Optimize partial data update support for QBuffer

Now both QBuffer setData/functor and partial data update can be called
without unexpected behavior. Optimize applying sequential updates.

Change-Id: I5d3a8bcb7eb6eeb3ae33f0fbedbb34acedd1c000
Reviewed-by: Oleg Evseev <ev.mipt@gmail.com>
Reviewed-by: Dmitry Volosnykh <dmitry.volosnykh@gmail.com>
Reviewed-by: Paul Lemire <paul.lemire@kdab.com>

2 files changed, 33 insertions, 12 deletions

diff --git a/src/render/geometry/buffer.cpp b/src/render/geometry/buffer.cpp
index 1133b8e5e..ae5ede731 100644
--- a/src/render/geometry/buffer.cpp
+++ b/src/render/geometry/buffer.cpp
@@ -134,7 +134,14 @@ void Buffer::sceneChangeEvent(const Qt3DCore::QSceneChangePtr &e)
         QByteArray propertyName = propertyChange->propertyName();
         if (propertyName == QByteArrayLiteral("data")) {
             QByteArray newData = propertyChange->value().value<QByteArray>();
-            m_bufferDirty |= m_data != newData;
+            bool dirty = m_data != newData;
+            m_bufferDirty |= dirty;
+            if (dirty) {
+                QBufferUpdate updateNewData;
+                updateNewData.offset = -1;
+                m_bufferUpdates.clear(); //previous updates are pointless
+                m_bufferUpdates.push_back(updateNewData);
+            }
             m_data = newData;
         } else if (propertyName == QByteArrayLiteral("updateData")) {
             Qt3DRender::QBufferUpdate updateData = propertyChange->value().value<Qt3DRender::QBufferUpdate>();
diff --git a/src/render/graphicshelpers/graphicscontext.cpp b/src/render/graphicshelpers/graphicscontext.cpp
index 6e585c0a2..65414e220 100644
--- a/src/render/graphicshelpers/graphicscontext.cpp
+++ b/src/render/graphicshelpers/graphicscontext.cpp
@@ -1528,21 +1528,35 @@ void GraphicsContext::uploadDataToGLBuffer(Buffer *buffer, GLBuffer *b, bool rel
     // * setData was called changing the whole data or functor (or the usage pattern)
     // * partial buffer updates where received
 
-    // Note: we assume the case where both setData/functor and updates are called to be a misuse
-    // with unexpected behavior
-    const QVector<Qt3DRender::QBufferUpdate> updates = std::move(buffer->pendingBufferUpdates());
-    if (!updates.empty()) {
-        for (const Qt3DRender::QBufferUpdate &update : updates) {
+    // TO DO: Handle usage pattern
+    QVector<Qt3DRender::QBufferUpdate> updates = std::move(buffer->pendingBufferUpdates());
+    for (auto it = updates.begin(); it != updates.end(); ++it) {
+        auto update = it;
+        if (update->offset >= 0) {
+            //accumulate sequential updates as single one
+            int bufferSize = update->data.size();
+            auto it2 = it + 1;
+            while ((it2 != updates.end())
+                   && (it2->offset - update->offset == bufferSize)) {
+                bufferSize += it2->data.size();
+                ++it2;
+            }
+            update->data.resize(bufferSize);
+            while (it + 1 != it2) {
+                ++it;
+                update->data.replace(it->offset - update->offset, it->data.size(), it->data);
+                it->data.clear();
+            }
             // TO DO: based on the number of updates .., it might make sense to
             // sometime use glMapBuffer rather than glBufferSubData
-            b->update(this, update.data.constData(), update.data.size(), update.offset);
+            b->update(this, update->data.constData(), update->data.size(), update->offset);
+        } else {
+            const int bufferSize = buffer->data().size();
+            b->allocate(this, bufferSize, false); // orphan the buffer
+            b->allocate(this, buffer->data().constData(), bufferSize, false);
         }
-    } else {
-        const int bufferSize = buffer->data().size();
-        // TO DO: Handle usage pattern
-        b->allocate(this, bufferSize, false); // orphan the buffer
-        b->allocate(this, buffer->data().constData(), bufferSize, false);
     }
+
     if (releaseBuffer) {
         b->release(this);
         if (bufferTypeToGLBufferType(buffer->type()) == GLBuffer::ArrayBuffer)