Too many texture interpolators would be used for ForwardBase pass

这是由于Input中定义的材质uv变量过多，当前版本的shader model不支持造成的。

将shader model改为更高的版本即可解决。比如我现在用的#pragma target 3.0不支持3个材质，改为#pragma target 4.0就行了。

如果非要用#pragma target 3.0，只能通过共用uv_MainTex或者使用屏幕坐标来解决了。

参考：

Your shaders model target does not support that many texture interpolators. You can specify a higher shader model target using #pragma target , for example #pragma target 4.0, or you could try to simplify your shader so it fits in target 2.0 or 3.0.

• Manual: Shader Targets

By default, Unity compiles shaders into roughly shader model 2.0 equivalent.

#pragma target 4.0 - compile to DX10 shader model 4.0. 
This target is currently only supported by DirectX 11 and XboxOne/PS4 platforms.

Note that all OpenGL-like platforms (including mobile) are treated as “capable of shader model 3.0”. WP8/WinRT platforms (DX11 feature level 9.x) are treated as only capable of shader model 2.0.