Precisely locating glyph text in WPF

Question

I am writing a chemical molecule editor for Windows. As it has to be used in a Word Add-In I am restricted to using WPF for rendering structures. This is working quite well, apart from one tiny niggling point.

I use GlyphRuns for rendering atom labels and they are always displaced slightly to the right. If you look on the screenshot you can see there is a leading whitespace, especially with the H2N, and Hg atom labels. Why? The white background is what you get when you get the outline geometry of the glyph run.

The GlyphRun class is so badly documented that I cannot see which of the properties to amend to precisely locate the text where I want it. So any suggestions to try would be welcome.

UPDATE: I've been asked to provide a sample. The code is complex, but not gratuitously so, so I'm cutting it down to focus on the essentials:

    public void MeasureAtCenter(Point center)
        {
            GlyphInfo = GlyphUtils.GetGlyphsAndInfo(Text, PixelsPerDip, out GlyphRun groupGlyphRun, center, _glyphTypeface, TypeSize);
            //compensate the main offset vector for any descenders
            Vector mainOffset = GlyphUtils.GetOffsetVector(groupGlyphRun, AtomShape.SymbolSize) + new Vector(0.0, -MaxBaselineOffset) + new Vector(-FirstBearing(groupGlyphRun), 0.0);



            TextRun = groupGlyphRun;
            TextMetrics = new AtomTextMetrics
            {
                BoundingBox = groupGlyphRun.GetBoundingBox(center + mainOffset),
                Geocenter = center,
                TotalBoundingBox = groupGlyphRun.GetBoundingBox(center + mainOffset),
                OffsetVector = mainOffset
            };
        }

  public static GlyphInfo GetGlyphs(string symbolText, GlyphTypeface glyphTypeFace, double size)
        {
            ushort[] glyphIndexes = new ushort[symbolText.Length];
            double[] advanceWidths = new double[symbolText.Length];
            double[] uprightBaselineOffsets = new double[symbolText.Length];
            double totalWidth = 0;

            for (int n = 0; n < symbolText.Length; n++)
            {
                ushort glyphIndex = glyphTypeFace.CharacterToGlyphMap[symbolText[n]];
                glyphIndexes[n] = glyphIndex;

                double width = glyphTypeFace.AdvanceWidths[glyphIndex] * size;
                advanceWidths[n] = width;

                double ubo = glyphTypeFace.DistancesFromHorizontalBaselineToBlackBoxBottom[glyphIndex] * size;
                uprightBaselineOffsets[n] = ubo;
                totalWidth += width;
            }
            return new GlyphInfo { AdvanceWidths = advanceWidths, Indexes = glyphIndexes, Width = totalWidth, UprightBaselineOffsets = uprightBaselineOffsets };
        }

        public static GlyphUtils.GlyphInfo GetGlyphsAndInfo(string symbolText, float pixelsPerDip, out GlyphRun hydrogenGlyphRun, Point point, GlyphTypeface glyphTypeFace, double symbolSize)
        {
            //measure the H atom first
            var glyphInfo = GlyphUtils.GetGlyphs(symbolText, glyphTypeFace, symbolSize);
            hydrogenGlyphRun = GlyphUtils.GetGlyphRun(glyphInfo, glyphTypeFace,
                symbolSize, pixelsPerDip, point);
            //work out exactly how much we should offset from the center to get to the bottom left
            return glyphInfo;
        }

 public static Vector GetOffsetVector(GlyphRun glyphRun, double symbolSize)
    {
        Rect rect = glyphRun.ComputeInkBoundingBox();

        //Vector offset = (rect.BottomLeft - rect.TopRight) / 2;
        Vector offset = new Vector(-rect.Width / 2, glyphRun.GlyphTypeface.CapsHeight * symbolSize / 2);
        return offset;
    }

Answer 1

Indeed the GlyphRun class is a lot of work to use. I would suggest working with FormattedText objects instead. If there are performance issues, you can consider converting the FormattedText to Geometry once and reusing that. The MSDN docs provide a comparison of the different approaches.