[Mesa-dev] [PATCH] egl/dri2: Implement swapInterval fallback in a conformant way (v2)

[Tomasz Figa]

dri2_fallback_swap_interval() currently used to stub out swap interval
support in Android backend does nothing besides returning EGL_FALSE.
This causes at least one known application (Android Snapchat) to fail
due to an unexpected error and my loose interpretation of the EGL 1.5
specification justifies it. Relevant quote below:

    The function

        EGLBoolean eglSwapInterval(EGLDisplay dpy, EGLint interval);

    specifies the minimum number of video frame periods per buffer swap
    for the draw surface of the current context, for the current rendering
    API. [...]

    The parameter interval specifies the minimum number of video frames
    that are displayed before a buffer swap will occur. The interval
    specified by the function applies to the draw surface bound to the
    context that is current on the calling thread. [...] interval is
    silently clamped to minimum and maximum implementation dependent
    values before being stored; these values are defined by EGLConfig
    attributes EGL_MIN_SWAP_INTERVAL and EGL_MAX_SWAP_INTERVAL
    respectively.

    The default swap interval is 1.

Even though it does not specify the exact behavior if the platform does
not support changing the swap interval, the default assumed state is the
swap interval of 1, which I interpret as a value that eglSwapInterval()
should succeed if called with, even if there is no ability to change the
interval (but there is no change requested). Moreover, since the
behavior is defined to clamp the requested value to minimum and maximum
and at least the default value of 1 must be present in the range, the
implementation might be expected to have a valid range, which in case of
the feature being unsupported, would correspond to {1} and any request
might be expected to be clamped to this value.

Fix this by defaulting dri2_dpy's min_swap_interval, max_swap_interval
and default_swap_interval to 1 in dri2_setup_screen() and let platforms,
which support this functionality set their own values after this
function returns. Thanks to patches merged earlier, we can also remove
the dri2_fallback_swap_interval() completely, as with a singular range
it would not be called anyway.

v2: Remove dri2_fallback_swap_interval() completely thanks to higher
    layer already clamping the requested interval and not calling the
    driver layer if the clamped value is the same as current.

Signed-off-by: Tomasz Figa <tfiga at chromium.org>
---
 src/egl/drivers/dri2/egl_dri2.c             | 12 ++++++++++++
 src/egl/drivers/dri2/egl_dri2_fallbacks.h   |  7 -------
 src/egl/drivers/dri2/platform_android.c     |  1 -
 src/egl/drivers/dri2/platform_drm.c         |  1 -
 src/egl/drivers/dri2/platform_surfaceless.c |  1 -
 src/egl/drivers/dri2/platform_x11.c         |  2 +-
 6 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/src/egl/drivers/dri2/egl_dri2.c b/src/egl/drivers/dri2/egl_dri2.c
index f0d1ded408..686dd68d29 100644
--- a/src/egl/drivers/dri2/egl_dri2.c
+++ b/src/egl/drivers/dri2/egl_dri2.c
@@ -630,6 +630,18 @@ dri2_setup_screen(_EGLDisplay *disp)
    struct dri2_egl_display *dri2_dpy = dri2_egl_display(disp);
    unsigned int api_mask;
 
+   /*
+    * EGL 1.5 specification defines the default value to 1. Moreover,
+    * eglSwapInterval() is required to clamp requested value to the supported
+    * range. Since the default value is implicitly assumed to be supported,
+    * use it as both minimum and maximum for the platforms that do not allow
+    * changing the interval. Platforms, which allow it (e.g. x11, wayland)
+    * override these values already.
+    */
+   dri2_dpy->min_swap_interval = 1;
+   dri2_dpy->max_swap_interval = 1;
+   dri2_dpy->default_swap_interval = 1;
+
    if (dri2_dpy->image_driver) {
       api_mask = dri2_dpy->image_driver->getAPIMask(dri2_dpy->dri_screen);
    } else if (dri2_dpy->dri2) {
diff --git a/src/egl/drivers/dri2/egl_dri2_fallbacks.h b/src/egl/drivers/dri2/egl_dri2_fallbacks.h
index 604db881a8..a664677572 100644
--- a/src/egl/drivers/dri2/egl_dri2_fallbacks.h
+++ b/src/egl/drivers/dri2/egl_dri2_fallbacks.h
@@ -55,13 +55,6 @@ dri2_fallback_create_image_khr(_EGLDriver *drv, _EGLDisplay *disp,
    return NULL;
 }
 
