Newsgroups: comp.answers,comp.graphics.api.opengl,news.answers Path: senator-bedfellow.mit.edu!bloom-beacon.mit.edu!grapevine.lcs.mit.edu!uhog.mit.edu!news.kei.com!newshost.marcam.com!usc!elroy.jpl.nasa.gov!swrinde!sgigate.sgi.com!fido.asd.sgi.com!sgi!dilow.asd.sgi.com!pho From: pho@dilow.asd.sgi.com (Paul Ho) Subject: OpenGL Frequently Asked Questions (FAQ) [3/3] Message-ID: Followup-To: poster Last-Modified: 1995 September 8 Summary: This contains a list of Frequently Asked Questions about OpenGL (R) Keywords: FAQ Sender: pho@dilow.asd.sgi.com Reply-To: pho@dilow.asd.sgi.com Organization: Silicon Graphics Inc. Posting-Frequency: twice a month Date: Mon, 2 Oct 1995 08:10:21 GMT Approved: mailnews@sgi.sgi.com Archive-Name: graphics/opengl-faq/part3 Lines: 412 Xref: senator-bedfellow.mit.edu comp.answers:14597 comp.graphics.api.opengl:1184 news.answers:54157 The FAQ has been split into 3 parts. This is Part 3 of 3. ------ Subject: Q22: Where can I find OpenGL source code examples? For instance, where is an example which combines OpenGL with Motif, using the Motif widget? You can get the source code examples which are found in the OpenGL Programming Guide via anonymous, public ftp from ftp://sgigate.sgi.com/pub/opengl/opengl.tar.Z Mark Kilgard has created an ftp site for source code, which is part of his articles in the X Journal magazine. This includes the GLUT toolkit (version 2.0) and OpenGL with Motif examples. The directory is: ftp://sgigate.sgi.com/pub/opengl/xjournal Some contributed source code of useful tools for developing OpenGL code can be found on ftp://sgigate.sgi.com/pub/opengl/contrib Source code found here includes: isfast--compares the performance of OpenGL states samples--more OpenGL program examples toogl--helps port IRIS GL code to OpenGL xglinfo--display information on X visuals extended for OpenGL xscope--examines OpenGL protocol sent to an extended X server ------ Subject: Q23: How do I contribute OpenGL code examples to a publicly accessible archive? A: To contribute to the public OpenGL archive, send mail to opengl-contrib@sgi.com. Your mail should contain: The material to be archived, or instructions for obtaining it. An announcement suitable for posting to comp.graphics.opengl. SGI will place the material in the opengl/contrib directory on sgigate.sgi.com and post the announcement to this newsgroup. To retrieve something from the archive, use anonymous ftp to sgigate.sgi.com. Once connected, cd to the directory OpenGL. (Case is significant.) Currently there are two subdirectories: doc Manual pages for OpenGL and related libraries. contrib Contributions from the public. Note that all contributions are distributed as-is; neither SGI nor the other companies on the OpenGL Architecture Review Board make any legally valid claims about the robustness or usefulness of this software. If you do not have access to anonymous ftp, consider using an "ftp-by-mail" server. For information on one such server, send mail to ftpmail@decwrl.dec.com with a message body containing only the word "help". ------ Subject: Q24: What is the GLUT toolkit? Where do I get it? GLUT is a portable toolkit which performs window and event operations to support OpenGL rendering. GLUT version 2.0 has: o window functions, including multiple windows for OpenGL rendering o callback driven event processing o sophisticated input devices, including dials and buttons box, tablet, Spaceball(TM) o idle routines and timers o a simple cascading pop-up menu facility o routines to generate wire and solid objects o bitmap and stroke fonts o request and queries for multisample and stereo windows o OpenGL extension query support The version 2 functionality is fully backward compatible with the version 1 functionality. The specification, source code (including FORTRAN bindings), and articles for GLUT (Graphics Library Utility Toolkit) is in: URL ftp://sgigate.sgi.com/pub/opengl/xjournal/GLUT This distribution of GLUT should compile on: o DEC Alpha workstation running OSF/1 with Open3D layered product o IBM RS/6000 workstations running AIX with OpenGL support o SGI workstation running IRIX 5.2 or higher supporting OpenGL o Template Graphics Software's OpenGL for Sun workstations o Mesa 1.1 for Unix workstations. ------ Subject: Q25: What is the relationship between IRIS GL and OpenGL? Is OpenGL source code or binary code compatible with IRIS GL? A: IRIS GL is the predecessor to OpenGL. After other implementors had experience trying to port the IRIS GL to their own machines, it was learned that the IRIS GL was too tied to a specific window system or hardware. Based upon consultations with several implementors, OpenGL is much more platform independent. IRIS GL is being maintained and bugs will be fixed, but SGI will no longer add enhancements. OpenGL is now the strategic interface for 3-D computer graphics. OpenGL code is neither binary nor source code compatible with IRIS GL code. It was decided to bite the bullet at this time to make OpenGL incompatible with IRIS GL and fix EVERYTHING that made IRIS GL difficult to port or use. For example, the gl prefix has been added to every command: glVertex(), glColor(), etc. ------ Subject: Q26: Why should I port my IRIS GL application to OpenGL? SGI will be maintaining the old IRIS GL, but not enhancing it. OpenGL is the API of choice on all new SGI machines. OpenGL has no subsets. You can use the same