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860 lines
43 KiB
XML
860 lines
43 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
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"http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">
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<refentry id="glReadPixels">
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<refmeta>
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<refmetainfo>
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<copyright>
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<year>1991-2006</year>
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<holder>Silicon Graphics, Inc.</holder>
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</copyright>
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</refmetainfo>
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<refentrytitle>glReadPixels</refentrytitle>
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<manvolnum>3G</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>glReadPixels</refname>
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<refpurpose>read a block of pixels from the frame buffer</refpurpose>
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</refnamediv>
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<refsynopsisdiv><title>C Specification</title>
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<funcsynopsis>
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<funcprototype>
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<funcdef>void <function>glReadPixels</function></funcdef>
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<paramdef>GLint <parameter>x</parameter></paramdef>
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<paramdef>GLint <parameter>y</parameter></paramdef>
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<paramdef>GLsizei <parameter>width</parameter></paramdef>
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<paramdef>GLsizei <parameter>height</parameter></paramdef>
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<paramdef>GLenum <parameter>format</parameter></paramdef>
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<paramdef>GLenum <parameter>type</parameter></paramdef>
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<paramdef>GLvoid * <parameter>data</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<!-- eqn: ignoring delim $$ -->
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<refsect1 id="parameters"><title>Parameters</title>
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<variablelist>
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<varlistentry>
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<term><parameter>x</parameter></term>
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<term><parameter>y</parameter></term>
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<listitem>
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<para>
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Specify the window coordinates of the first pixel
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that is read from the frame buffer.
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This location is the lower left corner of a rectangular block of pixels.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>width</parameter></term>
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<term><parameter>height</parameter></term>
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<listitem>
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<para>
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Specify the dimensions of the pixel rectangle.
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<parameter>width</parameter> and <parameter>height</parameter> of one correspond to a single pixel.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>format</parameter></term>
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<listitem>
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<para>
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Specifies the format of the pixel data.
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The following symbolic values are accepted:
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<constant>GL_COLOR_INDEX</constant>,
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<constant>GL_STENCIL_INDEX</constant>,
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<constant>GL_DEPTH_COMPONENT</constant>,
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<constant>GL_RED</constant>,
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<constant>GL_GREEN</constant>,
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<constant>GL_BLUE</constant>,
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<constant>GL_ALPHA</constant>,
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<constant>GL_RGB</constant>,
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<constant>GL_BGR</constant>,
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<constant>GL_RGBA</constant>,
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<constant>GL_BGRA</constant>,
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<constant>GL_LUMINANCE</constant>, and
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<constant>GL_LUMINANCE_ALPHA</constant>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>type</parameter></term>
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<listitem>
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<para>
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Specifies the data type of the pixel data.
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Must be one of
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<constant>GL_UNSIGNED_BYTE</constant>,
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<constant>GL_BYTE</constant>,
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<constant>GL_BITMAP</constant>,
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<constant>GL_UNSIGNED_SHORT</constant>,
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<constant>GL_SHORT</constant>,
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<constant>GL_UNSIGNED_INT</constant>,
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<constant>GL_INT</constant>,
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<constant>GL_FLOAT</constant>,
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<constant>GL_UNSIGNED_BYTE_3_3_2</constant>,
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<constant>GL_UNSIGNED_BYTE_2_3_3_REV</constant>,
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<constant>GL_UNSIGNED_SHORT_5_6_5</constant>,
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<constant>GL_UNSIGNED_SHORT_5_6_5_REV</constant>,
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<constant>GL_UNSIGNED_SHORT_4_4_4_4</constant>,
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<constant>GL_UNSIGNED_SHORT_4_4_4_4_REV</constant>,
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<constant>GL_UNSIGNED_SHORT_5_5_5_1</constant>,
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<constant>GL_UNSIGNED_SHORT_1_5_5_5_REV</constant>,
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<constant>GL_UNSIGNED_INT_8_8_8_8</constant>,
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<constant>GL_UNSIGNED_INT_8_8_8_8_REV</constant>,
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<constant>GL_UNSIGNED_INT_10_10_10_2</constant>, or
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<constant>GL_UNSIGNED_INT_2_10_10_10_REV</constant>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>data</parameter></term>
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<listitem>
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<para>
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Returns the pixel data.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1 id="description"><title>Description</title>
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<para>
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<function>glReadPixels</function> returns pixel data from the frame buffer,
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starting with the pixel whose lower left corner
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is at location (<parameter>x</parameter>, <parameter>y</parameter>),
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into client memory starting at location <parameter>data</parameter>.
