ComboBox OwnerDrawVariable Font format size problem

Question

I\'m trying to implement a auto-complete/search box similar to Visual Studio\'s Go To member search:

However, my formatting of the bold

Answer 1

When TextRenderer is used to render text in a non-generic Graphics context, this context needs to be considered: for this reason, TextRenderer provides overloads of both MeasureText and DrawText that accept a Graphics context (IDeviceContext) argument.
The Graphics context contains information that TextRenderer can use to better adapt to the DC specifics.

Also, we need to pass to the methods a combination of TextFormatFlags values that define how we want to measure and/or render the Text.

• Always declare the type of Alignment
• Specify the clipping/wrapping behavior (e.g., we want the Text to wrap or we really don't want it to, we want it clipped instead)
• If the Text should NOT be padded, specify TextFormatFlags.NoPadding, otherwise the Text will be stretched to fill the drawing bounds.
• If the the drawing bounds are not arranged manually (to draw text in specific positions), specify TextFormatFlags.LeftAndRightPadding to add a predefined padding to the text. The padding this setting applies (based on the Font kerning), matches the distance between the text and the borders of standard Controls (e.g., the ListBox or ListView)

More information about TextFormatFlags is (partially :) available in the Docs.

I've moved all the drawing parts to a single method, RenderText().
All measures and drawings are performed here: this way, it should be simpler to understand what is going on when the items are drawn.

The code in the DrawItem handler calls this method, passing some value that are proper when specific conditions are met (as changing the FontStyle, the alternative ForeColor of parts of the Text etc.)

Resulting in:

► The Font used here is Microsoft YaHei UI, 12pt. Of course you can use whatever other Font, but the System Font series with the UI appendix are designed (well) for this.

► Remember to dispose of the Graphics objects you create, it's very important, more important when theses objects are used to provide custom functionality to Controls, so probably constantly generated. Don't count on the Garbage Collector for this, it can do nothing for you in this context.

EDIT: Code optimization.

string searchTerm = string.Empty;
TextFormatFlags format = TextFormatFlags.Top | TextFormatFlags.Left | 
                         TextFormatFlags.NoClipping | TextFormatFlags.NoPadding;

private Size RenderText(string text, DrawItemEventArgs e, FontStyle style, Color altForeColor, Point offset)
{
    var color = altForeColor == Color.Empty ? e.ForeColor : altForeColor;
    using (var font = new Font(e.Font, style)) {
        var textSize = TextRenderer.MeasureText(e.Graphics, text, font, e.Bounds.Size, format);
        var rect = new Rectangle(offset, e.Bounds.Size);
        TextRenderer.DrawText(e.Graphics, text, font, rect, color, e.BackColor, format);
        return textSize;
    }
}

private IEnumerable<(string Text, bool Selected)> BuildDrawingString(string itemContent, string pattern)
{
    if (pattern.Length == 0) {
        yield return (itemContent, false);
    }
    else {
        var matches = Regex.Split(itemContent, $"(?i){pattern}");
        int pos = itemContent.IndexOf(pattern, StringComparison.CurrentCultureIgnoreCase);
        for (int i = 0; i < matches.Length; i++) {
            if (matches[i].Length == 0 && i < matches.Length - 1) {
                yield return (itemContent.Substring(pos, pattern.Length), matches[i].Length > 0 ? false : true);
            }
            else {
                yield return (matches[i], false);
                if (i < matches.Length - 1) {
                    yield return (itemContent.Substring(pos, pattern.Length), true);
                }
            }
        }
    }
}

private void comboBoxItems_DrawItem(object sender, DrawItemEventArgs e)
{
    var listItem = (sender as ComboBox).Items[e.Index] as DocGenFieldItem;
    e.DrawBackground();

    int drawingPosition = 0;
    foreach (var part in BuildDrawingString(listItem.Display, searchTerm)) {
        var style = part.Selected ? FontStyle.Bold : FontStyle.Regular;
        drawingPosition += RenderText(part.Text, e, style, Color.Empty, new Point(drawingPosition, e.Bounds.Y)).Width;
    }

    var offsetBottom = new Point(0, e.Bounds.Bottom - e.Font.Height - 2);
    var valueSize = RenderText("Value: ", e, FontStyle.Bold, Color.FromArgb(64, 64, 64), offsetBottom);

    offsetBottom.Offset(valueSize.Width, 0);
    RenderText(listItem.Value, e, FontStyle.Regular, Color.FromArgb(63, 63, 63), offsetBottom);
    e.DrawFocusRectangle();
}

private void comboBoxItems_MeasureItem(object sender, MeasureItemEventArgs e) 
    => e.ItemHeight = (sender as Control).Font.Height * 2 + 4;

---

In relation to Graphics.MeasureString() and Graphics.DrawString() methods used in the question before the update:

• When we measure Text with a specific StringFormat, then we draw the Text using the same StringFormat, if we want our drawings to respect the measured bounds.
• Graphics.TextRenderingHint = TextRenderingHint.AntiAlias doesn't work really well when Text is rendered with Graphics.DrawString(): use TextRenderingHint.ClearTypeGridFit instead.
• Possibly, avoid Microsoft Sans Serif as Font, use Segoe UI or Microsoft YaHei UI instead (for example): these Fonts are much better weighted and explicitly designed for this (the UI suffix gives it away).