rhi: Allow detecting texelFetch support

Change-Id: I166c89af99e1289ae60febf2f41fab07eab9f7e8
Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>

src/gui/rhi/qrhi.cpp

@@ -577,6 +577,11 @@ Q_LOGGING_CATEGORY(QRHI_LOG_INFO, "qt.rhi.general")
     specifying a non-zero level in QRhiReadbackDescription leads to returning
     an all-zero image. In practice this feature will be unsupported with OpenGL
     ES 2.0, while it will likely be supported everywhere else.
+
+    \value TexelFetch Indicates that texelFetch() is available in shaders. In
+    practice this will be reported as unsupported with OpenGL ES 2.0 and OpenGL
+    2.x contexts, because GLSL 100 es and versions before 130 do not support
+    this function.
  */
 
 /*!

src/gui/rhi/qrhi_p.h

@@ -1430,7 +1430,8 @@ public:
         BaseInstance,
         TriangleFanTopology,
         ReadBackNonUniformBuffer,
-        ReadBackNonBaseMipLevel
+        ReadBackNonBaseMipLevel,
+        TexelFetch
     };
 
     enum BeginFrameFlag {

src/gui/rhi/qrhid3d11.cpp

@@ -464,6 +464,8 @@ bool QRhiD3D11::isFeatureSupported(QRhi::Feature feature) const
         return true;
     case QRhi::ReadBackNonBaseMipLevel:
         return true;
+    case QRhi::TexelFetch:
+        return true;
     default:
         Q_UNREACHABLE();
         return false;

src/gui/rhi/qrhigles2.cpp

@@ -514,6 +514,8 @@ bool QRhiGles2::create(QRhi::Flags flags)
     else
         caps.nonBaseLevelFramebufferTexture = true;
 
+    caps.texelFetch = caps.ctxMajor >= 3; // 3.0 or ES 3.0
+
     if (!caps.gles) {
         f->glEnable(GL_VERTEX_PROGRAM_POINT_SIZE);
         f->glEnable(GL_POINT_SPRITE);
@@ -767,6 +769,8 @@ bool QRhiGles2::isFeatureSupported(QRhi::Feature feature) const
         return !caps.gles || caps.properMapBuffer;
     case QRhi::ReadBackNonBaseMipLevel:
         return caps.nonBaseLevelFramebufferTexture;
+    case QRhi::TexelFetch:
+        return caps.texelFetch;
     default:
         Q_UNREACHABLE();
         return false;

src/gui/rhi/qrhigles2_p_p.h

@@ -778,7 +778,8 @@ public:
               compute(false),
               textureCompareMode(false),
               properMapBuffer(false),
-              nonBaseLevelFramebufferTexture(false)
+              nonBaseLevelFramebufferTexture(false),
+              texelFetch(false)
         { }
         int ctxMajor;
         int ctxMinor;
@@ -811,6 +812,7 @@ public:
         uint textureCompareMode : 1;
         uint properMapBuffer : 1;
         uint nonBaseLevelFramebufferTexture : 1;
+        uint texelFetch : 1;
     } caps;
     QGles2SwapChain *currentSwapChain = nullptr;
     QVector<GLint> supportedCompressedFormats;

src/gui/rhi/qrhimetal.mm

@@ -562,6 +562,8 @@ bool QRhiMetal::isFeatureSupported(QRhi::Feature feature) const
         return true;
     case QRhi::ReadBackNonBaseMipLevel:
         return true;
+    case QRhi::TexelFetch:
+        return true;
     default:
         Q_UNREACHABLE();
         return false;

src/gui/rhi/qrhivulkan.cpp

@@ -3990,6 +3990,8 @@ bool QRhiVulkan::isFeatureSupported(QRhi::Feature feature) const
         return true;
     case QRhi::ReadBackNonBaseMipLevel:
         return true;
+    case QRhi::TexelFetch:
+        return true;
     default:
         Q_UNREACHABLE();
         return false;

tests/auto/gui/rhi/qrhi/tst_qrhi.cpp

@@ -294,7 +294,8 @@ void tst_QRhi::create()
             QRhi::BaseInstance,
             QRhi::TriangleFanTopology,
             QRhi::ReadBackNonUniformBuffer,
-            QRhi::ReadBackNonBaseMipLevel
+            QRhi::ReadBackNonBaseMipLevel,
+            QRhi::TexelFetch
         };
         for (size_t i = 0; i <sizeof(features) / sizeof(QRhi::Feature); ++i)
             rhi->isFeatureSupported(features[i]);