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<?xml version="1.0"?>
<ratified href="WEBGL_depth_texture/">
<name>WEBGL_depth_texture</name>
<aliases>
<alias>WEBKIT_WEBGL_depth_texture</alias>
<alias>MOZ_WEBGL_depth_texture</alias>
</aliases>
<contact>
<a href="https://www.khronos.org/webgl/public-mailing-list/">WebGL working group</a> (public_webgl 'at' khronos.org)
</contact>
<contributors>
<contributor>Members of the WebGL working group</contributor>
<contributor>Florian Bösch (pyalot 'at' gmail.com)</contributor>
</contributors>
<number>9</number>
<depends>
<api version="1.0"/>
<removed version="2.0" />
</depends>
<overview>
<p>This extension exposes the
<a href="http://angleproject.googlecode.com/svn/trunk/extensions/ANGLE_depth_texture.txt">ANGLE_depth_texture</a>
functionality to WebGL. ANGLE_depth_texture provides a subset of the
functionality from the OpenGL ES 2.0 extensions
<a href="http://www.khronos.org/registry/gles/extensions/OES/OES_depth_texture.txt">OES_depth_texture</a>
and
<a href="http://www.khronos.org/registry/gles/extensions/OES/OES_packed_depth_stencil.txt">OES_packed_depth_stencil</a>, with certain restrictions added for portability reasons. Specifically:</p>
<ul>
<li> ANGLE_depth_texture provides both depth and depth/stencil textures. </li>
<li> ANGLE_depth_texture does not provide the <code>DEPTH24_STENCIL8_OES</code> renderbuffer internal format from the OES_packed_depth_stencil extension. The core WebGL specification already supports allocation of depth/stencil renderbuffers. </li>
<li> ANGLE_depth_texture does not support loading image data via the TexImage or TexSubImage commands. Depth and depth/stencil textures created via this extension can only have their contents specified by rendering to them. </li>
</ul>
<p>Consult the Errors section below for specific restrictions.
</p>
<features>
<feature>
The <code>texImage2D</code> entry point is extended to accept the
<code>format</code> parameter <code>DEPTH_COMPONENT</code> and
<code>DEPTH_STENCIL</code>
</feature>
<feature>
The <code>texImage2D</code> entry point is extended to accept the
<code>internalFormat</code> parameter <code>DEPTH_COMPONENT</code>
and <code>DEPTH_STENCIL</code>
</feature>
<feature>
The <code>texImage2D</code> entry point is extended to accept
the <code>type</code> parameter <code>UNSIGNED_SHORT</code>,
<code>UNSIGNED_INT</code>, and
<code>UNSIGNED_INT_24_8_WEBGL</code>
</feature>
<feature>
The <code>framebufferTexture2D</code> entry point is extended to
accept the <code>target</code> parameter
<code>DEPTH_ATTACHMENT</code> and
<code>DEPTH_STENCIL_ATTACHMENT</code>
</feature>
<feature>
The <code>texImage2D</code> entry point is extended to accept
<code>ArrayBufferView</code> of type <code>Uint16Array</code> and
<code>Uint32Array</code>
</feature>
<feature>
<p>
The WebGL-specific constraints about <a href="http://www.khronos.org/registry/webgl/specs/1.0/#FBO_ATTACHMENTS">Framebuffer Object Attachments</a> are extended:</p>
<ul>
<li> A texture attached to an FBO's <code>DEPTH_ATTACHMENT</code> attachment point must be allocated with the <code>DEPTH_COMPONENT</code> internal format. </li>
<li> A texture attached to the <code>DEPTH_STENCIL_ATTACHMENT</code> attachment point must be allocated with the <code>DEPTH_STENCIL</code> internal format. </li>
</ul>
<p>
In the WebGL API, it is an error to concurrently attach either
renderbuffers or textures to the following combinations of
attachment points:</p>
<ul>
<li> <code>DEPTH_ATTACHMENT</code> + <code>DEPTH_STENCIL_ATTACHMENT</code> </li>
<li> <code>STENCIL_ATTACHMENT</code> + <code>DEPTH_STENCIL_ATTACHMENT</code> </li>
<li> <code>DEPTH_ATTACHMENT</code> + <code>STENCIL_ATTACHMENT</code> </li>
</ul>
<p>
See the section
<a href="http://www.khronos.org/registry/webgl/specs/1.0/#FBO_ATTACHMENTS">Framebuffer Object Attachments</a>
in the WebGL specification for the behavior if these
constraints are violated.
</p>
</feature>
<feature>
<p>
As per the OpenGL ES spec, there is no guarantee that the OpenGL ES implementation
will use the texture type to determine how to store the depth texture internally.
It may choose to downsample the 32-bit depth values to 16-bit or even 24-bit.
When a depth or depth/stencil texture is attached to a framebuffer object, calls to getParameter
with the DEPTH_BITS and STENCIL_BITS enums return the following:
<table>
<tr>
<th>Texture Type</th>
<th>DEPTH_BITS (GLint)</th>
<th>STENCIL_BITS (GLint)</th>
</tr>
<tr>
<td>UNSIGNED_SHORT</td>
<td>>= 16</td>
<td>0</td>
</tr>
<tr>
<td>UNSIGNED_INT</td>
<td>>= 16</td>
<td>0</td>
</tr>
<tr>
<td>UNSIGNED_INT_24_8_WEBGL</td>
<td>>= 24</td>
<td>>= 8</td>
</tr>
</table>
</p>
</feature>
</features>
</overview>
<idl xml:space="preserve">
[NoInterfaceObject]
interface WEBGL_depth_texture {
const GLenum UNSIGNED_INT_24_8_WEBGL = 0x84FA;
};
</idl>
<errors>
<error>
The error <code>INVALID_OPERATION</code> is generated by
<code>texImage2D</code> if the <code>format</code> parameter is
<code>DEPTH_COMPONENT</code> or <code>DEPTH_STENCIL</code> and the
<code>target</code> is
<code>TEXTURE_CUBE_MAP_{POSITIVE,NEGATIVE}_{X,Y,Z}</code>.
