Buffer: make sure we force allocate before doing partial updates

Change-Id: I229f9bcd21a10c0a4cff5c4f559cd285a3e50276
Reviewed-by: Mike Krus <mike.krus@kdab.com>

1 files changed, 20 insertions, 9 deletions

diff --git a/src/render/geometry/buffer.cpp b/src/render/geometry/buffer.cpp
index 0d634c911..6db3bab44 100644
--- a/src/render/geometry/buffer.cpp
+++ b/src/render/geometry/buffer.cpp
@@ -137,20 +137,31 @@ void Buffer::syncFromFrontEnd(const QNode *frontEnd, bool firstTime)
             m_manager->addDirtyBuffer(peerId());
     }
     {
-        QVariant v = node->property("QT3D_updateData");
-        if (v.isValid()) {
+        const QVariant v = node->property("QT3D_updateData");
+
+        // Make sure we record data if it's the first time we are called
+        // or if we have no partial updates
+        if (firstTime || !v.isValid()){
+            const QByteArray newData = node->data();
+            const bool dirty = m_data != newData;
+            m_bufferDirty |= dirty;
+            m_data = newData;
+
+            // Since frontend applies partial updates to its m_data
+            // if we enter this code block, there's no problem in actually
+            // ignoring the partial updates
+            if (v.isValid())
+                const_cast<QBuffer *>(node)->setProperty("QT3D_updateData", {});
+
+            if (dirty && !m_data.isEmpty())
+                forceDataUpload();
+        } else if (v.isValid()) {
+            // Apply partial updates and record them to allow partial upload to the GPU
             Qt3DRender::QBufferUpdate updateData = v.value<Qt3DRender::QBufferUpdate>();
             m_data.replace(updateData.offset, updateData.data.size(), updateData.data);
             m_bufferUpdates.push_back(updateData);
             m_bufferDirty = true;
             const_cast<QBuffer *>(node)->setProperty("QT3D_updateData", {});
-        } else {
-            QByteArray newData = node->data();
-            bool dirty = m_data != newData;
-            m_bufferDirty |= dirty;
-            m_data = newData;
-            if (dirty && !m_data.isEmpty())
-                forceDataUpload();
         }
     }
     markDirty(AbstractRenderer::BuffersDirty);