How can I add a normal to a text mesh so that it lights correctly?

Question

I'm using a text mesh to place text on a 3D object, but as you all know, the text mesh does not have any normals...

http://docs.unity3d.com/Documentation/Components/class-TextMesh.html

...so it does not light correctly. I've done a search and found many people having trouble with lighting 3D text mesh because of it doesn't have any normals, but I haven't found a solution to adding normals to a text mesh object, so that is my question.

How can I add a normal to a text mesh so that it lights correctly?

Thanks so much in advance for your wisdom!

Answer 1

I did something similar for lighting a 3D texture. I hope my answer isn't overkill. So this code was a hack I wrote awhile back, it's inefficient and only supports a single directional light (helpful cg lighting tuts here). Hopefully this is enough to get you started.

To create a 3D texture using my code below you have to go through a little more work:

1. Create an empty game object
2. Attach Component->Mesh->Text Mesh
3. Attach Component TextMeshNormals (included below)
4. Attach Component->Mesh->Mesh Renderer
5. Assign a material to the Mesh Renderer that uses my GUI/LitText shader below

In the shader you'll notice a text normal attribute. In practice you would have your gameObject's Update() method update the _Normal property with the direction the text is facing so that it reflects a change in orientation. The text is planar so 1 normal is all we need. To test I manually set the normal to (0,0,-1,1), since the default Text Mesh faces down -Z.

Because this script doesn't run in the editor, your text won't show up until you run a scene in preview.

The shader:

Shader "GUI/LitText" { 
Properties { 
   _MainTex ("Font Texture", 2D) = "white" {} 
   _Color ("Text Color", Color) = (1,1,1,1) 
   _Normal ("Text Normal",Vector) = (0,0,0,1)
} 

SubShader {
    Blend SrcAlpha OneMinusSrcAlpha
    Pass { 
        Color [_Color] 
        SetTexture [_MainTex] { 
            combine primary, texture * primary 
        } 
    } 
    pass {
         Tags { "LightMode" = "ForwardBase" } 

         CGPROGRAM

         #pragma vertex vert  
         #pragma fragment frag 

         uniform sampler2D _MainTex;  
         uniform float4 _Color; // define shader property for shaders
         uniform float4 _Normal;

         // The following built-in uniforms (apart from _LightColor0) 
         // are defined in "UnityCG.cginc", which could be #included 
         uniform float4 unity_Scale; // w = 1/scale; see _World2Object
         uniform float3 _WorldSpaceCameraPos;
         uniform float4x4 _Object2World; // model matrix
         uniform float4x4 _World2Object; // inverse model matrix 
            // (all but the bottom-right element have to be scaled 
            // with unity_Scale.w if scaling is important) 
         uniform float4 _WorldSpaceLightPos0; 
            // position or direction of light source
         uniform float4 _LightColor0; 
            // color of light source (from "Lighting.cginc")

         struct vertexInput {
            float4 vertex : POSITION;
            float3 normal : NORMAL;
            float4 texcoord : TEXCOORD0;
         };
         struct vertexOutput {
            float4 pos : SV_POSITION;
            float4 col : COLOR;
            float4 tex : TEXCOORD0;
         };

         vertexOutput vert(vertexInput input) 
         {
            vertexOutput output;

            float4x4 modelMatrix = _Object2World;
            float4x4 modelMatrixInverse = _World2Object; 

            float3 normalDirection = normalize(float3(mul(_Normal, modelMatrixInverse)));
            float3 lightDirection = normalize(float3(_WorldSpaceLightPos0));

            float3 diffuseReflection = float3(_LightColor0) * float3(_Color)
               * max(0.0, dot(normalDirection, lightDirection));

            output.col = float4(diffuseReflection, 1.0);
            output.pos = mul(UNITY_MATRIX_MVP, input.vertex);
            output.tex = input.texcoord;
            return output;
         }

         float4 frag(vertexOutput input) : COLOR
         {
            half4 color = tex2D(_MainTex, float2(input.tex));
            // use color.a to get alpha from text texture, rgb comes from vertex shader                        
            return float4(input.col.r,input.col.g,input.col.b,color.a);
         }

         ENDCG
    }
}
}

And the helper script:

public class TextMeshNormals : MonoBehaviour {
    private TextMesh textMesh;

    // Use this for initialization
    void Start () {
        // reassign font texture to our material
        textMesh = transform.GetComponent<TextMesh>();
        renderer.material.mainTexture = textMesh.font.material.mainTexture;
    }
}

Update Unity 4.5.X use this slightly updated version:

Shader "GUI/LitText" { 
Properties { 
   _MainTex ("Font Texture", 2D) = "white" {} 
   _Color ("Text Color", Color) = (1,1,1,1) 
   _Normal ("Text Normal",Vector) = (0,0,0,1)
} 

SubShader {
    Blend SrcAlpha OneMinusSrcAlpha
    Pass { 
        Color [_Color] 
        SetTexture [_MainTex] { 
            combine primary, texture * primary 
        } 
    } 
    pass {
         Tags { "LightMode" = "ForwardBase" } 

         CGPROGRAM

         #pragma vertex vert  
         #pragma fragment frag 

         uniform sampler2D _MainTex;  
         uniform float4 _Color; // define shader property for shaders
         uniform float4 _Normal;
         uniform float4 _LightColor0; 
             // color of light source (from "Lighting.cginc")
         struct vertexInput {
            float4 vertex : POSITION;
            float3 normal : NORMAL;
            float4 texcoord : TEXCOORD0;
         };
         struct vertexOutput {
            float4 pos : SV_POSITION;
            float4 col : COLOR;
            float4 tex : TEXCOORD0;
         };

         vertexOutput vert(vertexInput input) 
         {
            vertexOutput output;

            float4x4 modelMatrix = _Object2World;
            float4x4 modelMatrixInverse = _World2Object; 

            float3 normalDirection = normalize(float3(mul(_Normal, modelMatrixInverse)));
            float3 lightDirection = normalize(float3(_WorldSpaceLightPos0));

            float3 diffuseReflection = float3(_LightColor0) * float3(_Color)
               * max(0.0, dot(normalDirection, lightDirection));

            output.col = float4(diffuseReflection, 1.0);
            output.pos = mul(UNITY_MATRIX_MVP, input.vertex);
            output.tex = input.texcoord;
            return output;
         }

         float4 frag(vertexOutput input) : COLOR
         {
            half4 color = tex2D(_MainTex, float2(input.tex));
            // use color.a to get alpha from text texture, rgb comes from vertex shader                        
            return float4(input.col.r,input.col.g,input.col.b,color.a);
         }

         ENDCG
    }
}
}