WebGL EXT_color_buffer_half_float Extension Draft Specification

Name

EXT_color_buffer_half_float

Contact

WebGL working group (public_webgl 'at' khronos.org)

Contributors

Mark Callow, HI Corporation

Members of the WebGL working group

Version

Last modified date: November 26, 2012
Revision: 3

Number

WebGL extension #14

Dependencies

Written against the WebGL API 1.0 specification.

Implementations must also support the OES_texture_half_float extension.

Overview

This extension exposes the EXT_color_buffer_half_float functionality to WebGL.

The following WebGL-specific behavioral changes apply:

• All references to R16F and RG16F types are ignored.

Consult the above extension for documentation, issues and new functions and enumerants.

When this extension is enabled:

• The 16-bit floating-point types RGB16F and RGBA16F become available as color-renderable formats. Renderbuffers can be created in these formats. These and textures created with type = HALF_FLOAT_OES, which will have one of these internal formats, can be attached to framebuffer object color attachments for rendering.

• NOTE: fragment shaders outputs gl_FragColor and gl_FragData[0] will only be clamped and converted when the color buffer is fixed-point and BlendColor() and ClearColor() will no longer clamp their parameter values on input. Clamping will be applied as necessary at draw time according to the type of color buffer in use.

• The format and type combination RGBA and FLOAT becomes valid for reading from a floating-point rendering buffer. Note: RGBA and UNSIGNED_BYTE cannot be used for reading from a floating-point rendering buffer.

• The component types of framebuffer object attachments can be queried.

IDL

module webgl {
  interface EXT_color_buffer_half_float {
    const GLenum RGBA16F_EXT = 0x881A;
    const GLenum RGB16F_EXT = 0x881B;
    const GLenum FRAMEBUFFER_ATTACHMENT_COMPONENT_TYPE_EXT = 0x8211;
    const GLenum UNSIGNED_NORMALIZED_EXT = 0x8C17;
  }; // interface EXT_color_buffer_half_float
}; // module webgl

Additions to the WebGL Specification

In section 5.13.12 Reading back pixels, change the allowed format and types table to:

frame buffer type	format	type
normalized fixed-point	RGBA	UNSIGNED_BYTE
floating-point	RGBA	FLOAT

Change the paragraph beginning "If pixels is null ..." to

If frame buffer type is not that indicated in the table for the format and type combination, an INVALID_OPERATON error is generated. If pixels is null ...

Revision History

Revision 1, 2012/11/08

• Initial revision.

Revision 2, 2012/11/13

• "Add reading-pixels-as-FLOAT feature to the Overview and related changes to WebGL section 5.13.12.

Revision 3, 2012/11/26

• Move to draft.