hi all!
I have a custom widget which is pretty much a modified drawing widget from the pluginanddraw example. I loaded an image onto it, but it doesn't fully fit since the image might be too big for the widget. So i placed this widget insode a QScrollBar to be able to see the entire thing. However, the scroll bars for some odd reason do not show up.

In the documentations i read that custom widgets must have the sizeHint method and this widget does infect have it.

here is my code for the widget:

RenderArea.h
Qt Code: 
  1. #ifndef RENDERAREA_H
  2. #define RENDERAREA_H
  3.  
  4. #include <QColor>
  5. #include <QImage>
  6. #include <QPainterPath>
  7. #include <QWidget>
  8. #include <QFile>
  9. #include <QPainter>
  10. #include <QMouseEvent>
  11. #include <QByteArray>
  12. #include <QString>
  13. #include "interfaces.h"
  14.  
  15. class RenderArea : public QWidget
  16. {
  17. 	Q_OBJECT
  18.  
  19. public:
  20. 	RenderArea(QWidget *parent = 0);
  21.  
  22. 	bool openImage(const QString &fileName);
  23. 	bool saveImage(const QString &fileName, const char *fileFormat);
  24. 	void setImage(const QImage &image);
  25. 	void insertShape(const QPainterPath &path);
  26. 	void setBrushColor(const QColor &color);
  27. 	void setBrushWidth(int width);
  28. 	void setBrush(BrushInterface *brushInterface, const QString &brush);
  29.  
  30. 	QImage image() const { return theImage; }
  31. 	QColor brushColor() const { return color; }
  32. 	int brushWidth() const { return thickness; }
  33. 	QSize sizeHint() const;
  34.  
  35. protected:
  36. 	void paintEvent(QPaintEvent *event);
  37. 	void mousePressEvent(QMouseEvent *event);
  38. 	void mouseMoveEvent(QMouseEvent *event);
  39. 	void mouseReleaseEvent(QMouseEvent *event);
  40.  
  41. private:
  42. 	void setupPainter(QPainter &painter);
  43.  
  44. 	QImage theImage;
  45. 	QColor color;
  46. 	int thickness;
  47.  
  48. 	BrushInterface *brushInterface;
  49. 	QString brush;
  50. 	QPoint lastPos;
  51.  
  52. 	QPainterPath pendingPath;
  53. };
  54.  
  55.  
  56. #endif // RENDERAREA_H
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RenderArea.cpp
Qt Code: 
  1. #include "RenderArea.h"
  2.  
  3. RenderArea::RenderArea(QWidget *parent) :
  4. 		QWidget(parent),
  5. 		color(Qt::blue),
  6. 		thickness(3),
  7. 		brushInterface(0),
  8. 		lastPos(-1, -1)
  9. {
  10. 	setAttribute(Qt::WA_StaticContents);
  11. 	setAttribute(Qt::WA_NoBackground);
  12. 	theImage.load(":/resources/Screenshot.png");
  13.  
  14. }
  15.  
  16. bool RenderArea::openImage(const QString &fileName)
  17. {
  18. 	QImage image;
  19. 	if (!image.load(fileName))
  20. 		return false;
  21.  
  22. 	setImage(image);
  23. 	return true;
  24. }
  25.  
  26. bool RenderArea::saveImage(const QString &fileName, const char *fileFormat)
  27. {
  28. 	return theImage.save(fileName, fileFormat);
  29. }
  30.  
  31. void RenderArea::setImage(const QImage &image)
  32. {
  33. 	theImage = image.convertToFormat(QImage::Format_RGB32);
  34. 	update();
  35. 	updateGeometry();
  36. }
  37.  
  38. void RenderArea::insertShape(const QPainterPath &path)
  39. {
  40. 	pendingPath = path;
  41. #ifndef QT_NO_CURSOR
  42. 	setCursor(Qt::CrossCursor);
  43. #endif
  44. }
  45.  
  46. void RenderArea::setBrushColor(const QColor &color)
  47. {
  48. 	this->color = color;
  49. }
  50.  
  51. void RenderArea::setBrushWidth(int width)
  52. {
  53. 	thickness = width;
  54. }
  55.  
  56. void RenderArea::setBrush(BrushInterface *brushInterface, const QString &brush)
  57. {
  58. 	this->brushInterface = brushInterface;
  59. 	this->brush = brush;
  60. }
  61.  
  62. QSize RenderArea::sizeHint() const
  63. {
  64. 	return theImage.size();
  65. }
  66.  
  67. void RenderArea::paintEvent(QPaintEvent * /* event */)
  68. {
  69. 	QPainter painter(this);
  70. 	painter.drawImage(QPoint(0, 0), theImage);
  71. }
  72.  
  73. void RenderArea::mousePressEvent(QMouseEvent *event)
  74. {
  75. 	if (event->button() == Qt::LeftButton) {
  76. 		if (!pendingPath.isEmpty()) {
  77. 			QPainter painter(&theImage);
  78. 			setupPainter(painter);
  79.  
  80. 			const QRectF boundingRect = pendingPath.boundingRect();
  81. 			QLinearGradient gradient(boundingRect.topRight(),
  82. 									 boundingRect.bottomLeft());
  83. 			gradient.setColorAt(0.0, QColor(color.red(), color.green(),
  84. 											color.blue(), 63));
  85. 			gradient.setColorAt(1.0, QColor(color.red(), color.green(),
  86. 											color.blue(), 191));
  87. 			painter.setBrush(gradient);
  88. 			painter.translate(event->pos() - boundingRect.center());
  89. 			painter.drawPath(pendingPath);
  90.  
  91. 			pendingPath = QPainterPath();
  92. #ifndef QT_NO_CURSOR
  93. 			unsetCursor();
  94. #endif
  95. 			update();
  96. 		} else {
  97. 			if (brushInterface) {
  98. 				QPainter painter(&theImage);
  99. 				setupPainter(painter);
  100. 				const QRect rect = brushInterface->mousePress(brush, painter,
  101. 															  event->pos());
  102. 				update(rect);
  103. 			}
  104.  
  105. 			lastPos = event->pos();
  106. 		}
  107. 	}
  108. }
  109.  
  110. void RenderArea::mouseMoveEvent(QMouseEvent *event)
  111. {
  112. 	if ((event->buttons() & Qt::LeftButton) && lastPos != QPoint(-1, -1)) {
  113. 		if (brushInterface) {
  114. 			QPainter painter(&theImage);
  115. 			setupPainter(painter);
  116. 			const QRect rect = brushInterface->mouseMove(brush, painter, lastPos, event->pos());
  117. 			update(rect);
  118. 		}
  119.  
  120. 		lastPos = event->pos();
  121. 	}
  122. }
  123.  
  124. void RenderArea::mouseReleaseEvent(QMouseEvent *event)
  125. {
  126. 	if (event->button() == Qt::LeftButton && lastPos != QPoint(-1, -1)) {
  127. 		if (brushInterface) {
  128. 			QPainter painter(&theImage);
  129. 			setupPainter(painter);
  130. 			QRect rect = brushInterface->mouseRelease(brush, painter,
  131. 													  event->pos());
  132. 			update(rect);
  133. 		}
  134.  
  135. 		lastPos = QPoint(-1, -1);
  136. 	}
  137. }
  138.  
  139. void RenderArea::setupPainter(QPainter &painter)
  140. {
  141. 	painter.setRenderHint(QPainter::Antialiasing, true);
  142. 	painter.setPen(QPen(color, thickness, Qt::SolidLine, Qt::RoundCap,
  143. 						Qt::RoundJoin));
  144. }
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