我正在寻找或尝试实现一种算法来绘制框阴影（如在 CSS 3 规范中），它接受以下参数：
从哪儿开始。
我一直在寻找 Firefox / Chrome 源代码，看看我是否可以从那里提取一个实现，没有这样的运气！
我研究了线性渐变算法，用一个盒子来绘制它们，这种方法很有效，除了圆角矩形它会在阴影中留下空像素，大概是由于边缘的半径。
我正在使用 GDI+ 在 .NET 中执行此操作。我的目标不是为图像创建阴影。我已经看过这方面的文章。我想为使用 GDI+ 绘制的形状创建阴影。
任何帮助表示赞赏！
我为您编写了一个 DropShadowPanel，它处理其中的控件并根据控件标签的要求添加阴影（外部或内部）。
正如您在图像控件中看到的那样，按照定义获得它们的阴影：
标签：
文本框：DropShadow:5,5,5,10,#000000,noinset
日历：DropShadow:10,10,80,30,#0000FF,noinset
图片框左上角：DropShadow:-50,20,50,10,#888888,noinset
图片框左下角：DropShadow:10,10,20,20,#442200,inset
图片右下角：DropShadow:0,0,50,50,#442200,noinset
这是面板的代码：（它在绘制到控制 gdi 对象之前使用中间绘图到图像中，以不使表单爬行 - 这实际上工作得非常快）
using System;
using System.Collections.Generic;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Linq;
using System.Text;
using System.Windows.Forms;
namespace WindowsFormsApplication4
{
public class DropShadowPanel : Panel
{
protected override void OnControlAdded(ControlEventArgs e)
{
e.Control.Paint += new PaintEventHandler(Control_Paint);
base.OnControlAdded(e);
}
void Control_Paint(object sender, PaintEventArgs e)
{
CheckDrawInnerShadow(sender as Control, e.Graphics);
}
private void CheckDrawInnerShadow(Control sender, Graphics g)
{
var dropShadowStruct = GetDropShadowStruct(sender);
if (dropShadowStruct == null || !dropShadowStruct.Inset)
{
return;
}
DrawInsetShadow(sender as Control, g);
}
protected override void OnControlRemoved(ControlEventArgs e)
{
e.Control.Paint -= new PaintEventHandler(Control_Paint);
}
protected override void OnPaint(PaintEventArgs e)
{
base.OnPaint(e);
DrawShadow(Controls.OfType<Control>().Where(c => c.Tag != null && c.Tag.ToString().StartsWith("DropShadow")), e.Graphics);
}
void DrawInsetShadow(Control control, Graphics g)
{
var dropShadowStruct = GetDropShadowStruct(control);
var rInner = new Rectangle(Point.Empty, control.Size);
var img = new Bitmap(rInner.Width, rInner.Height, g);
var g2 = Graphics.FromImage(img);
g2.CompositingMode = CompositingMode.SourceCopy;
g2.FillRectangle(new SolidBrush(dropShadowStruct.Color), 0, 0, control.Width, control.Height);
rInner.Offset(dropShadowStruct.HShadow, dropShadowStruct.VShadow);
rInner.Inflate(dropShadowStruct.Blur, dropShadowStruct.Blur);
rInner.Inflate(-dropShadowStruct.Spread, -dropShadowStruct.Spread);
double blurSize = dropShadowStruct.Blur;
double blurStartSize = blurSize;
do
{
var transparency = blurSize/blurStartSize;
var color = Color.FromArgb(((int)(255 * (transparency * transparency))), dropShadowStruct.Color);
rInner.Inflate(-1,-1);
DrawRoundedRectangle(g2, rInner, (int)blurSize, Pens.Transparent, color);
blurSize--;
} while (blurSize > 0);
g.DrawImage(img, 0, 0);
g.Flush();
g2.Dispose();
img.Dispose();
}
void DrawShadow(IEnumerable<Control> controls, Graphics g)
{
foreach (var control in controls)
{
var dropShadowStruct = GetDropShadowStruct(control);
if (dropShadowStruct.Inset)
{
continue; // must be handled by the control itself
}
DrawOutsetShadow(g, dropShadowStruct, control);
}
}
// drawing the loop on an image because of speed
