| 1 | <?xml version="1.0" encoding="UTF-8"?>\r |
| 2 | <!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"\r |
| 3 | "http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">\r |
| 4 | <refentry id="gl_Layer">\r |
| 5 | <refmeta>\r |
| 6 | <refmetainfo>\r |
| 7 | <copyright>\r |
| 8 | <year>2012</year>\r |
| 9 | <holder>Khronos Group</holder>\r |
| 10 | </copyright>\r |
| 11 | </refmetainfo>\r |
| 12 | <refentrytitle>gl_Layer</refentrytitle>\r |
| 13 | <manvolnum>3G</manvolnum>\r |
| 14 | </refmeta>\r |
| 15 | <refnamediv>\r |
| 16 | <refname>gl_Layer</refname>\r |
| 17 | <refpurpose>contains the selected layer of a multi-layer framebuffer attachment</refpurpose>\r |
| 18 | </refnamediv>\r |
| 19 | <refsynopsisdiv><title>Declaration</title>\r |
| 20 | <funcsynopsis>\r |
| 21 | <function>out int gl_Layer; // Geometry stage</function>\r |
| 22 | </funcsynopsis>\r |
| 23 | <funcsynopsis>\r |
| 24 | <function>in int gl_Layer; // Fragment stage</function>\r |
| 25 | </funcsynopsis>\r |
| 26 | </refsynopsisdiv>\r |
| 27 | <refsect1 id="description"><title>Description</title>\r |
| 28 | <para>\r |
| 29 | In the geometry language, <function>gl_Layer</function> is used to select a specific\r |
| 30 | layer (or face and layer of cube map) in a multi-layer framebuffer attachment. The actual\r |
| 31 | layer used will come from one of the vertices in the primitive being shaded. Which vertex\r |
| 32 | the layer comes from is undefined and as such it is recommended to write the same value\r |
| 33 | to <function>gl_Layer</function> for all vertices in the primitive. If a shader statically\r |
| 34 | assigns a value to <function>gl_Layer</function>, layered rendering mode is enabled.\r |
| 35 | If a shader statically assigns a value to <function>gl_Layer</function>, and there is an execution path through\r |
| 36 | the shader that does not set <function>gl_Layer</function>, then the value of <function>gl_Layer</function>\r |
| 37 | is undefined for invocations of the shader that take that path.\r |
| 38 | </para>\r |
| 39 | <para>\r |
| 40 | When used with an array of cube map textures, the <function>gl_Layer</function> output variable\r |
| 41 | takes on a special value. Instead of referring to only the layer, it is used to select a cube map\r |
| 42 | face and a layer. Setting <function>gl_Layer</function> to the value\r |
| 43 | <inlineequation><mml:math><mml:mi>layer</mml:mi><mml:mo>*</mml:mo><mml:mn>6</mml:mn><mml:mo>+</mml:mo><mml:mi>face</mml:mi></mml:math></inlineequation>\r |
| 44 | will render to <inlineequation><mml:math><mml:mi>face</mml:mi></mml:math></inlineequation>\r |
| 45 | of the cube defined in <inlineequation><mml:math><mml:mi>layer</mml:mi></mml:math></inlineequation>.\r |
| 46 | The face values are as follows:\r |
| 47 | <informaltable frame="topbot">\r |
| 48 | <tgroup cols="2" align="left">\r |
| 49 | <colspec colwidth="1.1*" />\r |
| 50 | <colspec colwidth="1*" align="center" />\r |
| 51 | <thead>\r |
| 52 | <row>\r |
| 53 | <entry rowsep="1" align="left"><emphasis role="bold">\r |
| 54 | Face Value\r |
| 55 | </emphasis></entry>\r |
| 56 | <entry rowsep="1" align="left"><emphasis role="bold">\r |
| 57 | Resulting Target\r |
| 58 | </emphasis></entry>\r |
| 59 | </row>\r |
| 60 | <row>\r |
| 61 | <entry>\r |
| 62 | 0\r |
| 63 | </entry>\r |
| 64 | <entry>\r |
| 65 | <constant>GL_TEXTURE_CUBEMAP_POSITIVE_X</constant>\r |
| 66 | </entry>\r |
| 67 | </row>\r |
| 68 | <row>\r |
| 69 | <entry>\r |
| 70 | 1\r |
| 71 | </entry>\r |
| 72 | <entry>\r |
