Transfers gpu buffer data to cpu

Added some code to retrieve the data in the gpu back to a cpu pointer
in the opengl helpers.

Added a framegraph node which specifies if any data must be downloaded
from the gpu

Added a flag in the buffer object to specify if the data from that
buffer must be downloaded.

Added a job to send the data back to the frontend.

Added a path in the renderer to download the gpu data.

Task number: QTBUG-57727

Change-Id: I315a9221e5116c7d07f818e00c654fe1901144f4
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>

2 files changed, 14 insertions, 0 deletions

diff --git a/src/render/io/glbuffer.cpp b/src/render/io/glbuffer.cpp
index 074868528..4918f9a56 100644
--- a/src/render/io/glbuffer.cpp
+++ b/src/render/io/glbuffer.cpp
@@ -140,6 +140,18 @@ void GLBuffer::update(GraphicsContext *ctx, const void *data, uint size, int off
     ctx->openGLContext()->functions()->glBufferSubData(m_lastTarget, offset, size, data);
 }
 
+QByteArray GLBuffer::download(GraphicsContext *ctx, uint size)
+{
+    char *gpu_ptr = ctx->mapBuffer(m_lastTarget);
+    QByteArray data;
+    if (gpu_ptr != nullptr) {
+        data.resize(size);
+        std::copy(gpu_ptr, gpu_ptr+size, data.data());
+    }
+    ctx->unmapBuffer(m_lastTarget);
+    return data;
+}
+
 void GLBuffer::bindBufferBase(GraphicsContext *ctx, int bindingPoint, GLBuffer::Type t)
 {
     ctx->bindBufferBase(glBufferTypes[t], bindingPoint, m_bufferId);
diff --git a/src/render/io/glbuffer_p.h b/src/render/io/glbuffer_p.h
index e800d2bc4..731634b6b 100644
--- a/src/render/io/glbuffer_p.h
+++ b/src/render/io/glbuffer_p.h
@@ -53,6 +53,7 @@
 
 #include <QOpenGLContext>
 #include <Qt3DCore/qnodeid.h>
+#include <qbytearray.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -85,6 +86,7 @@ public:
     void allocate(GraphicsContext *ctx, uint size, bool dynamic = true);
     void allocate(GraphicsContext *ctx, const void *data, uint size, bool dynamic = true);
     void update(GraphicsContext *ctx, const void *data, uint size, int offset = 0);
+    QByteArray download(GraphicsContext *ctx, uint size);
     void bindBufferBase(GraphicsContext *ctx, int bindingPoint, Type t);
     void bindBufferBase(GraphicsContext *ctx, int bindingPoint);