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Bidi ordering #24

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ab27ea1
[render] use LineWrapper to compute bidi visual index; also set the o…
benoitkugler Dec 2, 2025
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benoitkugler Dec 2, 2025
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6 changes: 3 additions & 3 deletions go.mod
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Original file line number Diff line number Diff line change
Expand Up @@ -3,14 +3,14 @@ module github.com/go-text/render
go 1.19

require (
github.com/go-text/typesetting v0.2.0
github.com/go-text/typesetting-utils v0.0.0-20240317173224-1986cbe96c66
github.com/go-text/typesetting v0.3.0
github.com/go-text/typesetting-utils v0.0.0-20250620161931-017769003e3c
github.com/srwiley/oksvg v0.0.0-20221011165216-be6e8873101c
github.com/srwiley/rasterx v0.0.0-20220730225603-2ab79fcdd4ef
golang.org/x/image v0.23.0
)

require (
golang.org/x/net v0.9.0 // indirect
golang.org/x/net v0.25.0 // indirect
golang.org/x/text v0.21.0 // indirect
)
42 changes: 34 additions & 8 deletions go.sum
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Original file line number Diff line number Diff line change
@@ -1,47 +1,73 @@
github.com/go-text/typesetting v0.2.0 h1:fbzsgbmk04KiWtE+c3ZD4W2nmCRzBqrqQOvYlwAOdho=
github.com/go-text/typesetting v0.2.0/go.mod h1:2+owI/sxa73XA581LAzVuEBZ3WEEV2pXeDswCH/3i1I=
github.com/go-text/typesetting-utils v0.0.0-20240317173224-1986cbe96c66 h1:GUrm65PQPlhFSKjLPGOZNPNxLCybjzjYBzjfoBGaDUY=
github.com/go-text/typesetting-utils v0.0.0-20240317173224-1986cbe96c66/go.mod h1:DDxDdQEnB70R8owOx3LVpEFvpMK9eeH1o2r0yZhFI9o=
github.com/go-text/typesetting v0.3.0 h1:OWCgYpp8njoxSRpwrdd1bQOxdjOXDj9Rqart9ML4iF4=
github.com/go-text/typesetting v0.3.0/go.mod h1:qjZLkhRgOEYMhU9eHBr3AR4sfnGJvOXNLt8yRAySFuY=
github.com/go-text/typesetting-utils v0.0.0-20250620161931-017769003e3c h1:EkVgKYSt3+6Y2FdS5TDAe8WRSVpFzWaMoSk0KVzVy2c=
github.com/go-text/typesetting-utils v0.0.0-20250620161931-017769003e3c/go.mod h1:3/62I4La/HBRX9TcTpBj4eipLiwzf+vhI+7whTc9V7o=
github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
github.com/srwiley/oksvg v0.0.0-20221011165216-be6e8873101c h1:km8GpoQut05eY3GiYWEedbTT0qnSxrCjsVbb7yKY1KE=
github.com/srwiley/oksvg v0.0.0-20221011165216-be6e8873101c/go.mod h1:cNQ3dwVJtS5Hmnjxy6AgTPd0Inb3pW05ftPSX7NZO7Q=
github.com/srwiley/rasterx v0.0.0-20220730225603-2ab79fcdd4ef h1:Ch6Q+AZUxDBCVqdkI8FSpFyZDtCVBc2VmejdNrm5rRQ=
github.com/srwiley/rasterx v0.0.0-20220730225603-2ab79fcdd4ef/go.mod h1:nXTWP6+gD5+LUJ8krVhhoeHjvHTutPxMYl5SvkcnJNE=
github.com/yuin/goldmark v1.4.13/go.mod h1:6yULJ656Px+3vBD8DxQVa3kxgyrAnzto9xy5taEt/CY=
golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
golang.org/x/crypto v0.0.0-20210921155107-089bfa567519/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
golang.org/x/crypto v0.13.0/go.mod h1:y6Z2r+Rw4iayiXXAIxJIDAJ1zMW4yaTpebo8fPOliYc=
golang.org/x/crypto v0.19.0/go.mod h1:Iy9bg/ha4yyC70EfRS8jz+B6ybOBKMaSxLj6P6oBDfU=
golang.org/x/crypto v0.23.0/go.mod h1:CKFgDieR+mRhux2Lsu27y0fO304Db0wZe70UKqHu0v8=
golang.org/x/image v0.23.0 h1:HseQ7c2OpPKTPVzNjG5fwJsOTCiiwS4QdsYi5XU6H68=
golang.org/x/image v0.23.0/go.mod h1:wJJBTdLfCCf3tiHa1fNxpZmUI4mmoZvwMCPP0ddoNKY=
golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4/go.mod h1:jJ57K6gSWd91VN4djpZkiMVwK6gcyfeH4XE8wZrZaV4=
golang.org/x/mod v0.8.0/go.mod h1:iBbtSCu2XBx23ZKBPSOrRkjjQPZFPuis4dIYUhu/chs=
golang.org/x/mod v0.12.0/go.mod h1:iBbtSCu2XBx23ZKBPSOrRkjjQPZFPuis4dIYUhu/chs=
golang.org/x/mod v0.15.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
golang.org/x/mod v0.17.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
golang.org/x/net v0.0.0-20210226172049-e18ecbb05110/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
