attributes of an entity
Typically, any parameter that affects the display method of an entity is generally called a
property parameter (
attribute parameter). such as color and largeThe small equal attribute parameters determine the basic characteristics of the elements. Others indicate how the entities are displayed under certain conditions. Example of a specific condition attributeThe child has visibility or detectable in the interactive object selector. Such specific conditional attributes are discussed in detail in the following chapters. here, we only consider the properties that control the primitive display properties of the primitive, regardless of the specific conditions. For example, a line segment can be a pointlines or dashes, thick or thin lines, and blue or orange. Areas can be filled with a color or multicolor pattern. Text can be pressed from the leftto the right reading mode, you can also display diagonally in the diagonal direction of the screen or in a vertical column. Every word used by itselfdisplayed in different fonts, colors, and sizes. We can also apply brightness changes on the edges of objects to smooth the grating ladder effect.
One way to select an attribute to add a human graphics package is to expand the associated parameter table for each output element feature, which includesthe appropriate properties. For example, the draw line feature can include parameters for color, width, and other properties in addition to the endpoint coordinates.
Another approach is to provide a table of system current property values and use the standalone function contained in the graphics package to set the property tableThe current value. In order to generate an output entity, the system detects the related property and invokes the display program using the current property settings. Some graphics packages use two combinations of Set attribute value methods, while other graphics libraries, such as OpenGL, use the Update System attribute table independent function to set properties .
The graphics system that maintains the current value table for properties and other parameters is called the
State system or
state machine,other parameters, such as the attributes of the output entity and the current frame cache location, are called
State variable or
state parameter. when assigning a value to one or several state parameters, the system enters a specific state. The state is persisted until the value of the state parameter is changed again.
Properties of Computer Graphics (iii) _ Elements
