From e5196add6c88a4034109c516d6c338becfea7c6c Mon Sep 17 00:00:00 2001
From: Jaro <jaro@argonaut-constellation.org>
Date: Thu, 29 Jun 2023 20:03:50 +0200
Subject: [PATCH] Add options for vertical alignment.

---
 lib/Data/Text/ParagraphLayout/Rich.hs         |  6 ++
 .../ParagraphLayout/Internal/BoxOptions.hs    | 58 ++++++++++++++++++-
 2 files changed, 62 insertions(+), 2 deletions(-)

diff --git a/lib/Data/Text/ParagraphLayout/Rich.hs b/lib/Data/Text/ParagraphLayout/Rich.hs
index c0456b1..d00a64c 100644
--- a/lib/Data/Text/ParagraphLayout/Rich.hs
+++ b/lib/Data/Text/ParagraphLayout/Rich.hs
@@ -14,6 +14,11 @@ module Data.Text.ParagraphLayout.Rich
         )
     , BoxCollapse (AllowBoxCollapse, AvoidBoxCollapse)
     , BoxSpacing (BoxSpacingLeftRight)
+    , VerticalAlignment
+        ( AlignLineTop
+        , AlignLineBottom
+        , AlignBaseline
+        )
     , LineHeight (Absolute, Normal)
     , ParagraphOptions
     , defaultParagraphOptions
@@ -39,6 +44,7 @@ module Data.Text.ParagraphLayout.Rich
     -- as well as updating specific option fields.
     , boxSpacing
     , boxCollapse
+    , boxVerticalAlignment
     , activateBoxSpacing
     -- ** Text options
     -- | These are record selectors that can be used for reading
diff --git a/src/Data/Text/ParagraphLayout/Internal/BoxOptions.hs b/src/Data/Text/ParagraphLayout/Internal/BoxOptions.hs
index 0057086..397044b 100644
--- a/src/Data/Text/ParagraphLayout/Internal/BoxOptions.hs
+++ b/src/Data/Text/ParagraphLayout/Internal/BoxOptions.hs
@@ -2,6 +2,7 @@ module Data.Text.ParagraphLayout.Internal.BoxOptions
     ( BoxCollapse (..)
     , BoxOptions (..)
     , BoxSpacing (..)
+    , VerticalAlignment (..)
     , activateBoxSpacing
     , defaultBoxOptions
     )
@@ -14,6 +15,10 @@ import Data.Int (Int32)
 -- This record type is likely to be extended in the future.
 -- Use `defaultBoxOptions` and update it with specific record selectors
 -- instead of constructing `BoxOptions` directly.
+--
+-- In order to get CSS defaults, use:
+--
+-- > defaultBoxOptions { boxVerticalAlignment = AlignBaseline 0 }
 data BoxOptions = BoxOptions
 
     { boxSpacing :: BoxSpacing
@@ -30,7 +35,8 @@ data BoxOptions = BoxOptions
     -- ^ Determines how this box affects the height of a line that would
     -- otherwise be empty.
 
-    -- TODO: textVerticalAlign
+    , boxVerticalAlignment :: VerticalAlignment
+    -- ^ Determines how fragments are aligned vertically within a line.
 
     }
     deriving (Eq)
@@ -92,11 +98,59 @@ data BoxCollapse
 
     deriving (Eq, Read, Show)
 
--- | `BoxOptions` with default values.
+-- | Determines how the contents of a line should be aligned vertically,
+-- that is, how fragments should fill (and possibly extend) the vertical space
+-- inside a line.
+--
+-- Vertical alignment takes place after line breaking.
+data VerticalAlignment
+
+    = AlignLineTop
+    -- ^ Align the top of this box with the top of the line.
+    --
+    -- The /top of this box/ is the topmost coordinate of any fragment
+    -- descended from this box, except for fragments that are descended from
+    -- another box with `AlignLineTop` or `AlignLineBottom` closer to them.
+    --
+    -- t`Data.Text.ParagraphLayout.Rich.LineHeight` is included
+    -- when considering the /top/ coordinates of descended fragments,
+    -- and thus, leading is included.
+    --
+    -- This behaviour is equivalent to @vertical-align: top@ in CSS.
+
+    | AlignLineBottom
+    -- ^ Align the bottom of this box with the bottom of the line.
+    --
+    -- The /bottom of this box/ is the bottommost coordinate of any fragment
+    -- descended from this box, except for fragments that are descended from
+    -- another box with `AlignLineTop` or `AlignLineBottom` closer to them.
+    --
+    -- t`Data.Text.ParagraphLayout.Rich.LineHeight` is included
+    -- when considering the /bottom/ coordinates of descended fragments,
+    -- and thus, leading is included.
+    --
+    -- This behaviour is equivalent to @vertical-align: bottom@ in CSS.
+
+    | AlignBaseline Int32
+    -- ^ Align the baseline of this box with the baseline of its parent box,
+    -- optionally shifting it by a specified amount upwards.
+    --
+    -- @`AlignBaseline` 0@ is equivalent to @vertical-align: baseline@ in CSS.
+    --
+    -- @`AlignBaseline` x@ is equivalent to @vertical-align: \<length\>@ in CSS,
+    -- after an appropriate unit conversion.
+
+    deriving (Eq, Read, Show)
+
+-- | `BoxOptions` with backwards-compatible values.
+--
+-- Note that this sets `boxVerticalAlignment` to `AlignLineTop`,
+-- whereas the CSS default should be `AlignBaseline 0`.
 defaultBoxOptions :: BoxOptions
 defaultBoxOptions = BoxOptions
     { boxSpacing = BoxSpacingLeftRight 0 0
     , boxCollapse = AllowBoxCollapse
+    , boxVerticalAlignment = AlignLineTop
     }
 
 -- | Shorthand for updating `boxSpacing` and setting `boxCollapse`
-- 
2.30.2