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HLSL, or High-Level Shading Language, is a proprietary programming language developed by Microsoft for use with the Direct3D API. Its primary function is to handle the programmable parts of the rendering pipeline in graphics processing units (GPUs). HLSL allows developers to write shaders - programs that control how 3D images are drawn on screen - using a syntax and structure similar to C++, making it more accessible than low-level languages. It supports various data types and built-in functions specifically designed for efficient shader programming across different hardware platforms.

Ask the right questions secure the right HLSL talent among an increasingly shrinking pool of talent.

First 20 minutes

General HLSL app knowledge and experience

The first 20 minutes of the interview should seek to understand the candidate's general background in HLSL application development, including their experience with various programming languages, databases, and their approach to designing scalable and maintainable systems.

What are the main components of a HLSL program?

The main components of a HLSL program are data types, variables, constants, functions, and semantics.

How would you declare a 2D texture in HLSL?

You can declare a 2D texture in HLSL using the 'Texture2D' keyword, like this: 'Texture2D myTexture;'.

What is the role of a Pixel Shader in HLSL?

A Pixel Shader, also known as a fragment shader, is a type of shader in HLSL that calculates the color and other attributes of each pixel in a texture or a rasterized geometric shape.

How would you implement lighting in HLSL?

Lighting in HLSL can be implemented by calculating the dot product of the light direction and the surface normal, which gives the intensity of the light on the surface. This calculation is usually done in the pixel shader.

Describe the difference between 'mul' and 'dot' functions in HLSL.

'mul' performs a matrix multiplication, while 'dot' computes the dot product of two vectors. The results and usage of these two functions are quite different.

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What you’re looking for early on

Does the candidate have a solid understanding of HLSL?

Has the candidate demonstrated problem-solving skills in the interview?

Is the candidate familiar with DirectX or other graphics APIs?

Has the candidate shown the ability to work well in a team?

Next 20 minutes

Specific HLSL development questions

The next 20 minutes of the interview should focus on the candidate's expertise with specific backend frameworks, their understanding of RESTful APIs, and their experience in handling data storage and retrieval efficiently.

What are semantics in HLSL and how are they used?

Semantics in HLSL are special keywords that are appended to variables to specify how the variables should be used. They can be used to connect the output of a vertex shader to the input of a pixel shader, among other things.

How would you use the 'clip' function in HLSL?

The 'clip' function in HLSL discards a pixel if the value passed to it is less than zero. It can be used for effects like conditional rendering or discarding pixels based on some condition.

What is the role of a Compute Shader in HLSL?

A Compute Shader is a programmable shader stage introduced in DirectX 11 that is used for tasks that do not necessarily operate on vertices or pixels. They are used for tasks such as physics calculations, AI, or general data manipulation.

Describe the difference between a Vertex Shader and a Geometry Shader in HLSL.

A Vertex Shader operates on individual vertices and handles transformations from model space to screen space. A Geometry Shader, on the other hand, operates on entire primitives (like triangles or lines) and can generate new primitives.

How would you implement shadow mapping in HLSL?

Shadow mapping in HLSL involves several steps, including rendering the scene from the light's perspective to create a depth map, then using this depth map in the main render pass to determine whether each pixel is in shadow or not.

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At this point, a skilled HLSL engineer should demonstrate strong problem-solving abilities, proficiency in HLSL programming language, and knowledge of software development methodologies. Red flags include lack of hands-on experience, inability to articulate complex concepts, or unfamiliarity with standard coding practices.

Digging deeper

Code questions

These will help you see the candidate's real-world development capabilities with HLSL.

What does this simple HLSL shader code do?
float4 main(float2 uv : TEXCOORD0) : COLOR { return float4(uv, 0.0, 1.0); }
This is a simple shader code which takes in texture coordinates (uv) as input and returns a color. The color is a 4-component vector where the red and green components are set to the uv coordinates, the blue component is set to 0, and the alpha component is set to 1.
What will be the output of this HLSL code snippet?
float4 main(float4 color : COLOR0) : SV_Target { return color * 0.5; }
This shader code takes in a color as input and returns the same color but with all its components (red, green, blue, alpha) halved. This will effectively darken the color.
What does this HLSL code snippet do with the array?
float4 colors[4]; float4 main(int index : INDEX0) : SV_Target { return colors[index]; }
This shader code defines an array of 4 colors. It then takes an index as input and returns the color at that index in the array.
What does this HLSL code snippet do with threading?
[numthreads(8, 8, 1)] void main(uint3 id : SV_DispatchThreadID) { // perform computation }
This code defines a compute shader that is dispatched with a thread group size of 8x8x1. The SV_DispatchThreadID semantic gives each thread a unique id, which can be used to index into data or perform computation.

Wrap-up questions

Final candidate for HLSL Developer role questions

The final few questions should evaluate the candidate's teamwork, communication, and problem-solving skills. Additionally, assess their knowledge of microservices architecture, serverless computing, and how they handle HLSL application deployments. Inquire about their experience in handling system failures and their approach to debugging and troubleshooting.

What is the purpose of the 'register' keyword in HLSL?

The 'register' keyword in HLSL is used to explicitly specify the register where a variable should be stored. This can be used for optimization and fine control over resource assignments.

Describe the difference between 'struct' and 'cbuffer' in HLSL.

'struct' is used to define a custom data type that can group several variables of different data types together. 'cbuffer', on the other hand, is used to define a constant buffer, which is a special type of read-only resource that can be used to send data from the CPU to the GPU.

How would you optimize a HLSL shader for better performance?

There are several ways to optimize a HLSL shader, including minimizing texture lookups, avoiding complex mathematical operations, reducing instruction count, using efficient data types, and making use of hardware features like early-z rejection.

HLSL application related

Product Perfect's HLSL development capabilities

Beyond hiring for your HLSL engineering team, you may be in the market for additional help. Product Perfect provides seasoned expertise in HLSL projects, and can engage in multiple capacities.

HLSL Consultive assessments

HLSL Application Conversion Assessment HLSL Application Integration Assessment HLSL Data & Database Integration Assessment

Custom HLSL development projects

Custom HLSL App Conversion HLSL Custom App Development Process App UI Design for HLSL Facelifts

Hiring guide for HLSL Engineers

HLSL Developer Hiring Guide

What you’re looking for early on

The ideal back-end app developer

What you’re looking to see on the HLSL engineer at this point.

HLSL Consultive assessments

Custom HLSL development projects