GlyphRun和光标的准确位置(WPF)

Question

我想在鼠标光标的位置画一个文本。因为我需要非常高的性能，所以我想使用GlyphRun。所有工作几乎都很好，但不幸的是，我的文本略低于光标。

有人能帮我修改这个方法以消除这个垂直移位的吗？

现在看起来就像这样

我的期望(文本触及光标)

我的代码：

void MyDrawer_MouseMove(object sender, MouseEventArgs e)
{
    Test1();            
}

void Test1()
{
    MyDrawer.DeleteVisual(Dv);
    MyDrawer.Cursor = Cursors.Cross;
    string text = "Hello Word";
    double size = 40;
    Dv = new DrawingVisual();
    using (var dc = Dv.RenderOpen())
    {
        Typeface typeface = new Typeface("Arial");
        if (typeface.TryGetGlyphTypeface(out GlyphTypeface glyphTypeface))
        {
            ushort[] glyphIndexes = new ushort[text.Length];
            double[] advanceWidths = new double[text.Length];

            for (int i = 0; i < text.Length; i++)
            {
                ushort glyphIndex = glyphTypeface.CharacterToGlyphMap[text[i]];
                glyphIndexes[i] = glyphIndex;
                double width = glyphTypeface.AdvanceWidths[glyphIndex] * size;
                advanceWidths[i] = width;
            }

            Point origin = Mouse.GetPosition(MyDrawer);
            //Move text belowe the cursor
            origin = new Point { X = origin.X, Y = origin.Y + (glyphTypeface.Baseline * size) };
            GlyphRun glyphRun = new GlyphRun(glyphTypeface, 0, false, size,
            glyphIndexes, origin, advanceWidths, null, null, null, null,
            null, null);

            dc.DrawGlyphRun(Brushes.Red, glyphRun);
            MyDrawer.AddVisual(Dv);
        }
    }
}

当然，这只是一个测试，实际上它不会影响游标，但是所指示的点和文本将比本例中的要多得多。

Answer 1

为了寻找同样的问题，我遇到了这个问题。

字形内容(GlyphRun )被包装在一个黑匣子里.

黑匣子顶上有一点垫子.

就像这样：字形长跑的锻制技巧

// To get the box size
var blackBoxHeight = glyphTypeface.Height * fontSize;

// To get the actual character height
var characterHeight = glyphTypeface.Baseline * fontSize;

// To get the padding inside the black box
var blackBoxPadding = blackBoxHeight - characterHeight;

// set the point to draw a little bit up (skip the padding)
origin.Y -= blackBoxPadding;

// Create the glyph
var run = new GlyphRun
            (
                glyphTypeface: glyphTypeface,
                bidiLevel: 0,
                isSideways: false,
                renderingEmSize: fontSize,
                pixelsPerDip: 1.0f,
                glyphIndices: indices,
                baselineOrigin: origin, /* The point containing the padding offset */
                advanceWidths: widths,
                glyphOffsets: null,
                characters: null,
                deviceFontName: null,
                clusterMap: null,
                caretStops: null,
                language: null
            );

Answer 2

另一个答案缺乏一些细节。实际上没有魔法或者没有道理的拍子。图显示glyphTypeface高度参数与显示的GlyphRun之间的关系。

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根据GlyphRun原点Y计算相应的直线垂直位置的代码如下所示：

    var baseLine = origin.Y;
    var boxTop = baseLine - glyphTypeface.Baseline * FontSize;
    var boxBottom = boxTop + glyphTypeface.Height * FontSize;
    var capsHeight = baseLine - glyphTypeface.CapsHeight * FontSize;
    var lowHeight = baseLine - glyphTypeface.XHeight * FontSize;