Level: Beginner/Intermediate
One of the neat features that you can now leverage with .NET is the ability to easily generate dynamic
images from code, which you can then either save to disk or directly stream back to a browser client with ASP.NET.
The functionality to generate images with .NET is encapsulated within the System.Drawing namespace. It provides
built-in support for generating images with a numer of file formats including: JPEG, GIF, PNG, TIFF, BMP,
PhotoCD, FlashPIX, WMF, EMF and EXIF. Note that there are no license issues to worry about with any of
these file formats; Microsoft implementation of each format is license free (including for GIF images).
The general mechanism through which you generate these graphics images is by constructing a BitMap object
which provides an in-memory representation of your image. You can then call its "Save" method to
either save it to disk, or stream it out to any .NET output stream. Because ASP.NET exposes a .NET
OutputStream via the Response.OutputStream property. This means you can stream the image contents
directly to the browser without ever having to save it to disk.
For example, to do this in VB you would write code like:
' Create In-Memory BitMap of JPEG
Dim MyChartEngine as New ChartEngine
Dim StockBitMap as BitMap = MyChartEngine.DrawChart(600, 400, myChartData)
' Render BitMap Stream Back To Browser
StockBitMap.Save(Response.OutputStream, ImageFormat.JPEG)
If you are using an ASPX page to do this, you will want to make sure you set the appropriate HTTP ContentType
header as well, so that the browser client doesn't interpret the page's content as html but rather as an
image. You can do this either via setting the Response.ContentType property through code, or via the new
"ContentType" attribute that you can set on the top-level page directive:
<%@ Page Language="VB" ContentType="image/jpeg" %>
Note that the output caching features of ASP.NET work for both textual content as well as for binary output.
As such, if you are dynamically generating an image from a page, you can easily leverage the output cache
directive to avoid having to regenerate the image on each request. Note that image generation can be
expensive, so this feature is highly recommended. For example, the below directive could be used to
output cache the generated image for a 60 second interval:
<%@ Page Language="VB" ContentType="image/jpeg" %>
<%@ OutputCache Duration="60" %>
For a complete sample of how to use image generation, I've included a simple stock chart generation sample
below. Note that the stock prices aren't real, just wishful thinking on my part. The sample uses a custom
"ChartEngine" class that helps encapsulate the logic required to build up a generic chart. You should be
able to use this helper component to do any custom charting of your own, it is definitely not limited
to just stock data.
Feel free to use any of the code however you want and like with all my other samples, feel free to post
elsewhere as well as to use for articles, other samples, etc).
Instructions:
To run the sample, copy/paste/save the below files into an IIS Application VRoot. Then type the
below statements into a command line:
mkdir bin
csc /t:library /out:bin\chartgen.dll
ChartEngine.cs /r:System.Web.dll /r:System.Winforms.dll /r:System.Drawing.dll /r:System.dll
Once the chartengine helper utility
is compiled, hit the StockPicker.aspx page to run the sample (note that this in turn sets up a <img>
tag to point to the ImageGenerator_VB.aspx page that does the actual image generation work).
StockPicker.aspx:
<script language="VB" runat=server>
Sub ChartBtn_Click(Sender as Object, E as EventArgs)
chart.ImageUrl = "ImageGenerator_Vb.aspx?"
