rhi: Improve layout compatibility test performance

Also bump the non-heap buffer size in the binding list to 16,
in order to accommodate complex Quick3D materials with many
associated texture maps.

Change-Id: Id190e5f8304f5941cffc41a2605fce45dfeb72f0
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

src/gui/rhi/qrhi.cpp

@@ -2806,16 +2806,25 @@ bool QRhiShaderResourceBindings::isLayoutCompatible(const QRhiShaderResourceBind
     if (!other)
         return false;
 
-    const int count = m_bindings.count();
-    if (count != other->m_bindings.count())
-        return false;
+    // This can become a hot code path. Therefore we do not iterate and call
+    // isLayoutCompatible() on m_bindings, but rather check a pre-calculated
+    // hash code and then, if the hash matched, do a uint array comparison
+    // (that's still more cache friendly).
 
-    for (int i = 0; i < count; ++i) {
-        if (!m_bindings[i].isLayoutCompatible(other->m_bindings.at(i)))
-            return false;
+    return m_layoutDescHash == other->m_layoutDescHash
+            && m_layoutDesc == other->m_layoutDesc;
+}
+
+void QRhiImplementation::updateLayoutDesc(QRhiShaderResourceBindings *srb)
+{
+    srb->m_layoutDescHash = 0;
+    srb->m_layoutDesc.clear();
+    for (const QRhiShaderResourceBinding &b : qAsConst(srb->m_bindings)) {
+        const QRhiShaderResourceBinding::Data *d = b.data();
+        // must match QRhiShaderResourceBinding::isLayoutCompatible()
+        srb->m_layoutDescHash ^= uint(d->binding) ^ uint(d->stage) ^ uint(d->type);
+        srb->m_layoutDesc << uint(d->binding) << uint(d->stage) << uint(d->type);
     }
-
-    return true;
 }
 
 /*!

src/gui/rhi/qrhi_p.h

@@ -1012,7 +1012,10 @@ public:
 
 protected:
     QRhiShaderResourceBindings(QRhiImplementation *rhi);
-    QVarLengthArray<QRhiShaderResourceBinding, 8> m_bindings;
+    QVarLengthArray<QRhiShaderResourceBinding, 16> m_bindings;
+    uint m_layoutDescHash = 0;
+    QVarLengthArray<uint, 16 * 3> m_layoutDesc;
+    friend class QRhiImplementation;
 #ifndef QT_NO_DEBUG_STREAM
     friend Q_GUI_EXPORT QDebug operator<<(QDebug, const QRhiShaderResourceBindings &);
 #endif

src/gui/rhi/qrhi_p_p.h

@@ -211,6 +211,7 @@ public:
 
     bool sanityCheckGraphicsPipeline(QRhiGraphicsPipeline *ps);
     bool sanityCheckShaderResourceBindings(QRhiShaderResourceBindings *srb);
+    void updateLayoutDesc(QRhiShaderResourceBindings *srb);
 
     QRhi *q;
 

src/gui/rhi/qrhid3d11.cpp

@@ -3456,6 +3456,8 @@ bool QD3D11ShaderResourceBindings::create()
     if (!rhiD->sanityCheckShaderResourceBindings(this))
         return false;
 
+    rhiD->updateLayoutDesc(this);
+
     std::copy(m_bindings.cbegin(), m_bindings.cend(), std::back_inserter(sortedBindings));
     std::sort(sortedBindings.begin(), sortedBindings.end(),
               [](const QRhiShaderResourceBinding &a, const QRhiShaderResourceBinding &b)

src/gui/rhi/qrhigles2.cpp

@@ -4307,6 +4307,8 @@ bool QGles2ShaderResourceBindings::create()
     if (!rhiD->sanityCheckShaderResourceBindings(this))
         return false;
 
+    rhiD->updateLayoutDesc(this);
+
     generation += 1;
     return true;
 }

src/gui/rhi/qrhimetal.mm

@@ -3013,6 +3013,8 @@ bool QMetalShaderResourceBindings::create()
     if (!rhiD->sanityCheckShaderResourceBindings(this))
         return false;
 
+    rhiD->updateLayoutDesc(this);
+
     std::copy(m_bindings.cbegin(), m_bindings.cend(), std::back_inserter(sortedBindings));
     std::sort(sortedBindings.begin(), sortedBindings.end(),
               [](const QRhiShaderResourceBinding &a, const QRhiShaderResourceBinding &b)

src/gui/rhi/qrhinull.cpp

@@ -800,6 +800,12 @@ void QNullShaderResourceBindings::destroy()
 
 bool QNullShaderResourceBindings::create()
 {
+    QRHI_RES_RHI(QRhiNull);
+    if (!rhiD->sanityCheckShaderResourceBindings(this))
+        return false;
+
+    rhiD->updateLayoutDesc(this);
+
     return true;
 }
 

src/gui/rhi/qrhivulkan.cpp

@@ -6186,6 +6186,8 @@ bool QVkShaderResourceBindings::create()
     if (!rhiD->sanityCheckShaderResourceBindings(this))
         return false;
 
+    rhiD->updateLayoutDesc(this);
+
     for (int i = 0; i < QVK_FRAMES_IN_FLIGHT; ++i)
         descSets[i] = VK_NULL_HANDLE;