The WEBGL_draw_buffers
extension is part of the WebGL API and enables a fragment shader to write to several textures, which is useful for deferred shading, for example.
WebGL extensions are available using the WebGLRenderingContext.getExtension()
method. For more information, see also Using Extensions in the WebGL tutorial.
Availability: This extension is only available to WebGL1 contexts. In WebGL2, the functionality of this extension is available on the WebGL2 context by default. In WebGL 2, the constants
are available without the "WEBGL" suffix and the new GLSL built-ins require GLSL #version 300 es
.
Constants
This extension exposes new constants, which can be used in the gl.framebufferRenderbuffer()
, gl.framebufferTexture2D()
, gl.getFramebufferAttachmentParameter()
ext.drawBuffersWEBGL()
, and gl.getParameter()
methods.
ext.COLOR_ATTACHMENT0_WEBGL ext.COLOR_ATTACHMENT1_WEBGL ext.COLOR_ATTACHMENT2_WEBGL ext.COLOR_ATTACHMENT3_WEBGL ext.COLOR_ATTACHMENT4_WEBGL ext.COLOR_ATTACHMENT5_WEBGL ext.COLOR_ATTACHMENT6_WEBGL ext.COLOR_ATTACHMENT7_WEBGL ext.COLOR_ATTACHMENT8_WEBGL ext.COLOR_ATTACHMENT9_WEBGL ext.COLOR_ATTACHMENT10_WEBGL ext.COLOR_ATTACHMENT11_WEBGL ext.COLOR_ATTACHMENT12_WEBGL ext.COLOR_ATTACHMENT13_WEBGL ext.COLOR_ATTACHMENT14_WEBGL ext.COLOR_ATTACHMENT15_WEBGL
- A
GLenum
specifying a color buffer. ext.DRAW_BUFFER0_WEBGL ext.DRAW_BUFFER1_WEBGL ext.DRAW_BUFFER2_WEBGL ext.DRAW_BUFFER3_WEBGL ext.DRAW_BUFFER4_WEBGL ext.DRAW_BUFFER5_WEBGL ext.DRAW_BUFFER6_WEBGL ext.DRAW_BUFFER7_WEBGL ext.DRAW_BUFFER8_WEBGL ext.DRAW_BUFFER9_WEBGL ext.DRAW_BUFFER10_WEBGL ext.DRAW_BUFFER11_WEBGL ext.DRAW_BUFFER12_WEBGL ext.DRAW_BUFFER13_WEBGL ext.DRAW_BUFFER14_WEBGL ext.DRAW_BUFFER15_WEBGL
- A
GLenum
returning a draw buffer. ext.MAX_COLOR_ATTACHMENTS_WEBGL
- A
GLint
indicating the maximum number of framebuffer color attachment points. ext.MAX_DRAW_BUFFERS_WEBGL
- A
GLint
indicating the maximum number of draw buffers.
Methods
This extension exposes one new method.
ext.drawBuffersWEBGL()
- Defines the draw buffers to which all fragment colors are written. (When using
WebGL2
, this method is available asgl.drawBuffers()
by default).
Examples
Enabling the extension:
var ext = gl.getExtension('WEBGL_draw_buffers');
Binding multiple textures (to a tx[]
array) to different framebuffer color attachments:
var fb = gl.createFramebuffer();
gl.bindFramebuffer(gl.FRAMEBUFFER, fb);
gl.framebufferTexture2D(gl.FRAMEBUFFER, ext.COLOR_ATTACHMENT0_WEBGL, gl.TEXTURE_2D, tx[0], 0);
gl.framebufferTexture2D(gl.FRAMEBUFFER, ext.COLOR_ATTACHMENT1_WEBGL, gl.TEXTURE_2D, tx[1], 0);
gl.framebufferTexture2D(gl.FRAMEBUFFER, ext.COLOR_ATTACHMENT2_WEBGL, gl.TEXTURE_2D, tx[2], 0);
gl.framebufferTexture2D(gl.FRAMEBUFFER, ext.COLOR_ATTACHMENT3_WEBGL, gl.TEXTURE_2D, tx[3], 0);
Mapping the color attachments to draw buffer slots that the fragment shader will write to using gl_FragData
:
ext.drawBuffersWEBGL([
ext.COLOR_ATTACHMENT0_WEBGL, // gl_FragData[0]
ext.COLOR_ATTACHMENT1_WEBGL, // gl_FragData[1]
ext.COLOR_ATTACHMENT2_WEBGL, // gl_FragData[2]
ext.COLOR_ATTACHMENT3_WEBGL // gl_FragData[3]
]);
Shader code that writes to multiple textures:
<script type="x-shader/x-fragment">
#extension GL_EXT_draw_buffers : require
precision highp float;
void main(void) {
gl_FragData[0] = vec4(0.25);
gl_FragData[1] = vec4(0.5);
gl_FragData[2] = vec4(0.75);
gl_FragData[3] = vec4(1.0);
}
</script>
Specifications
Specification | Status | Comment |
WEBGL_draw_buffersThe definition of 'WEBGL_draw_buffers' in that specification. | Recommendation | Initial definition. |
Browser compatibility
The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.
Update compatibility data on GitHub
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
drawBuffersWEBGL
|
Chrome
Full support Yes |
Edge
Full support 17 |
Firefox No support ? — 28 No support ? — 28 Prefixed' Implemented with the vendor prefix: MOZ_
Disabled' Until version 28 (exclusive): this feature is behind the |
IE
? |
Opera
Full support Yes |
Safari
? |
WebView Android
Full support Yes |
Chrome Android
Full support Yes |
Firefox Android
? |
Opera Android
Full support Yes |
Safari iOS
? |
Samsung Internet Android
Full support Yes |
Legend
- Full support
- Full support
- No support
- No support
- Compatibility unknown
- Compatibility unknown
- User must explicitly enable this feature.'
- User must explicitly enable this feature.
- Requires a vendor prefix or different name for use.'
- Requires a vendor prefix or different name for use.
See also
WebGLRenderingContext.getExtension()
WebGL2RenderingContext.drawBuffers()
- WebGL deferred shading - Mozilla Hacks blog
WEBGL_draw_buffers by Mozilla Contributors is licensed under CC-BY-SA 2.5.