如何绘制亮化边框（外发光效果）？

Question

如何使用 gdi/gdi+ 绘制像这样的亮边框：

谁能给我一个思路？谢谢。

Answer 1

使用 GDI+，我建议您使用 PathGradientBrush。它允许您用边缘周围的一系列颜色填充区域，这些颜色都向中心颜色混合。在这种情况下，您可能只需要 1 种边缘颜色。为圆角矩形创建一个 GraphicsPath 并使用 FillPath() 用 PathGradientBrush 填充它：

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);

Answer 2

• 将边框绘制成比边框本身稍大的图像。
• 模糊它。
• 擦除边框内部。
• 在模糊图像上绘制边框。
• 将该图像绘制到目的地。