2.4. 怎样画一个带有透明色的图案？
画一个带有透明色的图象，需要设置ImageAttributes对象的透明色。目前.net精简框架支持单种颜色的透明色。虽然SetColorKey功能可以设置颜色范围，但颜色的最大值和最小值必须相同，不然在运行时会出现ArgumentException的错误：
//C#
using System.Drawing.Imaging;
ImageAttributes attr = new ImageAttributes();
'VB
Imports System.Drawing.Imaging
Dim attr As New ImageAttributes()
以下代码描述了如何根据图象左上角的颜色设置透明色。
//C#
attr.SetColorKey(bmp.GetPixel(0,0), bmp.GetPixel(0,0));
'VB
attr.SetColorKey(bmp.GetPixel(0,0), bmp.GetPixel(0,0))
以下方法可以准确的设置颜色：
//C#
attr.SetColorKey(Color.FromArgb(255,0,255),Color.FromArgb(255,0,255));
attr.SetColorKey(Color.Fuchsia, Color.Fuchsia);
'VB
attr.SetColorKey(Color.FromArgb(255,0,255),Color.FromArgb(255,0,255))
attr.SetColorKey(Color.Fuchsia, Color.Fuchsia)
图象会被重载的Graphics.DrawImage方法重画，并且使用ImageAttributes对象作为一个参数parameter：
//C#
g.DrawImage(bmp, 0, 0, bmp.Width, bmp.Height,GraphicsUnit.Pixel, attr);
'VB
g.DrawImage(bmp, 0, 0, bmp.Width, bmp.Height,GraphicsUnit.Pixel, attr)
2.5. 为什么从TextBox上调用CreateGraphics会失败？
只有Form类才支持Control.CreateGraphics().
2.6. 怎样获得屏幕上文字的大小？
使用Graphics的MeasureString方法。以下代码说明如何在文字周围画一个方框：
//C#
using System.Drawing;
protected override void OnPaint(PaintEventArgs e)
{
string s = "Hello World"
Pen pen = new Pen(Color.Fuchsia);
Font font = new Font("Arial", 18, FontStyle.Regular);
Brush brush = new SolidBrush(Color.Black);
SizeF sSize = e.Graphics.MeasureString(s, font);
Rectangle r = new Rectangle(9, 199,(int)sSize.Width + 1, (int)sSize.Height + 1);
e.Graphics.DrawRectangle(pen, r);
e.Graphics.DrawString(s, font, brush, 10.0f, 200.0f);
base.OnPaint (e);
}
'VB
Imports System.Drawing
Protected Overrides Sub OnPaint(e As PaintEventArgs)
Dim s As String = "Hello World"
Dim pen As New Pen(Color.Fuchsia)
Dim font As New Font("Arial", 18, FontStyle.Regular)
Dim brush = New SolidBrush(Color.Black)
Dim sSize As SizeF = e.Graphics.MeasureString(s, font)
Dim r As New Rectangle(9, 199, Fix(sSize.Width) + 1, Fix(sSize.Height) + 1)
e.Graphics.DrawRectangle(pen, r)
e.Graphics.DrawString(s, font, brush, 10F, 200F)
MyBase.OnPaint(e)
End Sub 'OnPaint
2.7. Can I set the width of a pen?
Setting the pen width is not available in the .NET Compact Framework. Some alternate solutions include:
Drawing filled rectangles with the Graphics.FillRectangle method
Drawing multiple lines next to each other
Writing a custom graphics routine with GAPI 2.8. How do I zoom an image?
While there is no inherent support for zooming or stretching a single image, these effects can be achieved quite easily by creating a new Bitmap object with an associated Graphics object and copying the desired portion of the original Bitmap into it. The following sample creates two bitmaps of the same size, where the second contains a zoomed center section of the first, provided the project has an embedded resource named MyImage.bmp. This same technique could be used to stretch images by modifying the source and destination rectangles such that they do not maintain their original aspect ratio. //C#
using System.Drawing;
using System.Reflection;
