How to add varying param to a shader that is applied on a TextureAtlas

cocos2d-x
1

Hi!

I have a very simple question, as stated in the title of this topic:

How can someone pass a varying parameter to a shader that is applied on a TextureAtlas.

We can’t subclass the TextureAtlas as the methods that pass those parameters are private (setupVBOandVAO, mapBuffers etc…)

My use case:

I need to add a varying parameter to my shader that is applied on a textureAtlas, let’s call it VERTEX_ATTRIB_TEX_STROKE.

Where could I put the:

 glEnableVertexAttribArray(GLProgram::VERTEX_ATTRIB_TEX_STROKE);
 glVertexAttribPointer(GLProgram::VERTEX_ATTRIB_TEX_STROKE, 4, GL_FLOAT, GL_FALSE, kQuadSize, (GLvoid*) offsetof( Vertex_t, MyStrokeData));

calls?

Right now I have duplicated the whole TextureAtlas class and duplicated all it’s method, however it causes problems of inheritance and signature function mismatch in issuing openGL command (command.init(…) requires a TextureAtlas and cannot take my custom atlas class that doesn’t inherit from the base TextureAtlas class)

If I am doing something wrong, or if it’s not the right way to do this, feel free to reply too.

Thanks

2

TextureAtlas has vertex objects in the form of V3F_C4B_T2F_Quad. They take a position, color and texture coordinate. You can’t change that functionality as far as I can tell. The problem with a lot of the Cocos2d-x classes are they don’t allow you to modify the VBO’s with ease.

Where is the use of command.init(… ) ?

3

it is used here, in The SpriteBatchNode

void SpriteBatchNode::draw(Renderer *renderer, const Mat4 &transform, uint32_t flags)
{
    // Optimization: Fast Dispatch
    if( _textureAtlas->getTotalQuads() == 0 )
    {
        return;
    }

    for (const auto &child : _children)
    {
        child->updateTransform();
    }

    _batchCommand.init(_globalZOrder, getGLProgram(), _blendFunc, _textureAtlas, transform, flags);
    renderer->addCommand(&_batchCommand);
}

I have also created a duplicate of the SpriteBatchNode class that inherit from node in order to be able to use my new atlas which doesn’t inherit from TextureAtlas.

Thanks for your reply!

4

Yes, I have also created a custom MyStrokeData that store the additional parameters I need to pass to my shader.

5

I’m glad you got it working

6

Actually It is not working right now, I have just listed what I have done, until I hit the command.init problem. It is where I stand now.

I tried to used the old way of drawing things, like this:

void StrokeQuadBatchNode::draw(Renderer *renderer, const Mat4 &transform, uint32_t flags)
{

    // [PORT] OUCH, That is messy, but we can't use commands as it expect a
    // valid TextureAtlas
    
    // Optimization: Fast Dispatch
    if( _textureAtlas->getTotalQuads() == 0 )
    {
        return;
    }

    CC_NODE_DRAW_SETUP();
    
    //arrayMakeObjectsPerformSelector(_children, updateTransform, Sprite*);

    do {
        if(_children.size() > 0)
        {
            for (int i = 0; i< _children.size(); ++i) {
                Sprite* pNode = dynamic_cast<Sprite*>(_children.at(i));
                if(pNode)
                {
                    pNode->updateTransform();
                }
            }
        }
    }
    while(false);

    glBlendFunc( _blendFunc.src, _blendFunc.dst );

    _textureAtlas->drawQuads();
    
    
    // Optimization: Fast Dispatch
//    if( _textureAtlas->getTotalQuads() == 0 )
//    {
//        return;
//    }
//    
//    for (const auto &child : _children)
//    {
//        child->updateTransform();
//    }
//    
//    this is where is doesn't compile using my _textureAtlas, which doesn't inherit from CCTextureAtlas...
//    _batchCommand.init(_globalZOrder, getGLProgram(), _blendFunc, _textureAtlas, transform, flags);
//    renderer->addCommand(&_batchCommand);

}

As you can see I commented out the command stuff and get back to the draw method of cocos2Dx v2, but I am REALLY not sure it still works, with the new way of passing command to the rendering pipeline etc.

7

It’s a bit hacky but since your custom textureatlas class is essentially identical to the original can’t you cast to to a pointer of type CCTextureAtlas then pass it through. Some sort of cast. I can’t think of anything else right now sorry.