From 0f7131a5849c78c78573ed1abc34893b3ad1f64d Mon Sep 17 00:00:00 2001
From: Jaro <jaro@argonaut-constellation.org>
Date: Thu, 25 May 2023 14:39:34 +0200
Subject: [PATCH] Propagate BiDi levels to layout algorithm.

BREAKING: Text direction of the root box is now correctly used for
ordering fragments. Previously, the order was always LTR.
---
 .../Text/ParagraphLayout/Internal/Layout.hs   |  3 ++-
 .../ParagraphLayout/Internal/ProtoFragment.hs | 21 ++++++++-----------
 .../ParagraphLayout/Internal/TextOptions.hs   |  4 +++-
 3 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/src/Data/Text/ParagraphLayout/Internal/Layout.hs b/src/Data/Text/ParagraphLayout/Internal/Layout.hs
index f8d50be..df3cfe3 100644
--- a/src/Data/Text/ParagraphLayout/Internal/Layout.hs
+++ b/src/Data/Text/ParagraphLayout/Internal/Layout.hs
@@ -295,9 +295,10 @@ layoutRunsH runs = map layoutRunH runs
 layoutRunH :: WithSpan d Run -> ProtoFragmentWithSpan d
 layoutRunH (WithSpan rs run) = WithSpan rs pf
     where
-        pf = PF.protoFragmentH dir glyphs
+        pf = PF.protoFragmentH dir lvl glyphs
         glyphs = shapeRun (WithSpan rs run)
         dir = runDirection run
+        lvl = runLevel run
 
 -- | Calculate layout for the given run independently of its position.
 shapeRun :: WithSpan d Run -> [(GlyphInfo, GlyphPos)]
diff --git a/src/Data/Text/ParagraphLayout/Internal/ProtoFragment.hs b/src/Data/Text/ParagraphLayout/Internal/ProtoFragment.hs
index 12f73d9..39fe69f 100644
--- a/src/Data/Text/ParagraphLayout/Internal/ProtoFragment.hs
+++ b/src/Data/Text/ParagraphLayout/Internal/ProtoFragment.hs
@@ -7,12 +7,15 @@ where
 import Data.Int (Int32)
 import Data.Text.Glyphize (Direction (..), GlyphInfo, GlyphPos (x_advance))
 
-import Data.Text.ParagraphLayout.Internal.BiDiLevels
+import qualified Data.Text.ParagraphLayout.Internal.BiDiLevels as BiDi
 
 -- | A box fragment which has not been positioned yet.
 data ProtoFragment = ProtoFragment
     { direction :: Maybe Direction
     -- ^ Text direction, which is constant within a fragment.
+    , level :: BiDi.Level
+    -- ^ BiDi embedding level.
+    -- Should be even for LTR fragments and odd for RTL fragments.
     , advance :: Int32
     -- ^ Total advance of glyphs in this fragment,
     -- depending on the text direction.
@@ -21,17 +24,11 @@ data ProtoFragment = ProtoFragment
 
 -- | Construct a `ProtoFragment`, automatically calculating the total advance
 -- for a horizontal text direction.
-protoFragmentH :: Maybe Direction -> [(GlyphInfo, GlyphPos)] -> ProtoFragment
-protoFragmentH dir gs = ProtoFragment dir adv gs
+protoFragmentH :: Maybe Direction -> BiDi.Level -> [(GlyphInfo, GlyphPos)] ->
+    ProtoFragment
+protoFragmentH dir lvl gs = ProtoFragment dir lvl adv gs
     where
         adv = sum $ map (x_advance . snd) gs
 
-instance WithLevel ProtoFragment where
-    level pf = case direction pf of
-        -- TODO: Allow externally set paragraph embedding level.
-        -- TODO: Properly calculate BiDi levels.
-        Just DirLTR -> 0
-        Just DirRTL -> 1
-        Just DirTTB -> 0
-        Just DirBTT -> 1
-        Nothing -> 0
+instance BiDi.WithLevel ProtoFragment where
+    level = level -- BiDi.level = ProtoFragment.level
diff --git a/src/Data/Text/ParagraphLayout/Internal/TextOptions.hs b/src/Data/Text/ParagraphLayout/Internal/TextOptions.hs
index 3a1a9bb..b1c8b59 100644
--- a/src/Data/Text/ParagraphLayout/Internal/TextOptions.hs
+++ b/src/Data/Text/ParagraphLayout/Internal/TextOptions.hs
@@ -33,10 +33,12 @@ data TextOptions = TextOptions
 
     , textDirection :: Direction
     -- ^ Base text direction.
+    --
     -- Used to determine which box fragment gets the left spacing and which
     -- gets the right spacing when broken over multiple lines.
     --
-    -- TODO: Also use for the visual order of boxes.
+    -- When applied to the root box in a paragraph, this is also used to
+    -- determine the base direction of the paragraph.
 
     -- TODO: textVerticalAlign
     -- TODO: textLetterSpacing
-- 
2.30.2