[Mesa-dev] [PATCH 2/2] egl: implement EGL_MESA_transparent_alpha for x11 and wayland

[Chad Versace]

On 02/23/2015 06:32 AM, Jonny Lamb wrote:
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=67676
> ---
>  include/EGL/eglmesaext.h                |  5 +++++
>  src/egl/drivers/dri2/platform_wayland.c |  9 +++++++--
>  src/egl/drivers/dri2/platform_x11.c     | 22 +++++++++++++---------
>  src/egl/main/eglapi.c                   | 13 +++++++++++++
>  src/egl/main/eglconfig.c                |  3 ++-
>  5 files changed, 40 insertions(+), 12 deletions(-)
> 
> diff --git a/include/EGL/eglmesaext.h b/include/EGL/eglmesaext.h
> index 5fcc527..3fa7c9c 100644
> --- a/include/EGL/eglmesaext.h
> +++ b/include/EGL/eglmesaext.h
> @@ -170,6 +170,11 @@ typedef EGLBoolean (EGLAPIENTRYP PFNEGLSWAPBUFFERSREGIONNOK) (EGLDisplay dpy, EG
>  #define EGL_NO_CONFIG_MESA			((EGLConfig)0)
>  #endif
>  
> +#ifndef EGL_MESA_transparent_alpha
> +#define EGL_MESA_transparent_alpha 1
> +#define EGL_TRANSPARENT_ALPHA_MESA		0x31E9
> +#endif

According to the EGL registry today, 0x31E9 is owned by Hitachi. The first unused enum
in Mesa's reserved range is 0x31D9, so you should use that.

> +
>  #ifdef __cplusplus
>  }
>  #endif
> diff --git a/src/egl/drivers/dri2/platform_wayland.c b/src/egl/drivers/dri2/platform_wayland.c
> index 3c34e07..ba071a5 100644
> --- a/src/egl/drivers/dri2/platform_wayland.c
> +++ b/src/egl/drivers/dri2/platform_wayland.c
> @@ -965,6 +965,10 @@ dri2_initialize_wayland(_EGLDriver *drv, _EGLDisplay *disp)
>        { 0xff0000, 0xff00, 0xff, 0xff000000 };
>     static const unsigned int rgb_masks[4] = { 0xff0000, 0xff00, 0xff, 0 };
>     static const unsigned int rgb565_masks[4] = { 0xf800, 0x07e0, 0x001f, 0 };
> +   static const EGLint argb_attrs[] = {
> +       EGL_TRANSPARENT_TYPE, EGL_TRANSPARENT_ALPHA_MESA,
> +       EGL_NONE
> +   };
>  
>     loader_set_logger(_eglLog);
>  
> @@ -1044,8 +1048,9 @@ dri2_initialize_wayland(_EGLDriver *drv, _EGLDisplay *disp)
>        config = dri2_dpy->driver_configs[i];
>        if (dri2_dpy->formats & HAS_XRGB8888)
>  	 dri2_add_config(disp, config, i + 1, types, NULL, rgb_masks);
> -      if (dri2_dpy->formats & HAS_ARGB8888)
> -	 dri2_add_config(disp, config, i + 1, types, NULL, argb_masks);
> +      if (dri2_dpy->formats & HAS_ARGB8888) {
> +	 dri2_add_config(disp, config, i + 1, types, argb_attrs, argb_masks);
> +      }
>        if (dri2_dpy->formats & HAS_RGB565)
>          dri2_add_config(disp, config, i + 1, types, NULL, rgb565_masks);
>     }

I tested this patch with X11 and Mesa, and it works as advertised. BUT...

Pre-patch, Wayland applications who requested an EGLConfig with alpha
received one. The EGLSurface had compositor-transparent alpha, which
the application may not have expected. But the alpha configs *were*
available.

Post-patch, existing Wayland applications that request an EGLConfig with
alpha will no longer receive one, because the existing applications
do not yet know about EGL_TRANSPARENT_ALPHA_MESA.

I believe a correct solution is to continue create EGLConfigs
with EGL_ALPHA and without EGL_TRANSPARENT_TYPE, as Mesa does today,
but tell the compositor to ignore the alpha channel. The alpha channel
will be used for client-side alpha-blending but not for compositing.
Jason says that should be possible by telling the compositor that
the buffer format is WL_DRM_FORMAT_XRGB8888. And in addition to the existing
EGLConfigs, also create new EGLConfigs with EGL_TRANSPARENT_ALPHA_MESA, as
this patch already does.

By the way, the X11 portion of the patch looks good to me.







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