    --------------------------------------------------------------------------------
    -- |
    -- Module      :  Graphics.Rendering.OpenGL.GL.LineSegments
    -- Copyright   :  (c) Sven Panne 2002-2006
    -- License     :  BSD-style (see the file libraries/OpenGL/LICENSE)
    --
    -- Maintainer  :  sven.panne@aedion.de
    -- Stability   :  stable
    -- Portability :  portable
    --
    -- This module corresponds to section 3.4 (Line Segments) of the OpenGL 2.1
    -- specs.
    --
    --------------------------------------------------------------------------------

    module Graphics.Rendering.OpenGL.GL.LineSegments (
       -- * Line Rasterization
       lineWidth,

       -- * Line Stipple
       lineStipple,

       -- * Line Antialiasing
      lineSmooth,

       -- * Implementation-Dependent Limits
       aliasedLineWidthRange, smoothLineWidthRange, smoothLineWidthGranularity
    ) where

    import Control.Monad ( liftM2 )
    import Graphics.Rendering.OpenGL.GL.Capability (
       EnableCap(CapLineSmooth,CapLineStipple), makeCapability, makeStateVarMaybe )
    import Graphics.Rendering.OpenGL.GL.BasicTypes (
       GLint, GLushort, GLfloat, Capability )
    import Graphics.Rendering.OpenGL.GL.QueryUtils (
       GetPName(GetLineWidth,GetAliasedLineWidthRange,GetSmoothLineWidthRange,
                GetSmoothLineWidthGranularity,GetLineStippleRepeat,
                GetLineStipplePattern),
       getInteger1, getFloat1, getFloat2 )
    import Graphics.Rendering.OpenGL.GL.StateVar (
       GettableStateVar, makeGettableStateVar, StateVar, makeStateVar )

    --------------------------------------------------------------------------------

    -- | 'lineWidth' contains the rasterized width of both aliased and antialiased
    -- lines. The initial value is 1. Using a line width other than 1 has different
    -- effects, depending on whether line antialiasing is enabled (see
    -- 'lineSmooth'). Line antialiasing is initially disabled.
    --
    -- If line antialiasing is disabled, the actual width is determined by rounding
    -- the supplied width to the nearest integer. (If the rounding results in the
    -- value 0, it is as if the line width were 1.) If /delta x/ >= /delta y/, /i/
    -- pixels are filled in each column that is rasterized, where /i/ is the
    -- rounded value of 'lineWidth'. Otherwise, /i/ pixels are filled in each row
    -- that is rasterized.
    --
    -- If antialiasing is enabled, line rasterization produces a fragment for each
    -- pixel square that intersects the region lying within the rectangle having
    -- width equal to the current line width, length equal to the actual length of
    -- the line, and centered on the mathematical line segment. The coverage value
    -- for each fragment is the window coordinate area of the intersection of the
    -- rectangular region with the corresponding pixel square. This value is saved
    -- and used in the final rasterization step.
    --
    -- Not all widths can be supported when line antialiasing is enabled. If an
    -- unsupported width is requested, the nearest supported width is used. Only
    -- width 1 is guaranteed to be supported; others depend on the implementation.
    --  Likewise, there is a range for aliased line widths as well. To query the
    -- range of supported widths of antialiased lines and the size difference
    -- between supported widths within the range, query 'smoothLineWidthRange' and
    -- 'smoothLineWidthGranularity', respectively. For aliased lines, query the
    -- supported range with 'aliasedLineWidthRange'.
    --
    -- The line width specified when 'lineWidth' is set is always returned when it
    -- is queried. Clamping and rounding for aliased and antialiased lines have no
    -- effect on the specified value.
    --
    -- A non-antialiased line width may be clamped to an implementation-dependent
    -- maximum.  Query 'aliasedLineWidthRange' to determine the maximum width.
    --
    -- An 'Graphics.Rendering.OpenGL.GLU.Errors.InvalidValue' is generated if
    -- 'lineWidth' is set to a value less than or equal to zero.
    --
    -- An 'Graphics.Rendering.OpenGL.GLU.Errors.InvalidOperation' is generated if
    -- 'lineWidth' is set during
    -- 'Graphics.Rendering.OpenGL.GL.BeginEnd.renderPrimitive'.

