Overview

本范例以创建 LayerColor 为例，演示如何使用 CustomCommand，以帮助开发者熟悉和理解 V4 API 使用。

创建 LayerColor

  1. auto layerColor = LayerColor::create(Color4B::RED, 
  2.                                      visibleSize.width, 
  3.                                      visibleSize.height);

接下来进入到 LayerColor 类内部，看看与 V3 相比，发生了哪些变化。

在 V3，创建 shader 过程如下：

  1. setGLProgramState(GLProgramState::getOrCreateWithGLProgramName(GLProgram::SHADER_NAME_POSITION_COLOR_NO_MVP));

与范例1一样，在初始化阶段，V4 需要完成以下几个步骤：

  • 创建 backend::ProgramState
  1. auto& pipelineDescriptor = _customCommand.getPipelineDescriptor();
  2. _programState = new (std::nothrow) backend::ProgramState(positionColor_vert, 
  3.                                                          positionColor_frag);
  4. pipelineDescriptor.programState = _programState;
  5. _mvpMatrixLocation = pipelineDescriptor.programState->getUniformLocation("u_MVPMatrix");
  • 创建 backend::VertexLayout
  1. auto& vertexLayout = _customCommand.getPipelineDescriptor().vertexLayout;
  2. const auto& attributeInfo = _programState->getProgram()->getActiveAttributes();
  3. auto iter = attributeInfo.find("a_position");
  4. if(iter != attributeInfo.end())
  5. {
  6.     vertexLayout.setAttribute("a_position", 
  7.                               iter->second.location, 
  8.                               backend::VertexFormat::FLOAT3, 
  9.                               0, 
  10.                               false);
  11. }
  12. iter = attributeInfo.find("a_color");
  13. if(iter != attributeInfo.end())
  14. {
  15.     vertexLayout.setAttribute("a_color", 
  16.                               iter->second.location, 
  17.                               backend::VertexFormat::FLOAT4,
  18.                               sizeof(_vertexData[0].vertices), 
  19.                               false);
  20. }
  21. vertexLayout.setLayout(sizeof(_vertexData[0]), backend::VertexStepMode::VERTEX);
  • 创建 backend::BlendDescriptor

CustomCommand 常见的初始化方式有两种：CustomCommand::init(float globalZOrder) 和 CustomCommand::init(float globalZOrder, const BlendFunc& blendFunc)。因此对于第一种，你需要在手动设置 Blend 状态：

  1. backend::BlendDescriptor& blendDescriptor = _customCommand.getPipelineDescriptor().blendDescriptor;
  2. blendDescriptor.blendEnabled = true;
  3. if (_blendFunc == BlendFunc::ALPHA_NON_PREMULTIPLIED)
  4. {
  5.     blendDescriptor.sourceRGBBlendFactor = backend::BlendFactor::SRC_ALPHA;
  6.     blendDescriptor.destinationRGBBlendFactor = backend::BlendFactor::ONE_MINUS_SRC_ALPHA;
  7.     blendDescriptor.sourceAlphaBlendFactor = backend::BlendFactor::SRC_ALPHA;
  8.     blendDescriptor.destinationAlphaBlendFactor = backend::BlendFactor::ONE_MINUS_SRC_ALPHA;
  9. }
  10. else
  11. {
  12.     blendDescriptor.sourceRGBBlendFactor = backend::BlendFactor::ONE;
  13.     blendDescriptor.destinationRGBBlendFactor = backend::BlendFactor::ONE_MINUS_SRC_ALPHA;
  14.     blendDescriptor.sourceAlphaBlendFactor = backend::BlendFactor::ONE;
  15.     blendDescriptor.destinationAlphaBlendFactor = backend::BlendFactor::ONE_MINUS_SRC_ALPHA;
  16. }

对于第二种初始化方式，需要指定 BlendFunc 即可，CustomCommand 初始化函数会根据 BlendFunc 设置对应的 Blend 状态。

  1. _blendFunc = BlendFunc::ALPHA_PREMULTIPLIED;
  2. _customCommand.init(_globalZOrder, _blendFunc);
  • 创建 backend::Buffer
  1. _customCommand.createIndexBuffer(CustomCommand::IndexFormat::U_SHORT, //index type format
  2.                                  6, //index count
  3.                                  CustomCommand::BufferUsage::STATIC);
  4. unsigned short indices[] = {0, 1, 2, 2, 1, 3};
  5. _customCommand.updateIndexBuffer(indices, sizeof(indices));
  7. _customCommand.createVertexBuffer(sizeof(_vertexData[0]), //vertex size
  8.                                   4, //vertex count
  9.                                   CustomCommand::BufferUsage::DYNAMIC);
  11. _customCommand.setDrawType(CustomCommand::DrawType::ELEMENT);
  12. _customCommand.setPrimitiveType(CustomCommand::PrimitiveType::TRIANGLE);

因为 index 数据在运行过程中并不会改变，所以在创建 index buffer 时，指定 bufferUsage 为 static，并在初始化阶段更新 index buffer。vertex buffer 数据需要动态更新，参考更新 Vertex buffer。

更新 Unifrom

  1. cocos2d::Mat4 projectionMat = Director::getInstance()->getMatrix(MATRIX_STACK_TYPE::MATRIX_STACK_PROJECTION);
  2. auto& pipelineDescriptor = _customCommand.getPipelineDescriptor();
  3. pipelineDescriptor.programState->setUniform(_mvpMatrixLocation, 
  4.                                             projectionMat.m, 
  5.                                             sizeof(projectionMat.m));

更新 Vertex buffer

CommandBuffer 提供了 updateVertexBuffer 接口用于更新顶点缓冲区数据。

  1. _customCommand.updateVertexBuffer(_vertexData, sizeof(_vertexData));

如果需要更新 vertex buffer 的子块，可以使用 CustomCommand::updateVertexBuffer(void* data, unsigned int offset, unsigned int length) 传入偏移量即可。

addCommand

  1. _customCommand.init(_globalZOrder, _blendFunc);
  2. renderer->addCommand(&_customCommand);