functionality on all machines from SGI or from other vendors. OpenGL is better integrated with the X Window System than the old IRIS GL. For example, you can mix OpenGL and X or Display PostScript drawing operations in the same window. The OpenGL naming scheme, argument list conventions, and rendering semantics are cleaner than those of IRIS GL. This should make OpenGL code easier to understand and maintain. ------ Subject: Q27: How much work is it to convert an IRIS GL program to OpenGL? What are the major differences between them? < from Mason Woo (woo@sgi.com) and Debbie Herrington (debbie@portable.com) > There is a fair amount of work, most of which is in substituting for window management or input handling routines, for which the equivalents are not OpenGL, but the local window system, such as the X Windows System or Windows NT. To help ease the way, port to "mixed model" right away, mixing the X Window System calls to open and manage windows, cursors, and color maps and read events of the window system, mouse and keyboard. You can do that now with IRIS GL, if you are running IRIX 4.0. In the X Window System, display mode choices (such as single or double buffering, color index or RGBA mode) must be declared before the window is initially opened. You may also substitute for other IRIS GL routines, such as using a OSF/Motif menu system, in place of the IRIS GL pop-up menus. You should use glXUseXFont(), whenever you were using the font manager with IRIS GL. OpenGL uses standard, predictable naming conventions, which required that all names have been changed from IRIS GL. The OpenGL naming scheme uses unique prefixes, suffixes, and capitalization to help prevent potential conflicts among application, system, and library routine names. And all routine names have changed, at least, minimally; for example: ortho() is now glOrtho(). Tables for states such as lighting or line and polygon stipples will be gone. Instead of using a def/set or def/bind sequence to load a table, you turn on the state with glEnable() and also declare the current values for that state. Colors are best stored as floating point values, scaled from 0.0 to 1.0 (0% to 100%). Alpha is fully integrated in the RGBA mode and at least source alpha will be available on all OpenGL implementations. OpenGL will not arbitrarily limit the number of bits per color to 8. Clearing the contents of buffers no longer uses the current color, but a special "clearing" color for each buffer (color, depth, stencil, and accumulation). The transformation matrix has changed. In OpenGL, there is no single matrix mode. Matrices are now column-major and are post-multiplied, although that does NOT change the calling order of these routines from IRIS GL to OpenGL. OpenGL's glRotate*() now allows for a rotation around an arbitrary axis, not just the x, y, and z axes. lookat() of IRIS GL is now gluLookAt(), which takes an up vector value, not merely a twist. There is no polarview() in OpenGL, but a series of glRotate*()s and glTranslate*()s can do the same thing. There are no separate depth cueing routines in OpenGL. Use linear fog. Feedback and selection (picking) return values, which are different from those found on any IRIS GL implementation. For selection and picking, depth values will be returned for each hit. In OpenGL, feedback and selection will now be standardized on all hardware platforms. ------ Subject: Q28: When using Xlib, how do I create a borderless window? A: Essentially you can create the window with override-redirect (see man xcreatewindow) which is the sledgehammer approach or you can change the _MOTIF_WM_HINTS property to tell the window manager to leave your windows undecorated. Also of note is that the window manager decorations of any client can be turned off by putting something like the following in the .Xdefaults file in your home directory - assuming you aren't overriding them in your app: 4Dwm*ClientAppOrClassName*clientDecoration: none ( see the 4Dwm / mwm man pages for a full description of this resource ) ( you must restart the window manager or logout/login for 4Dwm resources to take effect ) "none" will remove all of the window manager decorations - border, title bar etc. ------ Subject: Q29: How do I switch between single buffer and double buffer mode? A: When using OpenGL with X, switching between a double buffered and single buffered window can be accomplished by creating a "container" X window and creating two subwindows, one with a double buffer visual, the other with a single buffer visual. Make sure the subwindows are each the full size of their parent window. You can then use XRaiseWindow or XLowerWindow to change the stacking order of the two subwindows to switch between double buffering and single buffering. You will need to create a separate context for each of the two windows since they have different visual types. You will need to make the appropriate window/context pair current when you switch modes. IRIS GL made it easy to switch between double buffering and single buffering. But essentially, IRIS GL implemented the above process internally. ------ Subject: Q30: On my machine, it appears that glXChooseVisual is only able to match double-buffered visuals. I want to have more bits of color resolution, so how do I render in single buffer mode? A: On mid- to low-end machines with double buffer hardware, you'll probably find you get twice