RHI: handle uniforms of type arrays properly

We weren't handling the possible array stride for uniform arrays.
For a float[8], the GPU might expect each float to fit in a vec4 slot.
We therefore have to handle that when uploading the values otherwise
we could end having data in what the GPU believe is padding data.

This required modifying the UniformValue object to report the number
of elements it contains as it might not necessarely be the same as the
array dimension reported by the shader introspection.

Note: it seems that the arrayStride might not be reported properly.
To work around that, if we know we are dealing with an array, we
compute the stride ourselves.

Pick-to: 6.0
Change-Id: I12b5379927dd47be888a40db58c2e5aba6e0730b
Reviewed-by: Mike Krus <mike.krus@kdab.com>

1 files changed, 30 insertions, 0 deletions

diff --git a/src/plugins/renderers/rhi/renderer/pipelineuboset.cpp b/src/plugins/renderers/rhi/renderer/pipelineuboset.cpp
index 0031d927d..0578c6a09 100644
--- a/src/plugins/renderers/rhi/renderer/pipelineuboset.cpp
+++ b/src/plugins/renderers/rhi/renderer/pipelineuboset.cpp
@@ -444,6 +444,33 @@ QByteArray rawDataForUniformValue(const QShaderDescription::BlockVariable &block
               ? QByteArray(value.constData<char>(), std::min(value.byteSize(), blockVariable.size))
               : QByteArray::fromRawData(value.constData<char>(), std::min(value.byteSize(), blockVariable.size));
     const int matrixStride = blockVariable.matrixStride;
+    int arrayStride = blockVariable.arrayStride;
+    const int firstArrayDim = !blockVariable.arrayDims.empty() ? blockVariable.arrayDims.first() : 0;
+
+    if (blockVariable.arrayDims.size() > 1)
+        qCWarning(Backend) << "Multi Dimension arrays not handled yet";
+
+    if (arrayStride != 0 && matrixStride != 0)
+        qCWarning(Backend) << "Arrays of matrices not handled yet";
+
+    // Special cases for arrays
+    if (firstArrayDim > 0) {
+        // It appears that for a float myArray[8]; stride is reported as being
+        // 0 but expected size 128 bytes which means 16 bytes per float
+        // In that case we compute the arrayStride ourselves
+        if (arrayStride == 0)
+            arrayStride = blockVariable.size / firstArrayDim;
+        if (arrayStride != 0) {
+            QByteArray newRawData(firstArrayDim * arrayStride, '\0');
+            const int byteSizePerEntry = value.elementByteSize();
+            for (int i = 0, m = std::min(firstArrayDim, value.elementCount()); i < m; ++i) {
+                std::memcpy(newRawData.data() + i * arrayStride,
+                            rawData.constData() + i * byteSizePerEntry,
+                            byteSizePerEntry);
+            }
+            return newRawData;
+        }
+    }
 
     // Special cases for matrices which might have to be aligned to a vec4 stride
     if (matrixStride != 0 && value.byteSize() % matrixStride != 0) {
@@ -457,6 +484,9 @@ QByteArray rawDataForUniformValue(const QShaderDescription::BlockVariable &block
         }
         return newRawData;
     }
+
+    // Note: we currently don't handle array of matrices
+
     return rawData;
 }