Hey there, let's tackle this pink line issue you're facing after upgrading your Unity project—super common when moving from older versions to the latest, especially with custom drawing systems! Pink (or magenta) in Unity is almost always a sign that a Shader is missing, incompatible, or failing to load properly, which lines up with your hunch about material settings. Here's a step-by-step breakdown to fix it:

1. Check Shader Compatibility with the Render Pipeline #

Older Unity projects typically use the Built-in Render Pipeline, but the latest versions default to URP or HDRP. If your brush material is still using an old Built-in Shader, it'll break and fall back to that pink placeholder:

• Select your brush line material and look at the Shader field in the Inspector. If it says "Missing" or shows a Built-in Shader like Sprites/Default or Standard without SRP support, that's your culprit.
• Fix options:
  • Stick with Built-in Pipeline: Go to Project Settings > Graphics, set Scriptable Render Pipeline Settings to None, then restart Unity.
  • Migrate to URP/HDRP: Replace the material's Shader with one compatible with your new pipeline—for 2D drawing, use Universal Render Pipeline/2D/Sprite-Lit-Default; for 3D lines, use Universal Render Pipeline/Lit.

2. Audit Your Color Assignment Code #

Unity's API changes between versions can break how you pass color to materials. Let's fix common code pitfalls:

• Old code might directly modify the shared material, which can cause global issues or fail silently:

  // ❌ Bad: Modifies the shared material (affects all objects using it)
  GetComponent<LineRenderer>().material.color = selectedColor;
  

• Use MaterialPropertyBlock instead to safely modify individual instances without affecting others:

  // ✅ Good: Targets only this line renderer's color
  LineRenderer lineRenderer = GetComponent<LineRenderer>();
  MaterialPropertyBlock propBlock = new MaterialPropertyBlock();
  lineRenderer.GetPropertyBlock(propBlock);
  // Note: Match the property name to your Shader! Built-in uses _Color, URP uses _BaseColor
  propBlock.SetColor("_BaseColor", selectedColor); 
  lineRenderer.SetPropertyBlock(propBlock);
  

• Double-check the property name matches your Shader's color variable—if you use the wrong name, the color won't apply at all.

3. Ensure Proper Material Instantiation #

If you're generating brush lines dynamically (e.g., creating a new LineRenderer for each stroke), make sure you're using an instance of the material, not the shared original:

• ❌ Bad: Assigns the shared material, locking it or changing color for all strokes:

  newLine.GetComponent<LineRenderer>().material = originalBrushMaterial;
  

• ✅ Good: Creates a unique material instance for each stroke:

  Material instanceMat = new Material(originalBrushMaterial);
  instanceMat.SetColor("_BaseColor", selectedColor);
  newLine.GetComponent<LineRenderer>().material = instanceMat;
  

• Don't forget to clean up dynamic materials to avoid memory leaks:

  Destroy(GetComponent<LineRenderer>().material);
  

4. Verify Shader Inclusion in Build Settings #

Sometimes Unity strips unused Shaders during builds, even if you're using them dynamically:

• Go to Project Settings > Graphics, find the Always Included Shaders list, and add your brush's Shader to it.
• Disable Strip unused Shaders temporarily to test if that's causing the fallback to pink.

Work through these steps and your brush should start rendering the correct colors again. If you hit a snag, share a snippet of your color assignment code or a screenshot of your material's Inspector settings, and we can dig deeper!

内容的提问来源于stack exchange，提问作者DevWithZachary