作为Shadergraph新手在制作顶点动画的时候遇到了顶点着色器中Position节点没法连接的问题，在仔细阅读文档的时候，发了问题，这里特此记录。
这个时候需要去检查顶点着色器中是否存在纹理采样，如果存在纹理采样是不是使用的Sample Texture 2D LOD，如果不是就没法进行连接
The reason is that when you output to the vertex position, the shader is running in the vertex stage. And at that moment, the GPU can't have the informations needed to auto-compute the texture LOD, thus why you need to use this node and specify the LOD you want to use.
Shader Graph Editor, doesn't let me connect wires - Unity Forum