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Several parameters control the processing of the pixel data before
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it is placed into client memory.
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These parameters are set with three commands:
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<citerefentry><refentrytitle>glPixelStore</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glPixelTransfer</refentrytitle></citerefentry>, and
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<citerefentry><refentrytitle>glPixelMap</refentrytitle></citerefentry>.
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This reference page describes the effects on <function>glReadPixels</function> of most,
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but not all of the parameters specified by these three commands.
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</para>
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<para>
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If a non-zero named buffer object is bound to the <constant>GL_PIXEL_PACK_BUFFER</constant> target
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(see <citerefentry><refentrytitle>glBindBuffer</refentrytitle></citerefentry>) while a block of pixels is
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requested, <parameter>data</parameter> is treated as a byte offset into the buffer object's data store
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rather than a pointer to client memory.
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</para>
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<para>
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When the <code>ARB_imaging</code> extension is supported, the pixel data may
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be processed by additional operations including color table lookup,
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color matrix transformations, convolutions, histograms, and minimum and
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maximum pixel value computations.
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</para>
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<para>
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<function>glReadPixels</function> returns values from each pixel with lower left corner at
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<inlineequation><mml:math>
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<!-- eqn: (x + i, y + j):-->
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<mml:mfenced open="(" close=")">
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<mml:mrow>
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<mml:mi mathvariant="italic">x</mml:mi>
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<mml:mo>+</mml:mo>
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<mml:mi mathvariant="italic">i</mml:mi>
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</mml:mrow>
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<mml:mrow>
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<mml:mi mathvariant="italic">y</mml:mi>
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<mml:mo>+</mml:mo>
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<mml:mi mathvariant="italic">j</mml:mi>
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</mml:mrow>
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</mml:mfenced>
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</mml:math></inlineequation>
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for
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<inlineequation><mml:math>
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<!-- eqn: 0 <= i < width:-->
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<mml:mrow>
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<mml:mn>0</mml:mn>
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<mml:mo><=</mml:mo>
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<mml:mi mathvariant="italic">i</mml:mi>
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<mml:mo><</mml:mo>
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<mml:mi mathvariant="italic">width</mml:mi>
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</mml:mrow>
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</mml:math></inlineequation>
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and
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<inlineequation><mml:math>
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<!-- eqn: 0 <= j < height:-->
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<mml:mrow>
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<mml:mn>0</mml:mn>
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<mml:mo><=</mml:mo>
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<mml:mi mathvariant="italic">j</mml:mi>
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<mml:mo><</mml:mo>
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<mml:mi mathvariant="italic">height</mml:mi>
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</mml:mrow>
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</mml:math></inlineequation>.
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This pixel is said to be the
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<inlineequation><mml:math><mml:mi mathvariant="italic">i</mml:mi></mml:math></inlineequation>th
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pixel in the
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<inlineequation><mml:math><mml:mi mathvariant="italic">j</mml:mi></mml:math></inlineequation>th
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row.
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Pixels are returned in row order from the lowest to the highest row,
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left to right in each row.
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</para>
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<para>
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<parameter>format</parameter> specifies the format for the returned pixel values;
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accepted values are:
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</para>
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<variablelist>
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<varlistentry>
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<term><constant>GL_COLOR_INDEX</constant></term>
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<listitem>
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<para>
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Color indices are read from the color buffer
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selected by <citerefentry><refentrytitle>glReadBuffer</refentrytitle></citerefentry>.
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Each index is converted to fixed point,
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shifted left or right depending on the value and sign of <constant>GL_INDEX_SHIFT</constant>,
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and added to <constant>GL_INDEX_OFFSET</constant>.
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If <constant>GL_MAP_COLOR</constant> is <constant>GL_TRUE</constant>,
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indices are replaced by their mappings in the table <constant>GL_PIXEL_MAP_I_TO_I</constant>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_STENCIL_INDEX</constant></term>
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<listitem>
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<para>
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Stencil values are read from the stencil buffer.
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Each index is converted to fixed point,
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shifted left or right depending on the value and sign of <constant>GL_INDEX_SHIFT</constant>,
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and added to <constant>GL_INDEX_OFFSET</constant>.
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If <constant>GL_MAP_STENCIL</constant> is <constant>GL_TRUE</constant>,
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indices are replaced by their mappings in the table <constant>GL_PIXEL_MAP_S_TO_S</constant>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_DEPTH_COMPONENT</constant></term>
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<listitem>
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<para>
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Depth values are read from the depth buffer.
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Each component is converted to floating point such that the minimum depth
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value maps to 0 and the maximum value maps to 1.
