Mesh generates access violation in Vertexbuffer on second Draw() call

[satanorz]

• cocos2d-x version: 3.13.1
• devices test on: Windows 10
• developing environments
  • VS version: 2013 Community

Steps to Reproduce:

1. Create a mesh inside a class derived from Node, with an override Draw()
2. Retain the mesh
3. Add the instance of the derived class into a Scene with AddChild
4. Try to access mesh->getVertexBuffer() inside the second call to overriden Draw()

This will throw an access violation. Other attributes of mesh remain correct, including the indexBuffer, but not the vertexBuffer.

A more extensive explanation can be found in this forum post: http://discuss.cocos2d-x.org/t/custom-draw-not-working-on-mesh-object/32748
The code is based on this one found in the wiki: http://www.cocos2d-x.org/wiki/3D_Graphics#Building-a-Mesh

A minimal example of the offending code is attached here:
MeshProblem.zip

If you need something else, just ask.

[dumganhar]

For a glance, I didn't find any problem in your code.
I guess some Ref object is released while it should not. I will check it.

[satanorz]

I think I've found something. If the meshvertexdata object inside CCMesh.cpp::create is retained, the VBO containing the vertices doesn't get destroyed between draw calls.

Mesh* Mesh::create(const std::vector<float>& vertices, int perVertexSizeInFloat, const IndexArray& indices, const std::vector<MeshVertexAttrib>& attribs)
{
    MeshData meshdata;
    meshdata.attribs = attribs;
    meshdata.vertex = vertices;
    meshdata.subMeshIndices.push_back(indices);
    meshdata.subMeshIds.push_back("");
    auto meshvertexdata = MeshVertexData::create(meshdata);
    auto indexData = meshvertexdata->getMeshIndexDataByIndex(0);
    CC_SAFE_RETAIN(meshvertexdata); // <-- TEMPORAL FIX, CHECK FOR LEAKS (SHOULD BE RELEASED LATER?)
    return create("", indexData);
}

gDEBugger shows that both vertex and index buffers are OK, and no crash is generated on overrided draw calls.

However I'm not able to obtain a working example of a manually created mesh that draws something onto the screen, to be sure of the fix. I'm using:

void Mapa3D::draw(Renderer* renderer, const Mat4 &transform, uint32_t flags)
{
        auto programstate = mesh->getGLProgramState();
        auto& meshCommand = mesh->getMeshCommand();
        GLuint textureID = mesh->getTexture() ? mesh->getTexture()->getName() : 0;
        meshCommand.init(_globalZOrder
            , textureID
            , programstate
            , RenderState::StateBlock::_defaultState
            , mesh->getVertexBuffer() 
            , mesh->getIndexBuffer()
            , mesh->getPrimitiveType()
            , mesh->getIndexFormat()
            , mesh->getIndexCount()
            , transform
            , flags);
        renderer->addCommand(&meshCommand);
}

The command passes to the renderer pool, because the GL draw call counter is increased, but nothing is shown.

Hope this helps to find the bug.