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| 4 <head> | |
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| 6 <title>WebGL WEBGL_compress_texture Extension Draft Specification</title> | |
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| 19 | |
| 20 <h1>WebGL WEBGL_compress_texture Extension Draft Specification</h1> | |
| 21 | |
| 22 <h2 class="no-toc">Name</h2> | |
| 23 <p> WEBGL_compress_texture </p> | |
| 24 | |
| 25 <h2 class="no-toc">Contact</h2> | |
| 26 <p> <a href="https://www.khronos.org/webgl/public-mailing-list/">WebGL worki
ng group</a> (public_webgl 'at' khronos.org) </p> | |
| 27 | |
| 28 <h2 class="no-toc">Contributors</h2> | |
| 29 <p> Members of the WebGL working group </p> | |
| 30 | |
| 31 <h2 class="no-toc">Version</h2> | |
| 32 <p> Last modified date: April 5, 2011 | |
| 33 </p> | |
| 34 | |
| 35 <h2 class="no-toc">Number</h2> | |
| 36 <p> WebGL extension #6 </p> | |
| 37 | |
| 38 <h2 class="no-toc">Dependencies</h2> | |
| 39 <p> Written against the WebGL API 1.0 specification. </p> | |
| 40 | |
| 41 <h2 class="no-toc">Overview</h2> | |
| 42 <p> | |
| 43 This extension exposes compressed texture functionality to WebGL. | |
| 44 </p> | |
| 45 <p> | |
| 46 In WebGL we can not expose compressed texture formats directly to authors
because web content | |
| 47 is supposed to work everywhere. This proposal leaves the compression forma
ts up to the WebGL | |
| 48 implementation in an opaque way. The user provides hints to the implemenat
ion on what kind of compression | |
| 49 is appropriate and it is up to the WebGL implemenation to decide on a comp
ression format | |
| 50 or possibly no compression at all. | |
| 51 </p> | |
| 52 <p> | |
| 53 Because compression can be a slow the process of compression is handled as
ynchronously. The | |
| 54 user provides that data as an image, video, canvas or ArrayBufferView. The
implementation then | |
| 55 compressed the image and returns a WebGLCompressedTexture object. That obj
ect can then be | |
| 56 passed to the standard compressedTexImage2D function although with unneede
d argements removed. | |
| 57 </p> | |
| 58 <h2 class="no-toc">IDL</h2> | |
| 59 <p> | |
| 60 <pre class="idl"> | |
| 61 module webgl { | |
| 62 | |
| 63 interface WebGLCompressedTexture : WebGLObject { | |
| 64 readonly attribute long size; | |
| 65 readonly attribute GLenum error; | |
| 66 }; | |
| 67 | |
| 68 interface WEBGL_compress_texture { | |
| 69 const GLenum PRESERVE_ALPHA = 0x0001; | |
| 70 const GLenum PRESERVE_TRANSPARENCY = 0x0002; | |
| 71 const GLenum PRESERVE_RGB = 0x0004; | |
| 72 | |
| 73 compressTexture(GLenum usage, GLsizei width, GLsizei height, GLenum format,
GLenum type, | |
| 74 ArrayBufferView pixels, Function callback); | |
| 75 compressTexture(GLenum usage, ImageData pixels, Function callback); | |
| 76 compressTexture(GLenum usage, HTMLImageElement image, Function callback); | |
| 77 compressTexture(GLenum usage, HTMLCanvasElement canvas, Function callback); | |
| 78 compressTexture(GLenum usage, HTMLVideoElement video, Function callback); | |
| 79 | |
| 80 compressedTexImage2D(GLenum target, GLint level, GLint border, WebGLCompress
edTexture pixels); | |
| 81 }; | |
| 82 | |
| 83 }; | |
| 84 </pre> | |
| 85 <h2 class="no-toc">Description</h2> | |
| 86 <p> | |
| 87 All forms are asynchronous. When compression is finished the <code>callback<
/code> | |
| 88 is called and passed a <code>WebGLCompressedTexture</code> | |
| 89 object which can then be used with <code>compressedTexImage2D</code>. | |
| 90 </p> | |
| 91 <p> | |
| 92 <code>compressTexture</code> takes 5 forms. The first form takes an <code>Ar
rayBufferView</code>. | |
| 93 The <code>width</code>, <code>height</code>, <code>format</code>, and <code>
type</code> | |
| 94 arguments have the same meaning as they do in <code>texImage2D</code>. They
describe the format | |
| 95 of the pixels in the <code>ArrayBufferView</code>. | |
| 96 </p> | |
| 97 <p> | |
| 98 The other 4 forms of <code>compressTexture</code> take an <code>ImageData</c
ode>, | |
| 99 <code>HTMLImageElement</code>, <code>HTMLCanvasElement</code>, or an <code>H
TMLVideoElement</code> | |
| 100 repsectively. As such they derive width, height, type and format from the el
ement. | |
| 101 </p> | |
| 102 <p> | |
| 103 <code>usage</code> is a kind of hint to the implementation to help it choose
a | |
| 104 compression format. <code>usage</code> is some logical OR of the following b
its | |
| 105 </p> | |
| 106 <dl> | |
| 107 <dt><code>PRESERVE_ALPHA</code></dt> | |
| 108 <dd>The compression format chosen must support alpha more than 1 bit of alph
a. | |
| 109 </dd> | |
