Mercurial > sdl-ios-xcode
annotate docs/man3/SDL_OpenAudio.3 @ 1629:ef4a796e7f24
Fixed bug #55
From Christian Walther:
When writing my patch for #12, I ended up doing all sorts of changes to the way
application/window activating/deactivating is handled in the Quartz backend,
resulting in the attached patch. It does make the code a bit cleaner IMHO, but
as it might be regarded as a case of "if it ain't broken, don't fix it" I'd
like to hear other people's opinion about it. Please shout if some change
strikes you as unnecessary or wrong, and I'll explain the reasons behind it. As
far as I tested it, it does not introduce any new bugs, but I may well have
missed some.
- The most fundamental change (that triggered most of the others) is irrelevant
for the usual single-window SDL applications, it only affects the people who
are crazy enough to display other Cocoa windows alongside the SDL window (I'm
actually doing this currently, although the additional window only displays
debugging info and won't be present in the final product): Before, some things
were done on the application becoming active, some on the window becoming key,
and some on the window becoming main. Conceptually, all these actions belong to
the window becoming key, so that's what I implemented. However, since in a
single-window application these three events always happen together, the
previous implementation "ain't broken".
- This slightly changed the meaning of the SDL_APPMOUSEFOCUS flag from
SDL_GetAppState(): Before, it meant "window is main and mouse is inside window
(or mode is fullscreen)". Now, it means "window is key and mouse is inside
window (or mode is fullscreen)". It makes more sense to me that way. (See
http://developer.apple.com/documentation/Cocoa/Conceptual/WinPanel/Concepts/ChangingMainKeyWindow.html
for a discussion of what key and main windows are.) The other two flags are
unchanged: SDL_APPACTIVE = application is not hidden and window is not
minimized, SDL_APPINPUTFOCUS = window is key (or mode is fullscreen).
- As a side effect, the reorganization fixes the following two issues (and
maybe others) (but they could also be fixed in less invasive ways):
* A regression that was introduced in revision 1.42 of SDL_QuartzVideo.m
(http://libsdl.org/cgi/cvsweb.cgi/SDL12/src/video/quartz/SDL_QuartzVideo.m.diff?r1=1.41&r2=1.42)
(from half-desirable to undesirable behavior):
Situation: While in windowed mode, hide the cursor using
SDL_ShowCursor(SDL_DISABLE), move the mouse outside of the window so that the
cursor becomes visible again, and SDL_SetVideoMode() to a fullscreen mode.
What happened before revision 1.42: The cursor is visible, but becomes
invisible as soon as the mouse is moved (half-desirable).
What happens in revision 1.42 and after (including current CVS): The cursor is
visible and stays visible (undesirable).
What happens after my patch: The cursor is invisible from the beginning
(desirable).
* When the cursor is hidden and grabbed, switch away from the application using
cmd-tab (which ungrabs and makes the cursor visible), move the cursor outside
of the SDL window, then cmd-tab back to the application. In 1.2.8 and in the
current CVS, the cursor is re-grabbed, but it stays visible (immovable in the
middle of the window). With my patch, the cursor is correctly re-grabbed and
hidden. (For some reason, it still doesn't work correctly if you switch back to
the application using the dock instead of cmd-tab. I haven't been able to
figure out why. I can step over [NSCursor hide] being called in the debugger,
but it seems to have no effect.)
- The patch includes my patch for #12 (it was easier to obtain using cvs diff
that way). If you apply both of them, you will end up with 6 duplicate lines in
SDL_QuartzEvents.m.
