[Interest] Qt3D memory leaks

[Sean Harmer]

On 13/04/2017 10:14, Igor Mironchik wrote:
> Hi,
>
> 13.04.2017 12:02, Sean Harmer пишет:
>> Hi,
>>
>> On 13/04/2017 09:33, Igor Mironchik wrote:
>>> Hi,
>>>
>>>
>>> 13.04.2017 9:58, Sean Harmer пишет:
>>>> Hi,
>>>>
>>>> On 13/04/2017 07:09, Igor Mironchik wrote:
>>>>> Hello,
>>>>>
>>>>> 3Dtree has been updated. Now autumn is animated. Removed hand-made
>>>>> classes of leaf geometry and mesh. Now example uses ready mesh
>>>>> prepared
>>>>> in Blender. Modified a little constants of the tree. Example looks
>>>>> nice.
>>>>> This is a benchmark of your video card, because leafs and branches are
>>>>> stand alone objects (QEntity). For example 5 years tree has ~ 900
>>>>> objects. My Intel Pentium with Intel HD graphics normally paint only 5
>>>>> years tree, 6 years tree starts to slow down.
>>>>
>>>> Yes, at present each entity with a material/geometry renderer combo
>>>> gets translated to an OpenGL draw call. We are looking to add batching
>>>> (similar to how Qt Quick 2 works) but it's not there yet.
>>>>
>>>> If you don't need to address each individual leaf/branch in your
>>>> object model. E.g. if you're just rendering them, then you can get
>>>> *much* better performance by using instanced rendering.
>>>>
>>>> Essentially you have one entity representing all leaves. This entity
>>>> contains the material and geometry renderer as normal. The positions
>>>> and any other custom properties that vary between instances (rotation,
>>>> leaf size, leaf colour etc) should be placed into an additional
>>>> attribute/buffer and provided to the geometry renderer. On this
>>>> attribute, set the divisor property to 1 meaning that 1 piece of data
>>>> maps to 1 instance of the leave in the scene. With this approach you
>>>> will be able to render 10,000's leaves in a single draw call. It maps
>>>> through to a call to glDrawElementsInstanced() in case you want to
>>>> read up on it. Essentially you're moving the for loop over each leaf
>>>> on to the GPU.
>>>>
>>>> Typically, you'd have your data for the leaves in an array in C++ and
>>>> use this to populate the leaf instance buffer.
>>>
>>> Thank you Sean. Interesting technique. I read a little about it and
>>> looked at the OpenGL uses of such approach.
>>>
>>> But I have questions on how to implement this approach with Qt3D. I can
>>> set QAttribute to the QGeometryRenderer. If this attribute will have
>>> divisor = 1 then this attribute will affect only 1 instance. Cool, such
>>> I can use instancing.
>>>
>>> But I need to define attribute that will have QTransform matrix for
>>> transformation. And one attribute with diffuse colour. So 2 attributes
>>> per instance. Then leaves will be drawn instanced.
>>>
>>> And here I can't understand how to do it with Qt3D.
>>>
>>> Is it possible? Or I should do instancing in another way?
>>>
>>> I'm sorry for the noobs questions. And thank you again.
>>>
>>>>
>>>> The plan is to have a batcher that uses this instancing facility.
>>>
>>> It will be great. And with this batching my current code will render
>>> 10,000 leaves if I share a mesh only? Or material should be shared too?
>>
>> See
>> http://code.qt.io/cgit/qt/qt3d.git/tree/examples/qt3d/instanced-arrays-qml?h=5.9
>> for an example of instancing.
>>
>> You need to share the same geometry and same material for all
>> instances in that entity. I'd suggest starting simple and just storing
>> the position of each leaf in the per instance buffer/attribute to
>> start with.
>
> This I understood. With position or default colour I can do the trick.
> But with whole transformations...

Either build the transformation matrix in C++ and pass this in as an 
attribute, or pass in position/rotation/scale and build the matrix in 
the vertex shader.

Cheers,

Sean

>
>>
>> You will need a custom material as the built in materials don't
>> support instancing out of the box - this is waiting on the shader
>> generator that is in development at the moment.
>
> Ok. Thank you.
>
>>
>> Cheers,
>>
>> Sean
>>
>>>
>>>>
>>>> Cheers,
>>>>
>>>> Sean
>>>>
>>>>>
>>>>> And one more - now you can rotate the tree with the left mouse button.
>>>>>
>>>>>
>>>>> 11.04.2017 12:15, Igor Mironchik пишет:
>>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> I fixed a little 3Dtree. Now branches positions are correct. And I
>>>>>> know that not all leafs is visible (this is because leaf geometry is
>>>>>> implemented as plain which renders only on one side).
>>>>>>
>>>>>>
>>>>>> 10.04.2017 13:20, Igor Mironchik пишет:
>>>>>>>
>>>>>>> Hello,
>>>>>>>
>>>>>>> I guess that Qt3D has huge memory leaks.
>>>>>>>
>>>>>>> You can check it on this example:
>>>>>>> https://github.com/igormironchik/3Dtree
>>>>>>>
>>>>>>> It's 3D tree, that grows year by year.
>>>>>>>
>>>>>>> By default tree will grow 5 years (5 minutes).
>>>>>>>
>>>>>>> When tree grown you can restart tree. And here I delete all
>>>>>>> resources:
>>>>>>>
>>>>>>> void
>>>>>>>
>>>>>>> MainWindowPrivate::createTree()
>>>>>>> {
>>>>>>> if(m_tree)
>>>>>>> {
>>>>>>> for(constauto&e:m_rootEntity->childNodes())
>>>>>>> e->deleteLater();
>>>>>>> }
>>>>>>> m_tree=newBranch(m_startPos,m_endPos,c_startBranchRadius,
>>>>>>> true,m_rootEntity);
>>>>>>> m_tree->setAge(0.0f);
>>>>>>> m_tree->updatePosition();
>>>>>>> m_tree->placeLeafs();
>>>>>>> }
>>>>>>>
>>>>>>> But a lot of memory are eaten.
>>>>>>
>>>>>
>>>>>
>>>>>
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