as much color resolution using a single buffer visual. But if there is no hardware double buffering support, the double buffered and single buffered visuals are generally the same depth (the back buffer is "carved" out of software). Search again for a double buffered visual. If you find one, use it instead. Call glDrawBuffer(GL_FRONT) though to make sure you are drawing to the front buffer (the default for a double buffered visual is to draw into the back buffer). ------ Subject: Q31: I've got a 24-bit machine, but my OpenGL windows are not using the full color resolution. What's wrong? My program looks fine on one machine, but the depth buffer doesn't work on another. What's wrong? A: An unfortunate (but documented) semantic of glXChooseVisual is that if you don't request GLX_RED_SIZE, GLX_GREEN_SIZE, or GLX_BLUE_SIZE, glXChooseVisual assumes zero for these parameters which means pick the visual with the _smallest_ amount of red, green, and blue that matches the other visual attributes. Make sure you ask for at least 1 bit of GLX_RED_SIZE, GLX_GREEN_SIZE, and GLX_BLUE_SIZE. If these configuration parameters are non-zero, it matches the visual with the _largest_ amount of red, green, and blue with at least 1 bit of each (probably what you want). Similarly, if you don't request GLX_DEPTH_SIZE, you may get a visual with zero bits of depth buffer. Some systems may have few visuals available, and those visuals all have at least 1 bit of depth buffer. On other systems, there may be dozens of visuals available, some with zero bits for the depth buffer. In short, if hidden surface removal appears to fail, check to see if you have explicitly specified any bits of depth buffer you have requested. Also check to see what visual you have received. ------ Subject: Q32: What information is available about OpenGL extensions? A: Examples of extensions include vertex arrays (calling several vertexes or related data, such as normals or colors, with a single function call), blending of constant colors, polygon offset (multiple coplanar polygons can be rendered without interaction), Procedure names and tokens for OpenGL extensions are either suffixed with EXT or a vendor-specific acronym: such as SGI for Silicon Graphics machines, or INGR for Intergraph. Also note that Silicon Graphics extensions to OpenGL are suffixed to indicate whether they will be available on all machines (SGI), on just a subset of machines (SGIS), or are very experimental and may become unavailable or completely changed (SGIX). Vendors are encouraged to add extension information to their documentation. For Silicon Graphics, extension information is summarized on the glIntro man page. ------ Subject: Q33: How do I make shadows in OpenGL? A: There are no individual routines to control shadows nor an OpenGL state for shadows. However, code can be written to render shadows. To project a shadow onto a flat plane (such as in the insect demo), draw the stippled object, flattened using matrix transformations. The easiest way to flatten an object is to use the scale function. For example, use glScalef(1., 0., 1.) to create from an infinite light shining straight down the y axis. A transformation matrix can be used to cast a shadow from an infinite or local light source in an arbitrary direction. See the article: Thant Tessman, "Casting Shadows on Flat Surfaces," IRIS Universe, Winter, 1989. Check out the fast shadow and projective texture multi-pass algorithms for producing realistic shadows using texture mapping. See the SIGGRAPH paper: Mark Segal, Carl Korobkin, et al. "Fast Shadows and Lighting Effects using Texture Mapping" 1992 SIGGRAPH Proceedings ------ Subject: Q34: How can I use 16 bit X fonts? A: Here is some code that will load any font into the server and use glXUseXFont to build the display lists for you (this does work with 16 bit fonts, it has been tested on IBM, DEC and SGI machines at an OpenGL interop testing). Once your display lists are created for each character, you can use the same basic logic to figure out which characters are valid (using first, last, firstrow and lastrow in the sample code to get : firstchar = 256 * firstrow + first lastchar = 256 * lastrow + last ) and use glCallList with those characters to print them out. static int LoadFont(char *fontName) { Font id; int first, last, firstbitmap, i; GLuint base; Display *display=0; int firstrow, lastrow; int maxchars; tkGetSystem(TK_X_DISPLAY, &display); fontInfo = XLoadQueryFont(display, fontName); if (fontInfo == NULL) { return 0; } id = fontInfo->fid; /* * First and Last char in a row of chars */ first = (int)fontInfo->min_char_or_byte2; last = (int)fontInfo->max_char_or_byte2; /* * First and Last row of chars, important for multibyte charset's */ firstrow = (int)fontInfo->min_byte1; lastrow = (int)fontInfo->max_byte1; /* * How many chars in the charset */ maxchars = 256 * lastrow + last; base = glGenLists(maxchars+1); if (base == 0) { return 0; } /* * Get offset to first char in the charset */ firstbitmap = 256 * firstrow + first; /* * for each row of chars, call glXUseXFont to build the bitmaps. */ for(i=firstrow; i<=lastrow; i++) { glXUseXFont(id, firstbitmap, last-first+1, base+firstbitmap); firstbitmap += 256; } return base; } ------ Subject: Q35: What's in the new GLU 1.2 tesselator? A: Our friends at Digital have the answers: http://www.digital.com:80/pub/doc/opengl/opengl_new_glu.html