cocos2dx回调函数 (cocos2dx运行原理)

在Renderer初始化的时候，会对_buffersVAO进行初始化，同时告诉GPU数据的格式

void Renderer::setupVBOAndVAO()
{
    //generate vbo and vao for trianglesCommand
    glGenVertexArrays(1, &_buffersVAO);
    GL::bindVAO(_buffersVAO);
    glGenBuffers(2, &_buffersVBO[0]);
    glBindBuffer(GL_ARRAY_BUFFER, _buffersVBO[0]);
  	// 定义传递给VBO的数据如何解析
    // vertices
    glEnableVertexAttribArray(GLProgram::VERTEX_ATTRIB_POSITION);
    glVertexAttribPointer(GLProgram::VERTEX_ATTRIB_POSITION, 3, GL_FLOAT, GL_FALSE, sizeof(V3F_C4B_T2F), (GLvoid*) offsetof( V3F_C4B_T2F, vertices));

    // colors
    glEnableVertexAttribArray(GLProgram::VERTEX_ATTRIB_COLOR);
    glVertexAttribPointer(GLProgram::VERTEX_ATTRIB_COLOR, 4, GL_UNSIGNED_BYTE, GL_TRUE, sizeof(V3F_C4B_T2F), (GLvoid*) offsetof( V3F_C4B_T2F, colors));

    // tex coords
    glEnableVertexAttribArray(GLProgram::VERTEX_ATTRIB_TEX_COORD);
    glVertexAttribPointer(GLProgram::VERTEX_ATTRIB_TEX_COORD, 2, GL_FLOAT, GL_FALSE, sizeof(V3F_C4B_T2F), (GLvoid*) offsetof( V3F_C4B_T2F, texCoords));

    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, _buffersVBO[1]);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(_indices[0]) * INDEX_VBO_SIZE, _indices, GL_STATIC_DRAW);

    // Must unbind the VAO before changing the element buffer.
    GL::bindVAO(0);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
    glBindBuffer(GL_ARRAY_BUFFER, 0);
}

在TriangleCommand渲染的时候：

void Renderer::drawBatchedTriangles(){
  	// ... 
		fillVerticesAndIndices(cmd); // 填充顶点数据
  	// ...
 		auto conf = Configuration::getInstance();
    if (conf->supportsShareableVAO() && conf->supportsMapBuffer())
    {
    	 	//Bind VAO
        GL::bindVAO(_buffersVAO); // glBindVertexArray(vaoId);
        //Set VBO data
        glBindBuffer(GL_ARRAY_BUFFER, _buffersVBO[0]); // 在setupVBOAndVAO中已经声明了数据如何解析
 
      	// 将vbo的数据映射到CPU内存，修改后同步到GPU端
        glBufferData(GL_ARRAY_BUFFER, sizeof(_verts[0]) * _filledVertex, nullptr, GL_STATIC_DRAW);
        void *buf = glMapBuffer(GL_ARRAY_BUFFER, GL_WRITE_ONLY);
        memcpy(buf, _verts, sizeof(_verts[0]) * _filledVertex);
        glUnmapBuffer(GL_ARRAY_BUFFER);

        glBindBuffer(GL_ARRAY_BUFFER, 0);
        
        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, _buffersVBO[1]);
        glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(_indices[0]) * _filledIndex, _indices, GL_STATIC_DRAW);
    }
}

经过上边的分析，可以知道，cocos2dx的自定义RenderCommand如果继承自TriangsCommand，传递的数据格式为:

[vertext, color, textureCoord]，对应的shader，也必须有attribute

[a_position,a_color,a_texCoord]

const char* GLProgram::ATTRIBUTE_NAME_COLOR = "a_color";
const char* GLProgram::ATTRIBUTE_NAME_POSITION = "a_position";
const char* GLProgram::ATTRIBUTE_NAME_TEX_COORD = "a_texCoord";
const char* GLProgram::ATTRIBUTE_NAME_TEX_COORD1 = "a_texCoord1";
const char* GLProgram::ATTRIBUTE_NAME_TEX_COORD2 = "a_texCoord2";
const char* GLProgram::ATTRIBUTE_NAME_TEX_COORD3 = "a_texCoord3";
const char* GLProgram::ATTRIBUTE_NAME_NORMAL = "a_normal";
const char* GLProgram::ATTRIBUTE_NAME_BLEND_WEIGHT = "a_blendWeight";
const char* GLProgram::ATTRIBUTE_NAME_BLEND_INDEX = "a_blendIndex";
const char* GLProgram::ATTRIBUTE_NAME_TANGENT = "a_tangent";
const char* GLProgram::ATTRIBUTE_NAME_BINORMAL = "a_binormal";

void bindPredefinedVertexAttribs(){
		// ...
  	{GLProgram::ATTRIBUTE_NAME_POSITION, GLProgram::VERTEX_ATTRIB_POSITION},
		{GLProgram::ATTRIBUTE_NAME_COLOR, GLProgram::VERTEX_ATTRIB_COLOR},
		{GLProgram::ATTRIBUTE_NAME_TEX_COORD, GLProgram::VERTEX_ATTRIB_TEX_COORD},
		{GLProgram::ATTRIBUTE_NAME_TEX_COORD1, GLProgram::VERTEX_ATTRIB_TEX_COORD1},
		{GLProgram::ATTRIBUTE_NAME_TEX_COORD2, GLProgram::VERTEX_ATTRIB_TEX_COORD2},
		{GLProgram::ATTRIBUTE_NAME_TEX_COORD3, GLProgram::VERTEX_ATTRIB_TEX_COORD3},
		{GLProgram::ATTRIBUTE_NAME_NORMAL, GLProgram::VERTEX_ATTRIB_NORMAL},
    // ...
}

Sprite使用的shader为：

SHADER_NAME_POSITION_TEXTURE_COLOR_NO_MVP

attribute vec4 a_position;
attribute vec2 a_texCoord;
attribute vec4 a_color;

#ifdef GL_ES
varying lowp vec4 v_fragmentColor;
varying mediump vec2 v_texCoord;
#else
varying vec4 v_fragmentColor;
varying vec2 v_texCoord;
#endif

void main()
{
    gl_Position = CC_PMatrix * a_position;
    v_fragmentColor = a_color;
    v_texCoord = a_texCoord;
}

#ifdef GL_ES
precision lowp float;
#endif

varying vec4 v_fragmentColor;
varying vec2 v_texCoord;

void main()
{
    gl_FragColor = v_fragmentColor * texture2D(CC_Texture0, v_texCoord);
}

自定义RenderCommand的shader需要注意这个问题