Undefined size when drawing a foreground in QGraphicsView?

[johnratius]

I am a little confused; I am trying to draw a grid, and every 4/8 lines I am supposed to get a different brush to make it more appealing.
I create the function MyView::drawForeground(QPainter * painter, const QRectF & rect) and when I get the x & y & width & height and draw my grid in a loop, I don't see the other fancy lines. Here is what I mean:

main.cpp

#include <iostream>
#include <QApplication>
#include <QGraphicsView>
#include <QtWidgets>

class MyView : public QGraphicsView
{
public:
	MyView(QWidget * parent = 0);
	MyView(QGraphicsScene * scene, QWidget * parent = 0);
	~MyView();

protected:
	void drawForeground(QPainter * painter, const QRectF & rect);
};

void drawGrid(QPainter * painter, const QRectF & rect);

int main(int argc, char **argv)
{
	// Setup window and application
	QApplication *app = new QApplication(argc, argv);
	QMainWindow *window = new QMainWindow;
	window->setWindowTitle("Grid Example");
	window->resize(800, 600);

	// Setup Main Widget
	QWidget *mainWidget = new QWidget;
	window->setCentralWidget(mainWidget);

	// Setup graphics scene and view
	MyView *view = new MyView;
	QGraphicsScene *scene = new QGraphicsScene;
	view->setScene(scene);

	// Setup layout
	QHBoxLayout *layout = new QHBoxLayout;
	layout->addWidget(view);
	mainWidget->setLayout(layout);

	window->show();
	return app->exec();
}

MyView::MyView(QWidget *parent) : QGraphicsView(parent)
{
}

MyView::MyView(QGraphicsScene *scene, QWidget *parent) : QGraphicsView(scene, parent)
{
}

MyView::~MyView()
{
}

void MyView::drawForeground(QPainter *painter, const QRectF & rect)
{
	drawGrid(painter, rect);
}

void drawGrid(QPainter * painter, const QRectF & rect)
{
	int scale = 1;
	int size = 24;
	int startX = rect.width() / -2;
	int endX = rect.width();
	int x = startX;

	int startY = rect.height() / -2;
	int endY = rect.height();
	int y = startY;


	while (x <= endX)
	{
		x += size * scale;

		if (x % (size * scale * 8) == 0)
			painter->setPen(QPen(Qt::black, 2, Qt::DashLine));
		else if (x % (size * scale * 4) == 0)
			painter->setPen(QPen(Qt::black, 1, Qt::DashLine));
		else
			painter->setPen(QPen(Qt::black, 1, Qt::DotLine));

		painter->drawLine(x, startY, x, endY);
	}

	while (y <= endY)
	{
		y += size * scale;

		if (y % (size * scale * 8) == 0)
			painter->setPen(QPen(Qt::black, 2, Qt::DashLine));
		else if (y % (size * scale * 4) == 0)
			painter->setPen(QPen(Qt::black, 1, Qt::DashLine));
		else
			painter->setPen(QPen(Qt::black, 1, Qt::DotLine));

		painter->drawLine(startX, y, endX, y);
	}
}

When I resize my window, the grid glitches and I see the other pen strokes for a frame but then it reverts to the else statement in the if statement. I set the startX and startY to 0 and it worked fine, but I wanted the grid to start at the top of the screen, not the middle.

Any info why this happens, and how I can get my grid to work properly?

[SGaist]

Hi,

Can you provide a minimal compilable example that reproduce your case ?

[johnratius]

@SGaist Yes, I am referencing off of this python qt project. https://github.com/RoadrunnerWMC/Reggie-Next/blob/master/reggie.py Line 12681. This one compiles and works fine. This isn't much minimalist but it's what I got.

[johnratius]

This post is deleted!

[johnratius]

I found that using 0 as the start for X and Y draws it successfully, but it starts in the middle of the screen which is what I don't want. Does anyone have any suggestions?