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view docs/man3/SDL_AudioCVT.3 @ 1212:7663bb0f52c7
To: sdl@libsdl.org
From: Christian Walther <cwalther@gmx.ch>
Date: Thu, 15 Dec 2005 21:19:53 +0100
Subject: [SDL] More mouse enhancements for Mac OS X
The attached patch brings two more enhancements to mouse handling on Mac
OS X (Quartz):
1. Currently, after launching an SDL application, SDL's notion of the
mouse position is stuck in the top left corner (0,0) until the first
time the mouse is moved. That's because the UpdateMouse() function isn't
implemented in the Quartz driver. This patch adds it.
2. When grabbing input while the mouse cursor is hidden, the function
CGAssociateMouseAndMouseCursorPosition(0) is called, which prevents the
system's notion of the mouse location from moving (and therefore leaving
the SDL window) even when the mouse is moved. However, apparently the
Wacom tablet driver (and maybe other special pointing device drivers)
doesn't care about that setting and still allows the mouse location to
go outside of the window. Interestingly, the system cursor, which is
made visible by the existing code in SDL in that case, does not follow
the mouse location, but appears in the middle of the SDL window. The
mouse location being outside of the window however means that mouse
button events go to background applications (or the dock or whatever is
there), which is very confusing to the user who sees no cursor outside
of the SDL window.
I have not found any way of intercepting these events (and that's
probably by design, as "normal" applications shouldn't prevent the user
from bringing other applications' windows to the front by clicking on
them). An idea would be placing a fully transparent, screen-filling
window in front of everything, but I fear that this might affect
rendering performance (by doing unnecessary compositing, using up
memory, or whatever).
The deluxe solution to the problem would be talking to the tablet
driver using AppleEvents to tell it to constrain its mapped area to the
window (see Wacom's "TabletEventDemo" sample app,
http://www.wacomeng.com/devsupport/mac/downloads.html), but I think that
the bloat that solution would add to SDL would outweigh its usefulness.
What I did instead in my patch is reassociating mouse and cursor when
the mouse leaves the window while an invisible grab is in effect, and
restoring the grab when the window is entered. That way, the grab can
still be effectively broken by a tablet, but at least it's obvious to
the user that it is broken. That change is minimal - it doesn't affect
operation with a mouse (or a trackpad), and the code that it adds is not
executed on every PumpEvents() call, only when entering and leaving the
window.
Unless there are any concerns about the patch, please apply. Feel free
to shorten the lengthy comment in SDL_QuartzEvents.m if you think it's
too verbose.
Thanks
-Christian
| author | Ryan C. Gordon <icculus@icculus.org> |
|---|---|
| date | Mon, 02 Jan 2006 00:31:00 +0000 |
| parents | e5bc29de3f0a |
| children | 546f7c1eb755 |
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.TH "SDL_AudioCVT" "3" "Tue 11 Sep 2001, 22:58" "SDL" "SDL API Reference" .SH "NAME" SDL_AudioCVT\- Audio Conversion Structure .SH "STRUCTURE DEFINITION" .PP .nf \f(CWtypedef struct{ int needed; Uint16 src_format; Uint16 dest_format; double rate_incr; Uint8 *buf; int len; int len_cvt; int len_mult; double len_ratio; void (*filters[10])(struct SDL_AudioCVT *cvt, Uint16 format); int filter_index; } SDL_AudioCVT;\fR .fi .PP .SH "STRUCTURE DATA" .TP 20 \fBneeded\fR Set to one if the conversion is possible .TP 20 \fBsrc_format\fR Audio format of the source .TP 20 \fBdest_format\fR Audio format of the destination .TP 20 \fBrate_incr\fR Rate conversion increment .TP 20 \fBbuf\fR Audio buffer .TP 20 \fBlen\fR Length of the original audio buffer in bytes .TP 20 \fBlen_cvt\fR Length of converted audio buffer in bytes (calculated) .TP 20 \fBlen_mult\fR \fBbuf\fR must be \fBlen\fR*\fBlen_mult\fR bytes in size(calculated) .TP 20 \fBlen_ratio\fR Final audio size is \fBlen\fR*\fBlen_ratio\fR .TP 20 \fBfilters[10](\&.\&.)\fR Pointers to functions needed for this conversion .TP 20 \fBfilter_index\fR Current conversion function .SH "DESCRIPTION" .PP The \fBSDL_AudioCVT\fR is used to convert audio data between different formats\&. A \fBSDL_AudioCVT\fR structure is created with the \fI\fBSDL_BuildAudioCVT\fP\fR function, while the actual conversion is done by the \fI\fBSDL_ConvertAudio\fP\fR function\&. .PP Many of the fields in the \fBSDL_AudioCVT\fR structure should be considered private and their function will not be discussed here\&. .IP "\fBUint8 *\fP\fBbuf\fR" 10This points to the audio data that will be used in the conversion\&. It is both the source and the destination, which means the converted audio data overwrites the original data\&. It also means that the converted data may be larger than the original data (if you were converting from 8-bit to 16-bit, for instance), so you must ensure \fBbuf\fR is large enough\&. See below\&. .IP "\fBint\fP \fBlen\fR" 10This is the length of the original audio data in bytes\&. .IP "\fBint\fP \fBlen_mult\fR" 10As explained above, the audio buffer needs to be big enough to store the converted data, which may be bigger than the original audio data\&. The length of \fBbuf\fR should be \fBlen\fR*\fBlen_mult\fR\&. .IP "\fBdouble\fP \fBlen_ratio\fR" 10When you have finished converting your audio data, you need to know how much of your audio buffer is valid\&. \fBlen\fR*\fBlen_ratio\fR is the size of the converted audio data in bytes\&. This is very similar to \fBlen_mult\fR, however when the convert audio data is shorter than the original \fBlen_mult\fR would be 1\&. \fBlen_ratio\fR, on the other hand, would be a fractional number between 0 and 1\&. .SH "SEE ALSO" .PP \fI\fBSDL_BuildAudioCVT\fP\fR, \fI\fBSDL_ConvertAudio\fP\fR, \fI\fBSDL_AudioSpec\fR\fR ...\" created by instant / docbook-to-man, Tue 11 Sep 2001, 22:58