代码之家 › 专栏 › 技术社区 › Nicholas Murray

.NET图形-创建具有透明背景的椭圆

graphics c#

Nicholas Murray · 技术社区 · 14 年前

下面的代码将在图像上绘制一个椭圆,并用番茄色填充该椭圆

string imageWithTransEllipsePathToSaveTo = "~/Images/imageTest.png";
Graphics g = Graphics.FromImage(sourceImage);

g.FillEllipse(Brushes.Tomato, 50, 50, 200, 200);

sourceImage.Save(Server.MapPath(imageWithTransEllipsePathToSaveTo), ImageFormat.Png);

如果我将画笔更改为透明,它显然不会显示,因为椭圆将是透明的,下面的图像将显示。

如何将椭圆的“背景”设置为透明,以便图像包含透明点?

编辑:

很抱歉这么混乱。。。 alt text

3 回复 | 直到 14 年前

Greg Sansom 14 年前

这是我的第二个答案,使用图像而不是彩色画笔。不幸的是没有镭射刷子(我知道)。我包含了将图像保存到磁盘的代码,包括 usings 以确保导入正确的组件。这确实使用WPF,但它应该作为库或控制台应用程序的一部分工作。

using System.Windows.Media;
using System.Windows.Media.Imaging;
using System;
using System.Windows.Controls;
using System.Windows;
using System.Windows.Shapes;
namespace WpfApplication30
{
    class ImageEditor
    {
        public static void processImage(string loc)
        {
            ImageSource ic = new BitmapImage(new Uri(loc, UriKind.Relative));
            ImageBrush brush = new ImageBrush(ic);
            Path p = new Path();
            p.Fill = brush;
            CombinedGeometry cb = new CombinedGeometry();
            cb.GeometryCombineMode = GeometryCombineMode.Exclude;
            EllipseGeometry ellipse = new EllipseGeometry(new Point(50, 50), 5, 5);
            RectangleGeometry rect = new RectangleGeometry(new Rect(new Size(100, 100)));
            cb.Geometry1 = rect;
            cb.Geometry2 = ellipse;
            p.Data = cb;

            Canvas inkCanvas1 = new Canvas();
            inkCanvas1.Children.Add(p);
            inkCanvas1.Height = 96;
            inkCanvas1.Width = 96;

            inkCanvas1.Measure(new Size(96, 96));
            inkCanvas1.Arrange(new Rect(new Size(96, 96)));
            RenderTargetBitmap targetBitmap =
    new RenderTargetBitmap((int)inkCanvas1.ActualWidth,
                           (int)inkCanvas1.ActualHeight,
                           96d, 96d,
                           PixelFormats.Default);
            targetBitmap.Render(inkCanvas1);

            using (System.IO.FileStream outStream = new System.IO.FileStream( loc.Replace(".png","Copy.png"), System.IO.FileMode.Create))
            {
                PngBitmapEncoder encoder = new PngBitmapEncoder();
                encoder.Frames.Add(BitmapFrame.Create(targetBitmap));
                encoder.Save(outStream);
            }
        }
    }
}

结果如下: alt text

egrunin 14 年前

您需要使用半透明颜色创建画笔。

你这样做 Color.FromArgb(alpha, r, g, b) ,其中 alpha 设置不透明度。

Example copied from MSDN :

public void FromArgb1(PaintEventArgs e)
{
    Graphics     g = e.Graphics;

    // Transparent red, green, and blue brushes.
    SolidBrush trnsRedBrush = new SolidBrush(Color.FromArgb(120, 255, 0, 0));
    SolidBrush trnsGreenBrush = new SolidBrush(Color.FromArgb(120, 0, 255, 0));
    SolidBrush trnsBlueBrush = new SolidBrush(Color.FromArgb(120, 0, 0, 255));

    // Base and height of the triangle that is used to position the
    // circles. Each vertex of the triangle is at the center of one of the
    // 3 circles. The base is equal to the diameter of the circles.
    float   triBase = 100;
    float   triHeight = (float)Math.Sqrt(3*(triBase*triBase)/4);

    // Coordinates of first circle's bounding rectangle.
    float   x1 = 40;
    float   y1 = 40;

    // Fill 3 over-lapping circles. Each circle is a different color.
    g.FillEllipse(trnsRedBrush, x1, y1, 2*triHeight, 2*triHeight);
    g.FillEllipse(trnsGreenBrush, x1 + triBase/2, y1 + triHeight,
        2*triHeight, 2*triHeight);
    g.FillEllipse(trnsBlueBrush, x1 + triBase, y1, 2*triHeight, 2*triHeight);
}

Greg Sansom 14 年前

您需要使用RadialGradientBrush:

RadialGradientBrush b = new RadialGradientBrush();
b.GradientOrigin = new Point(0.5, 0.5);
b.Center = new Point(0.5, 0.5);
b.RadiusX = 0.5;
b.RadiusY = 0.5;
b.GradientStops.Add(new GradientStop(Colors.Transparent,0));
b.GradientStops.Add(new GradientStop(Colors.Transparent,0.25));
b.GradientStops.Add(new GradientStop(Colors.Tomato, 0.25));
g.FillEllipse(b, 50, 50, 200, 200);

alt text