CODEWITHSUNDEEP
c++qt
Smek
Smek

Reputation: 1208

Display bitmap data in QT view

I'm writing an image library from scratch I have written a console application that loads a bitmap image does some manipulation and writes the output to another bitmap. Now I would like to build a UI on top of my application. So I would like to do this in Qt Creator since I have some experience with Qt and I want it to work for multiple platforms.

Here is my code that loads a bitmap:

FILE *streamIn = fopen("path/to/file.bmp", "rb");

if (streamIn == (FILE *)0)
{
  printf("Unable to open file\n");
}

unsigned char bmpHeader[54];
unsigned char bmpColorTable[1024];

for (int i = 0; i < 54; i++)
{
  bmpHeader[i] = getc(streamIn);
}

int width = *(int *)&bmpHeader[18];
int height = *(int *)&bmpHeader[22];
int bitDepth = *(int *)&bmpHeader[28];

if (bitDepth <= 8)
{
  fread(bmpColorTable, sizeof(unsigned char), 1024, streamIn);
}
unsigned char buf[height * width];
fread(buf, sizeof(unsigned char), (height * width), streamIn);
fclose(streamIn);

How do I get this into my UI? I already tried something like:

const QImage image(buf, width, height, QImage::Format_Grayscale8);
imageLabel->setPixmap(QPixmap::fromImage(image));

But that results in a tiny white image not the image I just read. Perhaps I can skip creating a QImage and create a QPixmap right away? What I tried now does not work so maybe someone more experienced can tell me how to get it done. When I loaded the initial image I would like to update the view when I do some manipulation so the user can see the changes.

I know it can be done much easier with QImageReader but this is for learning purposes.

Upvotes: 1

Views: 2990

Answers (1)

Smek
Smek

Reputation: 1208

I don't know what I did wrong but now it just works like it should. But there is one issue with reading the bitmap format like this in the QImage see Why are bmps stored upside down?

So what I do now is this:

QImage img(width, height, QImage::Format_Grayscale8);
for (int row = 0; row < img.height(); row++) {
    for(int col = 0; col < img.width(); col++) {
        int color = (int)_imgInBuffer[row * img.width() + col];
        img.setPixel(col, height - row - 1, qRgb(color, color, color));
    }
}

I don't know why I need to set a red, green, blue value to a grayscale image but this is the only way to get it done.

Upvotes: 1

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