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Each component is then multiplied by <constant>GL_DEPTH_SCALE</constant>,
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added to <constant>GL_DEPTH_BIAS</constant>,
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and finally clamped to the range
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<inlineequation><mml:math>
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<!-- eqn: [0,1]:-->
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<mml:mfenced open="[" close="]">
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<mml:mn>0</mml:mn>
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<mml:mn>1</mml:mn>
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</mml:mfenced>
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</mml:math></inlineequation>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_RED</constant></term>
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<listitem>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_GREEN</constant></term>
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<listitem>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_BLUE</constant></term>
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<listitem>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_ALPHA</constant></term>
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<listitem>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_RGB</constant></term>
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<listitem>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_BGR</constant></term>
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<listitem>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_RGBA</constant></term>
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<listitem>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_BGRA</constant></term>
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<listitem>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_LUMINANCE</constant></term>
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<listitem>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_LUMINANCE_ALPHA</constant></term>
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<listitem>
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<para>
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Processing differs depending on whether color buffers store color indices
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or RGBA color components.
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If color indices are stored,
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they are read from the color buffer selected by <citerefentry><refentrytitle>glReadBuffer</refentrytitle></citerefentry>.
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Each index is converted to fixed point,
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shifted left or right depending on the value and sign of <constant>GL_INDEX_SHIFT</constant>,
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and added to <constant>GL_INDEX_OFFSET</constant>.
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Indices are then replaced by the red,
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green,
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blue,
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and alpha values obtained by indexing the tables
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<constant>GL_PIXEL_MAP_I_TO_R</constant>,
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<constant>GL_PIXEL_MAP_I_TO_G</constant>,
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<constant>GL_PIXEL_MAP_I_TO_B</constant>, and
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<constant>GL_PIXEL_MAP_I_TO_A</constant>.
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Each table must be of size
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<inlineequation><mml:math>
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<!-- eqn: 2 sup n:-->
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<mml:msup><mml:mn>2</mml:mn>
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<mml:mi mathvariant="italic">n</mml:mi>
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</mml:msup>
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</mml:math></inlineequation>,
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but
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<inlineequation><mml:math><mml:mi mathvariant="italic">n</mml:mi></mml:math></inlineequation>
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may be different for
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different tables.
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Before an index is used to look up a value in a table of
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size
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<inlineequation><mml:math>
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<!-- eqn: 2 sup n:-->
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<mml:msup><mml:mn>2</mml:mn>
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<mml:mi mathvariant="italic">n</mml:mi>
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</mml:msup>
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</mml:math></inlineequation>,
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it must be masked against
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<inlineequation><mml:math>
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<!-- eqn: 2 sup n - 1:-->
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<mml:mrow>
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<mml:msup><mml:mn>2</mml:mn>
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<mml:mi mathvariant="italic">n</mml:mi>
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</mml:msup>
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<mml:mo>-</mml:mo>
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<mml:mn>1</mml:mn>
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</mml:mrow>
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</mml:math></inlineequation>.
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</para>
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<para>
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If RGBA color components are stored in the color buffers,
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they are read from the color buffer selected by <citerefentry><refentrytitle>glReadBuffer</refentrytitle></citerefentry>.
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Each color component is converted to floating point such that zero intensity
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maps to 0.0 and full intensity maps to 1.0.
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Each component is then multiplied by <constant>GL_c_SCALE</constant> and
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added to <constant>GL_c_BIAS</constant>,
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where <emphasis>c</emphasis> is RED, GREEN, BLUE, or ALPHA.
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Finally,
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if <constant>GL_MAP_COLOR</constant> is <constant>GL_TRUE</constant>,
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each component is clamped to the range
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<inlineequation><mml:math>
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<!-- eqn: [0,1]:-->
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<mml:mfenced open="[" close="]">
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<mml:mn>0</mml:mn>
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<mml:mn>1</mml:mn>
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</mml:mfenced>
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</mml:math></inlineequation>,
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scaled to the size of its corresponding table, and is then
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replaced by its mapping in the table
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<constant>GL_PIXEL_MAP_c_TO_c</constant>,
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where <emphasis>c</emphasis> is R, G, B, or A.
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</para>
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<para>
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Unneeded data is then discarded.
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For example,
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<constant>GL_RED</constant> discards the green, blue, and alpha components,
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while <constant>GL_RGB</constant> discards only the alpha component.
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<constant>GL_LUMINANCE</constant> computes a single-component value as the sum of
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the red,
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green,
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and blue components,
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and <constant>GL_LUMINANCE_ALPHA</constant> does the same,
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while keeping alpha as a second value.