chart.Visible = true
For i=0 to Stocks.Items.Count-1
If (Stocks.Items(i).Selected = true) Then
chart.ImageUrl = chart.ImageUrl & "symbols=" & Stocks.Items(i).Value & "&"
End If
Next
End Sub
</script>
<html>
<body>
<form runat=server>
<h1>Scott's Stock Picker</h1>
<asp:checkboxlist id="Stocks" runat=server>
<asp:listitem>MSFT</asp:listitem>
<asp:listitem>SUN</asp:listitem>
</asp:checkboxlist>
<asp:button text="Chart Your Selected Stocks" OnClick="ChartBtn_Click" runat=server/>
<hr>
<asp:Image id="chart" ImageUrl="" Visible=false runat=server/>
</form>
</body>
</html>
ImageGenerator_VB.aspx:
<%@ Page Language="VB" ContentType="image/jpeg" %>
<%@ Import Namespace="System.Drawing" %>
<%@ Import Namespace="System.Drawing.Drawing2D" %>
<%@ Import Namespace="System.Drawing.Imaging" %>
<%@ Import Namespace="ChartGenerator" %>
<%@ OutputCache Duration="10" %>
<script language="VB" runat=server>
Function GetStockDetails(Symbol as String) as ChartLine
Dim myChartLine as new ChartLine
if (symbol = "msft") then
Dim StockValues() as Single = { 60, 110, 120, 180, 185, 190, 240, 290 }
myChartLine.Width = 5
myChartLine.Color = Color.Blue
myChartLine.LineStyle = DashStyle.Solid
myChartLine.Title = "Microsoft Corp. (MSFT)"
myChartLine.Symbol = "MSFT"
myChartLine.Values = StockValues
return myChartLine
elseif (symbol = "sun") then
Dim StockValues() as Single = { 180, 155, 125, 60, 25, 15, 10, 3 }
myChartLine.Width = 5
myChartLine.Color = Color.Red
myChartLine.LineStyle = DashStyle.Dot
myChartLine.Title = "Sun Corp. (Sun)"
myChartLine.Symbol = "Sun"
myChartLine.Values = StockValues
return myChartLine
end if
return nothing
End Function
Sub Page_Load(Sender as Object, E as EventArgs)
' Generate Chart Data For Image....
Dim XAxes() as String = { "9:00AM", "9:30AM", "10:00AM", "11:00AM", "12:00AM", "1:00PM", "1:30PM" }
Dim MyChartData as New ChartData
MyChartData.YTickSize = 20
MyChartData.YMax = 250
MyChartData.YMin = 0
MyChartData.XAxisTitles = XAxes
Dim Symbols() as String = Request.QueryString.GetValues("symbols")
if (Not Symbols = Nothing) then
for i=0 to Symbols.Length-1
Dim stockValue as ChartLine = GetStockDetails(symbols(i).ToLower)
If (stockValue <> nothing) then
myChartData.Lines.Add(stockValue)
End if
Next
end if
' Create In-Memory BitMap of JPEG
Dim MyChartEngine as New ChartEngine
Dim StockBitMap as BitMap = MyChartEngine.DrawChart(600, 400, myChartData)
' Render BitMap Stream Back To Client
StockBitMap.Save(Response.OutputStream, ImageFormat.JPEG)
End Sub
</script>
ChartEngine.cs:
using System.WinForms;
using System.Collections;
using System.Collections.Bases;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;
using System.ComponentModel;
using System;
using System.IO;
namespace ChartGenerator {
//Core Line Data structure
public struct LineData {
public float[] LineValues ;
public string LineTitle ;
public string LineSymbol ;
}
//Line Data plus display style information
public class ChartLine {
private Color lineColor ;
private LineData lineData ;
private DashStyle lineStyle ;
private int lineWidth ;
//Constructors
public ChartLine() :base() {}
public ChartLine(LineData lineData) :base() {
this.lineData = lineData;
}
//Properties
public Color Color {
get { return lineColor ; }
set { lineColor = value ; }
}
public DashStyle LineStyle {
get { return lineStyle ; }
set { lineStyle = value ; }
}
public string Symbol {
get { return lineData.LineSymbol ; }
set { lineData.LineSymbol = value ; }
}
public string Title {
get { return lineData.LineTitle ; }
set { lineData.LineTitle = value ; }
}
public float[] Values {
