Custom shader fundamentals in Unity - Mini Project: Build & Apply

Custom shader fundamentals

📖 Scenario: You are creating a simple visual effect in a Unity game. You want to write a custom shader that colors an object with a solid color.

🎯 Goal: Build a basic Unity shader that colors an object with a fixed color using shader code.

📋 What You'll Learn

Create a shader with a fixed color property

Write the shader code to output the fixed color

Apply the shader to an object in Unity

Print the final color output in the shader

💡 Why This Matters

🌍 Real World

Custom shaders let game developers create unique visual styles and effects for objects in games and apps.

💼 Career

Understanding shader fundamentals is important for graphics programmers, technical artists, and game developers working with Unity.

1

Create a shader with a fixed color property

Create a shader named SimpleColorShader with a _Color property set to (1, 0, 0, 1) (red). Write the shader declaration and properties block.

Unity

// Write the shader declaration and properties block
// Your code here

Hint

Start by declaring the shader name and add a Properties block with a color named _Color set to red.

2

Add a fixed color fragment shader

Inside the SubShader, add a Pass with a fragment shader named frag that returns the _Color value. Also add a vertex shader named vert that passes vertex data unchanged.

Unity

Shader "Custom/SimpleColorShader" {
    Properties {
        _Color ("Color", Color) = (1, 0, 0, 1)
    }
    SubShader {
        // Add a Pass with vert and frag shaders here
        // Your code here
    }
}

Hint

Inside SubShader, add a Pass with CGPROGRAM. Define vert and frag functions. The fragment shader should return the _Color.

3

Add a helper variable for color intensity

Add a float property named _Intensity with default value 1.0 in the Properties block. Then declare float _Intensity; inside the shader code and multiply _Color by _Intensity in the fragment shader before returning.

Unity

Shader "Custom/SimpleColorShader" {
    Properties {
        _Color ("Color", Color) = (1, 0, 0, 1)
        // Add _Intensity property here
        // Your code here
    }
    SubShader {
        Pass {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag

            // Declare _Intensity variable here
            // Your code here

            fixed4 _Color;

            v2f vert(appdata v) {
                v2f o;
                o.pos = UnityObjectToClipPos(v.vertex);
                return o;
            }

            fixed4 frag(v2f i) : SV_Target {
                // Multiply _Color by _Intensity here
                // Your code here
            }
            ENDCG
        }
    }
}

Hint

Add a float property _Intensity in Properties. Declare it in the shader code and multiply it with _Color in the fragment shader.

4

Print the final color output

Add a Debug.Log statement in the fragment shader to print the final color value before returning it. Then print the final color output in Unity console.

Unity

Shader "Custom/SimpleColorShader" {
    Properties {
        _Color ("Color", Color) = (1, 0, 0, 1)
        _Intensity ("Intensity", Float) = 1.0
    }
    SubShader {
        Pass {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag

            float _Intensity;

            struct appdata {
                float4 vertex : POSITION;
            };

            struct v2f {
                float4 pos : SV_POSITION;
            };

            fixed4 _Color;

            v2f vert(appdata v) {
                v2f o;
                o.pos = UnityObjectToClipPos(v.vertex);
                return o;
            }

            fixed4 frag(v2f i) : SV_Target {
                // Add Debug.Log to print final color
                // Your code here
                return _Color * _Intensity;
            }
            ENDCG
        }
    }
}

Hint

Shaders cannot use Debug.Log directly. Instead, return the final color multiplied by intensity. When applied to an object, the color should appear red with full intensity.

Practice

1. What is the main purpose of a custom shader in Unity?

easy

A. To control exactly how objects look by writing small programs

B. To create 3D models from scratch

C. To write game logic and rules

D. To manage user input events

Solution

1. Step 1: Understand the role of shaders

   Shaders define how surfaces appear by controlling colors, lighting, and textures.

2. Step 2: Identify what custom shaders do

   Custom shaders let you write small programs to control object appearance beyond built-in options.

3. Final Answer:

   To control exactly how objects look by writing small programs -> Option A

4. Quick Check:

   Custom shader = control object look [OK]

Hint: Shaders control object appearance with code [OK]

Common Mistakes:

• Confusing shaders with 3D modeling
• Thinking shaders handle game logic
• Assuming shaders manage input

2. Which of the following is the correct way to start a simple Unity shader code block?

easy

A. ShaderBegin

B. StartShader

C. CGPROGRAM

D. ProgramCG

Solution

1. Step 1: Recall Unity shader syntax

   Unity shaders use CGPROGRAM to start the programmable shader code block.

2. Step 2: Check options for correct keyword

   Only CGPROGRAM is the valid keyword to begin the shader code section.

