2D Clipping and Viewing Flashcards
What is the World Coordinate System?
The space in which the application model is defined.
What is the Screen Coordinate System?
The space in which the image is displayed.
What is the window?
The rectangle of the world we wish to display.
What is the Interface Window?
The window everything is displayed in.
What is the View-port?
Where the image is defined to be show, either entire screen or the interface window.
What is a Viewing Transformation?
Mapping from the world to the view-port.
What are the steps of a worldview transformation?
Choose window in world coordinates > Clip to the size of the window > translate it to the origin > Scale to the view-port size > Translate to the interface window.
What is Panning?
Moving the window through the world.
What is Zooming?
Reducing or Increasing the window size.
What is aspect ratio?
The relation between the width and height of a window.
What is Clipping?
Clipping is the removal of all objects or part of objects in a
modelled scene that are outside the real-world window.
What is the Clip Window?
The Area to be clipped.
What are the types of Clipping?
Point Clipping, Line Clipping, Area Clipping, Curve Clipping, Text Clipping.
What is point clipping?
Define 4 lines making a box, if point inside display else don’t.
When is line clip a trivial accept?
When the entire line is inside the clip box.
When is line clip a trivial reject?
When the entire line is outside the clip box.
What are the non-trivial cases for line clipping?
One end is inside the clip box while the other end is outside and when both ends are outside the clip box but pass through.
What is Brute Force Line Clipping?
When you use parametric line equations to look for window intersections. It’s Computationally expensive.
What is Cohen-Sutherland Algorithm?
A line clipping algorithm that segments the clipping area into nine regions and gives them a 4 bit op-code. line endpoints have corresponding op-codes.
How does Cohen-Sutherland Algorithm handle non-trivial cases?
Pick endpoint outside. > Pick crossed edge (set op-code bit) > find edge intersection point > replace the outside point with new point > repeat until trivial accept or reject.
What lines are a special case for Cohen-Sutherland Algorithm?
Vertical lines.
What is the Liang-Barsky Algorithm?
A line clipping algorithm that uses parametric equations.Algorithm text p. 257.
What are all the condition and the parameters for Liang-Barsky?
condition up <= q for k = 1,2,3,4 p1 = -dx, q1 = x0 - xwmin p2 = dx, q2 = xwmax - x0 p3 = -dy, q3 = y0 - ywmin q4 = dy, p4 = ywmax - y0 if pk != 0, u = qk/pk
What is the Sutherland-Hodgman Algorithm?
It is a polygon clipping algorithm, go around the polygon and record valid points clip otherwise.
