渲染场景图的转换顺序

Question

在我的 2D 游戏引擎中，如果 objects 处于 parent-child 关系中，我很难正确渲染精灵。图片说明了问题。我使用场景图进行渲染并使用访问者模式进行遍历。我希望 parent 的旋转仅将 child 旋转到位。

//spriterenderer.cpp

// sprites are positioned & rotated around the center
    GLfloat vertices[] = {
        // Pos      // Tex
        -0.5f, 0.5f, 0.0f, 1.0f,
        0.5f, -0.5f, 1.0f, 0.0f,
        -0.5f, -0.5f, 0.0f, 0.0f,

        -0.5f, 0.5f, 0.0f, 1.0f,
        0.5f, 0.5f, 1.0f, 1.0f,
        0.5f, -0.5f, 1.0f, 0.0f
    };

// this gets called if a GameObject has children
bool SpriteRenderer::Enter(GameObject & node)
{
...
RenderSprite(...);

// save the current modelMatrix on the stack
m_matrixStack.push_back(m_modelMatrix);

// apply transformation. I assume this is where the mistake is made
m_modelMatrix = glm::translate(m_modelMatrix, glm::vec3(node.GetLocalPosition(), 0.0f));
m_modelMatrix = glm::rotate(m_modelMatrix, node.GetLocalRotation(), glm::vec3(0.0f, 0.0f, 1.0f));
m_modelMatrix = glm::scale(m_modelMatrix, glm::vec3(node.GetLocalScale(), 1.0f));
return true;

}

// after drawing all children of a node restore the previous model matrix
bool SpriteRenderer::Leave(GameObject & node)
{
    m_modelMatrix = m_matrixStack.back();
    m_matrixStack.pop_back();
    return true;
}

// if a node doesn't have children
bool SpriteRenderer::Visit(GameObject & node)
{
    RenderSprite(...);
}

void SpriteRenderer::RenderSprite(...)
{
// save the current transformation
    m_matrixStack.push_back(m_modelMatrix);

    // apply model transform
    m_modelMatrix = glm::translate(m_modelMatrix, glm::vec3(gameObject.GetLocalPosition(), 0.0f));
    m_modelMatrix = glm::rotate(m_modelMatrix, gameObject.GetLocalRotation(), glm::vec3(0.0f, 0.0f, 1.0f));
    m_modelMatrix = glm::scale(m_modelMatrix, glm::vec3(textureSize, 1.0f));

....
//restore previous transform
    m_modelMatrix = m_matrixStack.back();
    m_matrixStack.pop_back();
}

Answer 1

我通过以附加方式跟踪旋转找到了一个可行的解决方案。

所以，而不是

// in SpriteRenderer::Enter
m_modelMatrix = glm::rotate(m_modelMatrix, node.GetLocalRotation(), glm::vec3(0.0f, 0.0f, 1.0f));

我使用 m_additiveRotation += node.GetLocalRotation(); 并在 SpriteRenderer::Leave 中再次减去金额。

最后，在 SpriteRenderer::RenderSprite 中变为

m_modelMatrix = glm::translate(m_modelMatrix, glm::vec3(gameObject.GetLocalPosition(), 0.0f));
m_modelMatrix = glm::rotate(m_modelMatrix, m_additiveRotation, glm::vec3(0.0f, 0.0f, 1.0f));
m_modelMatrix = glm::rotate(m_modelMatrix, gameObject.GetLocalRotation(), glm::vec3(0.0f, 0.0f, 1.0f));
m_modelMatrix = glm::scale(m_modelMatrix, glm::vec3(textureSize, 1.0f));

渲染场景图的转换顺序

Order of transformations for rendering a scenegraph

c++

opengl

transformation

scenegraph

glm-math