test/testaudio.c

#define SDL_MAIN_USE_CALLBACKS 1
#include <SDL3/SDL_test.h>
#include <SDL3/SDL_test_common.h>
#include <SDL3/SDL_main.h>
#include "testutils.h"

#define POOF_LIFETIME 250
#define VISUALIZER_WIDTH 100
#define VISUALIZER_HEIGHT 50

typedef struct Texture
{
    SDL_Texture *texture;
    float w;
    float h;
} Texture;

typedef enum ThingType
{
    THING_NULL,
    THING_PHYSDEV,
    THING_PHYSDEV_CAPTURE,
    THING_LOGDEV,
    THING_LOGDEV_CAPTURE,
    THING_TRASHCAN,
    THING_STREAM,
    THING_POOF,
    THING_WAV
} ThingType;


typedef struct Thing Thing;

struct Thing
{
    ThingType what;

    union {
        struct {
            SDL_AudioDeviceID devid;
            SDL_bool iscapture;
            SDL_AudioSpec spec;
            char *name;
        } physdev;
        struct {
            SDL_AudioDeviceID devid;
            SDL_bool iscapture;
            SDL_AudioSpec spec;
            Thing *physdev;
            SDL_bool visualizer_enabled;
            SDL_bool visualizer_updated;
            SDL_Texture *visualizer;
            SDL_Mutex *postmix_lock;
            float *postmix_buffer;
            int postmix_buflen;
            int postmix_allocated;
            SDL_AudioSpec postmix_spec;
            SDL_AtomicInt postmix_updated;
        } logdev;
        struct {
            SDL_AudioSpec spec;
            Uint8 *buf;
            Uint32 buflen;
        } wav;
        struct {
            float startw;
            float starth;
            float centerx;
            float centery;
        } poof;
        struct {
            SDL_AudioStream *stream;
            int total_bytes;
            Uint64 next_level_update;
            Uint8 levels[5];
        } stream;
    } data;

    Thing *line_connected_to;
    char *titlebar;
    SDL_FRect rect;
    float z;
    Uint8 r, g, b, a;
    float progress;
    float scale;
    Uint64 createticks;
    Texture *texture;
    const ThingType *can_be_dropped_onto;

    void (*ontick)(Thing *thing, Uint64 now);
    void (*ondrag)(Thing *thing, int button, float x, float y);
    void (*ondrop)(Thing *thing, int button, float x, float y);
    void (*ondraw)(Thing *thing, SDL_Renderer *renderer);

    Thing *prev;
    Thing *next;
};


static Uint64 app_ready_ticks = 0;
static SDLTest_CommonState *state = NULL;

static Thing *things = NULL;
static char *current_titlebar = NULL;

static Thing *mouseover_thing = NULL;
static Thing *droppable_highlighted_thing = NULL;
static Thing *dragging_thing = NULL;
static int dragging_button = -1;
static int dragging_button_real = -1;
static SDL_bool ctrl_held = SDL_FALSE;
static SDL_bool alt_held = SDL_FALSE;

static Texture *physdev_texture = NULL;
static Texture *logdev_texture = NULL;
static Texture *audio_texture = NULL;
static Texture *trashcan_texture = NULL;
static Texture *soundboard_texture = NULL;
static Texture *soundboard_levels_texture = NULL;


static void SetTitleBar(const char *fmt, ...)
{
    char *newstr = NULL;
    va_list ap;
    va_start(ap, fmt);
    SDL_vasprintf(&newstr, fmt, ap);
    va_end(ap);

    if (newstr && (!current_titlebar || (SDL_strcmp(current_titlebar, newstr) != 0))) {
        SDL_SetWindowTitle(state->windows[0], newstr);
        SDL_free(current_titlebar);
        current_titlebar = newstr;
    } else {
        SDL_free(newstr);
    }
}

static void SetDefaultTitleBar(void)
{
    SetTitleBar("testaudio: %s", SDL_GetCurrentAudioDriver());
}

static Thing *FindThingAtPoint(const float x, const float y)
{
    const SDL_FPoint pt = { x, y };
    Thing *retval = NULL;
    Thing *i;
    for (i = things; i; i = i->next) {
        if ((i != dragging_thing) && SDL_PointInRectFloat(&pt, &i->rect)) {
            retval = i;  /* keep going, though, because things drawn on top are later in the list. */
        }
    }
    return retval;
}

static Thing *UpdateMouseOver(const float x, const float y)
{
    Thing *thing;

    if (dragging_thing) {
        thing = dragging_thing;
    } else {
        thing = FindThingAtPoint(x, y);
    }

    mouseover_thing = thing;

    if (!thing) {
        SetDefaultTitleBar();
    } else if (thing->titlebar) {
        SetTitleBar("%s", thing->titlebar);
    }

    return thing;
}

static Thing *CreateThing(ThingType what, float x, float y, float z, float w, float h, Texture *texture, const char *titlebar)
{
    Thing *last = NULL;
    Thing *i;
    Thing *thing;

    thing = (Thing *) SDL_calloc(1, sizeof (Thing));
    if (!thing) {
        SDL_Log("Out of memory!");
        return NULL;
    }

    if ((w < 0) || (h < 0)) {
        SDL_assert(texture != NULL);
        if (w < 0) {
            w = texture->w;
        }
        if (h < 0) {
            h = texture->h;
        }
    }

    thing->what = what;
    thing->rect.x = x;
    thing->rect.y = y;
    thing->rect.w = w;
    thing->rect.h = h;
    thing->z = z;
    thing->r = 255;
    thing->g = 255;
    thing->b = 255;
    thing->a = 255;
    thing->scale = 1.0f;
    thing->createticks = SDL_GetTicks();
    thing->texture = texture;
    thing->titlebar = titlebar ? SDL_strdup(titlebar) : NULL;  /* if allocation fails, oh well. */