golang.org/x/net v0.0.0-20220722155237-a158d28d115b/go.mod h1:XRhObCWvk6IyKnWLug+ECip1KBveYUHfp+8e9klMJ9c=
golang.org/x/net v0.6.0/go.mod h1:2Tu9+aMcznHK/AK1HMvgo6xiTLG5rD5rZLDS+rp2Bjs=
golang.org/x/net v0.9.0 h1:aWJ/m6xSmxWBx+V0XRHTlrYrPG56jKsLdTFmsSsCzOM=
golang.org/x/net v0.9.0/go.mod h1:d48xBJpPfHeWQsugry2m+kC02ZBRGRgulfHnEXEuWns=
golang.org/x/net v0.10.0/go.mod h1:0qNGK6F8kojg2nk9dLZ2mShWaEBan6FAoqfSigmmuDg=
golang.org/x/net v0.15.0/go.mod h1:idbUs1IY1+zTqbi8yxTbhexhEEk5ur9LInksu6HrEpk=
golang.org/x/net v0.21.0/go.mod h1:bIjVDfnllIU7BJ2DNgfnXvpSvtn8VRwhlsaeUTyUS44=
golang.org/x/net v0.25.0 h1:d/OCCoBEUq33pjydKrGQhw7IlUPI2Oylr+8qLx49kac=
golang.org/x/net v0.25.0/go.mod h1:JkAGAh7GEvH74S6FOH42FLoXpXbE/aqXSrIQjXgsiwM=
golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
golang.org/x/sync v0.0.0-20220722155255-886fb9371eb4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
golang.org/x/sync v0.1.0/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
golang.org/x/sync v0.3.0/go.mod h1:FU7BRWz2tNW+3quACPkgCx/L+uEAv1htQ0V83Z9Rj+Y=
golang.org/x/sync v0.6.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
golang.org/x/sync v0.7.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
golang.org/x/sync v0.10.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
golang.org/x/sys v0.5.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
golang.org/x/sys v0.7.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
golang.org/x/sys v0.8.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
golang.org/x/sys v0.12.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
golang.org/x/sys v0.17.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
golang.org/x/sys v0.20.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
golang.org/x/telemetry v0.0.0-20240228155512-f48c80bd79b2/go.mod h1:TeRTkGYfJXctD9OcfyVLyj2J3IxLnKwHJR8f4D8a3YE=
golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
golang.org/x/term v0.0.0-20210927222741-03fcf44c2211/go.mod h1:jbD1KX2456YbFQfuXm/mYQcufACuNUgVhRMnK/tPxf8=
golang.org/x/term v0.5.0/go.mod h1:jMB1sMXY+tzblOD4FWmEbocvup2/aLOaQEp7JmGp78k=
golang.org/x/term v0.7.0/go.mod h1:P32HKFT3hSsZrRxla30E9HqToFYAQPCMs/zFMBUFqPY=
golang.org/x/term v0.8.0/go.mod h1:xPskH00ivmX89bAKVGSKKtLOWNx2+17Eiy94tnKShWo=
golang.org/x/term v0.12.0/go.mod h1:owVbMEjm3cBLCHdkQu9b1opXd4ETQWc3BhuQGKgXgvU=
golang.org/x/term v0.17.0/go.mod h1:lLRBjIVuehSbZlaOtGMbcMncT+aqLLLmKrsjNrUguwk=
golang.org/x/term v0.20.0/go.mod h1:8UkIAJTvZgivsXaD6/pH6U9ecQzZ45awqEOzuCvwpFY=
golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
golang.org/x/text v0.3.7/go.mod h1:u+2+/6zg+i71rQMx5EYifcz6MCKuco9NR6JIITiCfzQ=
golang.org/x/text v0.7.0/go.mod h1:mrYo+phRRbMaCq/xk9113O4dZlRixOauAjOtrjsXDZ8=
golang.org/x/text v0.9.0/go.mod h1:e1OnstbJyHTd6l/uOt8jFFHp6TRDWZR/bV3emEE/zU8=
golang.org/x/text v0.13.0/go.mod h1:TvPlkZtksWOMsz7fbANvkp4WM8x/WCo/om8BMLbz+aE=
golang.org/x/text v0.14.0/go.mod h1:18ZOQIKpY8NJVqYksKHtTdi31H5itFRjB5/qKTNYzSU=
golang.org/x/text v0.15.0/go.mod h1:18ZOQIKpY8NJVqYksKHtTdi31H5itFRjB5/qKTNYzSU=
golang.org/x/text v0.21.0 h1:zyQAAkrwaneQ066sspRyJaG9VNi/YJ1NfzcGB3hZ/qo=
golang.org/x/text v0.21.0/go.mod h1:4IBbMaMmOPCJ8SecivzSH54+73PCFmPWxNTLm+vZkEQ=
golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
golang.org/x/tools v0.1.12/go.mod h1:hNGJHUnrk76NpqgfD5Aqm5Crs+Hm0VOH/i9J2+nxYbc=
golang.org/x/tools v0.6.0/go.mod h1:Xwgl3UAJ/d3gWutnCtw505GrjyAbvKui8lOU390QaIU=
golang.org/x/tools v0.13.0/go.mod h1:HvlwmtVNQAhOuCjW7xxvovg8wbNq7LwfXh/k7wXUl58=
golang.org/x/tools v0.21.1-0.20240508182429-e35e4ccd0d2d/go.mod h1:aiJjzUbINMkxbQROHiO6hDPo2LHcIPhhQsa9DLh0yGk=
golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
12 changes: 12 additions & 0 deletions render.go
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@ import (
"image/color"
"image/draw"
"math"
"sort"

