src/third_party/angle/extensions/EGL_ANGLE_platform_angle.txt

Name

    ANGLE_platform_angle

Name Strings

    EGL_ANGLE_platform_angle

Contributors

    Scott Graham, Google
    Shannon Woods, Google
    Geoff Lang, Google

Contacts

    Scott Graham, Google (scottmg 'at' google 'dot' com)

Status

    Draft

Version

    Version 5, 2017-12-28

Number

    EGL Extension XXX

Extension Type

    EGL client extension

Dependencies

    Requires EGL_EXT_client_extensions to query its existence without
    a display.

    Requires EGL_EXT_platform_base.

    This extension is written against the wording of version 9 of the
    EGL_EXT_platform_base specification.

    ANGLE_platform_angle_d3d affects the definition of this extension.
    ANGLE_platform_angle_opengl affects the definition of this extension.

Overview

    This extension defines how to create EGL resources from native resources
    using the functions defined by EGL_EXT_platform_base.

New Types

    None

New Procedures and Functions

    None

New Tokens

    Accepted as the <platform> argument of eglGetPlatformDisplayEXT:

        EGL_PLATFORM_ANGLE_ANGLE                           0x3202

    Accepted as an attribute name in the <attrib_list> argument of
    eglGetPlatformDisplayEXT:

        EGL_PLATFORM_ANGLE_TYPE_ANGLE                      0x3203
        EGL_PLATFORM_ANGLE_MAX_VERSION_MAJOR_ANGLE         0x3204
        EGL_PLATFORM_ANGLE_MAX_VERSION_MINOR_ANGLE         0x3205
        EGL_PLATFORM_ANGLE_DEBUG_LAYERS_ENABLED            0x3451

    Accepted as values for the EGL_PLATFORM_ANGLE_TYPE_ANGLE attribute:

        EGL_PLATFORM_ANGLE_TYPE_DEFAULT_ANGLE              0x3206

    Accepted as values for the EGL_PLATFORM_ANGLE_DEVICE_TYPE_ANGLE attribute:

        EGL_PLATFORM_ANGLE_DEVICE_TYPE_HARDWARE_ANGLE      0x320A
        EGL_PLATFORM_ANGLE_DEVICE_TYPE_NULL_ANGLE          0x345E

Additions to the EGL Specification

    None.

New Behavior

    To determine if the EGL implementation supports this extension, clients
    should query the EGL_EXTENSIONS string of EGL_NO_DISPLAY.

    To obtain an EGLDisplay backed by a ANGLE display, call
    eglGetPlatformDisplayEXT with <platform> set to EGL_PLATFORM_ANGLE_ANGLE.

    The <native_display> parameter is of type EGLNativeDisplayType. If
    <native_display> is EGL_DEFAULT_DISPLAY a default display is returned.
    Multiple calls with the same <native_display> will return the same
    EGLDisplay handle. If <platform> is set to EGL_PLATFORM_ANGLE_ANGLE and
    the returned display is in an uninitialized state, its attributes are
    overwritten by those provided in the <attrib_list>, if any.

    If no <attrib_list> is specified, the value of
    EGL_PLATFORM_ANGLE_TYPE_ANGLE is implicitly set to
    EGL_PLATFORM_ANGLE_TYPE_DEFAULT_ANGLE.

    If no <attrib_list> is specified, the values of
    EGL_PLATFORM_ANGLE_MAX_VERSION_MAJOR_ANGLE and
    EGL_PLATFORM_ANGLE_MAX_VERSION_MINOR_ANGLE are implicitly set to
    EGL_DONT_CARE.

    If no <attrib_list> is specified, the value of
    EGL_PLATFORM_ANGLE_DEBUG_LAYERS_ENABLED is implicitly set to
    EGL_DONT_CARE.

    If no <attrib_list> is specified to eglGetPlatformDisplayEXT, the value of
    EGL_PLATFORM_ANGLE_DEVICE_TYPE_ANGLE is implicitly set to
    EGL_PLATFORM_ANGLE_DEVICE_TYPE_HARDWARE_ANGLE. Otherwise, the value of
    EGL_PLATFORM_ANGLE_DEVICE_TYPE_ANGLE should be:
      - EGL_PLATFORM_ANGLE_DEVICE_TYPE_HARDWARE_ANGLE to request a hardware
        accelerated device.
      - EGL_PLATFORM_ANGLE_DEVICE_TYPE_NULL_ANGLE to request a no-op driver
        for testing. If unavailable, the implementation will fall back to
        EGL_PLATFORM_ANGLE_DEVICE_TYPE_HARDWARE_ANGLE.

    If EGL_PLATFORM_ANGLE_MAX_VERSION_MAJOR_ANGLE is set to EGL_DONT_CARE and
    EGL_PLATFORM_ANGLE_MAX_VERSION_MINOR_ANGLE is not set to EGL_DONT_CARE,
    an EGL_BAD_ATTRIBUTE error is generated and EGL_NO_DISPLAY is returned.

    If no display matching the requested <native_display> or of the type
    requested by the value of EGL_PLATFORM_ANGLE_TYPE_ANGLE is available,
    EGL_NO_DISPLAY is returned. No error condition is raised in this case.

    If EGL_PLATFORM_ANGLE_DEBUG_LAYERS_ENABLED is specified, it
    controls enabling back-end validation layers. EGL_TRUE enables
    validation and EGL_FALSE disables it. If it is set to EGL_DONT_CARE, the
    default setting depends on the implementation. Any value other than these
    will result in an error.

Issues

    1) Should the validation layers default to on, off, or no guarantee?

       Defaulting to off offers some consistency. However, it's customary for
       some applications like ANGLE to turn on debugging features by default
       in Debug builds.

       RESOLVED: default to implementation-dependent behaviour.

Revision History

    Version 1, 2014-02-04 (Scott Graham)
      - Initial draft
    Version 2, 2014-06-05 (Geoff Lang)
      - Rename extension from ANGLE_platform_angle_d3d to ANGLE_platform_angle.
      - Add sub-extensions for specific platforms.
    Version 3, 2014-10-20 (Geoff Lang)
      - Add attributes to request specific feature level and context versions.
      - Moved descriptions of platforms to child extension specs.
    Version 4, 2017-07-19 (Jamie Madill)
      - Add a debug layers enabled attribute to control runtime validation.
    Version 5, 2017-12-28 (Jamie Madill)
      - Expose device type selection.