• 将不透明红和不透明蓝分别作为第三和第四个参数传递。

• 将不透明黑和不透明红分别作为第三和第四个参数传递。

下面的示例创建一个线性渐变画笔并使用它填充两个矩形。第一个矩形在填充时未启用伽玛矫正；第二个矩形在填充时启用了伽玛矫正。

下面的插图显示这两个实心矩形。上面的矩形未采用伽玛矫正，它的中间部分看上去较暗。下面的矩形采用了伽玛矫正，看上去亮度更均匀。

编译代码

请参见

• 将不透明蓝和不透明绿分别作为第三和第四个参数传递。

LinearGradientBrush linGrBrush = new LinearGradientBrush(
new Point(0, 0),
new Point(200, 100),
Color.FromArgb(255, 0, 0, 255),   // opaque blue
Color.FromArgb(255, 0, 255, 0));  // opaque green
Pen pen = new Pen(linGrBrush, 10);
e.Graphics.DrawLine(pen, 0, 0, 600, 300);
e.Graphics.FillEllipse(linGrBrush, 10, 100, 200, 100);

• 下面的示例用路径渐变画笔填充椭圆。中心的颜色设置为蓝色；边界的颜色设置为浅绿色。下面的插图显示已填充的椭圆。

默认情况下，路径渐变画笔不会延伸到路径边界以外。如果您使用路径渐变画笔来填充延伸到路径边界以外的图形，则无法填充路径以外的屏幕区域。

// Create a path that consists of a single ellipse.
GraphicsPath path = new GraphicsPath();
path.AddEllipse(0, 0, 140, 70);
// Use the path to construct a brush.
PathGradientBrush pthGrBrush = new PathGradientBrush(path);
// Set the color at the center of the path to blue.
pthGrBrush.CenterColor = Color.FromArgb(255, 0, 0, 255);
// Set the color along the entire boundary
// of the path to aqua.
Color[] colors = { Color.FromArgb(255, 0, 255, 255) };
pthGrBrush.SurroundColors = colors;
e.Graphics.FillEllipse(pthGrBrush, 0, 0, 140, 70);

在边界上指定点

• 下面的示例由星形轨迹构造路径渐变画笔。该代码设置 CenterColor 属性，它将星形中心的颜色设置为红色。然后，该代码设置 SurroundColors 属性，以便在 points 数组中的各个点处指定不同的颜色（存储在 colors 数组中）。最后一个代码语句用路径渐变画笔填充星形轨迹。

// Put the points of a polygon in an array.
Point[] points = {
new Point(75, 0),
new Point(100, 50),
new Point(150, 50),
new Point(112, 75),
new Point(150, 150),
new Point(75, 100),
new Point(0, 150),
new Point(37, 75),
new Point(0, 50),
new Point(50, 50)};
// Use the array of points to construct a path.
GraphicsPath path = new GraphicsPath();
path.AddLines(points);
// Use the path to construct a path gradient brush.
PathGradientBrush pthGrBrush = new PathGradientBrush(path);
// Set the color at the center of the path to red.
pthGrBrush.CenterColor = Color.FromArgb(255, 255, 0, 0);
// Set the colors of the points in the array.
Color[] colors = {
Color.FromArgb(255, 0, 0, 0),
Color.FromArgb(255, 0, 255, 0),
Color.FromArgb(255, 0, 0, 255),
Color.FromArgb(255, 255, 255, 255),
Color.FromArgb(255, 0, 0, 0),
Color.FromArgb(255, 0, 255, 0),
Color.FromArgb(255, 0, 0, 255),
Color.FromArgb(255, 255, 255, 255),
Color.FromArgb(255, 0, 0, 0),
Color.FromArgb(255, 0, 255, 0)};
pthGrBrush.SurroundColors = colors;
// Fill the path with the path gradient brush.
e.Graphics.FillPath(pthGrBrush, path);

• 下面的示例在代码中不使用 GraphicsPath 对象而绘制一个路径渐变。在该示例中，特定的 PathGradientBrush 构造函数接收一系列点，但是不需要 GraphicsPath 对象。同时，请注意，PathGradientBrush 用于填充矩形而不是填充路径。矩形比用于定义画笔的闭合轨迹大，因此矩形的某些部分未由画笔涂色。下面的插图显示该矩形（虚线）以及该矩形被路径渐变画笔涂色的那部分。

