CS426 Video 9 Anatomy of a GLUT program Flashcards

Flashcards covering key concepts and definitions from the OpenGL lecture notes.

What is OpenGL?

A cross-language, cross-platform application programming interface (API) for rendering 2D and 3D vector graphics.

What is freeGLUT?

A cross-platform windowing and keyboard-mouse handler.

What is GLEW?

The OpenGL Extension Wrangler Library (GLEW) is a cross-platform open-source C/C++ extension loading library that provides portability of code between platforms; normally used to load and compile shaders.

What is GLM?

OpenGL Mathematics is a header only C++ mathematics library for graphics software based on the OpenGL Shading Language (GLSL) specifications.

What is GLSL?

OpenGL Shading Language is a high-level shading language with a C-based syntax, giving users more control of the graphics pipeline.

What is the function of Vertex specification in the OpenGL pipeline?

Creation of an organised list of vertices – each group of vertices forms a primitive (typically triangles, quads, line-strip, fan).

What is the function of the Vertex shader in the OpenGL pipeline?

Converts each input vertex into an output vertex where user shader code can do further processing, applying model, view, and projection transformations; maps vertices into a box (-1,-1,-1) to (1,1,1).

What is the function of Tessellation in the OpenGL pipeline?

Combines vertex specification and transformed vertices into a list of simple primitives (triangles); may include splitting triangles into smaller triangles called patches.

What is the function of Vertex post-processing in the OpenGL pipeline?

Primitives intersecting the viewing frustrum are clipped to be contained within it; face culling based on winding order can be applied.

What is the function of Rasterization in the OpenGL pipeline?

The 2D version of primitive is coloured or textured; fragments contain individual pixel data (RGBA) for each primitive.

What is the function of the Fragment shader in the OpenGL pipeline?

User code can be run at this point to modify pixel values.

What is the function of Per sample operations in the OpenGL pipeline?

The fragment is combined with existing pixels described in the frame buffer.

What is the function of glutMainLoop()?

In computer programming, a callback is executable code that is passed as an argument to other code. It allows a lower-level software layer to call a subroutine (or function) defined in a higher-level layer (Wikipedia).

What is the function of the double buffer?

When using a double buffer we draw on one buffer whilst watching the other, once we have finished drawing we tell main loop it is ok to swap around so we can see what we have just drawn and start drawing the next frame.

What is Mipmaps?

As you render objects further away in the scene – single rendered pixels may be represented by multiple pixels in the texture. It becomes inefficient to work out the “average” (or less effective to choose just one texture pixel) to use for rendering. The solution is to create a set of images of different scales (powers of 2) that the renderer can then access directly depending on the scale.

What is Wrapping?

Describes how the texture should be sampled when a coordinate outside the range of 0 to 1 is used. In OpenGL texture coordinates (typically U,V) are represented by (s,t,r,q) where s=U and t=V q is a scale factor like w (and r, like z allows use of 3D textures). A texel is a texture element - a pixel that belongs to the (source) texture. A pixel is normally used to describe the rendered picture element (screen or image).

What is Polygon winding?

Polygon winding is the order in which vertices are passed to the graphics pipeline. They must be entered either clockwise or anticlockwise. OpenGL treats counterclockwise ordering of vertices as front facing (by default). If back face culling is enabled then back facing polygons are not rendered by the graphics pipeline.

What is the function of Vertex Shader?

The variable gl_Position is used by primitive assembly, clipping, culling, and other fixed functionality operations, if present, that operate on primitives after vertex processing has occurred.

What is the function of Fragment Shader?

A fragment shader in OpenGL processes the data required for OpenGL to render a single pixel.