Trying to draw a grid on a QGraphicsScene/View

[di_zou]

nevermind, m_gridsize is like how many lines I want right?

[robertson1]

Hi sorry, that was a bit vauge. This was for a map screen which could be panned, zoomed and rotated, the grid lines were drawn at specified intervals (m_gridSize) in scene coordinates, for example if m_gridSize was 10 you would get lines at 0, 10, 20 etc units on the X and Y axis in the scene regardless of any zooming.

Note also that in this example my scene was scaled (1,-1) so that I my Y axis was flipped (Y now increasing upwards)

'rect' is the view rect, as 'painter->setWorldMatrixEnabled(true), then the drawing is done in scene coordinates

Here's the example is simplified a bit:

void NavScreen::drawForeground(QPainter* painter, const QRectF& rect)
{
        int gridInterval = 100; //interval to draw grid lines at
	painter->setWorldMatrixEnabled(true);
 
	qreal left = int(rect.left()) - (int(rect.left()) % gridInterval );
	qreal top = int(rect.top()) - (int(rect.top()) % gridInterval );
 
	QVarLengthArray<QLineF, 100> linesX;
	for (qreal x = left; x < rect.right(); x += gridInterval )
		linesX.append(QLineF(x, rect.top(), x, rect.bottom()));
 
	QVarLengthArray<QLineF, 100> linesY;
	for (qreal y = top; y < rect.bottom(); y += gridInterval )
	        linesY.append(QLineF(rect.left(), y, rect.right(), y));
 
	painter->drawLines(linesX.data(), linesX.size());
	painter->drawLines(linesY.data(), linesY.size());
}

void NavScreen::drawForeground(QPainter* painter, const QRectF& rect)
{
        int gridInterval = 100; //interval to draw grid lines at
	painter->setWorldMatrixEnabled(true);
		
	qreal left = int(rect.left()) - (int(rect.left()) % gridInterval );
	qreal top = int(rect.top()) - (int(rect.top()) % gridInterval );

	QVarLengthArray<QLineF, 100> linesX;
	for (qreal x = left; x < rect.right(); x += gridInterval )
		linesX.append(QLineF(x, rect.top(), x, rect.bottom()));

	QVarLengthArray<QLineF, 100> linesY;
	for (qreal y = top; y < rect.bottom(); y += gridInterval )
	        linesY.append(QLineF(rect.left(), y, rect.right(), y));

	painter->drawLines(linesX.data(), linesX.size());
	painter->drawLines(linesY.data(), linesY.size());
}

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Hope it helps

[di_zou]

Thank you, I have got it working. Can you tell me more about your map screen?

I am trying to do something similar to what you did. I am trying to create a map with movable icons using satellite and terrain data from USGS.

So far I have the icons I am using at their appropriate Lat/Long points on the map. I am using QGraphicsPixmapItems as the icons. I also have the grid now for displaying the Lat/Long of the map area. I am working on getting the satellite imagery onto the QGraphicsScene.