1 - Intro and Primitives

Question 1

what is a pen plotter ?

Question 2

What is colour & how do you display it onscreen?

Answer 2

A pure colour is a wave on the electromagnetic spectrum. Colours are essentially just energy distributions.

Wavelength determines the colour we see and the energy intensity (amplitude) determines the brightness.

Colours represented by X = rR+gG+bG

Capitals = light sources
non capitals = intensities

Question 3

Primary Colours

Answer 3

magenta cyan yellow (centre white)

Question 4

Addictive colours

Answer 4

red green blue (centre black)

Question 5

Raster display:

Question 6

Raster display:

Answer 6

2D array of picture elements (pixels).

The number of pixels in a display depends on the hardware used; older displays may only have had 300x200 pixels

Question 7

Framebuffer

Answer 7

The framebuffer is an in-memory map of the display;

Uses one memory location for each pixel describe its properties (colour/intensity) – therefore, a buffer of size W x H x 3 is needed.

• Addressed in any order
• Read out sequentially

Question 8

Double-buffering

Answer 8

use of two framebuffers

one being drawn into by the program,
another currently being displayed on screen

Then they swap

Question 9

Rasterization

Answer 9

the pictures or scenes are written to the framebuffer by converting infinite precision specification into pixels

Question 10

What are primitives?

Answer 10

basic mathematical objects, such as lines, curves, and polygons, which can be combined to create more complex graphical images.

They are specified by location and dimension and are thought of as having zero width

Rendered with attributes – e.g. colour, line style etc.

Question 11

To model a scene:

Answer 11

⦁ Construct complex objects from simpler ones, in the local space

⦁ Apply some transformation (e.g. adjust position, scale, rotation etc.) from the local space to place objects into the world space

⦁Draw the object with visual attributes

Question 12

Order of object creation:

Answer 12

• Complex object created in the local coordinate system
• Complex Object translated into the world coordinate system and positioned in the scene
• the scene is clipped to the window ( window coordinate specifies the world coordinates it wasnt to include in the scene)
• The window is mapped to the device coordinates (view coordinates / viewport (ex. specific pixels))

Question 13

Difference between GL_LINE_STRIP and loop

Answer 13

the loop closes itself and loops the last point back to the first.

Question 14

Scene clipping

Answer 14

rendering a larger area, but clipping the scene to just a smaller window

Question 15

Viewport mapping

Answer 15

Mapping the window to the viewport involves translating the clipped 3D world (specified in world coordinates) to the 2D viewport coordinates.