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The final values are clamped to the range
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<inlineequation><mml:math>
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<!-- eqn: [0,1]:-->
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<mml:mfenced open="[" close="]">
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<mml:mn>0</mml:mn>
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<mml:mn>1</mml:mn>
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</mml:mfenced>
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</mml:math></inlineequation>.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>
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The shift,
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scale,
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bias,
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and lookup factors just described are all specified by
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<citerefentry><refentrytitle>glPixelTransfer</refentrytitle></citerefentry>.
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The lookup table contents themselves are specified by <citerefentry><refentrytitle>glPixelMap</refentrytitle></citerefentry>.
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</para>
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<para>
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Finally, the indices or components
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are converted to the proper format,
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as specified by <parameter>type</parameter>.
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If <parameter>format</parameter> is <constant>GL_COLOR_INDEX</constant> or <constant>GL_STENCIL_INDEX</constant>
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and <parameter>type</parameter> is not <constant>GL_FLOAT</constant>,
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each index is masked with the mask value given in the following table.
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If <parameter>type</parameter> is <constant>GL_FLOAT</constant>, then each integer index is converted to
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single-precision floating-point format.
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</para>
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<para>
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If <parameter>format</parameter> is
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<constant>GL_RED</constant>,
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<constant>GL_GREEN</constant>,
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<constant>GL_BLUE</constant>,
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<constant>GL_ALPHA</constant>,
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<constant>GL_RGB</constant>,
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<constant>GL_BGR</constant>,
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<constant>GL_RGBA</constant>,
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<constant>GL_BGRA</constant>,
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<constant>GL_LUMINANCE</constant>, or
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<constant>GL_LUMINANCE_ALPHA</constant> and <parameter>type</parameter> is not <constant>GL_FLOAT</constant>,
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each component is multiplied by the multiplier shown in the following table.
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If type is <constant>GL_FLOAT</constant>, then each component is passed as is
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(or converted to the client's single-precision floating-point format if
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it is different from the one used by the GL).
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</para>
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<para>
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</para>
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<informaltable frame="topbot">
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|
<tgroup cols="3" align="left">
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<colspec/>
