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How to draw a lightweight border (external glow effect)?

How can I draw a lightweight border like this with gdi / gdi +: enter image description here

Can anyone give me a train of thought? Thank.

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2 answers
  • Draw a border with an image slightly larger than the border itself.
  • Blur it.
  • Remove the inner border.
  • Draw a border over the blurry image.
  • Draw this image at your destination.
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GDI +, PathGradientBrush. , . , , 1 . GraphicsPath FillPath(), PathGradientBrush:

GraphicsPath graphicsPath;

//rect - for a bounding rect
//radius - for how 'rounded' the glow will look
int diameter = radius * 2;

graphicsPath.AddArc(Rect(rect.X, rect.Y, diameter, diameter) 180.0f, 90.0f);
graphicsPath.AddArc(Rect(rect.X + rect.Width - diameter, rect.Y, diameter, diameter), 270.0f, 90.0f);
graphicsPath.AddArc(Rect(rect.X + rect.Width - diameter, rect.Y + rect.Height - diameter, diameter, diameter), 0.0f, 90.0f);
graphicsPath.AddArc(Rect(rect.X, rect.Y + rect.Height - diameter, diameter, diameter), 90.0f, 90.0f);
graphicsPath.CloseFigure();

PathGradientBrush brush(&graphicsPath);
brush.SetCenterColor(centerColor); //would be some shade of blue, following your example
int colCount = 1;
brush.SetSurroundColors(surroundColor, &colCount); //same as your center color, but with the alpha channel set to 0

//play with these numbers to get the glow effect you want
REAL blendFactors[] = {0.0, 0.1, 0.3, 1.0};
REAL blendPos[] = {0.0, 0.4, 0.6, 1.0};
//sets how transition toward the center is shaped
brush.SetBlend(blendFactors, blendPos, 4);
//sets the scaling on the center. you may want to have it elongated in the x-direction
brush.SetFocusScales(0.2f, 0.2f);

graphics.FillPath(&brush, &graphicsPath);
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