Harfbuzz integration

[benoitkugler]

Hi !

This PR adds Harfbuzz to the go-text module, and uses the new opentype font package. This allows us to drop the dep on benoitkugler/textlayout, meaning go-text is now in full control of the entire text processing !

As a related topic, I think the font API should be reworked a little bit :

• it is essentially a duplicate of opentype/api/font
• the new opentype package exposes the difference between a read-only, concurrency safe *Font object, and its wrapper *Face, so that *Font may now be re-used across an entire app : we could probably include that in the API
• we should also consider an API for font collections.

But we can probably address theses issues in a separate PR.

[andydotxyz]

This works in renderer with the following diff - just checking you think it looks right, if so this patch is good with me.

diff --git a/render.go b/render.go
index 81ed972..ad0698d 100644
--- a/render.go
+++ b/render.go
@@ -5,7 +5,8 @@ import (
    "image/draw"
    "math"

-   "github.com/benoitkugler/textlayout/fonts"
+   "github.com/go-text/typesetting/font"
+   "github.com/go-text/typesetting/opentype/api"
    "github.com/go-text/typesetting/shaping"
    "github.com/srwiley/rasterx"
    "golang.org/x/image/math/fixed"
@@ -32,7 +33,7 @@ type Renderer struct {
 // The text will be drawn starting at the left edge, down from the image top by the
 // font ascent value, so that the text is all visible.
 // The return value is the X pixel position of the end of the drawn string.
-func (r *Renderer) DrawString(str string, img draw.Image, face fonts.Face) int {
+func (r *Renderer) DrawString(str string, img draw.Image, face font.Face) int {
    if r.PixScale == 0 {
        r.PixScale = 1
    }
@@ -52,7 +53,7 @@ func (r *Renderer) DrawString(str string, img draw.Image, face fonts.Face) int {
 // The text will be drawn starting at the x, y pixel position.
 // Note that x and y are not multiplied by the `PixScale` value as they refer to output coordinates.
 // The return value is the X pixel position of the end of the drawn string.
-func (r *Renderer) DrawStringAt(str string, img draw.Image, x, y int, face fonts.Face) int {
+func (r *Renderer) DrawStringAt(str string, img draw.Image, x, y int, face font.Face) int {
    if r.PixScale == 0 {
        r.PixScale = 1
    }
@@ -81,23 +82,22 @@ func (r *Renderer) DrawShapedRunAt(run shaping.Output, img draw.Image, startX, s
    scanner := rasterx.NewScannerGV(b.Dx(), b.Dy(), img, b)
    f := rasterx.NewFiller(b.Dx(), b.Dy(), scanner)
    f.SetColor(r.Color)
-   point := uint16(float32(run.Face.Upem()) * r.PixScale)
    x := float32(startX)
    y := float32(startY)
    for _, g := range run.Glyphs {
        x -= fixed266ToFloat(g.XOffset) * r.PixScale
-       outline, _ := run.Face.GlyphData(g.GlyphID, point, point).(fonts.GlyphOutline)
+       outline, _ := run.Face.GlyphData(g.GlyphID).(api.GlyphOutline)

        for _, s := range outline.Segments {
            switch s.Op {
-           case fonts.SegmentOpMoveTo:
+           case api.SegmentOpMoveTo:
                f.Start(fixed.Point26_6{X: floatToFixed266(s.Args[0].X*scale + x), Y: floatToFixed266(-s.Args[0].Y*scale + y)})
-           case fonts.SegmentOpLineTo:
+           case api.SegmentOpLineTo:
                f.Line(fixed.Point26_6{X: floatToFixed266(s.Args[0].X*scale + x), Y: floatToFixed266(-s.Args[0].Y*scale + y)})
-           case fonts.SegmentOpQuadTo:
+           case api.SegmentOpQuadTo:
                f.QuadBezier(fixed.Point26_6{X: floatToFixed266(s.Args[0].X*scale + x), Y: floatToFixed266(-s.Args[0].Y*scale + y)},
                    fixed.Point26_6{X: floatToFixed266(s.Args[1].X*scale + x), Y: floatToFixed266(-s.Args[1].Y*scale + y)})
-           case fonts.SegmentOpCubeTo:
+           case api.SegmentOpCubeTo:
                f.CubeBezier(fixed.Point26_6{X: floatToFixed266(s.Args[0].X*scale + x), Y: floatToFixed266(-s.Args[0].Y*scale + y)},
                    fixed.Point26_6{X: floatToFixed266(s.Args[1].X*scale + x), Y: floatToFixed266(-s.Args[1].Y*scale + y)},
                    fixed.Point26_6{X: floatToFixed266(s.Args[2].X*scale + x), Y: floatToFixed266(-s.Args[2].Y*scale + y)})

[benoitkugler]

This works in renderer with the following diff - just checking you think it looks right, if so this patch is good with me.

Yes it seems correct ! Note that if you need to handle bitmap glyphs in the future (for instance for emojis), you would have to add again the computation of point, and set it on the face with face.XPpem = point, face.YPpem = point so that the best glyph size is selected (several may be provided in the font file). But it is not needed for now.

[andydotxyz]

Sweet thanks

[whereswaldon]

Since we have our two approvals, I'm gonna merge this. :D Great work @benoitkugler!