Computer Graphics - Third Year Students 2023
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Questions and Answers

What is the name of the technique used to select and enlarge a portion of a drawing?

Windowing

What is the name of the area chosen for display in windowing?

Window

How is the window selected?

World-coordinate

What is the name of the imaginary box that encloses the desired area of an object?

<p>Window</p> Signup and view all the answers

What is a viewport?

<p>An area on the display device to which a window is mapped.</p> Signup and view all the answers

The window is an area in object space, while the viewport is an area on the display device.

<p>True</p> Signup and view all the answers

The viewport size is defined by the graphics packages used.

<p>True</p> Signup and view all the answers

A viewport can contain multiple windows, enabling the display of different aspects of the same object at various angles in a single display.

<p>True</p> Signup and view all the answers

What is clipping?

<p>A technique for not showing parts of the drawing that are not of interest.</p> Signup and view all the answers

What does the clipping window defines?

<p>What is to be displayed.</p> Signup and view all the answers

What does the viewport defines?

<p>Where it is to be displayed.</p> Signup and view all the answers

What are the two coordinate systems involved in window-to-viewport transformation?

<p>World Coordinates and Device Coordinates</p> Signup and view all the answers

Describe the primary goal of window-to-viewport transformation.

<p>Transform from window in world coordinates to viewport in device coordinates.</p> Signup and view all the answers

What is the general approach for setting up the viewing coordinate system?

<p>Set up viewing coordinate system with world coordinate frame.</p> Signup and view all the answers

What are the two transformations involved in converting from world coordinates to viewing coordinates?

<p>Translation and Rotation</p> Signup and view all the answers

What does the view up vector determine?

<p>Orientation</p> Signup and view all the answers

What are the three coordinate systems involved in the two-dimensional viewing pipeline?

<p>Local Coordinates, World Coordinates, and Viewing Coordinates.</p> Signup and view all the answers

What is the purpose of the workstation transform?

<p>Maps normalized coordinates to device coordinates.</p> Signup and view all the answers

Describe the impact of the window-to-viewport transformation on the viewing process.

<p>It makes the viewing process independent of output devices by using normalized coordinate systems.</p> Signup and view all the answers

Clipping is typically performed in normalized coordinates to simplify calculations and improve efficiency.

<p>True</p> Signup and view all the answers

What are the three main steps involved in the window-to-normalized square-to-viewport mapping?

<p>Transform the clipping window to a normalized square, clip the normalized square, and transfer the scene to the viewport.</p> Signup and view all the answers

What is the primary purpose of clipping algorithms?

<p>Eliminate portions of a picture that are inside or outside a specific region.</p> Signup and view all the answers

Describe the three primary categories of clipping.

<p>Point Clipping, Line Clipping, and Fill Polygon Clipping.</p> Signup and view all the answers

How does a point (x, y) determine if it should be clipped?

<p>It is not clipped if its coordinates fall within the range of the clipping window.</p> Signup and view all the answers

What are the two strategies for line clipping?

<p>Checking each point of the line to see if it falls inside the region and finding the intersection point of the line with the boundary.</p> Signup and view all the answers

Describe the key advantage of the Cohen-Sutherland line clipping algorithm.

<p>It vastly reduces the number of required intersection calculations.</p> Signup and view all the answers

What is the purpose of the region code assigned to each endpoint in the Cohen-Sutherland algorithm?

<p>To identify the region of the endpoint relative to the clipping window</p> Signup and view all the answers

How does the Cohen-Sutherland algorithm determine if a line should be completely visible, completely invisible, or partially visible?

<p>By applying logical operations, the algorithm analyzes the region codes of both endpoints. If the OR operation results in 0000, the line is completely visible. If the AND operation yields a non-zero value, the line is completely invisible. Otherwise, the line is considered partially visible.</p> Signup and view all the answers

What happens when the Cohen-Sutherland algorithm determines a line is partially visible?

<p>The line is intersected with the relevant edge of the window, and the new intersection point replaces the cut-away point for further processing.</p> Signup and view all the answers

What are the five cases that the Cohen-Sutherland line clipping algorithm considers when analyzing a line?

<p>The cases cover scenarios where both endpoints are inside the clipping window, one endpoint is inside and the other is outside, and both endpoints are outside with either no intersection or intersection with the clipping window.</p> Signup and view all the answers

How does the Cohen-Sutherland algorithm deal with lines that have a common set bit in their region codes?

<p>These lines can be clipped.</p> Signup and view all the answers

In the Cohen-Sutherland algorithm, how does the algorithm handle a line that has one endpoint inside the clipping window and one endpoint outside?

<p>It clips the line at the intersection point.</p> Signup and view all the answers

How does the Cohen-Sutherland algorithm handle lines that have both endpoints outside the clipping window?

<p>It analyzes the intersection with the clipping window, either rejecting the entire line if there is no intersection or clipping the line at both intersection points if there is an intersection.</p> Signup and view all the answers

What is the name of the algorithm used for clipping polygon areas?