    /* insert in list by Z order (furthest from the "camera" first, so they get drawn over; negative Z is not drawn at all). */
    if (!things) {
        things = thing;
        return thing;
    }

    for (i = things; i; i = i->next) {
        if (z > i->z) {  /* insert here. */
            thing->next = i;
            thing->prev = i->prev;

            SDL_assert(i->prev == last);

            if (i->prev) {
                i->prev->next = thing;
            } else {
                SDL_assert(i == things);
                things = thing;
            }
            i->prev = thing;
            return thing;
        }
        last = i;
    }

    if (last) {
        last->next = thing;
        thing->prev = last;
    }
    return thing;
}

static void DestroyThing(Thing *thing)
{
    if (!thing) {
        return;
    }

    if (mouseover_thing == thing) {
        mouseover_thing = NULL;
    }

    if (droppable_highlighted_thing == thing) {
        droppable_highlighted_thing = NULL;
    }

    if (dragging_thing == thing) {
        dragging_thing = NULL;
    }

    switch (thing->what) {
        case THING_POOF: break;
        case THING_NULL: break;
        case THING_TRASHCAN: break;

        case THING_LOGDEV:
        case THING_LOGDEV_CAPTURE:
            SDL_CloseAudioDevice(thing->data.logdev.devid);
            if (state->renderers[0] != NULL) {
                SDL_DestroyTexture(thing->data.logdev.visualizer);
            }
            SDL_DestroyMutex(thing->data.logdev.postmix_lock);
            SDL_free(thing->data.logdev.postmix_buffer);
            break;

        case THING_PHYSDEV:
        case THING_PHYSDEV_CAPTURE:
            SDL_free(thing->data.physdev.name);
            break;

        case THING_WAV:
            SDL_free(thing->data.wav.buf);
            break;

        case THING_STREAM:
            SDL_DestroyAudioStream(thing->data.stream.stream);
            break;
    }

    if (thing->prev) {
        thing->prev->next = thing->next;
    } else {
        SDL_assert(thing == things);
        things = thing->next;
    }

    if (thing->next) {
        thing->next->prev = thing->prev;
    }

    SDL_free(thing->titlebar);
    SDL_free(thing);
}

static void DrawOneThing(SDL_Renderer *renderer, Thing *thing)
{
    SDL_FRect dst;
    SDL_memcpy(&dst, &thing->rect, sizeof (SDL_FRect));
    if (thing->scale != 1.0f) {
        const float centerx = thing->rect.x + (thing->rect.w / 2);
        const float centery = thing->rect.y + (thing->rect.h / 2);
        const int w = thing->texture ? (int) thing->texture->w : 128;
        const int h = thing->texture ? (int) thing->texture->h : 128;
        dst.w = w * thing->scale;
        dst.h = h * thing->scale;
        dst.x = centerx - (dst.w / 2);
        dst.y = centery - (dst.h / 2);
    }

    if (thing->texture) {
        if (droppable_highlighted_thing == thing) {
            SDL_SetRenderDrawColor(renderer, 255, 0, 255, 100);
            SDL_RenderFillRect(renderer, &dst);
        }
        SDL_SetRenderDrawColor(renderer, thing->r, thing->g, thing->b, thing->a);
        SDL_RenderTexture(renderer, thing->texture->texture, NULL, &dst);
    } else {
        SDL_SetRenderDrawColor(renderer, thing->r, thing->g, thing->b, thing->a);
        SDL_RenderFillRect(renderer, &dst);
    }

    if (thing->ondraw) {
        thing->ondraw(thing, renderer);
    }

    if (thing->progress > 0.0f) {
        SDL_FRect r = { thing->rect.x, thing->rect.y + (thing->rect.h + 2.0f), 0.0f, 10.0f };
        r.w = thing->rect.w * ((thing->progress > 1.0f) ? 1.0f : thing->progress);
        SDL_SetRenderDrawColor(renderer, 255, 255, 255, 128);
        SDL_RenderFillRect(renderer, &r);
    }
}

static void DrawThings(SDL_Renderer *renderer)
{
    Thing *i;

    /* draw connecting lines first, so they're behind everything else. */
    for (i = things; i && (i->z >= 0.0f); i = i->next) {
        Thing *dst = i->line_connected_to;
        if (dst) {
            SDL_SetRenderDrawColor(renderer, 255, 0, 0, 255);
            SDL_RenderLine(renderer, i->rect.x + (i->rect.w / 2), i->rect.y + (i->rect.h / 2), dst->rect.x + (dst->rect.w / 2), dst->rect.y + (dst->rect.h / 2));
        }
    }

    /* Draw the actual things. */
    for (i = things; i && (i->z >= 0.0f); i = i->next) {
        if (i != dragging_thing) {
            DrawOneThing(renderer, i);
        }
    }

    if (dragging_thing) {
        DrawOneThing(renderer, dragging_thing);  /* draw last so it's always on top. */
    }
}

static void Draw(void)
{
    SDL_Renderer *renderer = state->renderers[0];
    if (renderer) {  /* might be NULL if we're shutting down. */
        SDL_SetRenderDrawBlendMode(renderer, SDL_BLENDMODE_BLEND);
        SDL_SetRenderDrawColor(renderer, 64, 0, 64, 255);
        SDL_RenderClear(renderer);
        DrawThings(renderer);
        SDL_RenderPresent(renderer);
    }
}

static void RepositionRowOfThings(const ThingType what, const float y)
{
    int total_things = 0;
    float texw = 0.0f;
    float texh = 0.0f;
    Thing *i;

    for (i = things; i; i = i->next) {
        if (i->what == what) {
            texw = i->rect.w;
            texh = i->rect.h;
            total_things++;
        }
    }

