Re: [Qemu-devel] [PATCH] egl-helpers: Support newer MESA versions

[Hans de Goede <hdegoede@redhat.com>]

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<resend with some more people added to the Cc>

Hi,

On 20-02-17 10:50, Frediano Ziglio wrote:
> According to
> https://www.khronos.org/registry/EGL/extensions/MESA/EGL_MESA_platform_gbm.txt
> if MESA_platform_gbm is supported display should be initialized
> from a GBM handle using eglGetPlatformDisplayEXT.
>
> Signed-off-by: Frediano Ziglio <fziglio@redhat.com>
> ---
> This should fix
> http://www.spinics.net/linux/fedora/libvir/msg142837.html
>
> Tested on Fedora rawhide.
> ---
>  ui/egl-helpers.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/ui/egl-helpers.c b/ui/egl-helpers.c
> index cd24568..964c5a5 100644
> --- a/ui/egl-helpers.c
> +++ b/ui/egl-helpers.c
> @@ -219,7 +219,11 @@ int qemu_egl_init_dpy(EGLNativeDisplayType dpy, bool gles, bool debug)
>      }
>
>      egl_dbg("eglGetDisplay (dpy %p) ...\n", dpy);
> +#ifdef EGL_MESA_platform_gbm
> +    qemu_egl_display = eglGetPlatformDisplayEXT(EGL_PLATFORM_GBM_MESA, dpy, NULL);
> +#else
>      qemu_egl_display = eglGetDisplay(dpy);
> +#endif
>      if (qemu_egl_display == EGL_NO_DISPLAY) {
>          error_report("egl: eglGetDisplay failed");
>          return -1;
>

That fix is incomplete, you need some magic to work properly on older libGL versions.

Attached is a (compile tested only) proper patch. I do not have a qemu git clone
handy atm, so this is not a git format-patch patch, it is against the Fedora Rawhide
srpm. I've a test build with these patches here:

https://fedorapeople.org/~jwrdegoede/qemu-glvnd/

I was planning on doing a git clone qemu and send a proper patch after I got some
testing feedback. Feel free to use this as a base for a v2 of your patch.

Regards,

Hans




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diff -up qemu-2.8.0/ui/egl-helpers.c~ qemu-2.8.0/ui/egl-helpers.c
--- qemu-2.8.0/ui/egl-helpers.c~	2016-12-20 21:16:54.000000000 +0100
+++ qemu-2.8.0/ui/egl-helpers.c	2017-03-13 08:56:32.402845087 +0100
@@ -172,6 +172,50 @@ EGLSurface qemu_egl_init_surface_x11(EGL
 
 /* ---------------------------------------------------------------------- */
 
+/*
+ * Taken from glamor_egl.h from the Xorg xserver, which is MIT licensed
+ *
+ * Create an EGLDisplay from a native display type. This is a little quirky
+ * for a few reasons.
+ *
+ * 1: GetPlatformDisplayEXT and GetPlatformDisplay are the API you want to
+ * use, but have different function signatures in the third argument; this
+ * happens not to matter for us, at the moment, but it means epoxy won't alias
+ * them together.
+ *
+ * 2: epoxy 1.3 and earlier don't understand EGL client extensions, which
+ * means you can't call "eglGetPlatformDisplayEXT" directly, as the resolver
+ * will crash.
+ *
+ * 3: You can't tell whether you have EGL 1.5 at this point, because
+ * eglQueryString(EGL_VERSION) is a property of the display, which we don't
+ * have yet. So you have to query for extensions no matter what. Fortunately
+ * epoxy_has_egl_extension _does_ let you query for client extensions, so
+ * we don't have to write our own extension string parsing.
+ *
+ * 4. There is no EGL_KHR_platform_base to complement the EXT one, thus one
+ * needs to know EGL 1.5 is supported in order to use the eglGetPlatformDisplay
+ * function pointer.
+ * We can workaround this (circular dependency) by probing for the EGL 1.5
+ * platform extensions (EGL_KHR_platform_gbm and friends) yet it doesn't seem
+ * like mesa will be able to adverise these (even though it can do EGL 1.5).
+ */
+static EGLDisplay qemu_egl_get_display(EGLint type, void *native)
+{
+    EGLDisplay dpy = NULL;
+
+    /* In practise any EGL 1.5 implementation would support the EXT extension */
+    if (epoxy_has_egl_extension(NULL, "EGL_EXT_platform_base")) {
+        PFNEGLGETPLATFORMDISPLAYEXTPROC getPlatformDisplayEXT =
+            (void *) eglGetProcAddress("eglGetPlatformDisplayEXT");
+        if (getPlatformDisplayEXT)
+            return getPlatformDisplayEXT(type, native, NULL);
+    }
+
+    /* Welp, everything is awful. */
+    return eglGetDisplay(native);
+}
+
 int qemu_egl_init_dpy(EGLNativeDisplayType dpy, bool gles, bool debug)
 {
     static const EGLint conf_att_gl[] = {
@@ -202,8 +246,8 @@ int qemu_egl_init_dpy(EGLNativeDisplayTy
         setenv("LIBGL_DEBUG", "verbose", true);
     }
 
-    egl_dbg("eglGetDisplay (dpy %p) ...\n", dpy);
-    qemu_egl_display = eglGetDisplay(dpy);
+    egl_dbg("qemu_egl_get_display (dpy %p) ...\n", dpy);
+    qemu_egl_display = qemu_egl_get_display(EGL_PLATFORM_GBM_MESA, dpy);
     if (qemu_egl_display == EGL_NO_DISPLAY) {
         error_report("egl: eglGetDisplay failed");
         return -1;