</error>
<error>
The error <code>INVALID_OPERATION</code> is generated by
<code>texImage2D</code> if <code>format</code> and
<code>internalformat</code> are <code>DEPTH_COMPONENT</code> and
<code>type</code> is not <code>UNSIGNED_SHORT</code> or
<code>UNSIGNED_INT</code>.
</error>
<error>
The error <code>INVALID_OPERATION</code> is generated by
<code>texImage2D</code> if <code>format</code> and
<code>internalformat</code> are not <code>DEPTH_COMPONENT</code>
and <code>type</code> is <code>UNSIGNED_SHORT</code> or
<code>UNSIGNED_INT</code>.
</error>
<error>
The error <code>INVALID_OPERATION</code> is generated by
<code>texImage2D</code> if <code>format</code> and
<code>internalformat</code> are <code>DEPTH_STENCIL</code> and
<code>type</code> is not <code>UNSIGNED_INT_24_8_WEBGL</code>.
</error>
<error>
The error <code>INVALID_OPERATION</code> is generated by
<code>texImage2D</code> if <code>format</code> and
<code>internalformat</code> are not <code>DEPTH_STENCIL</code> and
<code>type</code> is <code>UNSIGNED_INT_24_8_WEBGL</code>.
</error>
<error>
The error <code>INVALID_OPERATION</code> is generated in the following situations:
<ul>
<li>
<code>texImage2D</code> is called with <code>format</code> and
<code>internalformat</code> of <code>DEPTH_COMPONENT</code> or
<code>DEPTH_STENCIL</code> and
<ul>
<li> <code>target</code> is not TEXTURE_2D, </li>
<li> <code>data</code> is not NULL, or </li>
<li> <code>level</code> is not zero. </li>
</ul>
</li>
<li>
<code>texSubImage2D</code> is called with <code>format</code> of
<code>DEPTH_COMPONENT</code> or <code>DEPTH_STENCIL</code>.
</li>
<li>
<code>copyTexImage2D</code> is called with an
<code>internalformat</code> that has a base internal format of
<code>DEPTH_COMPONENT</code> or <code>DEPTH_STENCIL</code>.
</li>
<li>
<code>copyTexSubImage2D</code> is called with a target texture
that has a base internal format of <code>DEPTH_COMPONENT</code>
or <code>DEPTH_STENCIL</code>.
</li>
<li>
<code>generateMipmap</code> is called on a texture that has a
base internal format of <code>DEPTH_COMPONENT</code> or
<code>DEPTH_STENCIL</code>.
</li>
</ul>
</error>
</errors>
<issues>
<p>
As per the ANGLE_depth_texture specification, when a depth
texture is sampled, the value is stored into the RED channel.
The contents of the GREEN, BLUE and ALPHA channels are
implementation dependent. It is therefore recommended to use
only the <code>r</code> component of variables in GLSL shaders
that are used to reference depth textures.
</p>
</issues>
<history>
<revision date="2012/01/23">
<change>Initial revision.</change>
</revision>
<revision date="2012/01/25">
<change>Added provisions to exclude cube depth textures.</change>
</revision>
<revision date="2012/02/06">
<change>Changed referenced WebGL API version from 2.0 to 1.0</change>
</revision>
<revision date="2012/02/24">
<change>Removed the enumerants from the IDL which are contained in the context and added aliases to the extension name</change>
</revision>
<revision date="2012/03/01">
<change>
Renamed with OES prefix and removed the addendum due to expected harmonization between OES_depth_texture and ARB_depth_texture
(depth cube maps).
</change>
</revision>
<revision date="2012/06/04">
<change>
Renamed to WEBGL prefix, and changed to reference ANGLE_depth_texture, because of
limitations preventing the current ANGLE library from loading of image data to depth
textures. Incorporated errors from ANGLE_depth_texure extension specification.
</change>
</revision>
<revision date="2012/06/20">
<change>
Incorporated depth/stencil support and UNSIGNED_INT_24_8_WEBGL enum after discussion on
public_webgl mailing list, including supported behavior and additional error behavior.
Extended rules in Section 6.5 ("Framebuffer Object Attachments") to handle texture
attachments.
</change>
</revision>
<revision date="2012/06/27">
<change>
Updated references to texSubImage2D. Added
DEPTH_STENCIL_ATTACHMENT to framebufferTexture2D.
</change>
</revision>
<revision date="2013/01/26">
<change>Moved from draft to community approved status</change>
</revision>
<revision date="2013/02/28">
<change>Updated to track ANGLE_depth_texture, indicating that only red channel is guaranteed.</change>
</revision>
<revision date="2013/05/15">
<change>Ratified by Khronos Board of Promoters.</change>
</revision>
<revision date="2014/07/15">
<change>Added NoInterfaceObject extended attribute.</change>
</revision>
</history>
</ratified>
|