    if (total_things > 0) {
        int w, h;
        SDL_GetWindowSize(state->windows[0], &w, &h);
        const float spacing = w / ((float) total_things);
        float x = (spacing - texw) / 2.0f;
        for (i = things; i; i = i->next) {
            if (i->what == what) {
                i->rect.x = x;
                i->rect.y = (y >= 0.0f) ? y : ((h + y) - texh);
                x += spacing;
            }
        }
    }
}

static const char *AudioFmtToString(const SDL_AudioFormat fmt)
{
    switch (fmt) {
        #define FMTCASE(x) case SDL_AUDIO_##x: return #x
        FMTCASE(U8);
        FMTCASE(S8);
        FMTCASE(S16LE);
        FMTCASE(S16BE);
        FMTCASE(S32LE);
        FMTCASE(S32BE);
        FMTCASE(F32LE);
        FMTCASE(F32BE);
        #undef FMTCASE
    }
    return "?";
}

static const char *AudioChansToStr(const int channels)
{
    switch (channels) {
        case 1: return "mono";
        case 2: return "stereo";
        case 3: return "2.1";
        case 4: return "quad";
        case 5: return "4.1";
        case 6: return "5.1";
        case 7: return "6.1";
        case 8: return "7.1";
        default: break;
    }
    return "?";
}

static void PoofThing_ondrag(Thing *thing, int button, float x, float y)
{
    dragging_thing = NULL;   /* refuse to be dragged. */
}

static void PoofThing_ontick(Thing *thing, Uint64 now)
{
    const int lifetime = POOF_LIFETIME;
    const int elasped = (int) (now - thing->createticks);
    if (elasped > lifetime) {
        DestroyThing(thing);
    } else {
        const float pct = ((float) elasped) / ((float) lifetime);
        thing->a = (Uint8) (int) (255.0f - (pct * 255.0f));
        thing->scale = 1.0f - pct;  /* shrink to nothing! */
    }
}

static Thing *CreatePoofThing(Thing *poofing_thing)
{
    const float centerx = poofing_thing->rect.x + (poofing_thing->rect.w / 2);
    const float centery = poofing_thing->rect.y + (poofing_thing->rect.h / 2);
    const float z = poofing_thing->z;
    Thing *thing = CreateThing(THING_POOF, poofing_thing->rect.x, poofing_thing->rect.y, z, poofing_thing->rect.w, poofing_thing->rect.h, poofing_thing->texture, NULL);
    if (thing) {
        thing->data.poof.startw = poofing_thing->rect.w;
        thing->data.poof.starth = poofing_thing->rect.h;
        thing->data.poof.centerx = centerx;
        thing->data.poof.centery = centery;
        thing->ontick = PoofThing_ontick;
        thing->ondrag = PoofThing_ondrag;
    }
    return thing;
}

static void DestroyThingInPoof(Thing *thing)
{
    if (thing) {
        if (thing->what != THING_POOF) {
            CreatePoofThing(thing);
        }
        DestroyThing(thing);
    }
}

/* this poofs a thing and additionally poofs all things connected to the thing. */
static void TrashThing(Thing *thing)
{
    Thing *i, *next;
    for (i = things; i; i = next) {
        next = i->next;
        if (i->line_connected_to == thing) {
            TrashThing(i);
            next = things;  /* start over in case this blew up the list. */
        }
    }
    DestroyThingInPoof(thing);
}

static void StreamThing_ontick(Thing *thing, Uint64 now)
{
    if (!thing->line_connected_to) {
        return;
    }

    /* are we playing? See if we're done, or update state. */
    if (thing->line_connected_to->what == THING_LOGDEV) {
        const int available = SDL_GetAudioStreamAvailable(thing->data.stream.stream);
        if (!available) {
            DestroyThingInPoof(thing);
            return;
        } else {
            thing->progress = 1.0f - (thing->data.stream.total_bytes ? (((float) (available)) / ((float) thing->data.stream.total_bytes)) : 0.0f);
        }
    }

    if (thing->data.stream.next_level_update <= now) {
        Uint64 perf = SDL_GetPerformanceCounter();
        int i;
        for (i = 0; i < SDL_arraysize(thing->data.stream.levels); i++) {
            thing->data.stream.levels[i] = (Uint8) (perf % 6);
            perf >>= 3;
        }
        thing->data.stream.next_level_update += 150;
    }
}

static void StreamThing_ondrag(Thing *thing, int button, float x, float y)
{
    if (button == SDL_BUTTON_RIGHT) {  /* this is kinda hacky, but use this to disconnect from a playing source. */
        if (thing->line_connected_to) {
            SDL_UnbindAudioStream(thing->data.stream.stream); /* unbind from current device */
            if (thing->line_connected_to->what == THING_LOGDEV_CAPTURE) {
                SDL_FlushAudioStream(thing->data.stream.stream);
            }
            thing->line_connected_to = NULL;
        }
    }
}

static void StreamThing_ondrop(Thing *thing, int button, float x, float y)
{
    if (droppable_highlighted_thing) {
        if (droppable_highlighted_thing->what == THING_TRASHCAN) {
            TrashThing(thing);
        } else if (((droppable_highlighted_thing->what == THING_LOGDEV) || (droppable_highlighted_thing->what == THING_LOGDEV_CAPTURE)) && (droppable_highlighted_thing != thing->line_connected_to)) {
            /* connect to a logical device! */
            SDL_Log("Binding audio stream ('%s') to logical device %u", thing->titlebar, (unsigned int) droppable_highlighted_thing->data.logdev.devid);
            if (thing->line_connected_to) {
                SDL_UnbindAudioStream(thing->data.stream.stream); /* unbind from current device */
                if (thing->line_connected_to->what == THING_LOGDEV_CAPTURE) {
                    SDL_FlushAudioStream(thing->data.stream.stream);
                }
            }

