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module Data.Text.ParagraphLayout.Internal.Fragment
( Fragment (..)
, ShapedRun
, fragmentSpacedRect
, shapedRun
)
where
import Data.Int (Int32)
import Data.Text.Glyphize (GlyphInfo, GlyphPos)
import Data.Text.ParagraphLayout.Internal.AncestorBox
import Data.Text.ParagraphLayout.Internal.Rect
-- | A unit of text laid out in a rectangular area.
--
-- Roughly equivalent to the term /text fragment/ as used in
-- [CSS Display Module Level 3](https://www.w3.org/TR/css-display-3/).
--
-- An input span (or /text sequence/ in CSS terms) can be broken into multiple
-- fragments because of line breaking, because of bidirectional ordering,
-- or because it contains glyphs from multiple scripts.
data Fragment d = Fragment
{ fragmentUserData :: d
-- ^ User-defined data associated with the input text span that produced
-- this fragment.
, fragmentLine :: Int
-- ^ Logical number of the line box holding the fragment, starting at 1.
-- Fragments with the same line number are on the same line and will not be
-- separated by page breaks.
, fragmentAncestorBoxes :: [AncestorBox d]
-- ^ Information about inline boxes which contain this fragment
-- (starting from the nearest ancestor and continuing upwards through the
-- tree, up to but excluding the root) and the spacing required by them.
, fragmentRect :: Rect Int32
-- ^ Physical position of the fragment within the paragraph, calculated
-- using all glyph advances in this fragment and the calculated line height.
--
-- This is the space that the glyphs "take up" and is probably what you
-- want to use for detecting position-based events such as mouse clicks.
--
-- Beware that actual glyphs will not be drawn exactly to the borders of
-- this rectangle -- they may be offset inwards and they can also extend
-- outwards!
--
-- These are not the typographic bounding boxes that you use for determining
-- the area to draw on -- you need FreeType or a similar library for that.
--
-- The origin coordinates are relative to the paragraph.
--
-- This is the CSS equivalent of /content box/, before adding box spacing.
, fragmentPen :: (Int32, Int32)
-- ^ Coordinates of the initial pen position, from which the first glyph
-- should be drawn, relative to the origin of the `fragmentRect`. Each
-- glyph's `Data.Text.Glyphize.x_advance` or `Data.Text.Glyphize.y_advance`
-- are then used to move the pen position for the next glyph.
, fragmentGlyphs :: [(GlyphInfo, GlyphPos)]
-- ^ Glyphs contained in the fragment, as returned from HarfBuzz.
}
deriving (Eq, Read, Show)
-- | Physical position of the fragment within the paragraph, with spacing
-- added to the glyph advances. This is the space that the fragment takes up
-- in the paragraph.
fragmentSpacedRect :: Fragment d -> Rect Int32
fragmentSpacedRect (Fragment { fragmentRect = r, fragmentAncestorBoxes = bs })
| x_size r >= 0 = r
{ x_origin = x_origin r - leftSpacing
, x_size = x_size r + leftSpacing + rightSpacing
}
| otherwise = r
{ x_origin = x_origin r + rightSpacing
, x_size = x_size r - leftSpacing - rightSpacing
}
where
leftSpacing = totalLeftSpacing bs
rightSpacing = totalRightSpacing bs
-- | A simplified representation of a box fragment, suitable for passing to a
-- text drawing library but lacking detailed size information.
type ShapedRun = (Int32, Int32, [(GlyphInfo, GlyphPos)])
-- | Convert a `Fragment` to a `ShapedRun`.
shapedRun :: Fragment d -> ShapedRun
shapedRun f = (x, y, g)
where
x = x_origin r + px
y = y_origin r + py
g = fragmentGlyphs f
(px, py) = fragmentPen f
r = fragmentRect f