private void DrawOutsetShadow(Graphics g, dynamic dropShadowStruct, Control control)
{
var rOuter = control.Bounds;
var rInner = control.Bounds;
rInner.Offset(dropShadowStruct.HShadow, dropShadowStruct.VShadow);
rInner.Inflate(-dropShadowStruct.Blur, -dropShadowStruct.Blur);
rOuter.Inflate(dropShadowStruct.Spread, dropShadowStruct.Spread);
rOuter.Offset(dropShadowStruct.HShadow, dropShadowStruct.VShadow);
var originalOuter = rOuter;
var img = new Bitmap(originalOuter.Width, originalOuter.Height, g);
var g2 = Graphics.FromImage(img);
var currentBlur = 0;
do
{
var transparency = (rOuter.Height - rInner.Height)/(double) (dropShadowStruct.Blur*2 + dropShadowStruct.Spread*2);
var color = Color.FromArgb(((int)(255 * (transparency * transparency))), dropShadowStruct.Color);
var rOutput = rInner;
rOutput.Offset(-originalOuter.Left, -originalOuter.Top);
DrawRoundedRectangle(g2, rOutput, currentBlur, Pens.Transparent, color);
rInner.Inflate(1, 1);
currentBlur = (int) ((double) dropShadowStruct.Blur*(1 - (transparency*transparency)));
} while (rOuter.Contains(rInner));
g2.Flush();
g2.Dispose();
g.DrawImage(img, originalOuter);
img.Dispose();
}
private static dynamic GetDropShadowStruct(Control control)
{
if (control.Tag == null || !(control.Tag is string) || !control.Tag.ToString().StartsWith("DropShadow"))
return null;
string[] dropShadowParams = control.Tag.ToString().Split(':')[1].Split(',');
var dropShadowStruct = new
{
HShadow = Convert.ToInt32(dropShadowParams[0]),
VShadow = Convert.ToInt32(dropShadowParams[1]),
Blur = Convert.ToInt32(dropShadowParams[2]),
Spread = Convert.ToInt32(dropShadowParams[3]),
Color = ColorTranslator.FromHtml(dropShadowParams[4]),
Inset = dropShadowParams[5].ToLowerInvariant() == "inset"
};
return dropShadowStruct;
}
private void DrawRoundedRectangle(Graphics gfx, Rectangle bounds, int cornerRadius, Pen drawPen, Color fillColor)
{
int strokeOffset = Convert.ToInt32(Math.Ceiling(drawPen.Width));
bounds = Rectangle.Inflate(bounds, -strokeOffset, -strokeOffset);
var gfxPath = new GraphicsPath();
if (cornerRadius > 0)
{
gfxPath.AddArc(bounds.X, bounds.Y, cornerRadius, cornerRadius, 180, 90);
gfxPath.AddArc(bounds.X + bounds.Width - cornerRadius, bounds.Y, cornerRadius, cornerRadius, 270, 90);
gfxPath.AddArc(bounds.X + bounds.Width - cornerRadius, bounds.Y + bounds.Height - cornerRadius, cornerRadius,
cornerRadius, 0, 90);
gfxPath.AddArc(bounds.X, bounds.Y + bounds.Height - cornerRadius, cornerRadius, cornerRadius, 90, 90);
}
else
{
gfxPath.AddRectangle(bounds);
}
gfxPath.CloseAllFigures();
gfx.FillPath(new SolidBrush(fillColor), gfxPath);
if (drawPen != Pens.Transparent)
{
var pen = new Pen(drawPen.Color);
pen.EndCap = pen.StartCap = LineCap.Round;
gfx.DrawPath(pen, gfxPath);
}
}
}
}
代码编写很快，没有太多审查，因此可能存在错误，特别是如果您在控件上设置了 wring 标签）。
PS。您可能会注意到内部阴影不适用于某些控件。这是因为它们是 Windows 系统控件的包装器。小组无法自行克服这一点，但您可以在这里进行：http: //www.codeproject.com/Articles/4548/Generating-missing-Paint-event-for-TreeView-and-Li