{root layer (picture surface) graphics processing; OBJECT-OPEN (reference transformation parameter); OBJECT-1; graphics processing of component 1 in the body coordinate system OBJECT-CLOSE; ...... OBJECT-OPEN (reference transformation parameter); OBJECT-n; graphics processing of component n in the body coordinate system OBJECT-CLOSE; Other graphics processing at the root layer;} Among them, the lower-level components can be nested in the program modules of each component, so that a multiple nested structure can be formed. 2. Drawing information problem The content expressed in a drawing, in addition to the design of the object's own graphics, there are still information related to the drawing, such as dimensioning, text description, graphic marking and so on. This is a special problem in drawing drawings. It can be considered that the information of the drawing is defined in the world coordinate system of the drawing, that is, the root layer, so they can be drawn directly in the root layer. However, there is a kind of drawing information whose positioning points, orientations, etc. are related to a certain position and direction on the design object, such as dimensioning. If you draw them in the world coordinate system, their positioning points, orientations, etc. are defined in the body coordinate system of the design object, which is difficult to solve from the program flow and data flow. To this end, a special type of annotation pixels can be introduced, and their anchor points are defined in the current coordinate system, while other attribute values ​​(such as text height, size value, etc.) are always defined in the world coordinate system. In this way, as long as they are called in the body coordinate system of the design object, the corresponding drawing information can be completed, which is very convenient to use. In the PHIGS graphics standard, an augmented text output primitive is defined for generating a string on a normalized projected coordinate system to achieve a fill of the model, but other view information such as graphical markup is difficult to Implemented when modeling. Therefore, the PHIGS graphics standard has weaker functions in this respect. 3. Layer-to-layer association and cross-reference issues In a multi-layer graphics structure, when a program is working in the ontology coordinate space of a component, some data sometimes needs to be taken from the ontology coordinate space of the other component. In this way, the data between the layers is related and cross-references are required. A typical example is to reference data in the root world coordinate system, such as an anchor point or a direction vector, in the component's body coordinate system. Such data references cannot be resolved by conventional reference transformation rules. To this end, the concept of "virtual workspace" can be introduced, that is, the coordinate space of another component is temporarily copied in the body coordinate system of the current component to process the relevant data, and immediately after processing, the component is removed, and then returned to the current component. Under the ontology coordinate space. The operational details of the virtual workspace are auto-completed by the support function and completely transparent to the application designer. Previous page next page 3D Acoustic Panel,Sound Absorbing Panel,3D Decorate Acoustic Panel,Acoustic Panel Square Hebei RooAoo New Material Technology Co.,Ltd. , https://www.raacoustic.com
According to the hierarchical model method, the structure of the graphics program is as follows:
A Hierarchical Model for Developing CAD Application Systems (3)