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<colspec align="center"/>
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<colspec align="center"/>
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|
<thead>
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|
<row>
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|
<entry rowsep="1" align="left">
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<parameter>type</parameter>
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</entry>
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|
<entry rowsep="1" align="center"><emphasis role="bold">
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Index Mask
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</emphasis></entry>
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<entry rowsep="1" align="center"><emphasis role="bold">
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Component Conversion
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</emphasis></entry>
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</row>
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</thead>
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<tbody>
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<row>
|
|
<entry align="left">
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|
<constant>GL_UNSIGNED_BYTE</constant>
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|
</entry>
|
|
<entry align="center">
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|
<inlineequation><mml:math>
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|
<!-- eqn: 2 sup 8 - 1:-->
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|
<mml:mrow>
|
|
<mml:msup><mml:mn>2</mml:mn>
|
|
<mml:mn>8</mml:mn>
|
|
</mml:msup>
|
|
<mml:mo>-</mml:mo>
|
|
<mml:mn>1</mml:mn>
|
|
</mml:mrow>
|
|
</mml:math></inlineequation>
|
|
</entry>
|
|
<entry align="center">
|
|
<inlineequation><mml:math>
|
|
<!-- eqn: (2 sup 8 - 1) c:-->
|
|
<mml:mrow>
|
|
<mml:mfenced open="(" close=")">
|
|
<mml:mrow>
|
|
<mml:msup><mml:mn>2</mml:mn>
|
|
<mml:mn>8</mml:mn>
|
|
</mml:msup>
|
|
<mml:mo>-</mml:mo>
|
|
<mml:mn>1</mml:mn>
|
|
</mml:mrow>
|
|
</mml:mfenced>
|
|
<mml:mo>⁢</mml:mo>
|
|
<mml:mi mathvariant="italic">c</mml:mi>
|
|
</mml:mrow>
|
|
</mml:math></inlineequation>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry align="left">
|
|
<constant>GL_BYTE</constant>
|
|
</entry>
|
|
<entry align="center">
|
|
<inlineequation><mml:math>
|
|
<!-- eqn: 2 sup 7 - 1:-->
|
|
<mml:mrow>
|
|
<mml:msup><mml:mn>2</mml:mn>
|
|
<mml:mn>7</mml:mn>
|
|
</mml:msup>
|
|
<mml:mo>-</mml:mo>
|
|
<mml:mn>1</mml:mn>
|
|
</mml:mrow>
|
|
</mml:math></inlineequation>
|
|
</entry>
|
|
<entry align="center">
|
|
<inlineequation><mml:math>
|
|
<!-- eqn: {(2 sup 8 - 1) c - 1} / 2:-->
|
|
<mml:mfrac>
|
|
<mml:mfenced open="" close="">
|
|
<mml:mrow>
|
|
<mml:mfenced open="(" close=")">
|
|
<mml:mrow>
|
|
<mml:msup><mml:mn>2</mml:mn>
|
|
<mml:mn>8</mml:mn>
|
|
</mml:msup>
|
|
<mml:mo>-</mml:mo>
|
|
<mml:mn>1</mml:mn>
|
|
</mml:mrow>
|
|
</mml:mfenced>
|
|
<mml:mo>⁢</mml:mo>
|
|
<mml:mi mathvariant="italic">c</mml:mi>
|
|
<mml:mo>-</mml:mo>
|
|
<mml:mn>1</mml:mn>
|
|
</mml:mrow>
|
|
</mml:mfenced>
|
|
<mml:mn>2</mml:mn>
|
|
</mml:mfrac>
|
|
</mml:math></inlineequation>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry align="left">
|
|
<constant>GL_BITMAP</constant>
|
|
</entry>
|
|
<entry align="center">
|
|
<inlineequation><mml:math>
|
|
<!-- eqn: 1:-->
|
|
<mml:mn>1</mml:mn>
|
|
</mml:math></inlineequation>
|
|
</entry>
|
|
<entry align="center">
|
|
<inlineequation><mml:math>
|
|
<!-- eqn: 1:-->
|
|
<mml:mn>1</mml:mn>
|
|
</mml:math></inlineequation>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry align="left">
|
|
<constant>GL_UNSIGNED_SHORT</constant>
|
|
</entry>
|
|
<entry align="center">
|
|
<inlineequation><mml:math>
|
|
<!-- eqn: 2 sup 16 - 1:-->
|
|
<mml:mrow>
|
|
<mml:msup><mml:mn>2</mml:mn>
|
|
<mml:mn>16</mml:mn>
|
|
</mml:msup>
|
|
<mml:mo>-</mml:mo>
|
|
<mml:mn>1</mml:mn>
|
|
</mml:mrow>
|
|
</mml:math></inlineequation>
|
|
</entry>
|
|
<entry align="center">
|
|
<inlineequation><mml:math>
|
|
<!-- eqn: (2 sup 16 - 1) c:-->
|
|
<mml:mrow>
|
|
<mml:mfenced open="(" close=")">
|
|
<mml:mrow>
|
|
<mml:msup><mml:mn>2</mml:mn>
|
|
<mml:mn>16</mml:mn>
|
|
</mml:msup>
|
|
<mml:mo>-</mml:mo>
|
|
<mml:mn>1</mml:mn>
|
|
</mml:mrow>
|
|
</mml:mfenced>
