Unity solves the problem of Z-fighting caused by overlapping objects with the same material

problem

stay Unity Draw multiple objects that may partially or completely overlap , These objects may use the same material , At this time, the probability will be generated Z-Fighting

Solutions

Z-Fighting The reason is that the depth value calculated by the fragment is too close , Therefore, it is impossible to determine which one is closer to the camera , Competition leads to flickering . Then the solution is to let them Z Values are slightly different . The more common solution is Polgon Offset, namely Unity Shader Lab Of Offset attribute . But for objects with the same material , This method is invalid . Because when such objects overlap each other, even if the material is set Offset, Because it is the same material , Calculated depth It's still the same , It cannot be distinguished . So how can we distinguish the depth value of the same object ？ I think of it. GPU Instancing draw , Each object has a instance ID, Use this ID You can distinguish objects , So as to further find a way to distinguish the depth value . But the material Offset It cannot be set for objects , Fortunately, there are alternative methods , Because our ultimate goal is to offset the depth value , Then you can offset directly when calculating the depth value . I adopted the modification clip space Coordinate value method .

Concrete realization

notes ： The development environment I use is Unity2021+URP, The principle of built-in assembly line is the same .

First, we need to customize shader, stay Vertex Shader Just offset directly in ：

	#if UNITY_ANY_INSTANCING_ENABLED
    vertexInput.positionCS += _ClipSpaceOffset * unity_InstanceID;
    #else
    vertexInput.positionCS += _ClipSpaceOffset;
    #endif

With the help of Instancing Supported unity_InstanceID, We use an offset value pair clip space The coordinates are offset .
here _ClipSpaceOffset Defined as a material attribute ：

properties
{
	_ClipSpaceOffset("ClipsSpaceOffset", Float) = 0.0000002
}

It should be noted that , Yours shader Must be incompatible SRP Batcher, Otherwise, it cannot be enabled GPU Instancing, Here because I didn't _ClipSpaceOffset Put it in UnityPerMaterial Of CBuffer in , So nature destroys SRP Batcher.
Finally, open the material Enable GPU Instancing that will do .

A small problem

I found that after using this method , stay Play Mode Running , Dynamically added objects can be displayed normally and stably , No flicker . But in Unity Of Scene View Every time I refresh , The order of these objects will change , It could be Instance ID Changed . In fact, it is also very simple to solve this , Use MaterialProperty Bind each object with a unique ID, Use this ID Instead of Instance ID that will do .

Reference resources

About solving Z-Fighting, May refer to Unity This post of the Forum