OpenGL Shader Language (GLSL) Questions and Answers for Viva

Answer-1: GLSL (OpenGL Shading Language) is a C-like programming language used to write shaders for OpenGL.

Answer-2: Shaders are small programs that run on the GPU to perform rendering computations like vertex transformation and pixel shading.

Answer-3: The main types are vertex shaders, fragment shaders, geometry shaders, tessellation shaders, and compute shaders.

Answer-4: A vertex shader processes each vertex's attributes, such as position, normal, and texture coordinates.

Answer-5: A fragment shader computes the color and other attributes of each fragment (potential pixel) generated by rasterization.

Answer-6: A geometry shader takes vertices of a primitive as input and can generate additional vertices or modify primitives.

Answer-7: A GLSL shader is declared in a file with the appropriate extension (e.g., .vert for vertex shaders or .frag for fragment shaders).

Answer-8: gl_Position is a built-in output variable in vertex shaders that determines the position of a vertex in clip space.

Answer-9: gl_FragColor is a deprecated built-in variable used in fragment shaders to define the final output color of a fragment.

Answer-10: Uniform variables are global variables that are constant during a single draw call and set by the application.

Answer-11: Attribute variables are inputs to vertex shaders, typically containing per-vertex data like position and color.

Answer-12: Varying variables (now in and out in modern GLSL) are used to pass data from vertex shaders to fragment shaders.

Answer-13: Textures are passed to shaders using uniform samplers (e.g., sampler2D) and accessed with functions like texture().

Answer-14: layout qualifiers specify attributes like binding points for uniform buffers or input/output locations for variables.

Answer-15: A shader program is an OpenGL object that links together multiple shaders (e.g., vertex and fragment shaders) for execution.

Answer-16: Use glShaderSource() to provide the source code and glCompileShader() to compile it.

Answer-17: Attach compiled shaders to a program using glAttachShader() and link them using glLinkProgram().

Answer-18: Built-in GLSL functions include mathematical functions like sin(), cos(), dot(), and texture sampling functions like texture().

Answer-19: A sampler is a data type in GLSL used to represent textures (e.g., sampler2D, samplerCube).

Answer-20: vec4 is a GLSL data type representing a 4-component vector, often used for positions or colors.

Answer-21: in specifies an input to a shader, while out specifies an output from a shader.

Answer-22: Uniform Buffer Objects (UBOs) allow multiple uniform variables to be grouped together and bound to shaders.

Answer-23: The discard keyword in fragment shaders is used to discard the current fragment, preventing it from being written to the framebuffer.

Answer-24: Built-in GLSL variables are predefined variables like gl_Position and gl_FragCoord used for common operations.

Answer-25: Multiple light sources can be handled using loops and uniform arrays to store light properties like position, direction, and intensity.

Answer-26: mat4 represents a 4x4 matrix, commonly used for transformations like rotation, scaling, and translation.

Answer-27: Use the built-in normalize() function to normalize a vector to a unit length.

Answer-28: gl_FragCoord gives the window-space coordinates of a fragment, while gl_Position gives the clip-space position of a vertex.

Answer-29: Precision qualifiers like lowp, mediump, and highp specify the precision of floating-point variables in GLSL.

Answer-30: The mix function linearly interpolates between two values based on a given factor.

Answer-31: The step function generates a step function by comparing a value against a threshold.

Answer-32: A matrix is passed to a GLSL shader using uniform variables and functions like glUniformMatrix4fv().

Answer-33: A tessellation shader subdivides patches of vertices to create smoother geometry or add detail.

Answer-34: A compute shader is a type of shader used for general-purpose computation on the GPU, independent of the rendering pipeline.

Answer-35: Errors are handled by checking the compilation and linking status using glGetShaderiv() and glGetProgramiv().

Answer-36: The reflect function calculates the reflection vector given an incident vector and a normal vector.

Answer-37: The refract function computes the refraction vector given an incident vector, a normal vector, and a refraction index.

Answer-38: Subroutines allow shaders to dynamically switch between multiple functions at runtime.

Answer-39: The maximum number depends on the GPU and OpenGL version, retrievable using GL_MAX_VERTEX_UNIFORM_COMPONENTS or similar constants.

Answer-40: glslangValidator is a tool to validate and compile GLSL shaders into SPIR-V binary format for Vulkan.

Answer-41: Lighting calculations are handled using equations like Phong or Blinn-Phong shading, combining ambient, diffuse, and specular components.

Answer-42: dFdx and dFdy compute the partial derivatives of a value with respect to screen-space x and y coordinates, useful for effects like edge detection.

Answer-43: gl_PointSize specifies the size of points when rendering point primitives.

Answer-44: The clamp function constrains a value to lie within a specified range.

Answer-45: Shadows can be implemented using shadow mapping or ray tracing techniques in GLSL shaders.

Answer-46: Interpolation qualifiers like flat, noperspective, and smooth determine how varying variables are interpolated across fragments.

Answer-47: A shader pipeline is the sequence of shaders (vertex, fragment, etc.) executed during rendering.

Answer-48: A vertex shader processes individual vertices, while a geometry shader processes primitives and can generate new vertices.

Answer-49: The abs function computes the absolute value of a number.

Answer-50: GLSL shaders can be debugged using OpenGL debugging tools like RenderDoc, gDEBugger, or by outputting values as colors in the fragment shader.