Overview

本范例主要用于演示 Sprite 在 V4 中的绘制流程，以帮助开发者熟悉和理解 V4 API 使用。

创建 Sprite

Sprite 创建方式与 V3 一样，并未改动：

auto visibleSize = Director::getInstance()->getVisibleSize();
auto origin = Director::getInstance()->getVisibleOrigin();

auto mySprite = Sprite::create("mysprite.png");
sprite->setPosition(Vec2(visibleSize / 2) + origin);
this->addChild(sprite);

接下来进入到 Sprite 内部，看看与 V3 相比，发生了哪些变化。

Shader 与 program

在 V3，通过 setGLProgramState 为 Sprite 指定 shader。

setGLProgramState(GLProgramState::getOrCreateWithGLProgramName(GLProgram::SHADER_NAME_POSITION_TEXTURE_COLOR_NO_MVP, texture));

V4 移除了 GLProgramState，删除了在 app 中 直接使用 OpenGL ES API 的代码，OpenGL ES API 的使用只出现在 renderer/backend/opengl 文件中。

V4 在 RenderCommand 类中定义了一个 protected 成员 backend::PipelineDescriptor，用于保存 backend::ProgramState， backend::BlendDescriptor 及 backend::VertexLayout。

因此在初始化阶段，需要完成以下三个步骤：

  1. 创建 backend::ProgramState

    通过 ProgramState(const std::string& vertexShader, const std::string& fragmentShader) 创建 backend::ProgramState 对象，通过 backend::ProgramState 对象存储 uniform 和 texture，通过创建 backend::Buffer 存储顶点数据。

    auto& pipelineDescriptor = _trianglesCommand.getPipelineDescriptor();
_programState = new (std::nothrow) backend::ProgramState(positionTextureColor_vert, positionTextureColor_frag);
pipelineDescriptor.programState = _programState;

_mvpMatrixLocation = pipelineDescriptor.programState->getUniformLocation("u_MVPMatrix");
_textureLocation = pipelineDescriptor.programState->getUniformLocation("u_texture");
_alphaTextureLocation = pipelineDescriptor.programState->getUniformLocation("u_texture1");

  2. 创建 backend::VertexLayout

    //set vertexLayout according to V3F_C4B_T2F structure
auto& vertexLayout = _trianglesCommand.getPipelineDescriptor().vertexLayout;
const auto& attributeInfo = _programState->getProgram()->getActiveAttributes();
auto iter = attributeInfo.find("a_position");
if(iter != attributeInfo.end())
{
    vertexLayout.setAttribute("a_position", 
                              iter->second.location, 
                              backend::VertexFormat::FLOAT3, 
                              0, 
                              false);
}

iter = attributeInfo.find("a_texCoord");
if(iter != attributeInfo.end())
{
    vertexLayout.setAttribute("a_texCoord", 
                              iter->second.location, 
                              backend::VertexFormat::FLOAT2, 
                              offsetof(V3F_C4B_T2F, texCoords), 
                              false);
}

iter = attributeInfo.find("a_color");
if(iter != attributeInfo.end())
{
    vertexLayout.setAttribute("a_color", 
                              iter->second.location, 
                              backend::VertexFormat::UBYTE4, 
                              offsetof(V3F_C4B_T2F, colors), 
                              true);
}
vertexLayout.setLayout(sizeof(V3F_C4B_T2F), backend::VertexStepMode::VERTEX);

  3. 创建 backend::BlendDescriptor 

    backend::BlendDescriptor& blendDescriptor = _trianglesCommand.getPipelineDescriptor().blendDescriptor;
blendDescriptor.blendEnabled = true;
if (_blendFunc == BlendFunc::ALPHA_NON_PREMULTIPLIED)
{
    blendDescriptor.sourceRGBBlendFactor = backend::BlendFactor::SRC_ALPHA;
    blendDescriptor.destinationRGBBlendFactor = backend::BlendFactor::ONE_MINUS_SRC_ALPHA;
    blendDescriptor.sourceAlphaBlendFactor = backend::BlendFactor::SRC_ALPHA;
    blendDescriptor.destinationAlphaBlendFactor = backend::BlendFactor::ONE_MINUS_SRC_ALPHA;
}
else
{
    blendDescriptor.sourceRGBBlendFactor = backend::BlendFactor::ONE;
    blendDescriptor.destinationRGBBlendFactor = backend::BlendFactor::ONE_MINUS_SRC_ALPHA;
    blendDescriptor.sourceAlphaBlendFactor = backend::BlendFactor::ONE;
    blendDescriptor.destinationAlphaBlendFactor = backend::BlendFactor::ONE_MINUS_SRC_ALPHA;
}

更新 shader

通过 Node::setProgramState(backend::ProgramState* programState)，可以动态替换 shader。例如，当需要开启 alpha test 时，由于OpenGL ES 2.0 不支持 glAlphaFunc，此时需要将原来的 fragment shader 替换成 positionTextureColorAlphaTest_frag。

auto programState = new (std::nothrow) backend::ProgramState(positionTextureColor_vert, positionTextureColorAlphaTest_frag);
_sprite->setProgramState(programState);
auto alphaLocation = programState->getUniformLocation("u_alpha_value");
programState->setUniform(alphaLocation, &alphaThreshold, sizeof(alphaThreshold));
CC_SAFE_RELEASE_NULL(programState);

更新 uniform

const auto& projectionMat = Director::getInstance()->getMatrix(MATRIX_STACK_TYPE::MATRIX_STACK_PROJECTION);
auto programState = _trianglesCommand.getPipelineDescriptor().programState;
if (programState && _mvpMatrixLocation)
    programState->setUniform(_mvpMatrixLocation, projectionMat.m, sizeof(projectionMat.m));

更新 texture

if (_texture == nullptr || _texture->getBackendTexture() == nullptr)
    return;

auto programState = _trianglesCommand.getPipelineDescriptor().programState;
programState->setTexture(_textureLocation, 0, _texture->getBackendTexture());
auto alphaTexture = _texture->getAlphaTexture();
if(alphaTexture && alphaTexture->getBackendTexture())
{
    programState->setTexture(_alphaTextureLocation, 1, alphaTexture->getBackendTexture());
}

add triangle command

_trianglesCommand.init(_globalZOrder,
                       _texture,
                       _blendFunc,
                       _polyInfo.triangles,
                       transform,
                       flags);
renderer->addCommand(&_trianglesCommand);

为了减少 draw call 次数，在 Renderer 中会对 TriangleCommand 进行 batch。因此在 Sprite 中并未创建 backend::Buffer，而是放到了 Renderer 中。范例2 将演示当使用 CustomCommand 时如何创建 backend::Buffer 以及如何拷贝顶点数据。

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