You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: font.go
    path of file: ./repos/gdlv/vendor/golang.org/x/image/font
    
    the code of the file until where you have to start completion: // Copyright 2015 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package font defines an interface for font faces, for drawing text on an
// image.
//
// Other packages provide font face implementations. For example, a truetype
// package would provide one bas
    
func (d *Drawer) DrawString(s string) {
	prevC := rune(-1)
	for _, c := range s {
		if prevC >= 0 {
			d.Dot.X += d.Face.Kern(prevC, c)
		}
		dr, mask, maskp, advance, ok := d.Face.Glyph(d.Dot, c)
		if !ok {
			// TODO: is falling back on the U+FFFD glyph the responsibility of
			// the Drawer or the Face?
			// TODO: set prevC = '\ufffd'?
			continue
		}
		draw.DrawMask(d.Dst, dr, d.Src, image.Point{}, mask, maskp, draw.Over)
		d.Dot.X += advance
		prevC = c
	}
}