-static inline EGLBoolean
-dri2_fallback_swap_interval(_EGLDriver *drv, _EGLDisplay *dpy,
-                            _EGLSurface *surf, EGLint interval)
-{
-   return EGL_FALSE;
-}
-
 static inline EGLBoolean
 dri2_fallback_swap_buffers_with_damage(_EGLDriver *drv, _EGLDisplay *dpy,
                                       _EGLSurface *surf,
diff --git a/src/egl/drivers/dri2/platform_android.c b/src/egl/drivers/dri2/platform_android.c
index 50a8248695..c1bae34f2d 100644
--- a/src/egl/drivers/dri2/platform_android.c
+++ b/src/egl/drivers/dri2/platform_android.c
@@ -1118,7 +1118,6 @@ static const struct dri2_egl_display_vtbl droid_display_vtbl = {
    .create_pbuffer_surface = droid_create_pbuffer_surface,
    .destroy_surface = droid_destroy_surface,
    .create_image = droid_create_image_khr,
-   .swap_interval = dri2_fallback_swap_interval,
    .swap_buffers = droid_swap_buffers,
    .swap_buffers_with_damage = dri2_fallback_swap_buffers_with_damage,
    .swap_buffers_region = dri2_fallback_swap_buffers_region,
diff --git a/src/egl/drivers/dri2/platform_drm.c b/src/egl/drivers/dri2/platform_drm.c
index a952aa5456..8edfbcd07c 100644
--- a/src/egl/drivers/dri2/platform_drm.c
+++ b/src/egl/drivers/dri2/platform_drm.c
@@ -674,7 +674,6 @@ static const struct dri2_egl_display_vtbl dri2_drm_display_vtbl = {
    .create_pbuffer_surface = dri2_fallback_create_pbuffer_surface,
    .destroy_surface = dri2_drm_destroy_surface,
    .create_image = dri2_drm_create_image_khr,
-   .swap_interval = dri2_fallback_swap_interval,
    .swap_buffers = dri2_drm_swap_buffers,
    .swap_buffers_with_damage = dri2_fallback_swap_buffers_with_damage,
    .swap_buffers_region = dri2_fallback_swap_buffers_region,
diff --git a/src/egl/drivers/dri2/platform_surfaceless.c b/src/egl/drivers/dri2/platform_surfaceless.c
index 1091b4febd..678dc88532 100644
--- a/src/egl/drivers/dri2/platform_surfaceless.c
+++ b/src/egl/drivers/dri2/platform_surfaceless.c
@@ -234,7 +234,6 @@ static const struct dri2_egl_display_vtbl dri2_surfaceless_display_vtbl = {
    .create_pbuffer_surface = dri2_surfaceless_create_pbuffer_surface,
    .destroy_surface = surfaceless_destroy_surface,
    .create_image = dri2_create_image_khr,
-   .swap_interval = dri2_fallback_swap_interval,
    .swap_buffers = surfaceless_swap_buffers,
    .swap_buffers_with_damage = dri2_fallback_swap_buffers_with_damage,
    .swap_buffers_region = dri2_fallback_swap_buffers_region,
diff --git a/src/egl/drivers/dri2/platform_x11.c b/src/egl/drivers/dri2/platform_x11.c
index 4610ec579f..122e4c193d 100644
--- a/src/egl/drivers/dri2/platform_x11.c
+++ b/src/egl/drivers/dri2/platform_x11.c
@@ -1139,7 +1139,6 @@ static const struct dri2_egl_display_vtbl dri2_x11_swrast_display_vtbl = {
    .create_pbuffer_surface = dri2_x11_create_pbuffer_surface,
    .destroy_surface = dri2_x11_destroy_surface,
    .create_image = dri2_create_image_khr,
-   .swap_interval = dri2_fallback_swap_interval,
    .swap_buffers = dri2_x11_swap_buffers,
    .set_damage_region = dri2_fallback_set_damage_region,
    .swap_buffers_region = dri2_fallback_swap_buffers_region,
@@ -1283,6 +1282,7 @@ dri2_x11_setup_swap_interval(struct dri2_egl_display *dri2_dpy)
     */
    dri2_dpy->min_swap_interval = 0;
    dri2_dpy->max_swap_interval = 0;
+   dri2_dpy->default_swap_interval = 0;
 
    if (!dri2_dpy->swap_available)
       return;
-- 
2.14.0.434.g98096fd7a8-goog