|
|
<mml:mo>⁢</mml:mo>
|
|
<mml:mi mathvariant="italic">c</mml:mi>
|
|
</mml:mrow>
|
|
</mml:math></inlineequation>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry align="left">
|
|
<constant>GL_SHORT</constant>
|
|
</entry>
|
|
<entry align="center">
|
|
<inlineequation><mml:math>
|
|
<!-- eqn: 2 sup 15 - 1:-->
|
|
<mml:mrow>
|
|
<mml:msup><mml:mn>2</mml:mn>
|
|
<mml:mn>15</mml:mn>
|
|
</mml:msup>
|
|
<mml:mo>-</mml:mo>
|
|
<mml:mn>1</mml:mn>
|
|
</mml:mrow>
|
|
</mml:math></inlineequation>
|
|
</entry>
|
|
<entry align="center">
|
|
<inlineequation><mml:math>
|
|
<!-- eqn: {(2 sup 16 - 1) c - 1} / 2:-->
|
|
<mml:mfrac>
|
|
<mml:mfenced open="" close="">
|
|
<mml:mrow>
|
|
<mml:mfenced open="(" close=")">
|
|
<mml:mrow>
|
|
<mml:msup><mml:mn>2</mml:mn>
|
|
<mml:mn>16</mml:mn>
|
|
</mml:msup>
|
|
<mml:mo>-</mml:mo>
|
|
<mml:mn>1</mml:mn>
|
|
</mml:mrow>
|
|
</mml:mfenced>
|
|
<mml:mo>⁢</mml:mo>
|
|
<mml:mi mathvariant="italic">c</mml:mi>
|
|
<mml:mo>-</mml:mo>
|
|
<mml:mn>1</mml:mn>
|
|
</mml:mrow>
|
|
</mml:mfenced>
|
|
<mml:mn>2</mml:mn>
|
|
</mml:mfrac>
|
|
</mml:math></inlineequation>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry align="left">
|
|
<constant>GL_UNSIGNED_INT</constant>
|
|
</entry>
|
|
<entry align="center">
|
|
<inlineequation><mml:math>
|
|
<!-- eqn: 2 sup 32 - 1:-->
|
|
<mml:mrow>
|
|
<mml:msup><mml:mn>2</mml:mn>
|
|
<mml:mn>32</mml:mn>
|
|
</mml:msup>
|
|
<mml:mo>-</mml:mo>
|
|
<mml:mn>1</mml:mn>
|
|
</mml:mrow>
|
|
</mml:math></inlineequation>
|
|
</entry>
|
|
<entry align="center">
|
|
<inlineequation><mml:math>
|
|
<!-- eqn: (2 sup 32 - 1) c:-->
|
|
<mml:mrow>
|
|
<mml:mfenced open="(" close=")">
|
|
<mml:mrow>
|
|
<mml:msup><mml:mn>2</mml:mn>
|
|
<mml:mn>32</mml:mn>
|
|
</mml:msup>
|
|
<mml:mo>-</mml:mo>
|
|
<mml:mn>1</mml:mn>
|
|
</mml:mrow>
|
|
</mml:mfenced>
|
|
<mml:mo>⁢</mml:mo>
|
|
<mml:mi mathvariant="italic">c</mml:mi>
|
|
</mml:mrow>
|
|
</mml:math></inlineequation>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry align="left">
|
|
<constant>GL_INT</constant>
|
|
</entry>
|
|
<entry align="center">
|
|
<inlineequation><mml:math>
|
|
<!-- eqn: 2 sup 31 - 1:-->
|
|
<mml:mrow>
|
|
<mml:msup><mml:mn>2</mml:mn>
|
|
<mml:mn>31</mml:mn>
|
|
</mml:msup>
|
|
<mml:mo>-</mml:mo>
|
|
<mml:mn>1</mml:mn>
|
|
</mml:mrow>
|
|
</mml:math></inlineequation>
|
|
</entry>
|
|
<entry align="center">
|
|
<inlineequation><mml:math>
|
|
<!-- eqn: {(2 sup 32 - 1) c - 1} / 2:-->
|
|
<mml:mfrac>
|
|
<mml:mfenced open="" close="">
|
|
<mml:mrow>
|
|
<mml:mfenced open="(" close=")">
|
|
<mml:mrow>
|
|
<mml:msup><mml:mn>2</mml:mn>
|
|
<mml:mn>32</mml:mn>
|
|
</mml:msup>
|
|
<mml:mo>-</mml:mo>
|
|
<mml:mn>1</mml:mn>
|
|
</mml:mrow>
|
|
</mml:mfenced>
|
|
<mml:mo>⁢</mml:mo>
|
|
<mml:mi mathvariant="italic">c</mml:mi>
|
|
<mml:mo>-</mml:mo>
|
|
<mml:mn>1</mml:mn>
|
|
</mml:mrow>
|
|
</mml:mfenced>
|
|
<mml:mn>2</mml:mn>
|
|
</mml:mfrac>
|
|
</mml:math></inlineequation>
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry align="left">
|
|
<constant>GL_FLOAT</constant>
|
|
</entry>
|
|
<entry align="center">
|
|
none
|
|
</entry>
|
|
<entry align="center">
|
|
<inlineequation><mml:math><mml:mi mathvariant="italic">c</mml:mi></mml:math></inlineequation>
|
|
</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</informaltable>
|
|
<para>
|
|
Return values are placed in memory as follows.
|
|
If <parameter>format</parameter> is
|
|
<constant>GL_COLOR_INDEX</constant>,
|
|
<constant>GL_STENCIL_INDEX</constant>,
|
|
<constant>GL_DEPTH_COMPONENT</constant>,
|
|
<constant>GL_RED</constant>,
|
|
<constant>GL_GREEN</constant>,
|
|
<constant>GL_BLUE</constant>,
|
|
<constant>GL_ALPHA</constant>, or
|
|
<constant>GL_LUMINANCE</constant>,
|
|
a single value is returned and the data for the
|
|
<inlineequation><mml:math><mml:mi mathvariant="italic">i</mml:mi></mml:math></inlineequation>th
|
|
pixel in the
|
|
<inlineequation><mml:math><mml:mi mathvariant="italic">j</mml:mi></mml:math></inlineequation>th
|
|
row
|
|
is placed in location
|
|
<inlineequation><mml:math>
|
|
<!-- eqn: (j) width + i:-->
|
|
<mml:mrow>
|
|
<mml:mfenced open="(" close=")">
|
|
<mml:mi mathvariant="italic">j</mml:mi>
|
|
</mml:mfenced>
|
|
<mml:mo>⁢</mml:mo>
|
|
<mml:mi mathvariant="italic">width</mml:mi>
|
|
<mml:mo>+</mml:mo>
|
|
<mml:mi mathvariant="italic">i</mml:mi>
|
|
</mml:mrow>
|
|
</mml:math></inlineequation>.
