[Interest] Qt3D memory leaks

[Igor Mironchik]

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...

>
> 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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>>>
>>
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