Using negative values for the x and y args to QRectF when calling Qpainter.drawElipse

[edmhourigan]

What is the purpose of passing negative values to the QRect constructor for the x and y parameters?

Example:

QPainter painter(this);
    painter.setRenderHint(QPainter::Antialiasing, antialiased);
    painter.translate(width() / 2, height() / 2);
 
    for (int diameter = 0; diameter < 256; diameter += 9) 
   { 
       painter.drawEllipse(QRectF(-diameter / 2.0, -diameter / 2.0, diameter, diameter));
   }

QPainter painter(this);
    painter.setRenderHint(QPainter::Antialiasing, antialiased);
    painter.translate(width() / 2, height() / 2);

    for (int diameter = 0; diameter < 256; diameter += 9) 
   { 
       painter.drawEllipse(QRectF(-diameter / 2.0, -diameter / 2.0, diameter, diameter));
   }

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The code above draws a series of concentric circles centered at a fixed point. If I change to positive values, the center of each circle moves, drawing a 'cone effect' on the screen.



My question is what does negating the x and y arguments really do?
I have searched a lot for this topic but nothing comes up that really answers my question.

Thanks.