Portability | portable |
---|---|

Stability | stable |

Maintainer | sven.panne@aedion.de |

Safe Haskell | None |

This module corresponds to section 3.3 (Points) of the OpenGL 2.1 specs.

- pointSize :: StateVar GLfloat
- vertexProgramPointSize :: StateVar Capability
- pointSizeRange :: StateVar (GLfloat, GLfloat)
- pointDistanceAttenuation :: StateVar (GLfloat, GLfloat, GLfloat)
- pointFadeThresholdSize :: StateVar GLfloat
- pointSmooth :: StateVar Capability
- pointSprite :: StateVar Capability
- aliasedPointSizeRange :: GettableStateVar (GLfloat, GLfloat)
- smoothPointSizeRange :: GettableStateVar (GLfloat, GLfloat)
- smoothPointSizeGranularity :: GettableStateVar GLfloat

# Point Rasterization

pointSize :: StateVar GLfloatSource

`pointSize`

contains the rasterized diameter of both aliased and
antialiased points. The initial value is 1. Using a point size other than 1
has different effects, depending on whether point antialiasing is enabled
(see `pointSmooth`

) or point sprites are enabled (see `pointSprite`

). Both
are initially disabled.

The specified point size is multiplied with a distance attenuation factor
and clamped to the specified `pointSizeRange`

, and further clamped to the
implementation-dependent point size range to produce the derived point size
using

derivedSize=clamp(size*sqrt(1 / (a+b*d+c*d^2)))

where *d* is the eye-coordinate distance from the eye to the vertex, and *a*,
*b*, and *c* are the distance attenuation coefficients (see
`pointDistanceAttenuation`

).

If multisampling is disabled, the computed point size is used as the point's width.

If multisampling is enabled, the point may be faded by modifying the point
alpha value (see `sampleCoverage`

)
instead of allowing the point width to go below a given
`pointFadeThresholdSize`

. In this case, the width is further modified in
the following manner:

width= ifderivedSize>=thresholdthenderivedSizeelsethreshold

The point alpha value is modified by computing:

alpha= ifderivedSize>=thresholdthen 1 else (derivedSize/threshold)^2

If point antialiasing is disabled, the actual size is determined by rounding
the supplied size to the nearest integer. (If the rounding results in the
value 0, it is as if the point size were 1.) If the rounded size is odd,
then the center point (*x*, *y*) of the pixel fragment that represents
the point is computed as

(x,y) = (floorxw+ 0.5,flooryw+ 0.5)

where *xw* and *yw* indicate window coordinates. All pixels that lie within
the square grid of the rounded size centered at (*x*, *y*) make up the
fragment. If the size is even, the center point is

(x,y) = (floor(xw+ 0.5),floor(yw+ 0.5))

and the rasterized fragment's centers are the half-integer window
coordinates within the square of the rounded size centered at (*x*, *y*). All
pixel fragments produced in rasterizing a nonantialiased point are assigned
the same associated data, that of the vertex corresponding to the point.

If antialiasing is enabled, then point rasterization produces a fragment for
each pixel square that intersects the region lying within the circle having
diameter equal to the current point size and centered at the point's
(*xw*, *yw*). The coverage value for each fragment is the window coordinate
area of the intersection of the circular region with the corresponding pixel
square. This value is saved and used in the final rasterization step. The
data associated with each fragment is the data associated with the point
being rasterized.

Not all sizes are supported when point antialiasing is enabled. If an
unsupported size is requested, the nearest supported size is used. Only size
1 is guaranteed to be supported; others depend on the implementation. To
query the range of supported sizes for antialiased points and the size
difference between supported sizes within the range, query
`smoothPointSizeRange`

and `smoothPointSizeGranularity`

, respectively. For
aliased points, query the supported range with `aliasedPointSizeRange`

.

The point size specified when `pointSize`

is set is always returned when it
is queried. Clamping and rounding for aliased and antialiased points have no
effect on the specified value.

A non-antialiased point size may be clamped to an implementation-dependent maximum. Although this maximum cannot be queried, it must be no less than the maximum value for antialiased points, rounded to the nearest integer value.

An `InvalidValue`

is generated if
`pointSize`

is set to a value less than or equal to zero.

An `InvalidOperation`

is generated if
`pointSize`

is set during
`renderPrimitive`

.

# Controlling the Derived Size

pointSizeRange :: StateVar (GLfloat, GLfloat)Source

The range to which the derived point size is clamped, see `pointSize`

. Note
that the size is further clamped to the implementation-dependent limits, see
`aliasedPointSizeRange`

and `smoothPointSizeRange`

. The initial range is
(0, 1).

An `InvalidValue`

is generated if the
lower or upper bound of the range is set to a value less than zero. If the
lower bound is greater than the upper bound, the point size after clamping is
undefined, but no error is generated.

pointDistanceAttenuation :: StateVar (GLfloat, GLfloat, GLfloat)Source

The constant, linear, and quadratic distance attenuation coefficients, see
`pointSize`

. The initial coefficients are (1, 0, 0).

# Fading Points

pointFadeThresholdSize :: StateVar GLfloatSource

The threshold for alpha attenuation of points when multisampling is used,
see `pointSize`

. The initial threshold is 1.

An `InvalidValue`

is generated if the
threshold is set to a value less than zero.

# Point Antialiasing

pointSmooth :: StateVar CapabilitySource

Controls whether point antialiasing is enabled. The initial state is
`Disabled`

.

# Point Sprites

pointSprite :: StateVar CapabilitySource

Controls whether point sprites are enabled. The initial state is
`Disabled`

. When point sprites are
enabled, the state of point antialiasing (i.e. `pointSmooth`

) is ignored.

# Implementation-Dependent Limits

aliasedPointSizeRange :: GettableStateVar (GLfloat, GLfloat)Source

The smallest and largest supported size of aliased points.

smoothPointSizeRange :: GettableStateVar (GLfloat, GLfloat)Source

The smallest and largest supported size of antialiased points.

smoothPointSizeGranularity :: GettableStateVar GLfloatSource

The antialiased point size granularity, i.e. the size difference between supported sizes.