"github.com/go-text/typesetting/font"
"github.com/go-text/typesetting/font/opentype"
Expand All @@ -28,6 +29,7 @@ type Renderer struct {

segmenter shaping.Segmenter
shaper shaping.HarfbuzzShaper
wrapper shaping.LineWrapper
filler *rasterx.Filler
fillerScale float32
}
Expand All @@ -51,6 +53,16 @@ func (r *Renderer) shape(str string, face *font.Face) (_ shaping.Line, ascent in
ascent = a
}
}

// overall direction of the text, deduced from the first runes
direction := line[0].Direction
r.wrapper.Prepare(shaping.WrapConfig{Direction: direction}, text, shaping.NewSliceIterator(line))
wrapped, _ := r.wrapper.WrapNextLine(math.MaxInt)
line = wrapped.Line

// sort the line by visual order
sort.Slice(line, func(i, j int) bool { return line[i].VisualIndex < line[j].VisualIndex })
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@whereswaldon whereswaldon Dec 2, 2025

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This is fine if we aren't going to do any processing that might rely on the logical ordering, but it is a lossy operation. After this sort, we no longer have easy access to the logical ordering.

In Gio's code, I just traverse the line's VisualOrder array when doing display logic. It's still efficient, but doesn't discard anything.

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@benoitkugler benoitkugler Dec 2, 2025

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Acknowledged, thank you. We could apply your suggestion if required in future work.


return line, ascent
}

Expand Down
25 changes: 25 additions & 0 deletions render_test.go
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Expand Up @@ -171,5 +171,30 @@ func TestBitmapBaseline(t *testing.T) {
if !bytes.Equal(pngBytes.Bytes(), reference) {
t.Error("unexpected image output")
}
}

func TestMixedLTR_RTL(t *testing.T) {
s := "وَرَسُولِهِ وَإِنْ تُبْتُمْ فَلَكُمْ رُءُوسُ hello أَمْوَالِكُمْ لَا تَظْلِمُونَ وَلَا تُظْلَمُونَ ( 279 ) وَإِنْ كَانَ ذُو عُسْرَةٍ فَنَظِرَةٌ إِلَى مَيْسَرَةٍ"

data, _ := ot.Files.ReadFile("common/NotoSansArabic.ttf")
face, _ := font.ParseTTF(bytes.NewReader(data))

img := image.NewNRGBA(image.Rect(0, 0, 800, 40))
draw.Draw(img, img.Bounds(), &image.Uniform{color.White}, image.Point{}, draw.Src)

r := render.Renderer{FontSize: 15, Color: color.Black}
r.DrawString(s, img, face)

// w, _ := os.Create("testdata/mixed_ltr_rtl.png")
// _ = png.Encode(w, img)
// w.Close()

// compare against the reference
var pngBytes bytes.Buffer
png.Encode(&pngBytes, img)

reference, _ := os.ReadFile("testdata/mixed_ltr_rtl.png")
if !bytes.Equal(pngBytes.Bytes(), reference) {
t.Error("unexpected image output")
}
}
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