            SDL_BindAudioStream(droppable_highlighted_thing->data.logdev.devid, thing->data.stream.stream); /* bind to new device! */
            thing->data.stream.total_bytes = SDL_GetAudioStreamAvailable(thing->data.stream.stream);
            thing->progress = 0.0f;  /* ontick will adjust this if we're on an output device.*/
            thing->data.stream.next_level_update = SDL_GetTicks() + 100;
            thing->line_connected_to = droppable_highlighted_thing;
        }
    }
}

static void StreamThing_ondraw(Thing *thing, SDL_Renderer *renderer)
{
    if (thing->line_connected_to) {  /* are we playing? Update progress bar, and bounce the levels a little. */
        static const float xlocs[5] = { 18, 39, 59, 79, 99 };
        static const float ylocs[5] = { 49, 39, 29, 19, 10 };
        const float blockw = soundboard_levels_texture->w;
        const float blockh = soundboard_levels_texture->h / 5.0f;
        int i, j;
        SDL_SetRenderDrawColor(renderer, thing->r, thing->g, thing->b, thing->a);
        for (i = 0; i < SDL_arraysize(thing->data.stream.levels); i++) {
            const int level = (int) thing->data.stream.levels[i];
            const float x = xlocs[i];
            for (j = 0; j < level; j++) {
                const SDL_FRect src = { 0, soundboard_levels_texture->h - ((j+1) * blockh), blockw, blockh };
                const SDL_FRect dst = { thing->rect.x + x, thing->rect.y + ylocs[j], blockw, blockh };
                SDL_RenderTexture(renderer, soundboard_levels_texture->texture, &src, &dst);
            }
        }
    }
}

static Thing *CreateStreamThing(const SDL_AudioSpec *spec, const Uint8 *buf, const Uint32 buflen, const char *fname, const float x, const float y)
{
    static const ThingType can_be_dropped_onto[] = { THING_TRASHCAN, THING_LOGDEV, THING_LOGDEV_CAPTURE, THING_NULL };
    Thing *thing = CreateThing(THING_STREAM, x, y, 0, -1, -1, soundboard_texture, fname);
    if (thing) {
        SDL_Log("Adding audio stream for %s", fname ? fname : "(null)");
        thing->data.stream.stream = SDL_CreateAudioStream(spec, spec);
        if (buf && buflen) {
            SDL_PutAudioStreamData(thing->data.stream.stream, buf, (int) buflen);
            SDL_FlushAudioStream(thing->data.stream.stream);
            thing->data.stream.total_bytes = SDL_GetAudioStreamAvailable(thing->data.stream.stream);
        }
        thing->ontick = StreamThing_ontick;
        thing->ondrag = StreamThing_ondrag;
        thing->ondrop = StreamThing_ondrop;
        thing->ondraw = StreamThing_ondraw;
        thing->can_be_dropped_onto = can_be_dropped_onto;
    }
    return thing;
}

static void WavThing_ondrag(Thing *thing, int button, float x, float y)
{
    if (button == SDL_BUTTON_RIGHT) {  /* drag out a new audio stream. */
        dragging_thing = CreateStreamThing(&thing->data.wav.spec, thing->data.wav.buf, thing->data.wav.buflen, thing->titlebar, x - (thing->rect.w / 2), y - (thing->rect.h / 2));
    }
}

static void WavThing_ondrop(Thing *thing, int button, float x, float y)
{
    if (droppable_highlighted_thing) {
        if (droppable_highlighted_thing->what == THING_TRASHCAN) {
            TrashThing(thing);
        }
    }
}

static Thing *LoadWavThing(const char *fname, float x, float y)
{
    Thing *thing = NULL;
    char *path;
    SDL_AudioSpec spec;
    Uint8 *buf = NULL;
    Uint32 buflen = 0;

    path = GetNearbyFilename(fname);
    if (path) {
        fname = path;
    }

    if (SDL_LoadWAV(fname, &spec, &buf, &buflen) == 0) {
        static const ThingType can_be_dropped_onto[] = { THING_TRASHCAN, THING_NULL };
        char *titlebar = NULL;
        const char *nodirs = SDL_strrchr(fname, '/');
        #ifdef SDL_PLATFORM_WINDOWS
        const char *nodirs2 = SDL_strrchr(nodirs ? nodirs : fname, '\\');
        if (nodirs2) {
            nodirs = nodirs2;
        }
        #endif

        SDL_Log("Adding WAV file '%s'", fname);

        if (nodirs) {
            nodirs++;
        } else {
            nodirs = fname;
        }

        SDL_asprintf(&titlebar, "WAV file (\"%s\", %s, %s, %uHz)", nodirs, AudioFmtToString(spec.format), AudioChansToStr(spec.channels), (unsigned int) spec.freq);
        thing = CreateThing(THING_WAV, x - (audio_texture->w / 2), y - (audio_texture->h / 2), 5, -1, -1, audio_texture, titlebar);
        if (thing) {
            SDL_free(titlebar);
            SDL_memcpy(&thing->data.wav.spec, &spec, sizeof (SDL_AudioSpec));
            thing->data.wav.buf = buf;
            thing->data.wav.buflen = buflen;
            thing->can_be_dropped_onto = can_be_dropped_onto;
            thing->ondrag = WavThing_ondrag;
            thing->ondrop = WavThing_ondrop;
        }
    }

