12-06-2012, 04:29 PM
Computer Graphics Lecture Notes
computer graphics 3.pdf (Size: 1.38 MB / Downloads: 67)
Introduction to Graphics
Raster Displays
The convention in these notes will follow that of OpenGL, placing the origin in the lower left
corner, with that pixel being at location (0, 0). Be aware that placing the origin in the upper left is
another common convention.
One of 2N intensities or colors are associated with each pixel, where N is the number of bits per
pixel. Greyscale typically has one byte per pixel, for 28 = 256 intensities. Color often requires
one byte per channel, with three color channels per pixel: red, green, and blue.
Transformations
2D Transformations
Given a point cloud, polygon, or sampled parametric curve, we can use transformations for several
purposes:
1. Change coordinate frames (world, window, viewport, device, etc).
2. Compose objects of simple parts with local scale/position/orientation of one part defined
with regard to other parts. For example, for articulated objects.
3. Use deformation to create new shapes.
4. Useful for animation.
Transformations in OpenGL
OpenGL manages two 4 × 4 transformation matrices: the modelview matrix, and the projection
matrix. Whenever you specify geometry (using glVertex), the vertices are transformed by the
current modelview matrix and then the current projection matrix. Hence, you don’t have to perform
these transformations yourself. You can modify the entries of these matrices at any time. OpenGL
provides several utilities for modifying these matrices. The modelview matrix is normally used to
represent geometric transformations of objects; the projection matrix is normally used to store the
camera transformation. For now, we’ll focus just on the modelview matrix, and discuss the camera
transformation later.