[Mesa-dev] [PATCH 1/4] egl: rework handling EGL_CONTEXT_FLAGS

[Emil Velikov]

On 15 September 2015 at 14:27, Boyan Ding <boyan.j.ding at gmail.com> wrote:
> 2015-09-15 1:35 GMT+08:00 Emil Velikov <emil.l.velikov at gmail.com>:
>> From: Matthew Waters <ystreet00 at gmail.com>
>>
>> As of version 15 of the EGL_KHR_create_context spec, debug contexts
>> are allowed for ES contexts.  We should allow creation instead of
>> erroring.
>>
>> While we're here provide a more comprehensive checking for the other two
>> flags - ROBUST_ACCESS_BIT_KHR and FORWARD_COMPATIBLE_BIT_KHR
>>
>> v2 [Emil Velikov] Rebase. Minor tweak in commit message.
>>
>> Cc: Boyan Ding <boyan.j.ding at gmail.com>
>> Cc: Chad Versace <chad.versace at intel.com>
>> Cc: "10.6 11.0" <mesa-stable at lists.freedesktop.org>
>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91044
>> Signed-off-by: Matthew Waters <ystreet00 at gmail.com>
>> Signed-off-by: Emil Velikov <emil.l.velikov at gmail.com>
>> ---
>>  src/egl/main/eglcontext.c | 49 ++++++++++++++++++++++++++++++++++++++++++-----
>>  1 file changed, 44 insertions(+), 5 deletions(-)
>>
>> diff --git a/src/egl/main/eglcontext.c b/src/egl/main/eglcontext.c
>> index 588f489..ae19862 100644
>> --- a/src/egl/main/eglcontext.c
>> +++ b/src/egl/main/eglcontext.c
>> @@ -152,12 +152,51 @@ _eglParseContextAttribList(_EGLContext *ctx, _EGLDisplay *dpy,
>>
>>           /* The EGL_KHR_create_context spec says:
>>            *
>> -          *     "Flags are only defined for OpenGL context creation, and
>> -          *     specifying a flags value other than zero for other types of
>> -          *     contexts, including OpenGL ES contexts, will generate an
>> -          *     error."
>> +          *     "If the EGL_CONTEXT_OPENGL_DEBUG_BIT_KHR flag bit is set in
>> +          *     EGL_CONTEXT_FLAGS_KHR, then a <debug context> will be created.
>> +          *     [...]
>> +          *     In some cases a debug context may be identical to a non-debug
>> +          *     context. This bit is supported for OpenGL and OpenGL ES
>> +          *     contexts."
>> +          */
>> +         if ((val & EGL_CONTEXT_OPENGL_DEBUG_BIT_KHR) &&
>> +             (api != EGL_OPENGL_API && api != EGL_OPENGL_ES_API)) {
>> +            err = EGL_BAD_ATTRIBUTE;
>> +            break;
>> +         }
>> +
>> +         /* The EGL_KHR_create_context spec says:
>> +          *
>> +          *     "If the EGL_CONTEXT_OPENGL_FORWARD_COMPATIBLE_BIT_KHR flag bit
>> +          *     is set in EGL_CONTEXT_FLAGS_KHR, then a <forward-compatible>
>> +          *     context will be created. Forward-compatible contexts are
>> +          *     defined only for OpenGL versions 3.0 and later. They must not
>> +          *     support functionality marked as <deprecated> by that version of
>> +          *     the API, while a non-forward-compatible context must support
>> +          *     all functionality in that version, deprecated or not. This bit
>> +          *     is supported for OpenGL contexts, and requesting a
>> +          *     forward-compatible context for OpenGL versions less than 3.0
>> +          *     will generate an error."
>> +          */
>> +         if ((val & EGL_CONTEXT_OPENGL_FORWARD_COMPATIBLE_BIT_KHR) &&
>> +             (api != EGL_OPENGL_API || ctx->ClientMajorVersion < 3)) {
>> +            err = EGL_BAD_ATTRIBUTE;
>> +            break;
>> +         }
>> +
>> +         /* The EGL_KHR_create_context_spec says:
>> +          *
>> +          *     "If the EGL_CONTEXT_OPENGL_ROBUST_ACCESS_BIT_KHR bit is set in
>> +          *     EGL_CONTEXT_FLAGS_KHR, then a context supporting <robust buffer
>> +          *     access> will be created. Robust buffer access is defined in the
>> +          *     GL_ARB_robustness extension specification, and the resulting
>> +          *     context must also support either the GL_ARB_robustness
>> +          *     extension, or a version of OpenGL incorporating equivalent
>> +          *     functionality. This bit is supported for OpenGL contexts.
>>            */
>> -         if (api != EGL_OPENGL_API && val != 0) {
>> +         if ((val & EGL_CONTEXT_OPENGL_ROBUST_ACCESS_BIT_KHR) &&
>> +             (api != EGL_OPENGL_API ||
>> +              !dpy->Extensions.EXT_create_context_robustness)) {
>>              err = EGL_BAD_ATTRIBUTE;
>>              break;
>>           }
>
> I wonder if it's necessary to check the validity of the flags here,
> since driCreateContextAttribs in src/mesa/drivers/dri/common/dri_util.c
> also check those flags and the logic there seems to work.
>
Imho they are two are different things.

The glx/egl/etc ones are used to determine if the winsys layer
supports/sets them while, the DRI ones are used for internal
representation. As we don't know if tomorrow's new flags will require
changes within the loader(s), dri module(s) and/or both, it's nice to
have things separated.

Although I do see how they feel unnecessary atm. If people feel
against them we can nuke them.

-Emil