// Construct a path gradient brush based on an array of points.
PointF[] ptsF = {
new PointF(0, 0),
new PointF(160, 0),
new PointF(160, 200),
new PointF(80, 150),
new PointF(0, 200)};
PathGradientBrush pBrush = new PathGradientBrush(ptsF);
// An array of five points was used to construct the path gradient
// brush. Set the color of each point in that array.
Color[] colors = {
Color.FromArgb(255, 255, 0, 0),  // (0, 0) red
Color.FromArgb(255, 0, 255, 0),  // (160, 0) green
Color.FromArgb(255, 0, 255, 0),  // (160, 200) green
Color.FromArgb(255, 0, 0, 255),  // (80, 150) blue
Color.FromArgb(255, 255, 0, 0)}; // (0, 200) red
pBrush.SurroundColors = colors;
// Set the center color to white.
pBrush.CenterColor = Color.White;
// Use the path gradient brush to fill a rectangle.
e.Graphics.FillRectangle(pBrush, new Rectangle(0, 0, 160, 200));

自定义路径渐变

// Create a path that consists of a single ellipse.
GraphicsPath path = new GraphicsPath();
path.AddEllipse(0, 0, 200, 100);
// Create a path gradient brush based on the elliptical path.
PathGradientBrush pthGrBrush = new PathGradientBrush(path);
// Set the color along the entire boundary to blue.
Color[] color = { Color.Blue };
pthGrBrush.SurroundColors = color;
// Set the center color to aqua.
pthGrBrush.CenterColor = Color.Aqua;
// Use the path gradient brush to fill the ellipse.
e.Graphics.FillPath(pthGrBrush, path);
// Set the focus scales for the path gradient brush.
pthGrBrush.FocusScales = new PointF(0.3f, 0.8f);
// Use the path gradient brush to fill the ellipse again.
// Show this filled ellipse to the right of the first filled ellipse.
e.Graphics.TranslateTransform(220.0f, 0.0f);
e.Graphics.FillPath(pthGrBrush, path);

• 自定义路径渐变画笔的另一种方法是指定插值颜色数组和插值位置数组。

  下面的示例基于三角形创建路径渐变画笔。该代码设置路径渐变画笔的 InterpolationColors 属性，以便指定插值颜色数组（深绿色，浅绿色，蓝色）和插值位置数组 (0, 0.25, 1)。当从三角形的边界移到中心点时，颜色将从深绿色逐渐变成浅绿色，然后从浅绿色变成蓝色。深绿色到浅绿色的转变发生在深绿色到蓝色转变的距离的 25% 处。

  下面的插图显示用自定义路径渐变画笔填充的三角形。

  

// Vertices of the outer triangle
Point[] points = {
new Point(100, 0),
new Point(200, 200),
new Point(0, 200)};
// No GraphicsPath object is created. The PathGradientBrush
// object is constructed directly from the array of points.
PathGradientBrush pthGrBrush = new PathGradientBrush(points);
Color[] colors = {
Color.FromArgb(255, 0, 128, 0),    // dark green
Color.FromArgb(255, 0, 255, 255),  // aqua
Color.FromArgb(255, 0, 0, 255)};   // blue
float[] relativePositions = {
0f,       // Dark green is at the boundary of the triangle.
0.4f,     // Aqua is 40 percent of the way from the boundary
// to the center point.
1.0f};    // Blue is at the center point.
ColorBlend colorBlend = new ColorBlend();
colorBlend.Colors = colors;
colorBlend.Positions = relativePositions;
pthGrBrush.InterpolationColors = colorBlend;
// Fill a rectangle that is larger than the triangle
// specified in the Point array. The portion of the
// rectangle outside the triangle will not be painted.
e.Graphics.FillRectangle(pthGrBrush, 0, 0, 200, 200);

• 在默认情况下，路径渐变画笔的中心点位于用来构造梯度刷的轨迹的形心。可通过设置 PathGradientBrush 类的 CenterPoint 属性更改中心点的位置。

  下面的示例基于椭圆来创建路径渐变画笔。椭圆的中心位于 (70, 35)，但是路径渐变画笔的中心点设置在 (120, 40)。

// Create a path that consists of a single ellipse.
GraphicsPath path = new GraphicsPath();
path.AddEllipse(0, 0, 140, 70);
// Use the path to construct a brush.
PathGradientBrush pthGrBrush = new PathGradientBrush(path);
// Set the center point to a location that is not
// the centroid of the path.
pthGrBrush.CenterPoint = new PointF(120, 40);
// Set the color at the center of the path to blue.
pthGrBrush.CenterColor = Color.FromArgb(255, 0, 0, 255);
// Set the color along the entire boundary
// of the path to aqua.
Color[] colors = { Color.FromArgb(255, 0, 255, 255) };
pthGrBrush.SurroundColors = colors;
e.Graphics.FillEllipse(pthGrBrush, 0, 0, 140, 70);

• 可将路径渐变画笔的中心点设置在用于构造梯度刷的轨迹外部的某个位置。下面的示例通过替换调用来设置以上代码中的 CenterPoint 属性。

pthGrBrush.CenterPoint = new PointF(145, 35);

其他资源

使用渐变画笔填充形状