get { return lineData.LineValues ; }
set { lineData.LineValues = value ; }
}
public int Width {
get { return lineWidth ; }
set { lineWidth = value ; }
}
//Methods
public void SetLineData(LineData lineData) {
this.lineData = lineData;
}
}
//Chart Data structure
public class ChartData {
private float yTickSize;
private float yMax;
private float yMin;
private string[] xAxisTitles ;
private ChartLineList lines = new ChartLineList();
private Color gridColor=Color.Blue;
private bool showHGridLines=true;
private bool showVGridLines=true;
//Properties
public float YTickSize {
get { return yTickSize ; }
set { yTickSize = value ; }
}
public float YMax {
get { return yMax ; }
set { yMax = value ; }
}
public float YMin {
get { return yMin ; }
set { yMin = value ; }
}
public string[] XAxisTitles {
get { return xAxisTitles ; }
set { xAxisTitles = value ; }
}
public ChartLineList Lines {
get { return lines ; }
set { lines = value ; }
}
public Color GridColor {
get { return gridColor ; }
set { gridColor = value ; }
}
public bool ShowHGridLines {
get { return showHGridLines ; }
set { showHGridLines = value ; }
}
public bool ShowVGridLines {
get { return showVGridLines ; }
set { showVGridLines = value ; }
}
//Collection of Chart Lines
public class ChartLineList : TypedCollectionBase {
public ChartLine this[int index] {
get {
return (ChartLine)(List[index]);
}
set {
List[index] = value;
}
}
public int Add(ChartLine value) {
return List.Add(value);
}
public void Insert(int index, ChartLine value) {
List.Insert(index, value);
}
public int IndexOf(ChartLine value) {
return List.IndexOf(value);
}
public bool Contains(ChartLine value) {
return List.Contains(value);
}
public void Remove(ChartLine value) {
List.Remove(value);
}
public void CopyTo(ChartLine[] array, int index) {
List.CopyTo(array, index);
}
}
}
//Charting Engine - draws a chart based on the given ChartData
public class ChartEngine {
private ChartData chartData ;
private float left;
private float right;
private float top;
private float bottom;
private float tickCount;
private float yCount;
private float hspacing;
private float vspacing;
private Graphics g;
private Rectangle r;
private Color backColor;
private Color foreColor;
private Font baseFont;
private Font legendFont;
private RectangleF legendRect;
public ChartEngine() {
}
public Bitmap DrawChart(int width, int height, ChartData chartData) {
Bitmap newBitmap = new Bitmap(width,height,PixelFormat.Format32bppARGB);
Graphics g = Graphics.FromImage(newBitmap);
Rectangle r = new Rectangle(0, 0, width, height);
Color myForeColor = Color.Black;
Color myBackColor = Color.White;
Font myFont = new Font("Arial", 10);
this.DrawChart(g, r, myBackColor, myForeColor, myFont, chartData);
return newBitmap;
}
public void DrawChart(Graphics g, Rectangle r, Color backColor, Color foreColor, Font baseFont, ChartData chartData) {
this.chartData = chartData;
this.g = g;
this.r = r;
this.backColor = backColor;
this.foreColor = foreColor;
this.baseFont = baseFont;
this.legendFont = new Font(baseFont.FontFamily, (baseFont.Size * 2/3), baseFont.Style | FontStyle.Bold);
g.SmoothingMode = SmoothingMode.AntiAlias;
CalculateChartDimensions();
DrawBackground();
InternalDrawChart() ;
}
private void CalculateChartDimensions() {
right = r.Width - 5;
top = 5 * baseFont.Size ;
bottom = r.Height - baseFont.Size * 2;
tickCount = chartData.YMin ;
yCount = (chartData.YMax-chartData.YMin) / chartData.YTickSize ;
hspacing = (bottom-top) / yCount;
vspacing = (right) / chartData.XAxisTitles.Length;
//Left depends on width of text - for simplicities sake assume that largest yvalue is the biggest
