'\" t
.\"     Title: dFdx, dFdy
.\"    Author: [FIXME: author] [see http://docbook.sf.net/el/author]
.\" Generator: DocBook XSL Stylesheets v1.78.1 <http://docbook.sf.net/>
.\"      Date: 05/21/2015
.\"    Manual: [FIXME: manual]
.\"    Source: [FIXME: source]
.\"  Language: English
.\"
.TH "DFDX, DFDY" "3G" "05/21/2015" "[FIXME: source]" "[FIXME: manual]"
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.SH "NAME"
dFdx,_dFdy \- return the partial derivative of an argument with respect to x or y
.SH "DECLARATION"
.HP \w'genType\ dFdx('u
.BI "genType dFdx(genType\ " "p" ");"
.HP \w'genType\ dFdy('u
.BI "genType dFdy(genType\ " "p" ");"
.HP \w'genType\ dFdxCoarse('u
.BI "genType dFdxCoarse(genType\ " "p" ");"
.HP \w'genType\ dFdyCoarse('u
.BI "genType dFdyCoarse(genType\ " "p" ");"
.HP \w'genType\ dFdxFine('u
.BI "genType dFdxFine(genType\ " "p" ");"
.HP \w'genType\ dFdyFine('u
.BI "genType dFdyFine(genType\ " "p" ");"
.SH "PARAMETERS"
.PP
\fIp\fR
.RS 4
Specifies the expression of which to take the partial derivative\&.
.RE
.SH "DESCRIPTION"
.PP
\fIAvailable only in the fragment shader\fR, these functions return the partial derivative of expression
\fIp\fR
with respect to the window $x$ coordinate (for
\fBdFdx*\fR) and $y$ coordinate (for
\fBdFdy*\fR)\&.
.PP
\fBdFdxFine\fR
and
\fBdFdyFine\fR
calculate derivatives using local differencing based on on the value of
\fIp\fR
for the current fragment and its immediate neighbor(s)\&.
.PP
\fBdFdxCoarse\fR
and
\fBdFdyCoarse\fR
calculate derivatives using local differencing based on the value of
\fIp\fR
for the current fragment\*(Aqs neighbors, and will possibly, but not necessarily, include the value for the current fragment\&. That is, over a given area, the implementation can compute derivatives in fewer unique locations than would be allowed for the corresponding
\fBdFdxFine\fR
and
\fBdFdyFine\fR
functions\&.
.PP
\fBdFdx\fR
returns either
\fBdFdxCoarse\fR
or
\fBdFdxFine\fR\&.
\fBdFdy\fR
returns either
\fBdFdyCoarse\fR
or
\fBdFdyFine\fR\&. The implementation may choose which calculation to perform based upon factors such as performance or the value of the API
\fBGL_FRAGMENT_SHADER_DERIVATIVE_HINT\fR
hint\&.
.PP
Expressions that imply higher order derivatives such as
dFdx(dFdx(n))
have undefined results, as do mixed\-order derivatives such as
dFdx(dFdy(n))\&. It is assumed that the expression
\fIp\fR
is continuous and therefore, expressions evaluated via non\-uniform control flow may be undefined\&.
.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{
\fBFunction Name\fR
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\fB1\&.10\fR
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\fB1\&.20\fR
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\fB1\&.30\fR
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\fB1\&.40\fR
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\fB1\&.50\fR
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\fB3\&.30\fR
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\fB4\&.00\fR
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\fB4\&.10\fR
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\fB4\&.20\fR
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\fB4\&.30\fR
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\fB4\&.40\fR
T}:T{
\fB4\&.50\fR
T}
.T&
l c c c c c c c c c c c c
l c c c c c c c c c c c c
l c c c c c c c c c c c c.
T{
dFdx
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dFdy
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T{
dFdxCoarse, dFdxFine, dFdyCoarse, dFdyFine
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\-
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.TE
.sp
.SH "SEE ALSO"
.PP
\fBfwidth\fR(),
\fBglHint\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