-------------------------------------------------------------------------------- -- | -- 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