Custom Rendering

Warning

Fonts is still considered BETA quality and we still reserve the rights to change the API shapes.

Note

ImageSharp.Drawing already implements the glyph rendering for you unless you are rendering on other platforms we would recommend using the version provided by that library.. This is a more advanced topic.

Implementing a glyph renderer

The abstraction used by Fonts to allow implementing glyph rendering is the IGlyphRenderer and its brother IColoredGlypheRenderer (for colored emoji support).

 // `IColoredGlyphRenderer` implements `IGlyphRenderer` so if you don't want colored font support just implement `IGlyphRenderer`.
public class CustomGlyphRenderer : IColoredGlyphRenderer 
{

    /// <summary>
    /// Called before any glyphs have been rendered.
    /// </summary>
    /// <param name="bounds">The bounds the text will be rendered at and at whats size.</param>
    void IGlyphRenderer.BeginText(FontRectangle bounds)
    {
        // called before any thing else to provide access to the total required size to redner the text
    }

    /// <summary>
    /// Begins the glyph.
    /// </summary>
    /// <param name="bounds">The bounds the glyph will be rendered at and at what size.</param>
    /// <param name="paramaters">The set of paramaters that uniquely represents a version of a glyph in at particular font size, font family, font style and DPI.</param>
    /// <returns>Returns true if the glyph should be rendered othersie it returns false.</returns>
    bool IGlyphRenderer.BeginGlyph(FontRectangle bounds, GlyphRendererParameters paramaters)
    {
        // called before each glyph/glyph layer is rendered.
        // The paramaters can be used to detect the exact details
        // of the glyph so that duplicate glyphs could optionally 
        // be cached to reduce processing.

        // You can return false to skip all the figures within the glyph (if you return false EndGlyph will still be called)
    }

    /// <summary>
    /// Sets the color to use for the current glyph.
    /// </summary>
    /// <param name="color">The color to override the renders brush with.</param>
    void IColorGlyphRenderer.SetColor(GlyphColor color)
    {
        // from the IColorGlyphRenderer version, onlt called if the current glyph should override the forgound color of current glyph/layer        
    }

    /// <summary>
    /// Begins the figure.
    /// </summary>
    void IGlyphRenderer.BeginFigure()
    {
        // called at the start of the figure within the single glyph/layer
        // glyphs are rendered as a serise of arcs, lines and movements 
        // which together describe a complex shape.
    }

    /// <summary>
    /// Sets a new start point to draw lines from
    /// </summary>
    /// <param name="point">The point.</param>
    void IGlyphRenderer.MoveTo(Vector2 point)
    {
        // move current point to location marked by point without describing a line;
    }

    /// <summary>
    /// Draw a quadratic bezier curve connecting the previous point to <paramref name="point"/>.
    /// </summary>
    /// <param name="secondControlPoint">The second control point.</param>
    /// <param name="point">The point.</param>
    void IGlyphRenderer.QuadraticBezierTo(Vector2 secondControlPoint, Vector2 point)
    {
        // describes Quadratic Bezier curve from the 'current point' using the 
        // 'second control point' and final 'point' leaving the 'current point'
        // at 'point'
    }

    /// <summary>
    /// Draw a Cubics bezier curve connecting the previous point to <paramref name="point"/>.
    /// </summary>
    /// <param name="secondControlPoint">The second control point.</param>
    /// <param name="thirdControlPoint">The third control point.</param>
    /// <param name="point">The point.</param>
    void IGlyphRenderer.CubicBezierTo(Vector2 secondControlPoint, Vector2 thirdControlPoint, Vector2 point)
    {
        // describes Cubic Bezier curve from the 'current point' using the 
        // 'second control point', 'third control point' and final 'point' 
        // leaving the 'current point' at 'point'
    }

    /// <summary>
    /// Draw a straight line connecting the previous point to <paramref name="point"/>.
    /// </summary>
    /// <param name="point">The point.</param>
    void IGlyphRenderer.LineTo(Vector2 point)
    {
        // describes straight line from the 'current point' to the final 'point' 
        // leaving the 'current point' at 'point'
    }

    /// <summary>
    /// Ends the figure.
    /// </summary>
    void IGlyphRenderer.EndFigure()
    {
        // Called after the figure has completed denoting a straight line should 
        // be drawn from the current point to the first point
    }

    /// <summary>
    /// Ends the glyph.
    /// </summary>
    void IGlyphRenderer.EndGlyph()
    {
        // says the all figures have completed for the current glyph/layer.
        // NOTE this will be called even if BeginGlyph return false.
    }


    /// <summary>
    /// Called once all glyphs have completed rendering
    /// </summary>
    void IGlyphRenderer.EndText()
    {
        //once all glyphs/layers have been drawn this is called.
    }
}