Windows: Fallback to 0 samples if ARB::choosePixelFormat() fails with 1

This solves a problem when using a Qt application over remote desktop as
if it failed with even 1 sample then it would fallback to GDI which causes
an error if the software OpenGL option is used.

Change-Id: Ib311a7a657f92aab15277461bc8e040bebbe4753
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@theqtcompany.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/src/plugins/platforms/windows/qwindowsglcontext.cpp b/src/plugins/platforms/windows/qwindowsglcontext.cpp
index 3348241d37..908bc65843 100644
--- a/src/plugins/platforms/windows/qwindowsglcontext.cpp
+++ b/src/plugins/platforms/windows/qwindowsglcontext.cpp
@@ -597,6 +597,14 @@ static int choosePixelFormat(HDC hdc,
             break;
         if (iAttributes[samplesValuePosition] > 1) {
             iAttributes[samplesValuePosition] /= 2;
+        } else if (iAttributes[samplesValuePosition] == 1) {
+            // Fallback in case it is unable to initialize with any
+            // samples to avoid falling back to the GDI path
+            // NB: The sample attributes needs to be at the end for this
+            // to work correctly
+            iAttributes[samplesValuePosition - 1] = FALSE;
+            iAttributes[samplesValuePosition] = 0;
+            iAttributes[samplesValuePosition + 1] = 0;
         } else {
             break;
         }