//Take into account the first X Axis title
float maxYTextSize = g.MeasureString(chartData.YMax.ToString(), baseFont).Width;
float firstXTitle = g.MeasureString(chartData.XAxisTitles[0], baseFont).Width;
left = (maxYTextSize > firstXTitle) ? maxYTextSize : firstXTitle ;
left = r.X + left + 5 ;
//Calculate size of legend box
float maxLegendWidth = 0 ;
float maxLegendHeight = 0 ;
//Work out size of biggest legend
foreach (ChartLine cl in chartData.Lines) {
float currentWidth = g.MeasureString(cl.Title, legendFont).Width;
float currentHeight = g.MeasureString(cl.Title, legendFont).Height;
maxLegendWidth = (maxLegendWidth > currentWidth) ? maxLegendWidth : currentWidth ;
maxLegendHeight = (maxLegendHeight > currentHeight) ? maxLegendHeight : currentHeight ;
}
legendRect = new RectangleF(r.X+2, r.Y+2, maxLegendWidth + 25 + 5, ((maxLegendHeight+2)*chartData.Lines.Count) + 3) ;
}
private void DrawBackground() {
LinearGradientBrush b = new LinearGradientBrush(r, Color.SteelBlue, backColor,LinearGradientMode.Horizontal);
g.FillRectangle(b, r);
b.Dispose();
}
private void InternalDrawChart() {
DrawGrid() ;
foreach (ChartLine cl in chartData.Lines) {
DrawLine(cl);
}
DrawLegend() ;
//Draw time on chart
string timeString = "Generated:" + DateTime.Now.ToLongTimeString() ;
SizeF textsize = g.MeasureString(timeString,baseFont);
g.DrawString(timeString, baseFont, new SolidBrush(foreColor), r.Width - textsize.Width - 5, textsize.Height * 2 / 3) ;
}
private void DrawGrid() {
Pen gridPen = new Pen(chartData.GridColor) ;
//Vertical - include tick desc's
if (chartData.ShowVGridLines) {
for (int i = 0 ; (vspacing * i) < right; i++) {
float x = left + (vspacing *i);
string desc = chartData.XAxisTitles[i];
g.DrawLine(gridPen, x,top,x,bottom +(baseFont.Size*1/3));
SizeF textsize = g.MeasureString(desc,baseFont);
g.DrawString(desc, baseFont, new SolidBrush(chartData.GridColor), x-(textsize.Width/2), bottom + (baseFont.Size*2/3)) ;
}
}
//Horizontal
if (chartData.ShowHGridLines) {
for (float i = bottom ; i > top; i-=hspacing) {
string desc = tickCount.ToString();
tickCount+=chartData.YTickSize;
g.DrawLine(gridPen, right, i, left-3, i);
SizeF textsize = g.MeasureString(desc,baseFont);
g.DrawString(desc, baseFont, new SolidBrush(chartData.GridColor), left-textsize.Width - 3, i - (textsize.Height/2)) ;
}
}
}
private void DrawLine(ChartLine chartLine) {
Pen linePen = new Pen(chartLine.Color);
linePen.StartCap = LineCap.Round;
linePen.EndCap = LineCap.Round;
linePen.Width = chartLine.Width ;
linePen.DashStyle = chartLine.LineStyle;
PointF[] Values = new PointF[chartLine.Values.Length];
float scale = hspacing / chartData.YTickSize ;
for (int i = 0 ; i < chartLine.Values.Length; i++) {
float x = left + vspacing * i;
Values[i] = new PointF(x, bottom-chartLine.Values[i]*scale);
}
g.DrawLines(linePen, Values);
}
private void DrawLegend() {
//Draw Legend Box
ControlPaint.DrawBorder(g, (Rectangle)legendRect, SystemColors.WindowFrame, ButtonBorderStyle.Solid);
LinearGradientBrush b = new LinearGradientBrush(legendRect, backColor, Color.SteelBlue, LinearGradientMode.Horizontal);
r.Inflate(-1, -1);
g.FillRectangle(b, legendRect);
b.Dispose();
float startY = 5;
foreach (ChartLine cl in chartData.Lines) {
Pen p = new Pen(cl.Color) ;
p.Width = p.Width*4;
SizeF textsize = g.MeasureString(cl.Title, legendFont);
float lineY = startY + textsize.Height / 2 ;
g.DrawLine(p, r.X + 7, lineY, r.X + 25, lineY);
g.DrawString(cl.Title, legendFont, new SolidBrush(foreColor), r.X + 30, startY);
startY += (textsize.Height+2);
}
}
}
}
本文地址：http://com.8s8s.com/it/it9397.htm