I have the following code that render a 10 x 10 grid, I was expecting the grid start at {0, 0}, which should be the top left of the window, but the result is that {0, 0} is the center of the window.

Qt Code: 
  1. void GameScene::drawBackground(QPainter *painter, const QRectF &rect)
  2. {
  3.     int colCount = 10;
  4.     int rowCount = 10;
  5.     int tileWidth = 32;
  6.     int tileHeight = 32;
  7.  
  8.     // clear background
  9.     painter->fillRect(rect, QBrush(Qt::black));    
  10.  
  11.     //painter->translate(rect.width() / -2.0, rect.height() / -2.0);
  12.  
  13.     painter->setRenderHint(QPainter::Antialiasing, true);
  14.  
  15.     QPen pen;
  16.     pen.setStyle(Qt::DotLine);
  17.     pen.setColor(QColor(Qt::gray));
  18.     painter->setPen(pen);
  19.  
  20.     int x, y, x2, y2;
  21.  
  22.     y = 0; //painter->window().top();
  23.     y2 = y + (rowCount * tileHeight);
  24.     for(int c = 0; c <= colCount; c++)
  25.     {
  26.         x = c * tileWidth;
  27.         x2 = x;
  28.  
  29.         painter->drawLine(x, y, x2, y2);
  30.     }
  31.  
  32.     x = 0; //painter->window().left();
  33.     x2 = x + (colCount * tileWidth);// painter->window().right();
  34.     for(int r = 0; r <= rowCount; r++){
  35.         y = r * tileHeight;
  36.         y2 = y;    
  37.         painter->drawLine(x, y, x2, y2);
  38.     }
  39. }
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So, is this normal? Or I must translate the painter to have {0,0} be the top left corner?

shot.jpg