|
|
<constant>GL_RGB</constant> and <constant>GL_BGR</constant> return three values,
|
|
<constant>GL_RGBA</constant> and <constant>GL_BGRA</constant> return four values,
|
|
and <constant>GL_LUMINANCE_ALPHA</constant> returns two values for each pixel,
|
|
with all values corresponding to a single pixel occupying contiguous space
|
|
in <parameter>data</parameter>.
|
|
Storage parameters set by <citerefentry><refentrytitle>glPixelStore</refentrytitle></citerefentry>,
|
|
such as <constant>GL_PACK_LSB_FIRST</constant> and <constant>GL_PACK_SWAP_BYTES</constant>,
|
|
affect the way that data is written into memory.
|
|
See <citerefentry><refentrytitle>glPixelStore</refentrytitle></citerefentry> for a description.
|
|
</para>
|
|
</refsect1>
|
|
<refsect1 id="notes"><title>Notes</title>
|
|
<para>
|
|
Values for pixels that lie outside the window
|
|
connected to the current GL context are undefined.
|
|
</para>
|
|
<para>
|
|
If an error is generated,
|
|
no change is made to the contents of <parameter>data</parameter>.
|
|
</para>
|
|
</refsect1>
|
|
<refsect1 id="errors"><title>Errors</title>
|
|
<para>
|
|
<constant>GL_INVALID_ENUM</constant> is generated if <parameter>format</parameter> or <parameter>type</parameter> is not an
|
|
accepted value.
|
|
</para>
|
|
<para>
|
|
<constant>GL_INVALID_ENUM</constant> is generated if <parameter>type</parameter> is <constant>GL_BITMAP</constant> and <parameter>format</parameter> is
|
|
not <constant>GL_COLOR_INDEX</constant> or <constant>GL_STENCIL_INDEX</constant>.
|
|
</para>
|
|
<para>
|
|
<constant>GL_INVALID_VALUE</constant> is generated if either <parameter>width</parameter> or <parameter>height</parameter> is negative.
|
|
</para>
|
|
<para>
|
|
<constant>GL_INVALID_OPERATION</constant> is generated if <parameter>format</parameter> is <constant>GL_COLOR_INDEX</constant>
|
|
and the color buffers store RGBA color components.
|
|
</para>
|
|
<para>
|
|
<constant>GL_INVALID_OPERATION</constant> is generated if <parameter>format</parameter> is <constant>GL_STENCIL_INDEX</constant>
|
|
and there is no stencil buffer.
|
|
</para>
|
|
<para>
|
|
<constant>GL_INVALID_OPERATION</constant> is generated if <parameter>format</parameter> is <constant>GL_DEPTH_COMPONENT</constant>
|
|
and there is no depth buffer.
|
|
</para>
|
|
<para>
|
|
<constant>GL_INVALID_OPERATION</constant> is generated if <parameter>type</parameter> is one of
|
|
<constant>GL_UNSIGNED_BYTE_3_3_2</constant>,
|
|
<constant>GL_UNSIGNED_BYTE_2_3_3_REV</constant>,
|
|
<constant>GL_UNSIGNED_SHORT_5_6_5</constant>, or
|
|
<constant>GL_UNSIGNED_SHORT_5_6_5_REV</constant>
|
|
and <parameter>format</parameter> is not <constant>GL_RGB</constant>.
