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_buffers The definition of 'WEBGL_draw_buffers' in that specification. |
Recommendation | Initial definition. |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | ? | 28 (28) [1] | ? | ? | ? |
Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|
Basic support | ? | ? | ? | ? | ? | ? |
[2] This extension was prefixed with MOZ_
or disabled behind the webgl.enable-draft-extensions
preference in prior versions.