    SDL_free(path);

    return thing;
}

static Thing *LoadStockWavThing(const char *fname)
{
    char *path = GetNearbyFilename(fname);
    Thing *thing = LoadWavThing(path ? path : fname, 0.0f, 0.0f);  /* will reposition in a moment. */
    SDL_free(path);
    return thing;
}

static void LoadStockWavThings(void)
{
    LoadStockWavThing("sample.wav");
    RepositionRowOfThings(THING_WAV, -10.0f);
}

static void DestroyTexture(Texture *tex)
{
    if (tex) {
        if (state->renderers[0] != NULL) {  /* if the renderer went away, this pointer is already bogus. */
            SDL_DestroyTexture(tex->texture);
        }
        SDL_free(tex);
    }
}

static Texture *CreateTexture(const char *fname)
{
    Texture *tex = (Texture *) SDL_calloc(1, sizeof (Texture));
    if (!tex) {
        SDL_Log("Out of memory!");
    } else {
        int texw, texh;
        tex->texture = LoadTexture(state->renderers[0], fname, SDL_TRUE, &texw, &texh);
        if (!tex->texture) {
            SDL_Log("Failed to load '%s': %s", fname, SDL_GetError());
            SDL_free(tex);
            return NULL;
        }
        SDL_SetTextureBlendMode(tex->texture, SDL_BLENDMODE_BLEND);
        tex->w = (float) texw;
        tex->h = (float) texh;
    }
    return tex;
}

static Thing *CreateLogicalDeviceThing(Thing *parent, const SDL_AudioDeviceID which, const float x, const float y);

static void DeviceThing_ondrag(Thing *thing, int button, float x, float y)
{
    if ((button == SDL_BUTTON_MIDDLE) && (thing->what == THING_LOGDEV_CAPTURE)) {  /* drag out a new stream. This is a UX mess. :/ */
        dragging_thing = CreateStreamThing(&thing->data.logdev.spec, NULL, 0, NULL, x, y);
        if (dragging_thing) {
            dragging_thing->data.stream.next_level_update = SDL_GetTicks() + 100;
            SDL_BindAudioStream(thing->data.logdev.devid, dragging_thing->data.stream.stream); /* bind to new device! */
            dragging_thing->line_connected_to = thing;
        }
    } else if (button == SDL_BUTTON_RIGHT) {  /* drag out a new logical device. */
        const SDL_AudioDeviceID which = ((thing->what == THING_LOGDEV) || (thing->what == THING_LOGDEV_CAPTURE)) ? thing->data.logdev.devid : thing->data.physdev.devid;
        const SDL_AudioDeviceID devid = SDL_OpenAudioDevice(which, NULL);
        dragging_thing = devid ? CreateLogicalDeviceThing(thing, devid, x - (thing->rect.w / 2), y - (thing->rect.h / 2)) : NULL;
    }
}

static void SetLogicalDeviceTitlebar(Thing *thing)
{
    SDL_AudioSpec *spec = &thing->data.logdev.spec;
    int frames = 0;
    SDL_GetAudioDeviceFormat(thing->data.logdev.devid, spec, &frames);
    SDL_free(thing->titlebar);
    SDL_asprintf(&thing->titlebar, "Logical device #%u (%s, %s, %s, %uHz, %d frames)", (unsigned int) thing->data.logdev.devid, thing->data.logdev.iscapture ? "CAPTURE" : "OUTPUT", AudioFmtToString(spec->format), AudioChansToStr(spec->channels), (unsigned int) spec->freq, frames);
}

static void LogicalDeviceThing_ondrop(Thing *thing, int button, float x, float y)
{
    if (droppable_highlighted_thing) {
        if (droppable_highlighted_thing->what == THING_TRASHCAN) {
            TrashThing(thing);
        }
    }
}

static void SDLCALL PostmixCallback(void *userdata, const SDL_AudioSpec *spec, float *buffer, int buflen)
{
    Thing *thing = (Thing *) userdata;

    SDL_LockMutex(thing->data.logdev.postmix_lock);

    if (thing->data.logdev.postmix_allocated < buflen) {
        void *ptr = SDL_realloc(thing->data.logdev.postmix_buffer, buflen);
        if (!ptr) {
            SDL_UnlockMutex(thing->data.logdev.postmix_lock);
            return;  /* oh well. */
        }
        thing->data.logdev.postmix_buffer = (float *) ptr;
        thing->data.logdev.postmix_allocated = buflen;
    }

    SDL_copyp(&thing->data.logdev.postmix_spec, spec);
    SDL_memcpy(thing->data.logdev.postmix_buffer, buffer, buflen);
    thing->data.logdev.postmix_buflen = buflen;
    SDL_AtomicSet(&thing->data.logdev.postmix_updated, 1);

    SDL_UnlockMutex(thing->data.logdev.postmix_lock);
}

static void UpdateVisualizer(SDL_Renderer *renderer, SDL_Texture *visualizer, const int channels, const float *buffer, const int buflen)
{
    static const SDL_Color channel_colors[8] = {
        { 255, 255, 255, 255 },
        { 255, 0, 0, 255 },
        { 0, 255, 0, 255 },
        { 0, 0, 255, 255 },
        { 255, 255, 0, 255 },
        { 0, 255, 255, 255 },
        { 255, 0, 255, 255 },
        { 127, 127, 127, 255 }
    };

    SDL_SetRenderTarget(renderer, visualizer);
    SDL_SetRenderDrawColor(renderer, 0, 0, 0, 0);
    SDL_RenderClear(renderer);

    if (buffer && buflen) {
        const int frames = (buflen / sizeof (float)) / channels;
        const int skip = frames / (VISUALIZER_WIDTH * 2);
        int i, j;

        for (i = channels - 1; i >= 0; i--) {
            const SDL_Color *color = &channel_colors[i % SDL_arraysize(channel_colors)];
            SDL_FPoint points[VISUALIZER_WIDTH + 2];
            float prevx = 0.0f;
            int pointidx = 1;

            points[0].x = 0.0f;
            points[0].y = VISUALIZER_HEIGHT * 0.5f;

            for (j = 0; j < (SDL_arraysize(points)-1); j++) {
                const float val = buffer[((j * skip) * channels) + i];
                const float x = prevx + 2;
                const float y = (VISUALIZER_HEIGHT * 0.5f) - (VISUALIZER_HEIGHT * (val * 0.5f));
                SDL_assert(pointidx < SDL_arraysize(points));
                points[pointidx].x = x;
                points[pointidx].y = y;
                pointidx++;
                prevx = x;
            }

