Custom shader fundamentals in Unity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a simple shader with a name.

Unity

Shader "[1]" {
    SubShader {
        Pass {
        }
    }
}

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AMyShader

BStandard

CCustom/Basic

DSimple/Color

Attempts:

3 left

💡 Hint

Common Mistakes

Using a name without quotes

Using an invalid format for the shader name

The shader name must be a string with a path-like format, such as "Custom/Basic".

2fill in blank

medium

Complete the code to define a color property in the Properties block.

Unity

Properties {
    _Color ("Main Color", [1]) = (1,1,1,1)
}

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ARange(0,1)

BColor

CVector

DFloat

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Float' or 'Range' for colors

Forgetting the parentheses around the default value

The property type for colors in Unity shaders is Color.

3fill in blank

hard

Fix the error in the fragment shader function declaration.

Unity

fixed4 [1](v2f i) : SV_Target {
    return _Color;
}

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Afrag

Bvert

Cvertex

Dfragment

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'vert' which is for vertex shader

Using 'vertex' or 'fragment' which are not standard function names here

The fragment shader function is commonly named frag in Unity shaders.

4fill in blank

hard

Fill both blanks to sample the main texture color in the fragment shader.

Unity

sampler2D _MainTex;

fixed4 frag(v2f i) : SV_Target {
    fixed4 col = tex2D([1], [2]);
    return col * _Color;
}

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A_MainTex

Bi.uv

Ci.vertex

D_Color

Attempts:

3 left

💡 Hint

Common Mistakes

Using _Color instead of the texture sampler

Using i.vertex instead of i.uv for texture coordinates

Use _MainTex as the texture sampler and i.uv as the UV coordinates to sample the texture color.

5fill in blank

hard

Fill all three blanks to declare a vertex input struct with position and UV, and pass UV to fragment shader.

Unity

struct appdata {
    float4 [1] : POSITION;
    float2 [2] : TEXCOORD0;
};

struct v2f {
    float2 [3] : TEXCOORD0;
    float4 vertex : SV_POSITION;
};

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Avertex

Buv

Dpos

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'pos' instead of 'vertex' for position

Using different names for UV in appdata and v2f structs

The vertex input struct uses vertex for position and uv for texture coordinates. The v2f struct passes uv to the fragment shader.

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