Can't refresh QLabel's Pixmap properly

I have been stuck on this issue for 2 days now. I'm using the Qt plugin for VisualStudio2013 on Window 7-64bit.

I have been trying to display a pair of images in Qlabels. I need to manipulate the pixel data regularly, so I store them in QImages, and every time I want to refresh the display I set the QPixmap of a Qlabel. The problem is, it only seems to refresh if I change/move the window in some way.

This problems goes away if I just make the QLabels children of my QWidget, but never set a layout. If I then add repaint() or update(), the problem comes back.

(this is a very similar post to one I posted using QGraphicsScene, but the problem seems to be more fundamental than that, so I am reposting)

Here is my code. First the .h

Code:

---

#ifndef DISPLAYWIDGET_H
	#define DISPLAYWIDGET_H
 
	#include <QtWidgets/QWidget>
	#include <qpixmap.h>
	#include <QGraphicsScene>
	#include <QGraphicsView>
	#include <QGraphicsPixmapItem>
	#include <QPushButton>
	#include <QHBoxLayout>
	#include <qtimer.h>
	#include <qlabel.h>
 
 
	#define FULLSCALE 255
	#define IM_X_MIN -5.0
	#define IM_X_MAX 5.0
	#define IM_Z_MIN 0.0
	#define IM_Z_MAX 15.0
	#define IM_PIXEL_WIDTH 200
	#define IM_PIXEL_HEIGHT IM_PIXEL_WIDTH * (IM_Z_MAX-IM_Z_MIN)/(IM_X_MAX - IM_X_MIN)
	#define BORDER_WIDTH	10
	#define RAND_SEED 7
 
	class DisplayWidget : public QWidget
	{
		Q_OBJECT
 
	public:
		DisplayWidget(int width, int height, QWidget *parent = 0);
		~DisplayWidget();
 
	private:
		QLabel *bimageLabel;
		QLabel *dimageLabel;
		QImage * bImage;
		QImage * dImage;
		QTimer * frameGrab;
 
		QPushButton * debugButton;
 
		void CreateWidgets();
		void SetupGui();
 
		int w, h;
 
	public slots:
		void GenerateNewData();
	};
 
	#endif // DISPLAYWIDGET_H

---

and the .cpp.

Code:

---

#include "displaywidget.h"
 
	DisplayWidget::DisplayWidget(int width, int height, QWidget *parent): QWidget(parent)
	{
		//ui.setupUi(this);
 
		w = width;
		h = height;
 
		CreateWidgets();
		SetupGui();
 
		// seed the random number generator
		srand(RAND_SEED);
		GenerateNewData();
	}
 
	DisplayWidget::~DisplayWidget()
	{
	}
	void DisplayWidget::CreateWidgets()
	{
		bImage = new QImage(w, h, QImage::Format_ARGB32);
		dImage = new QImage(w, h, QImage::Format_ARGB32);
		bimageLabel = new QLabel(this);
		dimageLabel = new QLabel(this);
 
		debugButton = new QPushButton("DEBUG", this);
		bimageLabel->setStyleSheet("QLabel {background-color: black};");
		dimageLabel->setStyleSheet("QLabel {background-color: white};");
 
		frameGrab = new QTimer(this);
	}
	void DisplayWidget::SetupGui()
	{
		QHBoxLayout * layout = new QHBoxLayout();
		setLayout(layout); // commenting this line out makes it refresh
		layout->addWidget(bimageLabel);
		layout->addWidget(dimageLabel);
		layout->addWidget(debugButton);
 
		connect(frameGrab, SIGNAL(timeout()),this, SLOT(GenerateNewData()));
		connect(debugButton, SIGNAL(clicked()), this, SLOT(GenerateNewData()));
		frameGrab->start(50);
	}
	void DisplayWidget::GenerateNewData()
	{
		QRgb * bImageData = (QRgb *)bImage->scanLine(0);
		QRgb * dImageData = (QRgb *)dImage->scanLine(0);
 
		for (int i; i < w * h; i++)
		{
			bImageData[i] = qRgba(rand() % FULLSCALE, 0, 0, FULLSCALE);
			dImageData[i] = qRgba(0, 0, rand() % FULLSCALE, FULLSCALE);
		}
 
		bimageLabel->setPixmap(QPixmap::fromImage(*bImage).scaled(QSize(IM_PIXEL_WIDTH, IM_PIXEL_HEIGHT)));
		dimageLabel->setPixmap(QPixmap::fromImage(*dImage).scaled(QSize(IM_PIXEL_WIDTH, IM_PIXEL_HEIGHT)));
 
		//this->update(); // this breaks it again
	}

---

Losing my mind here. I have very limited experience with Qt, but I believe I have the right approach.

Please help!

Line 51,you are not initialising the loop counter to zero. Chances are good that whatever random rubbish is in the variable causes immediate loop termination.

THANK YOU!!!!! I'll never make that mistake again.

We have all been there ;)