|
|
</para>
|
|
<para>
|
|
<constant>GL_INVALID_OPERATION</constant> is generated if <parameter>type</parameter> is one of
|
|
<constant>GL_UNSIGNED_SHORT_4_4_4_4</constant>,
|
|
<constant>GL_UNSIGNED_SHORT_4_4_4_4_REV</constant>,
|
|
<constant>GL_UNSIGNED_SHORT_5_5_5_1</constant>,
|
|
<constant>GL_UNSIGNED_SHORT_1_5_5_5_REV</constant>,
|
|
<constant>GL_UNSIGNED_INT_8_8_8_8</constant>,
|
|
<constant>GL_UNSIGNED_INT_8_8_8_8_REV</constant>,
|
|
<constant>GL_UNSIGNED_INT_10_10_10_2</constant>, or
|
|
<constant>GL_UNSIGNED_INT_2_10_10_10_REV</constant>
|
|
and <parameter>format</parameter> is neither <constant>GL_RGBA</constant> nor <constant>GL_BGRA</constant>.
|
|
</para>
|
|
<para>
|
|
The formats <constant>GL_BGR</constant>, and <constant>GL_BGRA</constant> and types
|
|
<constant>GL_UNSIGNED_BYTE_3_3_2</constant>,
|
|
<constant>GL_UNSIGNED_BYTE_2_3_3_REV</constant>,
|
|
<constant>GL_UNSIGNED_SHORT_5_6_5</constant>,
|
|
<constant>GL_UNSIGNED_SHORT_5_6_5_REV</constant>,
|
|
<constant>GL_UNSIGNED_SHORT_4_4_4_4</constant>,
|
|
<constant>GL_UNSIGNED_SHORT_4_4_4_4_REV</constant>,
|
|
<constant>GL_UNSIGNED_SHORT_5_5_5_1</constant>,
|
|
<constant>GL_UNSIGNED_SHORT_1_5_5_5_REV</constant>,
|
|
<constant>GL_UNSIGNED_INT_8_8_8_8</constant>,
|
|
<constant>GL_UNSIGNED_INT_8_8_8_8_REV</constant>,
|
|
<constant>GL_UNSIGNED_INT_10_10_10_2</constant>, and
|
|
<constant>GL_UNSIGNED_INT_2_10_10_10_REV</constant> are available only if the GL version
|
|
is 1.2 or greater.
|
|
</para>
|
|
<para>
|
|
<constant>GL_INVALID_OPERATION</constant> is generated if a non-zero buffer object name is bound to the
|
|
<constant>GL_PIXEL_PACK_BUFFER</constant> target and the buffer object's data store is currently mapped.
|
|
</para>
|
|
<para>
|
|
<constant>GL_INVALID_OPERATION</constant> is generated if a non-zero buffer object name is bound to the
|
|
<constant>GL_PIXEL_PACK_BUFFER</constant> target and the data would be packed to the buffer
|
|
object such that the memory writes required would exceed the data store size.
|
|
</para>
|
|
<para>
|
|
<constant>GL_INVALID_OPERATION</constant> is generated if a non-zero buffer object name is bound to the
|
|
<constant>GL_PIXEL_PACK_BUFFER</constant> target and <parameter>data</parameter> is not evenly divisible
|
|
into the number of bytes needed to store in memory a datum indicated by <parameter>type</parameter>.
|
|
</para>
|
|
<para>
|
|
<constant>GL_INVALID_OPERATION</constant> is generated if <function>glReadPixels</function>
|
|
is executed between the execution of <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry>
|
|
and the corresponding execution of <citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>.
|
|
</para>
|
|
</refsect1>
|
|
<refsect1 id="associatedgets"><title>Associated Gets</title>
|
|
<para>
|
|
<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_INDEX_MODE</constant>
|
|
</para>
|
|
<para>
|
|
<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_PIXEL_PACK_BUFFER_BINDING</constant>
|
|
</para>
|
|
</refsect1>
|
|
<refsect1 id="seealso"><title>See Also</title>
|
|
<para>
|
|
<citerefentry><refentrytitle>glCopyPixels</refentrytitle></citerefentry>,
|
|
<citerefentry><refentrytitle>glDrawPixels</refentrytitle></citerefentry>,
|
|
<citerefentry><refentrytitle>glPixelMap</refentrytitle></citerefentry>,
|
|
<citerefentry><refentrytitle>glPixelStore</refentrytitle></citerefentry>,
|
|
<citerefentry><refentrytitle>glPixelTransfer</refentrytitle></citerefentry>,
|
|
<citerefentry><refentrytitle>glReadBuffer</refentrytitle></citerefentry>
|
|
</para>
|
|
</refsect1>
|
|
<refsect1 id="Copyright"><title>Copyright</title>
|
|
<para>
|
|
Copyright <trademark class="copyright"></trademark> 1991-2006
|
|
Silicon Graphics, Inc. This document is licensed under the SGI
|
|
Free Software B License. For details, see
|
|
<ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>.
|
|
</para>
|
|
</refsect1>
|
|
</refentry>
|