            SDL_SetRenderDrawColor(renderer, color->r, color->g, color->b, 255);
            SDL_RenderLines(renderer, points, pointidx);
        }
    }

    SDL_SetRenderTarget(renderer, NULL);
}

static void LogicalDeviceThing_ontick(Thing *thing, Uint64 now)
{
    const SDL_bool ismousedover = (thing == mouseover_thing);

    if (!thing->data.logdev.visualizer || !thing->data.logdev.postmix_lock) {  /* need these to work, skip if they failed. */
        return;
    }

    if (thing->data.logdev.visualizer_enabled != ismousedover) {
        thing->data.logdev.visualizer_enabled = ismousedover;
        if (!ismousedover) {
            SDL_SetAudioPostmixCallback(thing->data.logdev.devid, NULL, NULL);
        } else {
            if (thing->data.logdev.postmix_buffer) {
                SDL_memset(thing->data.logdev.postmix_buffer, '\0', thing->data.logdev.postmix_buflen);
            }
            SDL_AtomicSet(&thing->data.logdev.postmix_updated, 1);  /* so this will at least clear the texture later. */
            SDL_SetAudioPostmixCallback(thing->data.logdev.devid, PostmixCallback, thing);
        }
    }
}

static void LogicalDeviceThing_ondraw(Thing *thing, SDL_Renderer *renderer)
{
    if (thing->data.logdev.visualizer_enabled) {
        SDL_FRect dst;
        dst.w = thing->rect.w;
        dst.h = thing->rect.h;
        dst.x = thing->rect.x + ((thing->rect.w - dst.w) / 2);
        dst.y = thing->rect.y + ((thing->rect.h - dst.h) / 2);

        if (SDL_AtomicGet(&thing->data.logdev.postmix_updated)) {
            float *buffer;
            int channels;
            int buflen;

            SDL_LockMutex(thing->data.logdev.postmix_lock);
            channels = thing->data.logdev.postmix_spec.channels;
            buflen = thing->data.logdev.postmix_buflen;
            buffer = (float *) SDL_malloc(thing->data.logdev.postmix_buflen);
            if (buffer) {
                SDL_memcpy(buffer, thing->data.logdev.postmix_buffer, thing->data.logdev.postmix_buflen);
                SDL_AtomicSet(&thing->data.logdev.postmix_updated, 0);
            }
            SDL_UnlockMutex(thing->data.logdev.postmix_lock);

            UpdateVisualizer(renderer, thing->data.logdev.visualizer, channels, buffer, buflen);
            SDL_free(buffer);
        }

        SDL_SetRenderDrawColor(renderer, 255, 255, 255, 30);
        SDL_RenderTexture(renderer, thing->data.logdev.visualizer, NULL, &dst);
    }
}

static Thing *CreateLogicalDeviceThing(Thing *parent, const SDL_AudioDeviceID which, const float x, const float y)
{
    static const ThingType can_be_dropped_onto[] = { THING_TRASHCAN, THING_NULL };
    Thing *physthing = ((parent->what == THING_LOGDEV) || (parent->what == THING_LOGDEV_CAPTURE)) ? parent->data.logdev.physdev : parent;
    const SDL_bool iscapture = physthing->data.physdev.iscapture;
    Thing *thing;

    SDL_Log("Adding logical audio device %u", (unsigned int) which);
    thing = CreateThing(iscapture ? THING_LOGDEV_CAPTURE : THING_LOGDEV, x, y, 5, -1, -1, logdev_texture, NULL);
    if (thing) {
        thing->data.logdev.devid = which;
        thing->data.logdev.iscapture = iscapture;
        thing->data.logdev.physdev = physthing;
        thing->data.logdev.visualizer = SDL_CreateTexture(state->renderers[0], SDL_PIXELFORMAT_RGBA8888, SDL_TEXTUREACCESS_TARGET, VISUALIZER_WIDTH, VISUALIZER_HEIGHT);
        thing->data.logdev.postmix_lock = SDL_CreateMutex();
        if (thing->data.logdev.visualizer) {
            SDL_SetTextureBlendMode(thing->data.logdev.visualizer, SDL_BLENDMODE_BLEND);
        }
        thing->line_connected_to = physthing;
        thing->ontick = LogicalDeviceThing_ontick;
        thing->ondrag = DeviceThing_ondrag;
        thing->ondrop = LogicalDeviceThing_ondrop;
        thing->ondraw = LogicalDeviceThing_ondraw;
        thing->can_be_dropped_onto = can_be_dropped_onto;

        SetLogicalDeviceTitlebar(thing);
    }
    return thing;
}

static void SetPhysicalDeviceTitlebar(Thing *thing)
{
    int frames = 0;
    SDL_AudioSpec *spec = &thing->data.physdev.spec;
    SDL_GetAudioDeviceFormat(thing->data.physdev.devid, spec, &frames);
    SDL_free(thing->titlebar);
    if (thing->data.physdev.devid == SDL_AUDIO_DEVICE_DEFAULT_CAPTURE) {
        SDL_asprintf(&thing->titlebar, "Default system device (CAPTURE, %s, %s, %uHz, %d frames)", AudioFmtToString(spec->format), AudioChansToStr(spec->channels), (unsigned int) spec->freq, frames);
    } else if (thing->data.physdev.devid == SDL_AUDIO_DEVICE_DEFAULT_OUTPUT) {
        SDL_asprintf(&thing->titlebar, "Default system device (OUTPUT, %s, %s, %uHz, %d frames)", AudioFmtToString(spec->format), AudioChansToStr(spec->channels), (unsigned int) spec->freq, frames);
    } else {
        SDL_asprintf(&thing->titlebar, "Physical device #%u (%s, \"%s\", %s, %s, %uHz, %d frames)", (unsigned int) thing->data.physdev.devid, thing->data.physdev.iscapture ? "CAPTURE" : "OUTPUT", thing->data.physdev.name, AudioFmtToString(spec->format), AudioChansToStr(spec->channels), (unsigned int) spec->freq, frames);
    }
}

