Question
Answer and Explanation
The unexpected behavior of transparent draw order in Unity often stems from the way Unity handles rendering and the inherent complexities of transparency.
Here are several key reasons why you might be experiencing this issue:
1. Rendering Queue:
Unity renders objects based on their rendering queue. Transparent objects are typically rendered in the "Transparent" queue (3000), which renders after opaque objects to ensure proper blending. However, objects within the same queue are sorted based on their distance from the camera, and this sorting can lead to issues.
2. Z-Fighting:
Z-fighting occurs when two transparent surfaces are nearly at the same depth from the camera. The order in which they are rendered becomes ambiguous, leading to flickering or incorrect rendering. This is particularly noticeable when transparent objects intersect or overlap.
3. Transparency Mode:
The transparency mode in your shader matters. Simple alpha blending doesn't account for proper depth sorting. Using additive blending can bypass depth sorting issues, but may not produce the desired visual effect.
4. Shader Code:
The shader code itself can influence transparency behavior. Custom shaders might have errors in the blending equation or depth writing that cause unexpected results. Ensure your shader properly handles transparency and depth buffer interactions. A typical transparent shader might include:
Shader "Custom/Transparent"{
Properties{
_Color ("Color", Color) = (1,1,1,1)
_MainTex ("Albedo (RGB)", 2D) = "white" {}
_Glossiness ("Smoothness", Range(0,1)) = 0.5
_Metallic ("Metallic", Range(0,1)) = 0.0
}
SubShader{
Tags { "RenderType"="Transparent" "Queue"="Transparent" }
LOD 200
Blend SrcAlpha OneMinusSrcAlpha // Traditional transparency
ZWrite Off // Disable writing to the depth buffer
Cull Off //Render both sides of the object
CGPROGRAM
#pragma surface surf Standard fullforwardshadows alpha:fade
#pragma target 3.0
sampler2D _MainTex;
struct Input{
float2 uv_MainTex;
};
half _Glossiness;
half _Metallic;
fixed4 _Color;
void surf (Input IN, inout SurfaceOutputStandard o){
fixed4 c = tex2D (_MainTex, IN.uv_MainTex) _Color;
o.Albedo = c.rgb;
o.Metallic = _Metallic;
o.Smoothness = _Glossiness;
o.Alpha = c.a;
}
ENDCG
}
FallBack "Diffuse"
}
5. Camera Settings:
The camera's near and far clipping planes can affect depth buffer precision. If these values are too far apart, it can exacerbate depth-sorting issues with transparent objects. Adjust these values for better depth buffer accuracy.
6. Transparency Sorting Mode:
Unity provides transparency sorting modes in the Camera component. You can set the transparencySortMode to different options like 'Perspective' or 'Orthographic' and transparencySortAxis to determine the direction of sorting. Experimenting with these settings might resolve issues related to camera perspective.
7. Shader Graph:
If using Shader Graph, ensure you have set up the material to be transparent and adjust the blend mode accordingly in the graph's settings. Improper blend modes are a common cause of transparency issues.
By addressing these factors, you can often resolve unexpected transparent draw order issues in Unity, leading to visually correct and stable rendering.