mono / libgdiplus

C-based implementation of the GDI+ API
http://www.mono-project.com/
MIT License
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DrawString clips text #736

Open jhergens opened 2 years ago

jhergens commented 2 years ago

The DrawString method clips text. At least for some fonts. The following code:

using var font = new Font("Liberation Sans", 11f, GraphicsUnit.Pixel);
using var backBuffer = new Bitmap(50, 80);
using (var graphics = Graphics.FromImage(backBuffer))
using (var stringFormat = new StringFormat())
{
    graphics.Clear(Color.White);

    // Draw a right aligned string with clipping on.
    var text = "Hello";
    var bounds = new RectangleF(10, 10, 30, 16);
    stringFormat.Alignment = StringAlignment.Far;
    graphics.FillRectangle(Brushes.Red, bounds);
    graphics.DrawString(text, font, Brushes.Black, bounds, stringFormat);

    // Draw it without clipping
    bounds.Offset(0, 25);
    stringFormat.FormatFlags |= StringFormatFlags.NoClip;
    graphics.FillRectangle(Brushes.Red, bounds);
    graphics.DrawString(text, font, Brushes.Black, bounds, stringFormat);

    // Measure string and render in resulting rectangle
    stringFormat.Alignment = StringAlignment.Near;
    bounds.Offset(0, 25);
    var size = graphics.MeasureString(text, font);
    bounds.Size = size;
    graphics.FillRectangle(Brushes.Red, bounds);
    graphics.DrawString(text, font, Brushes.Black, bounds, stringFormat);
}

Yields the following result: text_linux

The first line is rendered with clipping. The other two without. It is clear that the last glyph will not be rendered correctly when clipping is on.

We are building libgdiplus with Pango backend.