamer4yu]

741 * 2000000 = 1482000000 pixels
Considering 32 bit per pixel
741 * 2000000 * 32 bits are required
ie. 741 * 2000000 * 4 == 5928000000 bytes
ie 5789062 KB
ie 5653 MB
ie 5.5 GB

Do you even have that much RAM ??? Where do you think the memory will be allocated ?
Obviously its gonna crash !!

[sagirahmed]

Hi,

So How can I solve this problem. If I have to create QPixmap of this size(741*2000000)

[nish]

Hi,

So How can I solve this problem. If I have to create QPixmap of this size(741*2000000)

create them in short parts. and store then on to the disk. while reading back just do the reverse.

[sagirahmed]

Hi,

How store short part Qpixmap on to disk. that I have I drawn using QPainter.

[aamer4yu]

Am not sure, but you can try this -
pixmap is a IO device,, so you can use seek() to write to a particular point.
So use that and try writing smaller rects into the pixmap..

[tbscope]

Be aware that for some picture formats, you can't just load a certain part of it.
Thus, when you want to save such a large file, you're going to get into trouble at some point. Always save files in managable parts and then create software that can stich those parts together. Look at google maps for example.

[sagirahmed]

Hi,

so can you suggest me other way to create very large Qpixmap or any other class that will handle this. If I have to create QPixmap of this size(741*2000000)
I know take very huge amount of memory.

[tbscope]

I'll give you an extremely powerfull tip:
Do NOT paint what is NOT on screen.

Unfortunatly, when you're dealing with jpg files for example, and you want to save a stupendously large file, you WILL get into problems very fast.
Either use another format that allows you to stream the file to disk or from disk or rethink what you're doing (like splitting up the very large jpg into 10 or 100 smaller jpg's)