static void PhysicalDeviceThing_ondrop(Thing *thing, int button, float x, float y)
{
    if (droppable_highlighted_thing) {
        if (droppable_highlighted_thing->what == THING_TRASHCAN) {
            TrashThing(thing);
        }
    }
}

static void PhysicalDeviceThing_ontick(Thing *thing, Uint64 now)
{
    const int lifetime = POOF_LIFETIME;
    const int elasped = (int) (now - thing->createticks);
    if (elasped > lifetime) {
        thing->scale = 1.0f;
        thing->a = 255;
        thing->ontick = NULL;  /* no more ticking. */
    } else {
        const float pct = ((float) elasped) / ((float) lifetime);
        thing->a = (Uint8) (int) (pct * 255.0f);
        thing->scale = pct;  /* grow to normal size */
    }
}


static Thing *CreatePhysicalDeviceThing(const SDL_AudioDeviceID which, const SDL_bool iscapture)
{
    static const ThingType can_be_dropped_onto[] = { THING_TRASHCAN, THING_NULL };
    static float next_physdev_x = 0;
    Thing *thing;
    int winw, winh;

    SDL_GetWindowSize(state->windows[0], &winw, &winh);
    if (next_physdev_x > (winw-physdev_texture->w)) {
        next_physdev_x = 0;
    }

    SDL_Log("Adding physical audio device %u", (unsigned int) which);
    thing = CreateThing(iscapture ? THING_PHYSDEV_CAPTURE : THING_PHYSDEV, next_physdev_x, 170, 5, -1, -1, physdev_texture, NULL);
    if (thing) {
        thing->data.physdev.devid = which;
        thing->data.physdev.iscapture = iscapture;
        thing->data.physdev.name = SDL_GetAudioDeviceName(which);
        thing->ondrag = DeviceThing_ondrag;
        thing->ondrop = PhysicalDeviceThing_ondrop;
        thing->ontick = PhysicalDeviceThing_ontick;
        thing->can_be_dropped_onto = can_be_dropped_onto;

        SetPhysicalDeviceTitlebar(thing);
        if (SDL_GetTicks() <= (app_ready_ticks + 2000)) {  /* assume this is the initial batch if it happens in the first two seconds. */
            RepositionRowOfThings(THING_PHYSDEV, 10.0f);  /* don't rearrange them after the initial add. */
            RepositionRowOfThings(THING_PHYSDEV_CAPTURE, 170.0f);  /* don't rearrange them after the initial add. */
            next_physdev_x = 0.0f;
        } else {
            next_physdev_x += physdev_texture->w * 1.5f;
        }
    }

    return thing;
}

static Thing *CreateTrashcanThing(void)
{
    int winw, winh;
    SDL_GetWindowSize(state->windows[0], &winw, &winh);
    return CreateThing(THING_TRASHCAN, winw - trashcan_texture->w, winh - trashcan_texture->h, 10, -1, -1, trashcan_texture, "Drag things here to remove them.");
}

static Thing *CreateDefaultPhysicalDevice(const SDL_bool iscapture)
{
    return CreatePhysicalDeviceThing(iscapture ? SDL_AUDIO_DEVICE_DEFAULT_CAPTURE : SDL_AUDIO_DEVICE_DEFAULT_OUTPUT, iscapture);
}

static void TickThings(void)
{
    Thing *i;
    Thing *next;
    const Uint64 now = SDL_GetTicks();
    for (i = things; i; i = next) {
        next = i->next;  /* in case this deletes itself. */
        if (i->ontick) {
            i->ontick(i, now);
        }
    }
}

static void WindowResized(const int newwinw, const int newwinh)
{
    Thing *i;
    const float neww = (float) newwinw;
    const float newh = (float) newwinh;
    const float oldw = (float) state->window_w;
    const float oldh = (float) state->window_h;
    for (i = things; i; i = i->next) {
        const float halfw = i->rect.w / 2.0f;
        const float halfh = i->rect.h / 2.0f;
        const float x = (i->rect.x + halfw) / oldw;
        const float y = (i->rect.y + halfh) / oldh;
        i->rect.x = (x * neww) - halfw;
        i->rect.y = (y * newh) - halfh;
    }
    state->window_w = newwinw;
    state->window_h = newwinh;
}

int SDL_AppInit(void **appstate, int argc, char *argv[])
{
    int i;

    state = SDLTest_CommonCreateState(argv, SDL_INIT_VIDEO | SDL_INIT_AUDIO);
    if (!state) {
        return -1;
    }

    state->window_flags |= SDL_WINDOW_RESIZABLE;

    for (i = 1; i < argc;) {
        int consumed = SDLTest_CommonArg(state, i);
        if (consumed == 0) {
            consumed = -1;
            /* add our own command lines here. */
        }
        if (consumed < 0) {
            static const char *options[] = {
                /* add our own command lines here. */
                /*"[--blend none|blend|add|mod|mul|sub]",*/
                NULL
            };
            SDLTest_CommonLogUsage(state, argv[0], options);
            return -1;
        }
        i += consumed;
    }

    if (!SDLTest_CommonInit(state)) {
        return -1;
    }

    if (state->audio_id) {
        SDL_CloseAudioDevice(state->audio_id);
        state->audio_id = 0;
    }