<p>Sutherland-Hodgman Area Clipping Algorithm</p> Signup and view all the answers

The Sutherland-Hodgman algorithm requires a convex clipping window, but the polygon to be clipped can be either convex or non-convex.

<p>True</p> Signup and view all the answers

What happens when the Sutherland-Hodgman algorithm encounters a vertex inside the clipping window?

<p>The vertex is saved for processing against the subsequent edges of the window.</p> Signup and view all the answers

When a line crosses a clipping window boundary, what information is used to create the new set of vertices for the clipped polygon?

<p>The intersection point of the line with the boundary is used.</p> Signup and view all the answers

How is the initial vertex list processed in the Sutherland-Hodgman algorithm?

<p>It is processed in a circular manner, ensuring that every pair of consecutive vertices is evaluated.</p> Signup and view all the answers

Describe the purpose of the post-processing step in the Sutherland-Hodgman algorithm.

<p>Remove degenerate sections that have collapsed to the clipping window boundary.</p> Signup and view all the answers

The Sutherland-Hodgman algorithm is a versatile approach that can be used for clipping polygons against windows of various sizes and shapes.

<p>True</p> Signup and view all the answers

What is the outcome of clipping a polygon with vertices {V1, V2, V3, V4} against the left edge in the Sutherland-Hodgman algorithm?

<p>The output list becomes {V2, I1, I2, V1}</p> Signup and view all the answers

Study Notes

Computer Graphics - Third Year Students

  • The course is taught by Dr. Rehab Emad El-Dein Sayed Mohamed at FCI-Minia University in 2023.

Course Outline

  • Survey of Computer Graphics
  • Overview of Graphics Systems
  • Graphics Output Primitives
  • Attributes of Graphics Primitives
  • Geometric Transformations
  • Two-Dimensional Viewing
    • Three-Dimensional Viewing
    • Three-Dimensional Object Representations
    • Visible-Surface Detection Methods
    • Illumination Models and Surface-Rendering Methods

Contents

  • Computer Graphics Window
  • Two-dimensional Viewing
  • Two-dimensional Viewing Pipeline
  • The Clipping Window
  • Normalization and Viewport Transformation
  • Clipping Algorithms
    • Two-Dimensional Point Clipping
    • Two-Dimensional Line Clipping
    • Polygon Fill Area Clipping

Two-Dimensional Viewing

  • Computer Graphics Window: The method of selecting and enlarging a portion of a drawing is called windowing. The area chosen for this display is called a window. Sometimes only a portion of an object is needed, which is defined as a window.
  • Viewport: An area on a display device where the window's contents are mapped. Most graphics packages allow customizing viewport size. Viewports can be used to display the same object from different angles.

Two-Dimensional Viewing Pipeline

  • Model Transformation
  • World Coordinates
  • View Transformation
  • Viewing Coordinates

Two-Dimensional Viewing

  • Clipping: A technique to hide parts of a drawing that are not needed.
  • Viewport: The area that the window will be mapped to on the device (e.g., screen).
  • A viewport defines where the window will be displayed.

The Clipping Window

  • The clipping window can have any shape, but it is easier to use a rectangular window with edges aligned with the x and y axes.
  • It's defined using the coordinates of two opposite corners in world coordinates.

Normalization and Viewport Transformation

  • Transforming from world coordinates to device coordinates.
  • Independent of the requirements of the output device.
  • Graphics systems use normalized coordinates.
  • Viewports are defined in normalized coordinates or screen coordinates after normalization.
  • Clipping is usually performed in normalized coordinates.

The Clipping Window

  • Any shape can be used for clipping, but a rectangle (edges aligned with x and y axes) is common.
  • Defined by two opposite corners, in world coordinates.

Viewport

  • An area on a display device where a window is mapped.
  • Defines the location where the window contents will be displayed.

Matrix Representations and Homogeneous Coordinates

  • World coordinates: Cartesian coordinates.
  • Device coordinates: Screen coordinates.
  • Window: Area on world coordinates selected for display.
  • Viewport: Area on device coordinates where graphics are displayed.

Two-Dimensional Polygon Clipping

  • Sutherland-Hodgman Algorithm: An algorithm to clip polygons against a window boundary.
    • Input are vertices that define the polygon
    • The algorithm clips against each window edge (one at a time)
    • Output are clipped vertices

Other Two-Dimensional Transformations

  • For clipping, each window edge is tested against pairs of consecutive vertices in the input list. This helps to produce the output vertices list. Multiple test cases are possible.

Cohen-Sutherland Line Clipping

  • An efficient line-clipping algorithm.
  • It minimizes the number of intersection calculations.
  • Uses region codes to determine if an endpoint is inside or outside the window.

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Computer Graphics - Third Year Students 2023 PDF

Description

This quiz covers key concepts in Computer Graphics taught by Dr. Rehab Emad El-Dein Sayed Mohamed at FCI-Minia University. Topics include graphics systems, primitives, transformations, and viewing methods in both 2D and 3D. Test your understanding of critical algorithms and techniques used in computer graphics.

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