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.\"     Title: gl_ClipDistance
.\"    Author: [FIXME: author] [see http://docbook.sf.net/el/author]
.\" Generator: DocBook XSL Stylesheets v1.79.1 <http://docbook.sf.net/>
.\"      Date: 01/03/2018
.\"    Manual: [FIXME: manual]
.\"    Source: [FIXME: source]
.\"  Language: English
.\"
.TH "GL_CLIPDISTANCE" "3G" "01/03/2018" "[FIXME: source]" "[FIXME: manual]"
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.SH "NAME"
gl_ClipDistance \- provides a forward\-compatible mechanism for vertex clipping
.SH "DECLARATION"
.PP
\fIgl_ClipDistance\fR
is a member of the
\fIgl_PerVertex\fR
named block:
.sp
.nf
    out gl_PerVertex {
        vec4 gl_Position;
        float gl_PointSize;
        float gl_ClipDistance[];
    };
.fi
.PP
In fragment shaders, it is intrinsically declared as:
in\ \&float\ \&gl_ClipDistance[]\ \&;
.SH "DESCRIPTION"
.PP
The
\fIgl_ClipDistance\fR
variable provides a forward compatible mechanism for controlling user clipping\&. The element
\fIgl_ClipDistance\fR[\fIi\fR] specifies a clip distance for each user clip plane
\fIi\fR\&. A distance of 0\&.0 means that the vertex is on the plane, a positive distance means that the vertex is insider the clip plane, and a negative distance means that the point is outside the clip plane\&. The clip distances will be linearly interpolated across the primitive and the portion of the primitive with interpolated distances less than 0\&.0 will be clipped\&.
.PP
The
\fIgl_ClipDistance\fR
array is initially predeclared as unsized and must be sized by the shader either by redeclaring it with an explicit size, or by indexing it with only integral constant expressions\&. The array must be sized to include all clip planes that are enabled via the OpenGL API; if the size does not include all enabled planes, results are undefined\&. The size may be at most
\fIgl_MaxClipDistances\fR\&. The number of varying components consumed by
\fIgl_ClipDistance\fR
will match the size of the array, no matter how many planes are enabled\&. The shader must also set all values in
\fIgl_ClipDistance\fR
that have been enabled via the OpenGL API, or results are undefined\&. Values written into
\fIgl_ClipDistance\fR
planes that are not enabled have no effect\&.
.PP
In the vertex, tessellation evaluation and geometry languages, a single global instance of the
\fIgl_PerVertex\fR
named block is available and its
\fIgl_ClipDistance\fR
member is an output that receives the clip distances for the current vertex\&. It may be written at any time during shader execution\&. The value written to
\fIgl_ClipDistance\fR
will be used by primitive assembly, clipping, culling and other fixed functionality operations, if present, that operate on primitives after vertex processing has occurred\&.
.PP
In the tessellation control language, the
\fIgl_PerVertex\fR
named block is used to construct an array,
\fIgl_out[]\fR, whose
\fIgl_ClipDistance\fR
members hold clip distances for each of the control points, which become available as inputs to the subsequent tessellation evaluation shader\&.
.PP
The value of
\fIgl_ClipDistance\fR
(or the
\fIgl_ClipDistance\fR
member of the
\fIgl_out[]\fR
array, in the case of the tessellation control shader) is undefined after the vertex, tessellation control, and tessellation evaluation shading stages if the corresponding shader executable does not write to gl_ClipDistance\&. It is also undefined after the geometry processing stage if the geometry shader executable calls
\fBEmitVertex\fR()
without having written
\fIgl_ClipDistance\fR
since the last call to
\fBEmitVertex\fR()
(or hasn\*(Aqt written it at all)\&.
.PP
In the tessellation control, tessellation evaluation and geoemetry languages, the
\fIgl_PerVertex\fR
named block is used to construct an array,
\fIgl_in[]\fR
of per\-vertex or per\-control point inputs whose content represents the corresponding outputs written by the previous stage\&. Only elements of the
\fIgl_ClipDistance\fR
array that correspond to enabled clip planes have defined values\&.
.SH "VERSION SUPPORT"
.TS
allbox tab(:);
lB cB s s s s s s s s s s s
lB cB cB cB cB cB cB cB cB cB cB cB cB.
T{

T}:T{
\fBOpenGL Shading Language Version\fR
T}
T{
\fBVariable Name\fR
T}:T{
\fB1\&.10\fR
T}:T{
\fB1\&.20\fR
T}:T{
\fB1\&.30\fR
T}:T{
\fB1\&.40\fR
T}:T{
\fB1\&.50\fR
T}:T{
\fB3\&.30\fR
T}:T{
\fB4\&.00\fR
T}:T{
\fB4\&.10\fR
T}:T{
\fB4\&.20\fR
T}:T{
\fB4\&.30\fR
T}:T{
\fB4\&.40\fR
T}:T{
\fB4\&.50\fR
T}
.T&
l c c c c c c c c c c c c.
T{
gl_ClipDistance
T}:T{
\-
T}:T{
\-
T}:T{
✔
T}:T{
✔
T}:T{
✔
T}:T{
✔
T}:T{
✔
T}:T{
✔
T}:T{
✔
T}:T{
✔
T}:T{
✔
T}:T{
✔
T}
.TE
.sp 1
.PP
Versions 1\&.30 to 1\&.40 \- vertex shader only\&.
.PP
Versions 1\&.50 to 3\&.30 \- vertex and geometry shaders only\&.
.SH "SEE ALSO"
.PP
\fBgl_CullDistance\fR(),
\fBgl_PointSize\fR()
.SH "COPYRIGHT"
.PP
Copyright
\(co
2011\-2014 Khronos Group\&. This material may be distributed subject to the terms and conditions set forth in the Open Publication License, v 1\&.0, 8 June 1999\&.
\m[blue]\fBhttp://opencontent\&.org/openpub/\fR\m[]\&.
.SH "COPYRIGHT"
.br
Copyright \(co 2011-2014 Khronos Group
.br