3 files changed, 31 insertions, 6 deletions

diff --git a/src/gui/rhi/qrhi.cpp b/src/gui/rhi/qrhi.cpp
index 06781686fa..5db0791322 100644
--- a/src/gui/rhi/qrhi.cpp
+++ b/src/gui/rhi/qrhi.cpp
@@ -1202,12 +1202,19 @@ QDebug operator<<(QDebug dbg, const QRhiVertexInputBinding &b)
 /*!
     Constructs a vertex input attribute description with the specified \a
     binding number, \a location, \a format, and \a offset.
+
+    \a matrixSlice should be -1 except when this attribute corresponds to a row
+    or column of a matrix (for example, a 4x4 matrix becomes 4 vec4s, consuming
+    4 consecutive vertex input locations), in which case it is the index of the
+    row or column. \c{location - matrixSlice} must always be equal to the \c
+    location for the first row or column of the unrolled matrix.
  */
-QRhiVertexInputAttribute::QRhiVertexInputAttribute(int binding, int location, Format format, quint32 offset)
+QRhiVertexInputAttribute::QRhiVertexInputAttribute(int binding, int location, Format format, quint32 offset, int matrixSlice)
     : m_binding(binding),
       m_location(location),
       m_format(format),
-      m_offset(offset)
+      m_offset(offset),
+      m_matrixSlice(matrixSlice)
 {
 }
 
diff --git a/src/gui/rhi/qrhi_p.h b/src/gui/rhi/qrhi_p.h
index 977b68cd8e..6a141d13e1 100644
--- a/src/gui/rhi/qrhi_p.h
+++ b/src/gui/rhi/qrhi_p.h
@@ -212,7 +212,7 @@ public:
     };
 
     QRhiVertexInputAttribute() = default;
-    QRhiVertexInputAttribute(int binding, int location, Format format, quint32 offset);
+    QRhiVertexInputAttribute(int binding, int location, Format format, quint32 offset, int matrixSlice = -1);
 
     int binding() const { return m_binding; }
     void setBinding(int b) { m_binding = b; }
@@ -226,11 +226,15 @@ public:
     quint32 offset() const { return m_offset; }
     void setOffset(quint32 ofs) { m_offset = ofs; }
 
+    int matrixSlice() const { return m_matrixSlice; }
+    void setMatrixSlice(int slice) { m_matrixSlice = slice; }
+
 private:
     int m_binding = 0;
     int m_location = 0;
     Format m_format = Float4;
     quint32 m_offset = 0;
+    int m_matrixSlice = -1;
 };
 
 Q_DECLARE_TYPEINFO(QRhiVertexInputAttribute, Q_MOVABLE_TYPE);
diff --git a/src/gui/rhi/qrhid3d11.cpp b/src/gui/rhi/qrhid3d11.cpp
index 48e626106c..ce954c9fe0 100644
--- a/src/gui/rhi/qrhid3d11.cpp
+++ b/src/gui/rhi/qrhid3d11.cpp
@@ -4019,15 +4019,29 @@ bool QD3D11GraphicsPipeline::create()
     d3dTopology = toD3DTopology(m_topology);
 
     if (!vsByteCode.isEmpty()) {
+        QByteArrayList matrixSliceSemantics;
         QVarLengthArray<D3D11_INPUT_ELEMENT_DESC, 4> inputDescs;
         for (auto it = m_vertexInputLayout.cbeginAttributes(), itEnd = m_vertexInputLayout.cendAttributes();
              it != itEnd; ++it)
         {
             D3D11_INPUT_ELEMENT_DESC desc;
             memset(&desc, 0, sizeof(desc));
-            // the output from SPIRV-Cross uses TEXCOORD<location> as the semantic
-            desc.SemanticName = "TEXCOORD";
-            desc.SemanticIndex = UINT(it->location());
+            // The output from SPIRV-Cross uses TEXCOORD<location> as the
+            // semantic, except for matrices that are unrolled into consecutive
+            // vec2/3/4s attributes and need TEXCOORD<location>_ as
+            // SemanticName and row/column index as SemanticIndex.
+            const int matrixSlice = it->matrixSlice();
+            if (matrixSlice < 0) {
+                desc.SemanticName = "TEXCOORD";
+                desc.SemanticIndex = UINT(it->location());
+            } else {
+                QByteArray sem;
+                sem.resize(16);
+                qsnprintf(sem.data(), sem.size(), "TEXCOORD%d_", it->location() - matrixSlice);
+                matrixSliceSemantics.append(sem);
+                desc.SemanticName = matrixSliceSemantics.last().constData();
+                desc.SemanticIndex = UINT(matrixSlice);
+            }
             desc.Format = toD3DAttributeFormat(it->format());
             desc.InputSlot = UINT(it->binding());
             desc.AlignedByteOffset = it->offset();