如何解决在Windows Phone 7中，如何在后台线程的WriteableBitmap上呈现文本？
| 我正在尝试在Windows Phone 7应用程序中的位图上呈现文本。 在主线程上运行时，看起来或类似以下内容的代码可以正常工作：public ImageSource RenderText(string text,double x,double y)
{
var canvas = new Canvas();
var textBlock = new TextBlock { Text = text };
canvas.Children.Add(textBloxk);
Canvas.SetLeft(textBlock,x);
Canvas.SetTop(textBlock,y);
var bitmap = new WriteableBitmap(400,400);
bitmap.Render(canvas,null);
bitmap.Invalidate();
return bitmap;
}
BackgroundWorker
TextBlock
UnauthorizedAccessException
WriteableBitmap
UIElements
BackgroundWorker
解决方法
这种方法是从预制图像中复制字母，而不是使用TextBlock，它基于我对此问题的回答。主要的限制是要求每种字体和大小都需要不同的图像。大小为20的字体大约需要150kb。
使用SpriteFont2以所需的大小导出字体和xml度量文件。该代码假定它们的名称为\“ FontName FontSize \”。png和\“ FontName FontSize \”。xml将它们添加到您的项目中，并将构建操作设置为content。该代码还需要WriteableBitmapEx。
public static class BitmapFont
{
private class FontInfo
{
public FontInfo(WriteableBitmap image,Dictionary<char,Rect> metrics,int size)
{
this.Image = image;
this.Metrics = metrics;
this.Size = size;
}
public WriteableBitmap Image { get; private set; }
public Dictionary<char,Rect> Metrics { get; private set; }
public int Size { get; private set; }
}
private static Dictionary<string,List<FontInfo>> fonts = new Dictionary<string,List<FontInfo>>();
public static void RegisterFont(string name,params int[] sizes)
{
foreach (var size in sizes)
{
string fontFile = name + \" \" + size + \".png\";
string fontMetricsFile = name + \" \" + size + \".xml\";
BitmapImage image = new BitmapImage();
image.SetSource(App.GetResourceStream(new Uri(fontFile,UriKind.Relative)).Stream);
var metrics = XDocument.Load(fontMetricsFile);
var dict = (from c in metrics.Root.Elements()
let key = (char) ((int) c.Attribute(\"key\"))
let rect = new Rect((int) c.Element(\"x\"),(int) c.Element(\"y\"),(int) c.Element(\"width\"),(int) c.Element(\"height\"))
select new {Char = key,Metrics = rect}).ToDictionary(x => x.Char,x => x.Metrics);
var fontInfo = new FontInfo(new WriteableBitmap(image),dict,size);
if(fonts.ContainsKey(name))
fonts[name].Add(fontInfo);
else
fonts.Add(name,new List<FontInfo> {fontInfo});
}
}
private static FontInfo GetNearestFont(string fontName,int size)
{
return fonts[fontName].OrderBy(x => Math.Abs(x.Size - size)).First();
}
public static Size MeasureString(string text,string fontName,int size)
{
var font = GetNearestFont(fontName,size);
double scale = (double) size / font.Size;
var letters = text.Select(x => font.Metrics[x]).ToArray();
return new Size(letters.Sum(x => x.Width * scale),letters.Max(x => x.Height * scale));
}
public static void DrawString(this WriteableBitmap bmp,string text,int x,int y,int size,Color color)
{
var font = GetNearestFont(fontName,size);
var letters = text.Select(f => font.Metrics[f]).ToArray();
double scale = (double)size / font.Size;
double destX = x;
foreach (var letter in letters)
{
var destRect = new Rect(destX,y,letter.Width * scale,letter.Height * scale);
bmp.Blit(destRect,font.Image,letter,color,WriteableBitmapExtensions.BlendMode.Alpha);
destX += destRect.Width;
}
}
}
Canvas
TextBlock
<Canvas x:Name=\"userInfoCanvas\" Height=\"200\" Width=\"200\" Visibility=\"Collapsed\">
<Image x:Name=\"backgroundImage\"> </Image>
<TextBlock x:Name=\"messageTextBlock\" Canvas.ZIndex=\"3> </TextBlock> <!--ZIndex set the order of elements -->
</Canvas>
messageTextBlock.Text = message;
backgroundImage.Source = new BitmapImage(renderedImage);
Dispatcher.BeginInvoke(DispatcherPriority.Background,messageUpdate); //messageUpdate is an Action or anthing that can be infered to Delegate
public Bitmap RenderText(string text,double x,double y)
{
Bitmap bitmap = new Bitmap(400,400);
using (Graphics g = new Graphics(bitmap))
{
using (Font font = SystemFonts....)
{
using (Brush brush = new SolidColorBrush(...))
{
g.DrawString(text,font,brush,new Point(x,y));
}
}
}
return bitmap;
}
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