使用lambdas简化容器迭代

Question

void functionA() {
  // ...........

  auto meshIterator = mMeshes.begin();
  for (const Renderable &renderable : renderQueue) {
    if (renderable.mMesh == INVALID_MESH_ID) {
      JONS_LOG_ERROR(mLogger, "Renderable MeshID is invalid");
      throw std::runtime_error("Renderable MeshID is invalid");
    }

    if (renderable.mMesh < meshIterator->first->mMeshID)
      continue;

    while (renderable.mMesh > meshIterator->first->mMeshID) {
      meshIterator++;
      if (meshIterator == mMeshes.end()) {
        JONS_LOG_ERROR(mLogger, "Renderable MeshID out of range");
        throw std::runtime_error("Renderable MeshID out of range");
      }
    }

    const bool hasDiffuseTexture =
        renderable.mDiffuseTexture != INVALID_TEXTURE_ID;
    const bool hasNormalTexture =
        renderable.mNormalTexture != INVALID_TEXTURE_ID;

    mGeometryProgram.SetUniformData(
        UnifGeometry(renderable.mWVPMatrix, renderable.mWorldMatrix,
                     hasDiffuseTexture, hasNormalTexture,
                     renderable.mTextureTilingFactor));

    if (hasDiffuseTexture)
      BindTexture2D(OpenGLTexture::TEXTURE_UNIT_GEOMETRY_DIFFUSE,
                    renderable.mDiffuseTexture, mTextures, mLogger);

    if (hasNormalTexture)
      BindTexture2D(OpenGLTexture::TEXTURE_UNIT_GEOMETRY_NORMAL,
                    renderable.mNormalTexture, mTextures, mLogger);

    GLCALL(glBindVertexArray(meshIterator->second));
    GLCALL(glDrawElements(GL_TRIANGLES, meshIterator->first->mIndices,
                          GL_UNSIGNED_INT, 0));
    GLCALL(glBindVertexArray(0));
  }

  // ...........
}

void functionB() {
  //....................

  // both containers are assumed to be sorted by MeshID ascending
  auto meshIterator = mMeshes.begin();
  for (const Renderable &renderable : renderQueue) {
    if (renderable.mMesh == INVALID_MESH_ID) {
      JONS_LOG_ERROR(mLogger, "Renderable MeshID is invalid");
      throw std::runtime_error("Renderable MeshID is invalid");
    }

    if (renderable.mMesh < meshIterator->first->mMeshID)
      continue;

    while (renderable.mMesh > meshIterator->first->mMeshID) {
      meshIterator++;
      if (meshIterator == mMeshes.end()) {
        JONS_LOG_ERROR(mLogger, "Renderable MeshID out of range");
        throw std::runtime_error("Renderable MeshID out of range");
      }
    }

    const Mat4 wvp = lightVP * renderable.mWorldMatrix;
    mNullProgram.SetUniformData(UnifNull(wvp));

    GLCALL(glBindVertexArray(meshIterator->second));
    GLCALL(glDrawElements(GL_TRIANGLES, meshIterator->first->mIndices,
                          GL_UNSIGNED_INT, 0));
    GLCALL(glBindVertexArray(0));
  }

  // ...............
}

void DrawModels(const std::function<
    void(const Renderable &renderable)> &preDrawFunc) {
  // both containers are assumed to be sorted by MeshID ascending
  auto meshIterator = mMeshes.begin();
  for (const Renderable &renderable : renderQueue) {
    if (renderable.mMesh == INVALID_MESH_ID) {
      JONS_LOG_ERROR(mLogger, "Renderable MeshID is invalid");
      throw std::runtime_error("Renderable MeshID is invalid");
    }

    if (renderable.mMesh < meshIterator->first->mMeshID)
      continue;

    while (renderable.mMesh > meshIterator->first->mMeshID) {
      meshIterator++;
      if (meshIterator == mMeshes.end()) {
        JONS_LOG_ERROR(mLogger, "Renderable MeshID out of range");
        throw std::runtime_error("Renderable MeshID out of range");
      }
    }

    preDrawFunc(renderable);

    GLCALL(glBindVertexArray(meshIterator->second));
    GLCALL(glDrawElements(GL_TRIANGLES, meshIterator->first->mIndices,
                          GL_UNSIGNED_INT, 0));
    GLCALL(glBindVertexArray(0));
  }
}

void functionD() {
  auto preDrawRenderable = [&](const Renderable &renderable) {
    const bool hasDiffuseTexture =
        renderable.mDiffuseTexture != INVALID_TEXTURE_ID;
    const bool hasNormalTexture =
        renderable.mNormalTexture != INVALID_TEXTURE_ID;

    mGeometryProgram.SetUniformData(
        UnifGeometry(renderable.mWVPMatrix, renderable.mWorldMatrix,
                     hasDiffuseTexture, hasNormalTexture,
                     renderable.mTextureTilingFactor));

    if (hasDiffuseTexture)
      BindTexture2D(OpenGLTexture::TEXTURE_UNIT_GEOMETRY_DIFFUSE,
                    renderable.mDiffuseTexture, mTextures, mLogger);

    if (hasNormalTexture)
      BindTexture2D(OpenGLTexture::TEXTURE_UNIT_GEOMETRY_NORMAL,
                    renderable.mNormalTexture, mTextures, mLogger);
  };

  DrawModels(preDrawRenderable);
}

void functionE() {
  auto preDrawRenderable = [&](const Renderable &renderable) {
    const Mat4 wvp = lightVP * renderable.mWorldMatrix;
    mNullProgram.SetUniformData(UnifNull(wvp));
  };

  DrawModels(preDrawRenderable);
}

1)functionD和functionE每秒都需要运行60-100次。使用lambda和std：：function是否会对性能造成重大影响？例如，是否存在隐藏的动态内存分配调用或虚拟查找，或者其他可能会影响性能的东西？我不知道使用lambdas和std：：function的开销。

2）有没有比我天真的解决方案更好/更快/更干净的替代方案？

Answer 1

void DrawModels(const std::function< void(const Renderable &renderable)> &preDrawFunc)

与其这样做，不如这样做：

template<class RenderableFunc>
void DrawModels(RenderableFunc&& preDrawFunc)

并保持身体不变。将其放置在您正在替换的两个函数都可以看到的位置。

现在编译器有一个简单的优化问题来内联您的lambda。