| 110 <dt><code>PRESERVE_TRANSPARENCY</code></dt> | |
| 111 <dd>The compression format chosen must have at least 1 bit of alpha | |
| 112 </dd> | |
| 113 <dt><code>PRESERVE_RGB</code></dt> | |
| 114 <dd>The compression format chosen must not be lossy to a specific | |
| 115 color. In other words, it can not weight R less than G because | |
| 116 the intended use of the texture is not for color. | |
| 117 </dd> | |
| 118 </dl> | |
| 119 <p> | |
| 120 The implementation must choose a compression format that respects the <code>
usage</code> argument. | |
| 121 If no such compression format is available the implementation must choose an
uncompressed format. | |
| 122 </p> | |
| 123 <p class="issue"> | |
| 124 Should the spec define what is acceptable compression? For example PRESERVE_
TRANSPARENCY basically means use DXT1 where as | |
| 125 PRESERVE_ALPHA means use DXT5 on systems that support those formats. On syst
ems with no compression | |
| 126 using 5_6_5 or 5_5_5_1 is also fine assuming PRESERVE_ALPHA is not requested
. | |
| 127 Is 5_6_5 okay for PRESERVE_RGB? Is 4_4_4_4 ok for PRESERVE_ALPHA? | |
| 128 </p> | |
| 129 <p>The <code>callback</code> is always called and passed a <code>WebGLCompre
ssedTexture</code> object. If there was an error | |
| 130 the <code>error</code> attribute will be set to standard GL error value. Oth
erwise it is set to <code>NO_ERROR</code>. | |
| 131 </p> | |
| 132 <p><code>size</code> is the number of bytes used by the compressed texture.
It will be 0 | |
| 133 if there was an error. | |
| 134 </p> | |
| 135 <p>Passing a <code>WebGLCompressedTexture</code> who's <code>error</code> at
tribute is not <code>NO_ERROR</code> to <code>compressTexImage2D</code> generate
s | |
| 136 <code>INVALID_OPERATION</code>.</p> | |
| 137 <h2 class="no-toc">Errors</h2> | |
| 138 <p> | |
| 139 Errors are returned on the WebGLCompressedTexture object's <code>error</code
> attribute. | |
| 140 </p> | |
| 141 <p> | |
| 142 <code>error</code> is set to <code>INVALID_VALUE</code> if | |
| 143 <code>width</code> or <code>height</code> would generate an <code>INVALID_VA
LUE</code> when calling | |
| 144 texImage2D. | |
| 145 </p> | |
| 146 <p> | |
| 147 <code>error</code> is set to <code>INVALID_ENUM</code> if type or format is
not one of the types | |
| 148 or formats excepted by texImage2D. | |
| 149 </p> | |
| 150 <p> | |
| 151 <code>error</code> is set to <code>INVALID_OPERATION</code> if the size of t
he <code>ArrayBufferView</code> is | |
| 152 not greater than or equal to the size of the data described by width, height
, format and type. | |
| 153 </p> | |
| 154 <h2 class="no-toc">Notes</h2> | |
| 155 <p> | |
| 156 compressedTexSubImage2D is not implemented. | |
| 157 </p> | |
| 158 <p> | |
| 159 <code>texSubImage2D</code> and <code>copyTexSubImage2D</code> must both fa
il on textures created with <code>compressedTexImage2D</code>. | |
| 160 For consistency this is true even if the implementation did not actually c
ompress the texture. | |
| 161 </p> | |
| 162 <p> | |
| 163 Rendering to a framebuffer object with an attached texture created by <cod
e>compressedTexImage2D</code> must fail | |
| 164 with <code>INVALID_FRAMEBUFFER_OPERATION</code> even if the implemenation
did not actually compress the texture. | |
| 165 </p> | |
| 166 <p> | |
| 167 <code>compressTexture</code> must succeed for all valid dimensions defined
by <code>gl.getParameter(gl.MAX_TEXTURE_SIZE).</code> | |
| 168 That means for example a 7x5 texture passed to compressTexture on a system
who's texture compression | |
| 169 format requires textures that are a multiple of 4 or 8 in each dimension w
ould choose not to compress | |
| 170 a 7x5 texture but instead provide it uncompressed or in some other format
that can handle a 7x5 texture. | |
| 171 </p> | |
| 172 <p> | |
| 173 If both <code>PRESERVE_ALPHA</code> and <code>PRESERVE_TRANSPARENCY</code> a
re specified | |
| 174 <code>PRESERVE_ALPHA</code> takes precedence. In other words the implementio
n must choose | |
| 175 a compression format with more than 1 bit of alpha. | |
| 176 </p> | |
| 177 <h2 class="no-toc">Unresolved issues</h2> | |
| 178 <h2 class="no-toc">Revision History</h2> | |
| 179 <p> | |
| 180 <ul> | |
| 181 <li> 2011/04/04 Initial draft.</li> | |
| 182 <li> 2011/04/05 Fixed typos. Changed error mechanism. Added size.</li> | |
| 183 </ul> | |
| 184 </p> | |
| 185 </body> | |
| 186 </html> | |
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Chromium Code Reviews
Issue 9360034:
Remove everthing except conformance tests in the deps/third_party/webgl (Closed)
Base URL: svn://chrome-svn/chrome/trunk/deps/