一个opengl中文教程

--===BBS水木清华站∶精华区===-- -===BBS水木清华站∶精华区===- * 41 � The OpenGL Graphics Library + OpenGL Overview + Basic OpenGL Concepts + Initialization + Drawing with OpenGL + Additional Libraries + Writing OpenGL Windows Applications in C + OpenGL Initialization + The Window Procedure + Compiling and Running the Application + OpenGL in MFC Applications + OpenGL initialization + Drawing the Cube + Running the Application + Summary 41 � The OpenGL Graphics Library OpenGL is a device- and operating system-independent library for three-dimensional graphics and graphics rendering. OpenGL was originally developed by Silicon Graphics Inc. (SGI) for use on their high-end graphics workstations. Since then, OpenGL has become a widely accepted standard with implementations on many operating system and hardware platforms, including the Windows NT and Windows 95 operating systems. --------------------------------------------------------------------------- [Image]Note: OpenGL support under Windows 95 has just become available recently. The Windows 95 version of the OpenGL development system and redistributable run-time files are available as part of the October, 1995 or later release of the Microsoft Developer Library, level 2. There is no support for OpenGL under Win32s. --------------------------------------------------------------------------- In addition to the standard OpenGL Library implementation, Windows also provides a series of functions that integrate OpenGL with the operating system. In particular, functions are provided that associate OpenGL rendering contexts with GDI device contexts. These Windows extensions to the OpenGL Library are identified by names that begin with wgl. In addition to these OpenGL extensions, a series of new Win32 API functions has also been defined to facilitate certain aspects of OpenGL programming. The OpenGL Library is large and complex. If you wish to have access to a comprehensive set of manuals, you should consider purchasing The OpenGL Reference Manual from the OpenGL Architecture Review Board, or The OpenGL Programming Guide by Jackie Neider, Tom Davis, and Mason Woo. Both books are published by Addison-Wesley. In this chapter, in addition to presenting a brief (and far from comprehensive!) overview of the OpenGL Library, I place the focus on using OpenGL from Windows and MFC applications. OpenGL Overview The purpose of the OpenGL Library is to render two- and three-dimensional objects into a frame buffer, such as the pixel memory of your computer's graphics hardware. The OpenGL Library is fundamentally procedural. What this means is that in your application, you don't describe what an object looks like; instead, you specify how an object is to be drawn. Complex geometric objects are described in terms of simple elements that your application defines. The OpenGL Library implementation follows the client-server model. OpenGL clients and servers need not even reside on the same machine. Basic OpenGL Concepts At the basic level, the OpenGL Library deals with vertices. A vertex is a point, for example the end point of a line, or a corner of a polygon. Vertices can be two- or three-dimensional. At the next level are primitives. Primitives consist of a group of one or more vertices. For example, a rectangle described as a set of four vertices is a primitive. How vertices are assembled into primitives and how primitives are drawn into a frame buffer are controlled by a variety of settings. For example, applications can specify a three-dimensional transformation matrix that defines how the coordinates of an object are translated into coordinates on the drawing surface. In addition to its ability to draw points and lines, OpenGL can also draw surfaces, apply lighting specifications, and use texture bitmaps. Another set of features enables applications to selectively use or discard pixels. For example, drawing a pixel can be made conditional upon properties such as the pixel's depth or its opacity. A greatly simplified view of how OpenGL works is presented in Figure 41.1. Figure 41.1. Simplified overview of OpenGL operations. Initialization Before the OpenGL Library can be used, a number of initialization steps must be executed. Every Windows OpenGL application must associate a rendering context with a device context. The device context must be a display device context or a memory device context that is compatible with the display device context. To set up a rendering context, applications must first use the SetPixelFormat Win32 function to set up a pixel format for the device; next, they must call wglCreateContext with the device context handle as its parameter. If successful, wglCreateContext returns a rendering context handle of type HGLRC. --------------------------------------------------------------------------- [Image]Note: Windows does not support drawing into a printer device context using the OpenGL Library. If you wish to print an image created with OpenGL, one possible workaround is to draw into a memory device context that is compatible with the display device and then transfer the resulting bitmap to the printer device. --------------------------------------------------------------------------- OpenGL under Windows recognizes two types of pixel data modes: RGBA formats and color index-based modes. When the RGBA mode is selected, pixel colors are specified in the form of RGB color values. When color index mode is selected, pixel colors are selected from the system palette using an index value. These two modes become relevant on palette-based 256-color devices (many VGA-compatible display cards). When your application uses the RGBA mode on such a device, it must manage its own palette, and respond to Windows palette notification messages. There are specific requirements that must be met by a window that is to be used for OpenGL operations. Specifically, such windows cannot be created using a window class that has the CS_PARENTDC style set. The window itself must have the WS_CLIPCHILDREN and the WS_CLIPSIBLINGS styles in order to be compatible with OpenGL. Note that to increase your application's performance, you may wish to use a window class that has a null background brush; the window background will be erased through the OpenGL Library anyway. Before a rendering context can be used, it must be set up as the current context using the wglMakeCurrent function. This function takes two parameters, one of which is a device-context handle. Interestingly, this handle does not need to be identical to the handle used in wglCreateContext梑ut it must refer to the same device). Thus it is possible, for example, to set up an OpenGL rendering context using a device-context handle returned by GetDC, but use wglMakeCurrent with a device-context handle returned by BeginPaint. Once a rendering context is ready to accept commands, you may wish to send additional initialization commands; for example, you may wish to erase the frame buf