Hi,
first what I'm doing.
I'm coding a small GUI system for a game I'm writing. The existing GUI Toolkits usable on Ogre3D don't convince me enought that I use them. I'd like to use Qt, I even tried it but had some major issues doing so (major performance loss, Mouse/Keyboard events not working, etc.). So I decided to write my own toolkit. I already did write one, but it was very dirty and I didn't write it as an own library but coded it directly to the game. So I decided to re-write it.

Now my issue.
When rendering the Widgets, everything is fine, until I add a border radius. I guess, an image showing it is way easier than explaining:
click me
I'm rendering directly on a QImage, using QPainter/QPainterPath.
The Pen is defined as follows:
Qt Code: 
  1. painter.setPen(QPen(b, wB, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin));
To copy to clipboard, switch view to plain text mode 
The Brush is either a QColor or a QLinearGradient.
As render hint I only use Antialiasing.
The QImage is in the ARGB32 format.
I tried both approaches for the border radius, arcTo and cubicTo. Both ways have the same issue.

The problem occurs on different Graphics Systems.

here is the code I use for the rendering:
Qt Code: 
  1. QImage AWidget::paint()
  2. 	{
  3. 		if (!visible())
  4. 		{
  5. 			cHasChange	= false;
  6. 			return QImage();
  7. 		}
  8. 		if (!hasChange())
  9. 		{
  10. 			cHasChange	= false;
  11. 			if (cLastImage != 0)
  12. 			{
  13. 				return *cLastImage;
  14. 			}
  15. 		}
  16. 		cHasChange	= false;
  17.  
  18. 		short w			= width();
  19. 		short h			= height();
  20. 		short radTL		= 10;
  21. 		short radTR		= 10;
  22. 		short radBR		= 10;
  23. 		short radBL		= 10;
  24.  
  25. 		QBrush bg(QColor(100, 200, 100, 100));
  26.  
  27. 		QColor b(0, 0, 0, 255);
  28.  
  29. 		short wB = 1;
  30.  
  31.  
  32. 		if (cHasStyle)
  33. 		{
  34. 			if (cBorder->radius()->isValid())
  35. 			{
  36. 				radTL		= cBorder->radius()->tl();
  37. 				radTR		= cBorder->radius()->tr();
  38. 				radBR		= cBorder->radius()->br();
  39. 				radBL		= cBorder->radius()->bl();
  40. 			}
  41. 			if (cBackground->color()->isValid())
  42. 			{
  43. 				bg	= QBrush(cBackground->color()->toQColor());
  44. 			}
  45. 			else if (cBackground->gradient()->isValid())
  46. 			{
  47. 				bg	= QBrush(cBackground->gradient()->toQGradient());
  48. 			}
  49. 			if (cBorder->color()->isValid())
  50. 			{
  51. 				b	= (cBorder->color()->toQColor());
  52. 			}
  53. 			if (cBorder->size()->isValid())
  54. 			{
  55. 				wB	= cBorder->size()->left();
  56. 			}
  57. 		}
  58.  
  59. 		bool useCubic		= false;
  60.  
  62. 		path.moveTo(radTL, 0);
  63. 		path.lineTo(w - radTR, 0);
  64. 		if (radTR > 0)
  65. 		{
  66. 			if (useCubic)
  67. 			{
  68. 				path.cubicTo(w, 0, w, radTR, w, radTR);
  69. 			}
  70. 			else
  71. 			{
  72. 				path.arcTo(w - radTR * 2, 0, radTR * 2, radTR * 2, 90, -90);
  73. 			}
  74. 		}
  75. 		path.lineTo(w, h - radBR);
  76. 		if (radBR > 0)
  77. 		{
  78. 			if (useCubic)
  79. 			{
  80. 				path.cubicTo(w, h, w - radBR, h, w - radBR, h);
  81. 			}
  82. 			else
  83. 			{
  84. 				path.arcTo(w - radBR * 2, h - radBR * 2, radBR * 2, radBR * 2, 0, -90);
  85. 			}
  86. 		}
  87. 		path.lineTo(radBL, h);
  88. 		if (radBL > 0)
  89. 		{
  90. 			if (useCubic)
  91. 			{
  92. 				path.cubicTo(0, h, 0, h - radBL, 0, h - radBL);
  93. 			}
  94. 			else
  95. 			{
  96. 				path.arcTo(0, h - radBL * 2, radBL * 2, radBL * 2, -90, -90);
  97. 			}
  98. 		}
  99. 		path.lineTo(0, radTL);
  100. 		if (radTL > 0)
  101. 		{
  102. 			if (useCubic)
  103. 			{
  104. 				path.cubicTo(0, radTL, 0, 0, radTL, 0);
  105. 			}
  106. 			else
  107. 			{
  108. 				path.arcTo(0, 0, radTL * 2, radTL * 2, -180, -90);
  109. 			}
  110. 		}
  111. 		path.closeSubpath();
  112.  
  113.  
  114. 		QImage *img = new QImage(w, h, QImage::Format_ARGB32);
  115. 		img->fill(0);
  116. 		QPainter painter;
  117. 		painter.begin(img);
  118. 		painter.setRenderHints(QPainter::Antialiasing);
  119. 		painter.setPen(QPen(b, wB, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin));
  120. 		painter.setBrush(bg);
  121.  
  122. 		painter.drawPath(path);
  123.  
  124. 		paintEvent(&painter);
  125.  
  126. 		// +++ draw children
  127. 		if (children().length() > 0)
  128. 		{
  129. 			for (int i = 0; i < children().length(); i++)
  130. 			{
  131. 				painter.drawImage(child(i)->x(), child(i)->y(), child(i)->paint());
  132. 			}
  133. 		}
  134. 		// --- draw children
  135.  
  136. 		painter.end();
  137.  
  138. 		cLastImage	= img;
  139.  
  140. 		return *img;
  141. 	}
To copy to clipboard, switch view to plain text mode 

Furthermore would I like to ask, what the better way to render the border radius is - an arc or a bezier curve?

If some information is missing, feel free to tell.

cheers