    lineWidth :: StateVar GLfloat
    lineWidth = makeStateVar (getFloat1 id GetLineWidth) glLineWidth

    foreign import CALLCONV unsafe "glLineWidth" glLineWidth :: GLfloat -> IO ()

    --------------------------------------------------------------------------------

    -- | Line stippling masks out certain fragments produced by rasterization; those
    -- fragments will not be drawn. The masking is achieved by using three
    -- parameters: the repeat count (1st element of the 'lineStipple' pair, clamped
    -- to the range [ 1 .. 256 ]), the 16-bit line stipple pattern (2nd element),
    -- and an integer stipple counter /s/.
    --
    -- The counter /s/ is reset to 0 at before the first action during
    -- 'Graphics.Rendering.OpenGL.GL.BeginEnd.renderPrimitive' is called and before
    -- each line segment during
    -- 'Graphics.Rendering.OpenGL.GL.BeginEnd.renderPrimitive' is generated. It is
    -- incremented after each fragment of a unit width aliased line segment is
    -- generated or after each /i/ fragments of an /i/ width line segment are
    -- generated. The /i/ fragments associated with count /s/ are masked out if
    -- @'Data.Bits.testBit' /pattern/ (( /s/ \/ /factor/ ) /mod/ 16)@ is 'False',
    -- otherwise these fragments are sent to the frame buffer. Bit zero of the
    -- pattern is the least significant bit, i.e. it is used first.
    --
    -- Antialiased lines are treated as a sequence of rectangles of height 1 for
    -- purposes of stippling. Whether rectangle /s/ is rasterized or not depends on
    -- the fragment rule described for aliased lines, counting rectangles rather
    -- than groups of fragments.
    --
    -- The initial value of 'lineStipple' is 'Nothing', i.e. line stippling is
    -- disabled.
    --
    -- An 'Graphics.Rendering.OpenGL.GLU.Errors.InvalidOperation' is generated if
    -- 'lineStipple' is set during
    -- 'Graphics.Rendering.OpenGL.GL.BeginEnd.renderPrimitive'.

    lineStipple :: StateVar (Maybe (GLint, GLushort))
    lineStipple =
       makeStateVarMaybe
          (return CapLineStipple)
          (liftM2 (,) (getInteger1 id GetLineStippleRepeat)
                      (getInteger1 fromIntegral GetLineStipplePattern))
          (uncurry glLineStipple)

    foreign import CALLCONV unsafe "glLineStipple" glLineStipple ::
       GLint -> GLushort -> IO ()

    --------------------------------------------------------------------------------

    -- | Controls whether line antialiasing is enabled. The initial state is
    -- 'Graphics.Rendering.OpenGL.GL.BasicTypes.Disabled'.

    lineSmooth :: StateVar Capability
    lineSmooth = makeCapability CapLineSmooth

    --------------------------------------------------------------------------------

    -- | The smallest and largest supported width of aliased lines.

    aliasedLineWidthRange :: GettableStateVar (GLfloat, GLfloat)
    aliasedLineWidthRange =
       makeGettableStateVar $ getFloat2 (,) GetAliasedLineWidthRange

    -- | The smallest and largest supported width of antialiased lines.

    smoothLineWidthRange :: GettableStateVar (GLfloat, GLfloat)
    smoothLineWidthRange =
       makeGettableStateVar $ getFloat2 (,) GetSmoothLineWidthRange

    -- | The antialiased line width granularity, i.e. the size difference between
    -- supported widths.

    smoothLineWidthGranularity :: GettableStateVar GLfloat
    smoothLineWidthGranularity =
       makeGettableStateVar $ getFloat1 id GetSmoothLineWidthGranularity