Silverlight WriteableBitmap not converting custom font correctly

问题

We use custom fonts to represent road signs and shapes that we plot on a graph.

Initially I plotted everything to a canvas, which worked fine, but was slow to scroll horizontally.

Then I fixed the scrolling issue by converting the canvas to a image using the WriteableBitmap, like this:

#if SILVERLIGHT
    ImageSource ConvertCanvas(Canvas canvas) {

        WriteableBitmap Source = new WriteableBitmap(canvas, /* transform = */ null);

        Source.Invalidate();

        return Source;
    }
#endif

This conversion works fine for most of the elements on the canvas, except the TextBlocks that use the custom font.

So, instead of the proper "custom font" images (characters), I get normal Arial characters, like 'p', 'q', etc...

If I display the canvas again instead the converted image then I can confirm that the custom font works and renders the textblock correctly, so it does not seem to be a loading issue...

Please help or give some pointers I can look into...

Thank you in advance

EDIT:

OK, I found a solution here which boils down to either 1. creating a hidden textblock that use the font before doing the conversion, or 2. creating a FontSource.

I used the first because it was simpler for now.

Inside the control, I added the following:

void Grid_Loaded(object sender, RoutedEventArgs e) {
#if SILVERLIGHT
        Grid Grid = (Grid)sender;
        AddFontLoaderTextBox(Grid, "Signs Road Features");
        AddFontLoaderTextBox(Grid, "Signs G Old");
        AddFontLoaderTextBox(Grid, "Signs G");
        AddFontLoaderTextBox(Grid, "Signs G1");
        AddFontLoaderTextBox(Grid, "Signs G2");
        AddFontLoaderTextBox(Grid, "Signs G3");
        AddFontLoaderTextBox(Grid, "Signs Info");
        AddFontLoaderTextBox(Grid, "Signs Regulatory");
        AddFontLoaderTextBox(Grid, "Signs Regulatory1");
        AddFontLoaderTextBox(Grid, "Road Manager");
        AddFontLoaderTextBox(Grid, "Signs Temporary");
        AddFontLoaderTextBox(Grid, "Road Manager");
        AddFontLoaderTextBox(Grid, "Signs Warning");
        AddFontLoaderTextBox(Grid, "Signs Warning1");
#endif
    }

#if SILVERLIGHT
    void AddFontLoaderTextBox(Grid Grid, string fontName) {

        TextBlock TextBlock = new TextBlock();
        TextBlock.FontFamily = new FontFamily(string.Format(
            "pack://application:,,,/ITIS.Controls.LinearViewer.Silverlight;component/Fonts/{0}.ttf#{0}", fontName));
        TextBlock.Opacity = 0; /* hide the text block, we only load it for the font to be cached */
        Grid.SetRowSpan(TextBlock, 3); /* just to ensure the text block doesn't affect the size of the first row */
        Grid.Children.Insert(0, TextBlock); /* keep underneath other children */
    }
#endif

来源：https://stackoverflow.com/questions/12296887/silverlight-writeablebitmap-not-converting-custom-font-correctly

标签

silverlight

canvas

embedded-fonts

writeablebitmap