author | Sam Lantinga <slouken@libsdl.org> |
---|---|
date | Thu, 13 Apr 2006 14:17:48 +0000 |
parents | e5bc29de3f0a |
children | 546f7c1eb755 |
rev | line source |
---|---|
181
e5bc29de3f0a
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Sam Lantinga <slouken@libsdl.org>
parents:
55
diff
changeset
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1 .TH "SDL_OpenAudio" "3" "Tue 11 Sep 2001, 22:58" "SDL" "SDL API Reference" |
0 | 2 .SH "NAME" |
3 SDL_OpenAudio\- Opens the audio device with the desired parameters\&. | |
4 .SH "SYNOPSIS" | |
5 .PP | |
6 \fB#include "SDL\&.h" | |
7 .sp | |
8 \fBint \fBSDL_OpenAudio\fP\fR(\fBSDL_AudioSpec *desired, SDL_AudioSpec *obtained\fR); | |
9 .SH "DESCRIPTION" | |
10 .PP | |
11 This function opens the audio device with the \fBdesired\fR parameters, and returns 0 if successful, placing the actual hardware parameters in the structure pointed to by \fBobtained\fR\&. If \fBobtained\fR is NULL, the audio data passed to the callback function will be guaranteed to be in the requested format, and will be automatically converted to the hardware audio format if necessary\&. This function returns -1 if it failed to open the audio device, or couldn\&'t set up the audio thread\&. | |
12 .PP | |
13 To open the audio device a \fBdesired\fR \fI\fBSDL_AudioSpec\fR\fR must be created\&. | |
14 .PP | |
15 .nf | |
16 \f(CWSDL_AudioSpec *desired; | |
17 \&. | |
18 \&. | |
19 desired=(SDL_AudioSpec *)malloc(sizeof(SDL_AudioSpec));\fR | |
20 .fi | |
21 .PP | |
22 You must then fill this structure with your desired audio specifications\&. | |
23 .IP "\fBdesired\fR->\fBfreq\fR" 10The desired audio frequency in samples-per-second\&. | |
24 .IP "\fBdesired\fR->\fBformat\fR" 10The desired audio format (see \fI\fBSDL_AudioSpec\fR\fR) | |
25 .IP "\fBdesired\fR->\fBsamples\fR" 10The desired size of the audio buffer in samples\&. This number should be a power of two, and may be adjusted by the audio driver to a value more suitable for the hardware\&. Good values seem to range between 512 and 8192 inclusive, depending on the application and CPU speed\&. Smaller values yield faster response time, but can lead to underflow if the application is doing heavy processing and cannot fill the audio buffer in time\&. A stereo sample consists of both right and left channels in LR ordering\&. Note that the number of samples is directly related to time by the following formula: ms = (samples*1000)/freq | |
26 .IP "\fBdesired\fR->\fBcallback\fR" 10This should be set to a function that will be called when the audio device is ready for more data\&. It is passed a pointer to the audio buffer, and the length in bytes of the audio buffer\&. This function usually runs in a separate thread, and so you should protect data structures that it accesses by calling \fI\fBSDL_LockAudio\fP\fR and \fI\fBSDL_UnlockAudio\fP\fR in your code\&. The callback prototype is: | |
27 .PP | |
28 .nf | |
29 \f(CWvoid callback(void *userdata, Uint8 *stream, int len);\fR | |
30 .fi | |
31 .PP | |
32 \fBuserdata\fR is the pointer stored in \fBuserdata\fR field of the \fBSDL_AudioSpec\fR\&. \fBstream\fR is a pointer to the audio buffer you want to fill with information and \fBlen\fR is the length of the audio buffer in bytes\&. | |
33 .IP "\fBdesired\fR->\fBuserdata\fR" 10This pointer is passed as the first parameter to the \fBcallback\fP function\&. | |
34 .PP | |
35 \fBSDL_OpenAudio\fP reads these fields from the \fBdesired\fR \fBSDL_AudioSpec\fR structure pass to the function and attempts to find an audio configuration matching your \fBdesired\fR\&. As mentioned above, if the \fBobtained\fR parameter is \fBNULL\fP then SDL with convert from your \fBdesired\fR audio settings to the hardware settings as it plays\&. | |
