COMP3421 - Graphics

# Definitions

modeling
the mathematical representation and computer implementation of lines, curves, surfaces, and transformations
rendering
the mathematics of projection, hidden surface removal and local and global illumination; the computer implementation of this in the graphics pipeline
Ambient Fudge Term
Global ambient value. Prevents surfaces not facing a light from being black.
Attenuation
the gradual loss of intensity of any kind of flux (e.g. light) through a medium
Camera
A way of visualising the movement of the world view - it is the global coordinate system. Often we consider it to be an object itself. Hence conversions to global coords are conversions to camera local coords.
Depth Slope
Depth slope m is a measure of how quickly a polygon is sloping away from the camera. Sloping polygons need a bit more offset in order to resolve properly.
Foreshortening
The experience of objects further away appearing smaller than those closer (because our eye is a point camera)
Lerping
Linear Interpolation is a way of finding a value between two points, based on the percentage of the way between the two points.
Model Matrix
A transformation matrix representing the transform from local coords to world coords
Model View Matrix
The matrix used to convert local coords into global (camera) coords
Non-Photorealistic Rendering (NPR)
Catch all term for stylised rendering (e.g. oil painting, technical diagrams)
Point
A vector representing displacement from the origin.
Projection Matrix
The matrix used to describe the view volume. This is usually called on reshape
Rasterisation
Conversion of a polygon into a group of fragments
Scene graph
way to represent complex relationships between objects - e.g. between a foot, leg, torso. Is hierarchical to display which objects move when other objects move. A node draws itself, then does a transformation(s) before drawing its children nodes.
Transformation Matrix
Any matrix representing a series of rotates, translates, scales and shears.
Vector
A displacement between 2 points in x-dimensional space.
Viewport
rectangular-shaped canvas that things are drawn on
View Matrix
A transformation matrix representing the transformation from world coords to camera coords.
View Volume
3D rectangular prism representing the area of space displayed in the viewport. View volume is in camera co-ords.
Axis-Aligned View Volume
A rectangular prism shaped view volume - either used for orthographic, or the result of a perspective view volume that has been perspective transformed.
Canonical View Volume
Axis-aligned view volume with every point between (-1,-1,-1) and (1,1,1)
Perspective View Volume
Frustum shaped view volume (enables foreshortening).
World Window
an axis-aligned rectangle representing the portion of the world that we can see (2D)
Screen Coords or Window coords
refer to the coordinate space from (-w,-h) to (w,h)
Z-Fighting
The result of two polygons being almost parallel is that due to limited precision, they will ‘fight’ for which is on top and create weird jagged lines. We can enable GL_POLYGON_OFFSET_FILL and set a polygon offset of -1 -1 to whatever want to be on top to fix this.
page revision: 5, last edited: 09 Sep 2014 09:43