Custom shader fundamentals in Unity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output color of this simple shader?

Consider this Unity shader code snippet that sets the output color. What color will the shader output on the object?

Unity

Shader "Custom/SimpleColor" {
  SubShader {
    Pass {
      CGPROGRAM
      #pragma vertex vert
      #pragma fragment frag

      struct appdata {
        float4 vertex : POSITION;
      };

      struct v2f {
        float4 pos : SV_POSITION;
      };

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

      fixed4 frag(v2f i) : SV_Target {
        return fixed4(0.0, 1.0, 0.0, 1.0); // green color
      }
      ENDCG
    }
  }
}

A The object will appear solid red.

B The object will appear solid green.

C The object will appear solid blue.

D The object will be fully transparent.

💡 Hint

Look at the color values in the fragment shader's return statement. The format is (red, green, blue, alpha).

The fragment shader returns fixed4(0.0, 1.0, 0.0, 1.0), which means red=0, green=1, blue=0, alpha=1 (fully opaque). So the output color is solid green.

🧠 Conceptual

intermediate

Which shader stage transforms vertex positions to clip space?

In a Unity shader, which stage is responsible for converting vertex positions from object space to clip space?

A Compute shader

B Fragment shader

C Geometry shader

D Vertex shader

💡 Hint

Think about which shader stage handles the shape and position of the object before pixels are drawn.

The vertex shader processes each vertex and transforms its position from object space to clip space, preparing it for rasterization.

🔧 Debug

advanced

Why does this shader produce a black screen?

Examine the following fragment shader code. Why does the rendered object appear completely black?

Unity

fixed4 frag(v2f i) : SV_Target {
  fixed4 color = fixed4(1.0, 0.5, 0.0, 0.0);
  return color;
}

A The fragment shader is missing a return statement.

B The RGB values are invalid and cause the shader to fail.

C Alpha is zero, so the output is fully transparent and appears black.

D The color is orange, so the object should appear orange, not black.

💡 Hint

Consider if the alpha value affects the rendering. Is there a Blend mode specified in the Pass?

The fragment shader returns fixed4(1.0, 0.5, 0.0, 0.0), an orange color with alpha=0. If the shader or material uses blending, the alpha=0 causes full transparency, making the object appear black (or invisible). Without a Blend mode, opaque rendering ignores alpha, but the question implies the black screen is due to transparency.

📝 Syntax

advanced

Which option correctly declares a float4 color variable in HLSL?

Choose the correct syntax to declare a float4 variable named color with red=1, green=0, blue=0, alpha=1 in a Unity shader.

A float4 color = float4(1, 0, 0, 1);

B float4 color = (1, 0, 0, 1);

C float4 color = {1, 0, 0, 1};

D float4 color = [1, 0, 0, 1];

💡 Hint

Remember the constructor syntax for vector types in HLSL.

In HLSL, vector types like float4 are constructed using the type name followed by parentheses enclosing the values.

🚀 Application

expert

What is the output of this shader code with conditional color?

Given this fragment shader code, what color will be output when i.pos.x is 0.3?

Unity

fixed4 frag(v2f i) : SV_Target {
  fixed4 color = (i.pos.x > 0.5) ? fixed4(0, 0, 1, 1) : fixed4(1, 1, 0, 1);
  return color;
}

A Yellow color (1,1,0,1)

B Blue color (0,0,1,1)

C Transparent color (0,0,0,0)

D Black color (0,0,0,1)

💡 Hint

Check the condition and compare the value of i.pos.x to 0.5.

Since 0.3 is not greater than 0.5, the condition is false, so the color is fixed4(1,1,0,1), which is yellow.