Qt crash at drawImage

[Chaitra Sridhar]

Hi,
I am relatively new to Qt programming. I have hit a dead end and seek help.
I am running Qt in Linux.
Following is my code -

QPainter painter;
    QImage rcptImage(216, 560, QImage::Format_Mono);
 
    painter.begin(&rcptImage);
 
    QImage img("./test1.bmp");
    QImage::Format f = img.format();
    printf("%d\n", f);
    uchar* tempData = img.bits();
 
   QImage img1(img.bits(), 320, 240, QImage::Format_Mono);
   QImage::Format f1 = img1.format();
 
    painter.drawImage(QPoint(10,10), img1);
 
    painter.end();
 
    rcptImage.save("/home/chaitras/output1.bmp");

QPainter painter;
    QImage rcptImage(216, 560, QImage::Format_Mono);

    painter.begin(&rcptImage);

    QImage img("./test1.bmp");
    QImage::Format f = img.format();
    printf("%d\n", f);
    uchar* tempData = img.bits();

   QImage img1(img.bits(), 320, 240, QImage::Format_Mono);
   QImage::Format f1 = img1.format();

    painter.drawImage(QPoint(10,10), img1);

    painter.end();

    rcptImage.save("/home/chaitras/output1.bmp");

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Program is crashing at "painter.drawImage(QPoint(10,10), img1);"

test1.bmp is a 1bpp image - 360 x 260 x 1. Attached the image.

I am trying to reading the bits from "img" and create a new image img1 using these bits.
And using img1, which results in a crash.

Stacktrace is pointing to a function "convertIndexedToARGB32PM Line 95"


convertIndexedToARGB32PM Line 95
blend_untransformed_generic Line 4264
fillRect_normalized Line 1491
QRasterPaintEngine::drawImage Line 2187
QPainter::drawImage Line 5356
QPainter::drawImage qpainter.h Line 852
main


Any help on this would be appreciated.

[d_stranz]

So none of the sizes of your images match. One is 216 x 560, one is 320 x 240, another is 360 x 260. What do you think will happen if you try to load one image of 360 x 260 into another image of 320 x 240, and then try to paint that into an image of 216 x 560? Do you expect QImage and QPainter to try to understand what you really want to do and just do it for you despite the fact that nothing matches?

[Chaitra Sridhar]

The "rcptImage" is a sort of canvas I am using to use to either drawImage or drawText.

Sorry, that was a typo.
My image is 360 x 240, I mean the one I uploaded.

Anyways even after changing all sizes to 320x240, the crash is still happening...

---

Added after 8 minutes:

Also, the surprising thing is that, if use "img" with "drawImage", it works absolutely fine.
When I use "img1", it is crashing.

[d_stranz]

If your input image is 360 x 240 and the image you are trying to paint into is smaller (320 x 240), then it is still probably going to blow up.

Do you know that the image you say you loaded has actually been loaded (QImage::isNull()) or that the pointer returned by QImage::bits() is not NULL or that the image you create from the bits is not null??

[Chaitra Sridhar]

I changed the canvas size to 500x500(rcptImage),
img.isNull() is false. I printed out img.Bits(), it has data and it is not Null

img1.isNull() is false. and img1.Bits() is not null.

I also looped through the bits and subtracted the pixel values of img and img1. The differences for all pixels are all zeros.

Also, img and img1 are both 320 x 240.. a total of 9600 bytes of data.

Another observation is that when I use loadFromData function with img1, i.e., tried the following
const uchar* temp = img.constBits();
QImage img1;
bool result = img1.loadFromData(temp, 9600, "BMP");

The result is false.

---

Added after 25 minutes:

Hi d_stranz,

I just tried couple of things, and when I changed the image format as follows, the program does not crash

QImage img1(tempData, 320, 240, QImage::Format_ARGB32);

When I use
QImage img1(tempData, 320, 240, QImage::Format_Mono);

there is a crash.

Why is this happening. As per my understanding, "QImage img("/home/chaitras/work/Printer/NipponPrinter/Printer_Test/test1.bmp");" is a QImage::Format_Mono. I confirmed this by printing "QImage::Format f = img.format();"
But when I read the get the img.bits() and create QImage img1(img.bits(), 320, 240, QImage::Format_Mono); it does not work..

Why is it like that? Do u have any idea on this??
Let me know your thoughts..

[ChrisW67]

You have a mono input image and you appear to want an exact copy of that image. Why are you playing with the internal data buffer at all?

QImage img1(img);

QImage img1(img);

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Should achieve the goal.

[Chaitra Sridhar]

Thanks for your reply.

In my project, I am expecting the image as a byte stream. And I need to use this byte stream in to QImage and then print this image out.
So, I happened to write a small test program that intends to do this.
But, it is crashing at the mentioned point.

Could you please give an example as to how to load a byte stream into QImage and do a "drawImage"?