From: gfoot AT mc31 DOT merton DOT ox DOT ac DOT uk (George Foot) Newsgroups: comp.os.msdos.djgpp Subject: Re: Some Allegro questions (Shawn?) Date: 3 Mar 1997 17:26:35 GMT Organization: Oxford University Lines: 51 Message-ID: <5ff1kb$qpj@news.ox.ac.uk> References: <5fdsds$p42 AT freenet-news DOT carleton DOT ca> NNTP-Posting-Host: mc31.merton.ox.ac.uk To: djgpp AT delorie DOT com DJ-Gateway: from newsgroup comp.os.msdos.djgpp Paul Derbyshire (ao950 AT FreeNet DOT Carleton DOT CA) wrote: : I have several questions about Allegro, mostly out of curiosity... : * Why, when using a SVGA mode e.g. GFX_AUTODETECT 640x480, does a : fade_in(palette) or a fade_out() seem to do 4 fades in series instead of : just 1? Fades work as expected in GFX_MODEX. Is it a bug or a "feature"? Most likely, you're defining the colour strenghts in your palette from 0 to 255; this is incorrect, the VGA hardware only recognises values from 0 to 63. For example, white is (63,63,63) [R,G,B], red is (63,0,0), orange is (63,31,0), ... : * Is the video manipulation ultimately done with super-fast nearptrs or far : pointers? Near pointers are thought not to work on some DPMI hosts, : so an optimal Allegro would detect the DPMI host, if it is a known safe : one i.e. cwsdpmi use nearptrs, else use farptrs for safety... : * What functions in allegro are typically inlined? : * Which graphics functions use inline asm for optimisation? Read the sources for answers to those three. : * Was Allegro compiled with -m486? Read the makefile. : * When an allegro program that uses sound starts, there is a popping noise. : The noise also happens at exit. I have learned to dread this pop, since : usually if it happens when I'm not expecting it, I find myself staring at : a stack dump a few seconds later. What is it? It's your sound card; probably objecting to the change in mixer settings. Some cards make a pop when they receive initialisation commands, some don't. : * There is a definite link between using allegro and GCC making funny noises : during compile. For instance, using RHIDE and Allegro, I ran a program, : and it hit a breakpoint. I inspected a few variables, then changed some : source and ran Make. GCC was called, and five seconds into the compile a : bunch of queer repeating and *LOUD* sound effects started coming from my SB! : It has happened a total of 3 times now. All 3 times after an allegro : program a) used sound and b) never got to allegro_exit. If the program doesn't exit smoothly, it's not surprising that it leaves a mess. BTW my Allegro programs always seem to say "Shutting down Allegro" when they crash; don't yours? If not, try making a short program which initialises Allegro and the sound card, then exits. When your programs die you can run this program, and it might tidy up a bit. -- George Foot Merton College, Oxford.