More graceful handling of QSurfaceFormat::samples() with EGL.

Earlier, if we asked for say 16 and the implementation only handled 4,
we defaulted to 0 (no antialiasing). Now, we instead try a progressively
lower number until we find a match.

Task-number: QTBUG-22669
Change-Id: I63f4b8aadf8e06713d19fdc9b9d73672162c816a
Reviewed-by: Jørgen Lind <jorgen.lind@nokia.com>

1 files changed, 10 insertions, 4 deletions

diff --git a/src/platformsupport/eglconvenience/qeglconvenience.cpp b/src/platformsupport/eglconvenience/qeglconvenience.cpp
index f9ccde6b52..4ba9c1f5ac 100644
--- a/src/platformsupport/eglconvenience/qeglconvenience.cpp
+++ b/src/platformsupport/eglconvenience/qeglconvenience.cpp
@@ -152,13 +152,19 @@ bool q_reduceConfigAttributes(QVector<EGLint> *configAttributes)
         }
     }
 
+    i = configAttributes->indexOf(EGL_SAMPLES);
+    if (i >= 0) {
+        EGLint value = configAttributes->value(i+1, 0);
+        if (value > 1)
+            configAttributes->replace(i+1, qMin(EGLint(16), value / 2));
+        else
+            configAttributes->remove(i, 2);
+        return true;
+    }
+
     i = configAttributes->indexOf(EGL_SAMPLE_BUFFERS);
     if (i >= 0) {
         configAttributes->remove(i,2);
-        i = configAttributes->indexOf(EGL_SAMPLES);
-        if (i >= 0) {
-            configAttributes->remove(i,2);
-        }
         return true;
     }