It took me some time to find a copy of freeglut.dll to place into my system folder, eventually retrieving it from http://www.turtle.dds.nl/gl4newlisp/index.html

On windows the freeglut source is currently only meant to be built with MSVC, as opposed to mingw/msys, and it may be some time until thats resolved. So it might be a good idea to make a copy of the above mentioned freeglut.dll available at the common-lisp.net/project/cl-opengl page.

A couple other minor notes with the redbook examples so far. With CLISP, the character #\Esc is mentioned in rb3-lines.lisp and rb4-poly.lisp, and above, and had to be changed to #\Escape

As I understand it cl-opengl is currently dependent on freeglut to open a GL canvas. Is there any interest in having a few C functions to call in to, or perhaps written entirely in Lisp as CFFI to each of the required underlying functions, to generate the Windows HWND and XWindows surfaces? On windows, the WndProc functions which takes care of mouse and keyboard events would be handled with a separate package, and similarly for XWindows with its Xevents. The benefit here is that for many applications you may not need the extensive menu system of freeglut and thus can eliminate the dependency on that library.

The other question I have is about the scope of cl-opengl, in terms of handling applications meant to run at 60hz frame rate in the following sense; it would seem that cl-opengl would be the place to have a compiler of sorts, to handle a common situation where conditionals are placed in the main rendering loop to draw sets of Gl primitives. Suppose in my application I toggle one of these such that now the rendering loop makes an additional call into a function that has a glDrawArrays call for some set of polygons, along with other conditionals in the function that branches for choosing between other GL primitives. An extra set of polygons may be drawn with a bright color to draw attention to some part of the visual model, and so on. This is where cl-opengl functions or macros would step in because my Lisp code thus wrapped with some opengl-with statements would effectively have these gl primatives bundled into consecutive display lists where applicable such that in the final analysis there are just a minimal set of glCallList statements being made to the hardware. Those very same calls to glCallList would persist for many frames until the application toggles additional code so that only the affected and adjacent display lists get rebuilt. The programmer would use these wrappers only around code that would benefit from having these display lists built to persist over more than a few frames.

As I understand it that was one of the stated goals of the cells opengl framework though having looked through the current cl-opengl code the closest thing I can come to this is found in util.lisp, and no examples as of yet to do the above. If this can be cleanly addressed conceptually by adopting some layout when implementing applications I'd like to hear about that too. Currently for my OpenGL programs I've amassed a set of lower level C functions that take variables representing states, i.e. packed into an unsigned 32 bit value, and use display lists and just recompute the important ones where appropriate. A set of Lisp wrappers would probably dramatically change the way such code would look and is approached, making it much more compact in terms of number of lines and perhaps even packed maximally linearly efficient, so to speak, for eliminating unnecessary gl statements in the main loop, all with little effort from the programmer.

As a specific example, a call to reset the glColor to white at the beginning of a functions processing that may have much more work to do, depending on its current toggles, could actually be tossed into a preexisting display list from the previous function that had its trailing end of work to do. However doing that manually is out of the question since it would involve much more code, either a dedicated display list for that one area or even more time consuming if statements in other functions so it can be tacked on. Overall, once packed into the list it would be a very minor performance win by reducing just that one call for a gl primitive, for sure, however it could add up when you consider the overlap of various functions in the main loop each of which are doing some subwork.

In a C language perhaps the framework would look something like having function pointers to a heading and trailing set of gl primitive code which would be considered static for each of the subwork functions, perhaps labeled header and footer, and the actual dynamic code that the subwork function implements itself. Assuming the guts of the subwork function becomes ``static'' for at least a few frames, then all of it can be absorbed into a display list and in fact the entire function with all its conditionals effectively disappears, from a gl runtime perspective. Later that portion of the display list can be regenerated to that depth when requested by a mouse or key toggle, i.e., an outside function, and be called again down to that depth so it is fully rebuilt with current values, and re-absorbed into the current master chain or set of the minimal amount of display lists.

Imagine a scenario where hundreds of frames have gone by with no changes from network, mouse, or keyboard events. Then its possible that all the gl calls can be placed into a single display list and at some point the list will have to be split so that different code can be inserted. So if the main list was previously in two sublists before, and some feature was just toggled back on then it might be a good idea to have kept those sublists around for a while so now three lists are ready to be called; the outer two sublists, and the newly recomputed feature. After many frames pass, sublists that have gone unchanged can be merged together. And again, code that is likely to change every frame would simply never be wrapped with these lisp macros to begin with.