36 .PP | |
37 If \fBobtained\fR is \fBNULL\fP then the \fBdesired\fR \fBSDL_AudioSpec\fR is your working specification, otherwise the \fBobtained\fR \fBSDL_AudioSpec\fR becomes the working specification and the \fBdesirec\fR specification can be deleted\&. The data in the working specification is used when building \fBSDL_AudioCVT\fR\&'s for converting loaded data to the hardware format\&. | |
38 .PP | |
39 \fBSDL_OpenAudio\fP calculates the \fBsize\fR and \fBsilence\fR fields for both the \fBdesired\fR and \fBobtained\fR specifications\&. The \fBsize\fR field stores the total size of the audio buffer in bytes, while the \fBsilence\fR stores the value used to represent silence in the audio buffer | |
40 .PP | |
41 The audio device starts out playing \fBsilence\fR when it\&'s opened, and should be enabled for playing by calling \fI\fBSDL_PauseAudio\fP(\fB0\fR)\fR when you are ready for your audio \fBcallback\fR function to be called\&. Since the audio driver may modify the requested \fBsize\fR of the audio buffer, you should allocate any local mixing buffers after you open the audio device\&. | |
42 .SH "EXAMPLES" | |
43 .PP | |
44 .nf | |
45 \f(CW/* Prototype of our callback function */ | |
46 void my_audio_callback(void *userdata, Uint8 *stream, int len); | |
47 | |
48 /* Open the audio device */ | |
49 SDL_AudioSpec *desired, *obtained; | |
50 SDL_AudioSpec *hardware_spec; | |
51 | |
52 /* Allocate a desired SDL_AudioSpec */ | |
53 desired=(SDL_AudioSpec *)malloc(sizeof(SDL_AudioSpec)); | |
54 | |
55 /* Allocate space for the obtained SDL_AudioSpec */ | |
56 obtained=(SDL_AudioSpec *)malloc(sizeof(SDL_AudioSpec)); | |
57 | |
58 /* 22050Hz - FM Radio quality */ | |
59 desired->freq=22050; | |
60 | |
61 /* 16-bit signed audio */ | |
62 desired->format=AUDIO_S16LSB; | |
63 | |
181
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Sam Lantinga <slouken@libsdl.org>
parents:
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diff
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64 /* Mono */ |
e5bc29de3f0a
Updated from the SDL Documentation Project
Sam Lantinga <slouken@libsdl.org>
parents:
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diff
changeset
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65 desired->channels=0; |
e5bc29de3f0a
Updated from the SDL Documentation Project
Sam Lantinga <slouken@libsdl.org>
parents:
55
diff
changeset
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66 |
0 | 67 /* Large audio buffer reduces risk of dropouts but increases response time */ |
68 desired->samples=8192; | |
69 | |
70 /* Our callback function */ | |
71 desired->callback=my_audio_callback; | |
72 | |
73 desired->userdata=NULL; | |
74 | |
75 /* Open the audio device */ | |
76 if ( SDL_OpenAudio(desired, obtained) < 0 ){ | |
77 fprintf(stderr, "Couldn\&'t open audio: %s | |
78 ", SDL_GetError()); | |
79 exit(-1); | |
80 } | |
81 /* desired spec is no longer needed */ | |
82 free(desired); | |
83 hardware_spec=obtained; | |
84 \&. | |
85 \&. | |
86 /* Prepare callback for playing */ | |
87 \&. | |
88 \&. | |
89 \&. | |
90 /* Start playing */ | |
91 SDL_PauseAudio(0);\fR | |
92 .fi | |
93 .PP | |
94 .SH "SEE ALSO" | |
95 .PP | |
96 \fI\fBSDL_AudioSpec\fP\fR, \fI\fBSDL_LockAudio\fP\fR, \fI\fBSDL_UnlockAudio\fP\fR, \fI\fBSDL_PauseAudio\fP\fR | |
181
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Sam Lantinga <slouken@libsdl.org>
parents:
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97 ...\" created by instant / docbook-to-man, Tue 11 Sep 2001, 22:58 |