Research on Geometric Modeling Technology of Packaging Container Based on OpenGL(II)

Smooth curves and surfaces are approximated by a large number of line segments or polygonal lines. However, the special structure (curve and surface) of the packaging container can be described with a small number of control points. This description is accurate. NURBS is called non-uniform rational B-spline and is one of the most popular geometric modeling methods in computer graphics and CAD/CAM. Through it can be flexibly designed a variety of shapes of the surface.



The NURBS interface function provided by OpenGL was used to perform special structural modeling of the glass packaging container on the NURBS surface, which made the fitting surface more intuitive. Proceed as follows:

(1) Apply a gluNewNurbsRenderer function to create a NURBS object pointer. (2) Apply the gluNewNurbsProperty function to set the properties of the drawing object. (3) Call gluBeginCurve/gluBeginSurface to start drawing curves and surfaces. (4) Call the gluNurbsCurve/gluNurbsSurface function to draw the object using the control point, the node sequence, and the order of the polynomial basis function. (5) Call gluEndCurve/gluEndSurface to end the curve and surface drawing.

4 Reality Mapping Methods in Packaging CAD

Realistic graphics is a kind of computer graphics generation technology. It must first construct the geometric model of the desired scene. The brightness of the surface of each scene visible on the screen is then calculated based on the assumed lighting conditions. Realistic graphics need to combine decorative patterns and object shapes closely together on a computer. A real-world texture map is a kind of mapping. It is a corresponding mapping of ~2D graphics through a suitable mapping function and a 3D mapping object, plus reasonable lighting. The effect (rendering) forms a realistic image. A three-dimensional texture, ie, a texture map, maps a portion of a specified image to each segment that allows texture mapping. See FIG. 3 for a three-dimensional map effect. This mapping is accompanied by using the color of an image to the position indicated by the (s, t, r) coordinates of a map and modifying the RGBA color of the map. However, it is important to note that in OpenGL, texture mapping is only described in RGBA mode, and its use is not defined in the color index mode. The general steps for drawing using textures are:

1) Define the texture.
2) Define methods for using textures on pixels.
3) Allow texture mapping.
4) Apply the texture coordinates and geometry coordinates to draw the scene.

5 Conclusion

The two-dimensional design of packaging containers to three-dimensional design is the development direction of packaging design. In this paper, the geometric modeling technology of packaging containers based on OpenGL is proposed, the common structure of packaging containers is summarized, the three-dimensional modeling methods of these structures are studied, and the three-dimensional modeling using these technical methods is performed, and the effect of interior design is seen using the mapping technology. However, how to strengthen the processing technology information, taking into account the processing in the design stage, so that the design and processing of better convergence will need to be further improved. At the same time, how to combine the optimum design of the packaging container structure to achieve its compressive strength design, buffer performance, etc. also need to further study.

Source: Packaging Engineering Yang Tao 1 2, Zhu Yingjie 2, Chen Shaowei 2
(1. Tianjin Polytechnic University, 2. Tianjin Business School,)