| 73 | <constant>GL_TEXTURE_CUBEMAP_NEGATIVE_X</constant>\r |
| 74 | </entry>\r |
| 75 | </row>\r |
| 76 | <row>\r |
| 77 | <entry>\r |
| 78 | 2\r |
| 79 | </entry>\r |
| 80 | <entry>\r |
| 81 | <constant>GL_TEXTURE_CUBEMAP_POSITIVE_Y</constant>\r |
| 82 | </entry>\r |
| 83 | </row>\r |
| 84 | <row>\r |
| 85 | <entry>\r |
| 86 | 3\r |
| 87 | </entry>\r |
| 88 | <entry>\r |
| 89 | <constant>GL_TEXTURE_CUBEMAP_NEGATIVE_Y</constant>\r |
| 90 | </entry>\r |
| 91 | </row>\r |
| 92 | <row>\r |
| 93 | <entry>\r |
| 94 | 4\r |
| 95 | </entry>\r |
| 96 | <entry>\r |
| 97 | <constant>GL_TEXTURE_CUBEMAP_POSITIVE_Z</constant>\r |
| 98 | </entry>\r |
| 99 | </row>\r |
| 100 | <row>\r |
| 101 | <entry>\r |
| 102 | 5\r |
| 103 | </entry>\r |
| 104 | <entry>\r |
| 105 | <constant>GL_TEXTURE_CUBEMAP_NEGATIVE_Z</constant>\r |
| 106 | </entry>\r |
| 107 | </row>\r |
| 108 | </thead>\r |
| 109 | </tgroup>\r |
| 110 | </informaltable>\r |
| 111 | </para>\r |
| 112 | <para>\r |
| 113 | For example, to render to the positive y cube map face located in the 5<superscript>th</superscript> layer of the\r |
| 114 | cube map array, <function>gl_Layer</function> should be set to\r |
| 115 | <inlineequation><mml:math><mml:mn>5</mml:mn><mml:mo>*</mml:mo><mml:mn>6</mml:mn><mml:mo>+</mml:mo><mml:mn>2</mml:mn></mml:math></inlineequation>.\r |
| 116 | </para>\r |
| 117 | <para>\r |
| 118 | The input variable <function>gl_Layer</function> in the fragment language will have the same value that was written to the\r |
| 119 | output variable <function>gl_Layer</function> in the geometry language. If the geometry stage does not dynamically assign a\r |
| 120 | value to <function>gl_Layer</function>, the value of <function>gl_Layer</function> in the fragment stage will be undefined. If the geometry stage\r |
| 121 | makes no static assignment to <function>gl_Layer</function>, the input <function>gl_Layer</function> in the fragment stage will be zero. Otherwise,\r |
| 122 | the fragment stage will read the same value written by the geometry stage, even if that value is out of\r |
| 123 | range. If a fragment shader contains a static access to <function>gl_Layer</function>, it will count against the implementation\r |
| 124 | defined limit for the maximum number of inputs to the fragment stage.\r |
| 125 | </para>\r |
| 126 | </refsect1>\r |
| 127 | <refsect1 id="versions"><title>Version Support</title>\r |
| 128 | <informaltable frame="topbot">\r |
| 129 | #VARTABLECOLS#\r |
| 130 | <thead>\r |
| 131 | #FUNCTABLEHEADER#\r |
| 132 | <row>\r |
| 133 | <entry>gl_Layer (geometry stage)</entry>#newin15#\r |
| 134 | </row>\r |
| 135 | <row>\r |
| 136 | <entry>gl_Layer (fragment stage)</entry>#newin43#\r |
| 137 | </row>\r |
| 138 | </thead>\r |
| 139 | </tgroup>\r |
| 140 | </informaltable>\r |
| 141 | </refsect1>\r |
| 142 | <refsect1 id="seealso"><title>See Also</title>\r |
| 143 | <para>\r |
| 144 | <citerefentry><refentrytitle>gl_ViewportIndex</refentrytitle></citerefentry>\r |
| 145 | </para>\r |
| 146 | </refsect1>\r |
| 147 | <refsect1 id="Copyright"><title>Copyright</title>\r |
| 148 | <para>\r |
| 149 | Copyright <trademark class="copyright"></trademark> 2011-2012 Khronos Group. \r |
| 150 | This material may be distributed subject to the terms and conditions set forth in \r |
| 151 | the Open Publication License, v 1.0, 8 June 1999.\r |
| 152 | <ulink url="http://opencontent.org/openpub/">http://opencontent.org/openpub/</ulink>.\r |
| 153 | </para>\r |
| 154 | </refsect1>\r |
| 155 | </refentry>\r |