eecb4e626f
Package font defines an interface for font faces. Other packages provide font face implementations. For example, a truetype package (not part of this CL) would provide one based on .ttf font files. This CL also introduces the golang.org/x/exp/shiny/font/plan9font package, a concrete implementation of the font.Face interface for the Plan 9 bitmap font format. Change-Id: Iead8914caaa58c7562b18a86b45002ae47486903 Reviewed-on: https://go-review.googlesource.com/13463 Reviewed-by: Rob Pike <r@golang.org>
115 lines
3.9 KiB
Go
115 lines
3.9 KiB
Go
// Copyright 2015 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package font defines an interface for font faces, for drawing text on an
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// image.
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//
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// Other packages provide font face implementations. For example, a truetype
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// package would provide one based on .ttf font files.
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package font
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// TODO: move this from golang.org/x/exp to golang.org/x/image ??
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import (
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"image"
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"image/draw"
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"io"
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"golang.org/x/image/math/fixed"
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)
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// TODO: who is responsible for caches (glyph images, glyph indices, kerns)?
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// The Drawer or the Face?
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// Face is a font face. Its glyphs are often derived from a font file, such as
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// "Comic_Sans_MS.ttf", but a face has a specific size, style, weight and
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// hinting. For example, the 12pt and 18pt versions of Comic Sans are two
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// different faces, even if derived from the same font file.
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//
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// A Face is not safe for concurrent use by multiple goroutines, as its methods
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// may re-use implementation-specific caches and mask image buffers.
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//
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// To create a Face, look to other packages that implement specific font file
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// formats.
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type Face interface {
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io.Closer
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// Glyph returns the draw.DrawMask parameters (dr, mask, maskp) to draw r's
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// glyph at the sub-pixel destination location dot. It also returns the new
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// dot after adding the glyph's advance width. It returns !ok if the face
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// does not contain a glyph for r.
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//
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// The contents of the mask image returned by one Glyph call may change
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// after the next Glyph call. Callers that want to cache the mask must make
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// a copy.
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Glyph(dot fixed.Point26_6, r rune) (
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newDot fixed.Point26_6, dr image.Rectangle, mask image.Image, maskp image.Point, ok bool)
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// Kern returns the horizontal adjustment for the kerning pair (r0, r1). A
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// positive kern means to move the glyphs further apart.
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Kern(r0, r1 rune) fixed.Int26_6
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// TODO: per-font and per-glyph Metrics.
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// TODO: ColoredGlyph for various emoji?
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// TODO: Ligatures? Shaping?
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}
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type MultiFace struct {
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// TODO.
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}
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// TODO: Drawer.Layout or Drawer.Measure methods to measure text without
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// drawing?
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// Drawer draws text on a destination image.
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//
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// A Drawer is not safe for concurrent use by multiple goroutines, since its
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// Face is not.
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type Drawer struct {
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// Dst is the destination image.
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Dst draw.Image
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// Src is the source image.
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Src image.Image
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// Face provides the glyph mask images.
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Face Face
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// Dot is the baseline location to draw the next glyph. The majority of the
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// affected pixels will be above and to the right of the dot, but some may
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// be below or to the left. For example, drawing a 'j' in an italic face
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// may affect pixels below and to the left of the dot.
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Dot fixed.Point26_6
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// TODO: Clip image.Image?
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// TODO: SrcP image.Point for Src images other than *image.Uniform? How
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// does it get updated during DrawString?
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}
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// TODO: should DrawString return the last rune drawn, so the next DrawString
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// call can kern beforehand? Or should that be the responsibility of the caller
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// if they really want to do that, since they have to explicitly shift d.Dot
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// anyway?
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//
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// In general, we'd have a DrawBytes([]byte) and DrawRuneReader(io.RuneReader)
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// and the last case can't assume that you can rewind the stream.
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//
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// TODO: how does this work with line breaking: drawing text up until a
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// vertical line? Should DrawString return the number of runes drawn?
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// DrawString draws s at the dot and advances the dot's location.
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func (d *Drawer) DrawString(s string) {
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var prevC rune
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for i, c := range s {
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if i != 0 {
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d.Dot.X += d.Face.Kern(prevC, c)
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}
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newDot, dr, mask, maskp, ok := d.Face.Glyph(d.Dot, c)
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if !ok {
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// TODO: is falling back on the U+FFFD glyph the responsibility of
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// the Drawer or the Face?
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continue
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}
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draw.DrawMask(d.Dst, dr, d.Src, image.Point{}, mask, maskp, draw.Over)
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d.Dot, prevC = newDot, c
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}
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}
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