WXFontMetrics.hs

{-
   Copyright (C) Jeremy O'Donoghue (jeremy.odonoghue@gmail.com) 2007-2010.
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module Graphics.UI.WXContrib.WXFontMetrics 
    ( FontMetrics(..)
    , getFontMetrics 
    )
    where

import Graphics.UI.WXCore
import Graphics.UI.WX

-- | FontMetrics for a given device context.
data FontMetrics = FontMetrics { fm_x    :: !Int  -- | Largest X value
                               , fm_y    :: !Int  -- | Largest Y value
                               , fm_desc :: !Int  -- | Largest value of descender
                               , fm_el   :: !Int  -- | Largest external leader
                               } deriving Show


-- | Return font metrics (based on several selected characters) for 
--   a single character in a given window based on the supplied text 
--   attributes. An attempt is made to determine the maximum likely
--   space needed for any character in the font, although the reality
--   is that this is inevitably somewhat font dependent.
getFontMetrics :: Window a -> FontStyle -> IO FontMetrics
getFontMetrics win font =
    do
    dc <- windowDCCreate win
    dcSetFontStyle dc font
    (sz1, d1, el1) <- getFullTextExtent dc "W"  -- A wide character
    (sz2, d2, el2) <- getFullTextExtent dc "y"  -- A character with descender
    (sz3, d3, el3) <- getFullTextExtent dc "l"  -- May have external leading
    let szx1 = sizeW sz1
        szy1 = sizeH sz1
        szx2 = sizeW sz2
        szy2 = sizeH sz2
        szx3 = sizeW sz3
        szy3 = sizeH sz3
        fm   = FontMetrics (maximum [szx1, szx2, szx3]) -- Largest X value for size
                           (maximum [szy1, szy2, szy3]) -- Largest Y value for size
                           (maximum [d1, d2, d3])       -- Largest value of descender
                           (maximum [el1, el2, el3])    -- Largest value of external leading
    windowDCDelete dc 
    return fm