diff options
Diffstat (limited to 'pcsound/pcsound_sdl.c')
| -rw-r--r-- | pcsound/pcsound_sdl.c | 179 |
1 files changed, 179 insertions, 0 deletions
diff --git a/pcsound/pcsound_sdl.c b/pcsound/pcsound_sdl.c new file mode 100644 index 00000000..50820394 --- /dev/null +++ b/pcsound/pcsound_sdl.c @@ -0,0 +1,179 @@ +// Emacs style mode select -*- C++ -*- +//----------------------------------------------------------------------------- +// +// Copyright(C) 2007 Simon Howard +// +// This program is free software; you can redistribute it and/or +// modify it under the terms of the GNU General Public License +// as published by the Free Software Foundation; either version 2 +// of the License, or (at your option) any later version. +// +// This program is distributed in the hope that it will be useful, +// but WITHOUT ANY WARRANTY; without even the implied warranty of +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +// GNU General Public License for more details. +// +// You should have received a copy of the GNU General Public License +// along with this program; if not, write to the Free Software +// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA +// 02111-1307, USA. +// +// DESCRIPTION: +// PC speaker interface. +// +//----------------------------------------------------------------------------- + +#include <stdio.h> +#include <stdlib.h> + +#include "SDL.h" +#include "SDL_mixer.h" + +#include "pcsound.h" + +#define SQUARE_WAVE_AMP 0x2000 + +static pcsound_callback_func callback; + +// Output sound format + +static int mixing_freq; +static Uint16 mixing_format; +static int mixing_channels; + +// Currently playing sound +// current_remaining is the number of remaining samples that must be played +// before we invoke the callback to get the next frequency. + +static int current_remaining; +static int current_freq; + +static int phase_offset = 0; + +// Mixer function that does the PC speaker emulation + +static void PCSound_Mix_Callback(void *udata, Uint8 *stream, int len) +{ + Sint16 *leftptr; + Sint16 *rightptr; + Sint16 this_value; + int oldfreq; + int i; + int nsamples; + + // Number of samples is quadrupled, because of 16-bit and stereo + + nsamples = len / 4; + + leftptr = (Sint16 *) stream; + rightptr = ((Sint16 *) stream) + 1; + + // Fill the output buffer + + for (i=0; i<nsamples; ++i) + { + // Has this sound expired? If so, invoke the callback to get + // the next frequency. + + while (current_remaining == 0) + { + oldfreq = current_freq; + + // Get the next frequency to play + + callback(¤t_remaining, ¤t_freq); + + if (current_freq != 0) + { + // Adjust phase to match to the new frequency. + // This gives us a smooth transition between different tones, + // with no impulse changes. + + phase_offset = (phase_offset * oldfreq) / current_freq; + } + + current_remaining = (current_remaining * mixing_freq) / 1000; + } + + // Set the value for this sample. + + if (current_freq == 0) + { + // Silence + + this_value = 0; + } + else + { + int frac; + + // Determine whether we are at a peak or trough in the current + // sound. Multiply by 2 so that frac % 2 will give 0 or 1 + // depending on whether we are at a peak or trough. + + frac = (phase_offset * current_freq * 2) / mixing_freq; + + if ((frac % 2) == 0) + { + this_value = SQUARE_WAVE_AMP; + } + else + { + this_value = -SQUARE_WAVE_AMP; + } + + ++phase_offset; + } + + --current_remaining; + + // Use the same value for the left and right channels. + + *leftptr += this_value; + *rightptr += this_value; + + leftptr += 2; + rightptr += 2; + } +} + +static int PCSound_SDL_Init(pcsound_callback_func callback_func) +{ + // Check that SDL_mixer has been opened already + // If not, fail + + if (!Mix_QuerySpec(&mixing_freq, &mixing_format, &mixing_channels)) + { + return 0; + } + + // Only supports AUDIO_S16SYS + + if (mixing_format != AUDIO_S16SYS || mixing_channels != 2) + { + fprintf(stderr, + "PCSound_SDL only supports native signed 16-bit LSB, " + "stereo format!\n"); + return 0; + } + + callback = callback_func; + current_freq = 0; + current_remaining = 0; + + Mix_SetPostMix(PCSound_Mix_Callback, NULL); + + return 1; +} + +static void PCSound_SDL_Shutdown(void) +{ +} + +pcsound_driver_t pcsound_sdl_driver = +{ + "SDL", + PCSound_SDL_Init, + PCSound_SDL_Shutdown, +}; + |