From 9b3848c5d0e1e572d3e5c708676fd839852fca50 Mon Sep 17 00:00:00 2001
From: Laszlo Agocs <laszlo.agocs@qt.io>
Date: Fri, 16 Dec 2022 13:48:13 +0100
Subject: [PATCH] windows: gl: Fix WGL_SAMPLES reduction

The logic for writing 0 and false to the keys and values
is off by one.

While we are at it, unify the naming between the two settings
that are possible to reduce (samples and sRGB).

Amends d64f776a9a41a8d1144397b7b62efbdee8d24857

Fixes: QTBUG-109453
Change-Id: I97f3a3c7175bcb555c70967056ab2de45b077f48
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Andy Nichols <andy.nichols@qt.io>
(cherry picked from commit 3e619aff308dad02ee3d54aeda85a2bbaae77063)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
---
 .../platforms/windows/qwindowsglcontext.cpp       | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/src/plugins/platforms/windows/qwindowsglcontext.cpp b/src/plugins/platforms/windows/qwindowsglcontext.cpp
index 65740d69dac..cfd73519fa0 100644
--- a/src/plugins/platforms/windows/qwindowsglcontext.cpp
+++ b/src/plugins/platforms/windows/qwindowsglcontext.cpp
@@ -544,11 +544,14 @@ static int choosePixelFormat(HDC hdc,
         iAttributes[i++] = WGL_NUMBER_OVERLAYS_ARB;
         iAttributes[i++] = 1;
     }
+    // must be the one before the last one
     const int samples = format.samples();
     const bool sampleBuffersRequested = samples > 1
             && testFlag(staticContext.extensions, QOpenGLStaticContext::SampleBuffers);
+    int sampleBuffersKeyPosition = 0;
     int samplesValuePosition = 0;
     if (sampleBuffersRequested) {
+        sampleBuffersKeyPosition = i;
         iAttributes[i++] = WGL_SAMPLE_BUFFERS_ARB;
         iAttributes[i++] = TRUE;
         iAttributes[i++] = WGL_SAMPLES_ARB;
@@ -560,9 +563,9 @@ static int choosePixelFormat(HDC hdc,
     }
     // must be the last
     bool srgbRequested = format.colorSpace() == QColorSpace::SRgb;
-    int srgbValuePosition = 0;
+    int srgbCapableKeyPosition = 0;
     if (srgbRequested) {
-        srgbValuePosition = i;
+        srgbCapableKeyPosition = i;
         iAttributes[i++] = WGL_FRAMEBUFFER_SRGB_CAPABLE_EXT;
         iAttributes[i++] = TRUE;
     }
@@ -576,8 +579,9 @@ static int choosePixelFormat(HDC hdc,
                 && numFormats >= 1;
         if (valid || (!sampleBuffersRequested && !srgbRequested))
             break;
+        // NB reductions must be done in reverse order (disable the last first, then move on to the one before that, etc.)
         if (srgbRequested) {
-            iAttributes[srgbValuePosition] = 0;
+            iAttributes[srgbCapableKeyPosition] = 0;
             srgbRequested = false;
         } else if (sampleBuffersRequested) {
             if (iAttributes[samplesValuePosition] > 1) {
@@ -585,11 +589,8 @@ static int choosePixelFormat(HDC hdc,
             } 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[sampleBuffersKeyPosition] = 0;
                 iAttributes[samplesValuePosition] = 0;
-                iAttributes[samplesValuePosition + 1] = 0;
             } else {
                 break;
             }