QPainter: Colored matrix to paint

fem_dev

I'm learning about how to paint a widget using QPainter (pixel per pixel) and I already saw the Basic Tools Plugin example in the Qt Creator, but I'm a little bit confuse about how to do this simple task below:

std::vector< std::vector<QColor> > colored_matrix(3, 3);

// Fill the 'colored_matrix' with QColor data (RGB)
// Red:
colored_matrix[0][0] = QColor(256, 0, 0, 0);
colored_matrix[0][1] = QColor(256, 0, 0, 0);
colored_matrix[0][2] = QColor(256, 0, 0, 0);
// Green:
colored_matrix[1][0] = QColor(0, 256, 0, 0);
colored_matrix[1][1] = QColor(0, 256, 0, 0);
colored_matrix[1][2] = QColor(0, 256, 0, 0);
// Blue:
colored_matrix[2][0] = QColor(0, 0, 256, 0);
colored_matrix[2][1] = QColor(0, 0, 256, 0);
colored_matrix[2][2] = QColor(0, 0, 256, 0);

// Paint this matrix in a UI widget.

How can I get this output colored matrix UI (just the colors, without the cells names)?

fem_dev

@fem_dev here is the solution!

    // Set the image size:
    int sizeX = 400;
    int sizeY = 400;

    // Create and init the image:
    QImage image = QImage(sizeX, sizeY, QImage::Format_RGB32);

    // Fill the image with colors:
    for (int x = 0; x < sizeX; x++) {
        for (int y = 0; y < sizeY; y++) {
            image.setPixel(x, y, qRgb(x, y, 200));
        }
    }

    // Create a graphics scene:
    QGraphicsScene* graphic = new QGraphicsScene(this);

    // Set the image:
    graphic->addPixmap(QPixmap::fromImage(image));

    // Display it on the UI:
    ui->graphicsView->setScene(graphic);

SGaist

Hi,

Looks like you need two for loops that will draw the rectangles and pick the color from your matrix.

Do you need any more details ?

fem_dev

@SGaist yes...I understand the generic algorithm, but I don't know how to paint it on UI screen.

Could you help me?

fem_dev

@fem_dev here is the solution!

    // Set the image size:
    int sizeX = 400;
    int sizeY = 400;

    // Create and init the image:
    QImage image = QImage(sizeX, sizeY, QImage::Format_RGB32);

    // Fill the image with colors:
    for (int x = 0; x < sizeX; x++) {
        for (int y = 0; y < sizeY; y++) {
            image.setPixel(x, y, qRgb(x, y, 200));
        }
    }

    // Create a graphics scene:
    QGraphicsScene* graphic = new QGraphicsScene(this);

    // Set the image:
    graphic->addPixmap(QPixmap::fromImage(image));

    // Display it on the UI:
    ui->graphicsView->setScene(graphic);

SGaist

You are over-complicating things.

If you want to use a QGraphicsScene, then use QGraphicsScene::addRect and pass the colour to the brush.

Otherwise, QImage provides a fill method.

For QPainter, you have QPainter::drawRect. Just modify the painter brush before paiting the rectangle.

fem_dev

@SGaist thank you. For my given colored matrix above you are right!

I called this post above as a "solution" because, in the original first post, I was talking about a oversimplified view of my real problem. It was my fault!
I tried to simplify the real problem a lot and I ended up changing the focus / resolution target. Sorry about that!

Well, I want to develop a 2D histogram graph using Qt. So I have to set a color pixel per pixel on screen, like this example below:

Using the source-code in this post above I can set the color values pixel per pixel.

QUESTION:
Is there a better/correct way to do this?

In the nexts steps I need to understand how to:
a) Create the X and Y axis (with ticks ans labels)
b) Create the right-side color pallet (with ticks ans labels)
c) Set a graph title

Please, if you have any sugestions about how to implement these things, let me know.

Thank you again!

JohanSolo

It's always nice to see ROOT plots ;-)

Would QCustomPlot fullfill your needs?

fem_dev

@JohanSolo Unfortunately the QCustomPlot doesn't have the 2D histogram plot.

I tryed to use ROOT and I saw that there was a ROOT + Qt 3/4 integration in the past.

So I downloaded the binary ROOT installer for Windows 10 x64 and installed it.
After that, i tryed to run the ROOT installed executable file.
It open the Windows Console and give a error about missing #include <new> and another things....and closes the console window...

May be there is a another plot library that can plot a 2D histogram and is better to integrate with Qt C++ GUI application.
Do you know another library?