CSci 480 Lecture Notes
Week Two, (Fall) Wednesday; (Summer) Tuesday: Interactions, Features, and Limitations
2.2 Basic Interaction Handling
Human Factors
Guidelines:
- Provide simple and consistent interaction sequences
- Show the available options clearly at every stage of the interaction
- Give appropriate feedback to the user
- Allow the user to recover gracefully from his mistakes
Logical Input Devices
A "logical" input device is an abastraction that shields the application
(programmer) from the details of the physical devices.
- Locator (usually a mouse)
- Keyboard
Sampling vs Event-Driven Processing
Pick Correlation
Which object receives the "click" event? A boolean function (predicate)
determines whether a point lies in a given rectangle.
2.3 Raster Graphics Features
Canvases
Canvases are off-screen images in memory.
Clipping Rectangles
A sub-region of a canvas: primitives outside a clipping rectangle
are not drawn.
SRGP_copyPixel
Often called a bitBlt (bit block transfer).
Write Mode or RasterOp
- Replace (destructive mode)
- or (bilevel painting)
- xor (sometimes used for bilevel cursor display)
- and
2.4 Limitations of SRGP
- Integer canvas coordinate system
- No object-level operations: delete, move, etc.
Image scaling: easy to shrink, hard to enlarge.
This page established September 9, 1998; last updated September 12, 1999.