Rhi: Add SampleVariables feature

The feature is required to check if gl_sampleID etc are available in the
fragment shaders.

Task-number: QTBUG-134999
Change-Id: Id26c75780011a7553d332ae22e69aab632891998
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>
(cherry picked from commit 86e3573671ec3ea919e534957bf9dc320f853575)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/gui/rhi/qrhi.cpp

@@ -1091,6 +1091,12 @@ Q_LOGGING_CATEGORY(QRHI_LOG_RUB, "qt.rhi.rub")
     blending modes. In practice this can be expected to be supported everywhere
     except OpenGL ES, where it is only available with GLES 3.2 implementations.
     This enum value has been introduced in Qt 6.9.
+
+    \value SampleVariables Indicates that gl_SampleID, gl_SamplePosition,
+    gl_SampleMaskIn and gl_SampleMask variables are available in fragment shaders.
+    In practice this can be expected to be supported everywhere except OpenGL ES,
+    where it is only available with GLES 3.2 implementations.
+    This enum value has been introduced in Qt 6.9.
  */
 
 /*!

src/gui/rhi/qrhi.h

@@ -1912,6 +1912,7 @@ public:
         VariableRateShadingMap,
         VariableRateShadingMapWithTexture,
         PerRenderTargetBlending,
+        SampleVariables
     };
 
     enum BeginFrameFlag {

src/gui/rhi/qrhid3d11.cpp

@@ -657,6 +657,7 @@ bool QRhiD3D11::isFeatureSupported(QRhi::Feature feature) const
     case QRhi::VariableRateShadingMapWithTexture:
         return false;
     case QRhi::PerRenderTargetBlending:
+    case QRhi::SampleVariables:
         return true;
     default:
         Q_UNREACHABLE();

src/gui/rhi/qrhid3d12.cpp

@@ -808,6 +808,7 @@ bool QRhiD3D12::isFeatureSupported(QRhi::Feature feature) const
     case QRhi::VariableRateShadingMapWithTexture:
         return caps.vrsMap;
     case QRhi::PerRenderTargetBlending:
+    case QRhi::SampleVariables:
         return true;
     }
     return false;

src/gui/rhi/qrhigles2.cpp

@@ -1141,6 +1141,16 @@ bool QRhiGles2::create(QRhi::Flags flags)
     else
         caps.perRenderTargetBlending = caps.ctxMajor >= 4;
 
+    if (caps.gles) {
+        if (caps.ctxMajor == 3 && caps.ctxMinor < 2) {
+            caps.sampleVariables = ctx->hasExtension("GL_OES_sample_variables");
+        } else {
+            caps.sampleVariables = caps.ctxMajor > 3 || (caps.ctxMajor == 3 && caps.ctxMinor >= 2);
+        }
+    } else {
+        caps.sampleVariables = caps.ctxMajor >= 4;
+    }
+
     nativeHandlesStruct.context = ctx;
 
     contextLost = false;
@@ -1555,6 +1565,8 @@ bool QRhiGles2::isFeatureSupported(QRhi::Feature feature) const
         return false;
     case QRhi::PerRenderTargetBlending:
         return caps.perRenderTargetBlending;
+    case QRhi::SampleVariables:
+        return caps.sampleVariables;
     default:
         Q_UNREACHABLE_RETURN(false);
     }

src/gui/rhi/qrhigles2_p.h

@@ -1090,6 +1090,7 @@ public:
         uint glesMultiviewMultisampleRenderToTexture : 1;
         uint unpackRowLength : 1;
         uint perRenderTargetBlending : 1;
+        uint sampleVariables : 1;
     } caps;
     QGles2SwapChain *currentSwapChain = nullptr;
     QSet<GLint> supportedCompressedFormats;

src/gui/rhi/qrhimetal.mm

@@ -868,6 +868,7 @@ bool QRhiMetal::isFeatureSupported(QRhi::Feature feature) const
     case QRhi::VariableRateShadingMapWithTexture:
         return false;
     case QRhi::PerRenderTargetBlending:
+    case QRhi::SampleVariables:
         return true;
     default:
         Q_UNREACHABLE();

src/gui/rhi/qrhivulkan.cpp

@@ -5252,6 +5252,7 @@ bool QRhiVulkan::isFeatureSupported(QRhi::Feature feature) const
     case QRhi::VariableRateShadingMapWithTexture:
         return caps.renderPass2KHR && caps.imageBasedShadingRate;
     case QRhi::PerRenderTargetBlending:
+    case QRhi::SampleVariables:
         return true;
     default:
         Q_UNREACHABLE_RETURN(false);