3. Final Answer:

   CGPROGRAM -> Option C

4. Quick Check:

   Shader code block starts with CGPROGRAM [OK]

Hint: Look for CGPROGRAM to start shader code [OK]

Common Mistakes:

• Using made-up keywords like StartShader
• Confusing CGPROGRAM with other terms
• Misspelling the keyword

3. What will be the output color of this simple shader fragment code?

fixed4 frag() : SV_Target {
    return fixed4(1, 0, 0, 1);
}

medium

A. Solid red color

B. Solid green color

C. Solid blue color

D. Transparent black color

Solution

1. Step 1: Analyze the returned color vector

   The function returns fixed4(1, 0, 0, 1), which means red=1, green=0, blue=0, alpha=1.

2. Step 2: Interpret color components

   Red is full intensity, green and blue are zero, alpha is fully opaque.

3. Final Answer:

   Solid red color -> Option A

4. Quick Check:

   fixed4(1,0,0,1) = red [OK]

Hint: RGBA (1,0,0,1) means solid red [OK]

Common Mistakes:

• Mixing up color channel order
• Ignoring alpha channel
• Assuming zero means white

4. Identify the error in this shader snippet:

Shader "Custom/Simple" {
    Properties {
        _Color ("Color", Color) = (1,1,1,1)
    }
    SubShader {
        Pass {
            CGPROGRAM
            fixed4 frag() : SV_Target {
                return _Color;
            }
            ENDCG
        }
    }
}

medium

A. Missing semicolon after _Color property declaration

B. _Color cannot be used directly in fragment shader

C. frag function missing input parameters

D. Incorrect use of ENDCG keyword

Solution

1. Step 1: Check Properties block syntax

   The property declaration is correct: no semicolon needed, parentheses balanced.

2. Step 2: Verify shader code block

   Properties like _Color must be declared inside CGPROGRAM as 'uniform fixed4 _Color;' to be used; direct use causes undeclared identifier error.

3. Final Answer:

   _Color cannot be used directly in fragment shader -> Option B

4. Quick Check:

   Properties need uniform declaration [OK]

Hint: Declare Properties as uniforms in CGPROGRAM [OK]

Common Mistakes:

• Assuming semicolons are needed in Properties
• Not declaring uniform for _Color
• Thinking ENDCG is incorrect

5. You want to write a custom shader that colors an object red only if its x-coordinate is positive, otherwise blue. Which fragment shader code correctly implements this?

hard

A. fixed4 frag() : SV_Target {
if (POSITION.x > 0) return fixed4(1,0,0,1);
else return fixed4(0,0,1,1);
}

B. fixed4 frag(float3 pos) : SV_Target {
if (pos.x > 0) return fixed4(1,0,0,1);
else return fixed4(0,0,1,1);
}

C. fixed4 frag(float3 pos : TEXCOORD0) : SV_Target {
return pos.x > 0 ? fixed4(1,0,0,1) : fixed4(0,0,1,1);
}

D. fixed4 frag(float3 pos : POSITION) : SV_Target {
return pos.x > 0 ? fixed4(1,0,0,1) : fixed4(0,0,1,1);
}

Solution

1. Step 1: Understand input semantics

   To access vertex position in fragment shader, use input parameter with semantic POSITION.

2. Step 2: Check code correctness

   fixed4 frag(float3 pos : POSITION) : SV_Target { return pos.x > 0 ? fixed4(1,0,0,1) : fixed4(0,0,1,1); } correctly declares pos with POSITION semantic and uses conditional operator to return red or blue.

3. Step 3: Identify errors in other options

   fixed4 frag(float3 pos) : SV_Target { if (pos.x > 0) return fixed4(1,0,0,1); else return fixed4(0,0,1,1); } lacks semantic, fixed4 frag(float3 pos : TEXCOORD0) : SV_Target { return pos.x > 0 ? fixed4(1,0,0,1) : fixed4(0,0,1,1); } uses TEXCOORD0 which is wrong for position, fixed4 frag() : SV_Target { if (POSITION.x > 0) return fixed4(1,0,0,1); else return fixed4(0,0,1,1); } uses POSITION as variable incorrectly.

4. Final Answer:

   fixed4 frag(float3 pos : POSITION) : SV_Target { return pos.x > 0 ? fixed4(1,0,0,1) : fixed4(0,0,1,1); } -> Option D

5. Quick Check:

   Use POSITION semantic for position input [OK]

Hint: Use POSITION semantic to get vertex position [OK]

Common Mistakes:

• Missing POSITION semantic in input
• Using wrong semantic like TEXCOORD0
• Referencing POSITION as variable directly