    SetDefaultTitleBar();

    if ((physdev_texture = CreateTexture("physaudiodev.bmp")) == NULL) { return -1; }
    if ((logdev_texture = CreateTexture("logaudiodev.bmp")) == NULL) { return -1; }
    if ((audio_texture = CreateTexture("audiofile.bmp")) == NULL) { return -1; }
    if ((trashcan_texture = CreateTexture("trashcan.bmp")) == NULL) { return -1; }
    if ((soundboard_texture = CreateTexture("soundboard.bmp")) == NULL) { return -1; }
    if ((soundboard_levels_texture = CreateTexture("soundboard_levels.bmp")) == NULL) { return -1; }

    LoadStockWavThings();
    CreateTrashcanThing();
    CreateDefaultPhysicalDevice(SDL_FALSE);
    CreateDefaultPhysicalDevice(SDL_TRUE);

    return 0;
}


static SDL_bool saw_event = SDL_FALSE;

int SDL_AppEvent(void *appstate, const SDL_Event *event)
{
    Thing *thing = NULL;

    saw_event = SDL_TRUE;

    switch (event->type) {
        case SDL_EVENT_MOUSE_MOTION:
            thing = UpdateMouseOver(event->motion.x, event->motion.y);
            if ((dragging_button == -1) && event->motion.state) {
                if (event->motion.state & SDL_BUTTON_LMASK) {
                    /* for people that don't have all three buttons... */
                    if (ctrl_held) {
                        dragging_button = SDL_BUTTON_RIGHT;
                    } else if (alt_held) {
                        dragging_button = SDL_BUTTON_MIDDLE;
                    } else {
                        dragging_button = SDL_BUTTON_LEFT;
                    }
                    dragging_button_real = SDL_BUTTON_LEFT;
                } else if (event->motion.state & SDL_BUTTON_RMASK) {
                    dragging_button = SDL_BUTTON_RIGHT;
                    dragging_button_real = SDL_BUTTON_RIGHT;
                } else if (event->motion.state & SDL_BUTTON_MMASK) {
                    dragging_button = SDL_BUTTON_MIDDLE;
                    dragging_button_real = SDL_BUTTON_MIDDLE;
                }

                if (dragging_button != -1) {
                    dragging_thing = thing;
                    if (thing && thing->ondrag) {
                        thing->ondrag(thing, dragging_button, event->motion.x, event->motion.y);
                    }
                }
            }

            droppable_highlighted_thing = NULL;
            if (dragging_thing) {
                dragging_thing->rect.x = event->motion.x - (dragging_thing->rect.w / 2);
                dragging_thing->rect.y = event->motion.y - (dragging_thing->rect.h / 2);
                if (dragging_thing->can_be_dropped_onto) {
                    thing = FindThingAtPoint(event->motion.x, event->motion.y);
                    if (thing) {
                        int i;
                        for (i = 0; dragging_thing->can_be_dropped_onto[i]; i++) {
                            if (dragging_thing->can_be_dropped_onto[i] == thing->what) {
                                droppable_highlighted_thing = thing;
                                break;
                            }
                        }
                    }
                }
            }
            break;

        case SDL_EVENT_MOUSE_BUTTON_DOWN:
            thing = UpdateMouseOver(event->button.x, event->button.y);
            break;

        case SDL_EVENT_MOUSE_BUTTON_UP:
            if (dragging_button_real == event->button.button) {
                Thing *dropped_thing = dragging_thing;
                dragging_thing = NULL;
                dragging_button = -1;
                dragging_button_real = -1;
                if (dropped_thing && dropped_thing->ondrop) {
                    dropped_thing->ondrop(dropped_thing, event->button.button, event->button.x, event->button.y);
                }
                droppable_highlighted_thing = NULL;
            }
            thing = UpdateMouseOver(event->button.x, event->button.y);
            break;

        case SDL_EVENT_MOUSE_WHEEL:
            UpdateMouseOver(event->wheel.mouse_x, event->wheel.mouse_y);
            break;

        case SDL_EVENT_KEY_DOWN:
        case SDL_EVENT_KEY_UP:
            ctrl_held = ((event->key.keysym.mod & SDL_KMOD_CTRL) != 0);
            alt_held = ((event->key.keysym.mod & SDL_KMOD_ALT) != 0);
            break;

        case SDL_EVENT_DROP_FILE:
            SDL_Log("Drop file! '%s'", event->drop.data);
            LoadWavThing(event->drop.data, event->drop.x, event->drop.y);
            /* SDL frees event->drop.data for you when you use SDL_AppEvent(). */
            break;

        case SDL_EVENT_WINDOW_RESIZED:
            WindowResized(event->window.data1, event->window.data2);
            break;

        case SDL_EVENT_AUDIO_DEVICE_ADDED:
            CreatePhysicalDeviceThing(event->adevice.which, event->adevice.iscapture);
            break;

        case SDL_EVENT_AUDIO_DEVICE_REMOVED: {
            const SDL_AudioDeviceID which = event->adevice.which;
            Thing *i, *next;
            SDL_Log("Removing audio device %u", (unsigned int) which);
            for (i = things; i; i = next) {
                next = i->next;
                if (((i->what == THING_PHYSDEV) || (i->what == THING_PHYSDEV_CAPTURE)) && (i->data.physdev.devid == which)) {
                    TrashThing(i);
                    next = things;  /* in case we mangled the list. */
                } else if (((i->what == THING_LOGDEV) || (i->what == THING_LOGDEV_CAPTURE)) && (i->data.logdev.devid == which)) {
                    TrashThing(i);
                    next = things;  /* in case we mangled the list. */
                }
            }
            break;
        }

        default: break;
    }

    return SDLTest_CommonEventMainCallbacks(state, event);
}

int SDL_AppIterate(void *appstate)
{
    if (app_ready_ticks == 0) {
        app_ready_ticks = SDL_GetTicks();
    }

    TickThings();
    Draw();

    if (saw_event) {
        saw_event = SDL_FALSE;  /* reset this so we know when SDL_AppEvent() runs again */
    } else {
        SDL_Delay(10);
    }

    return 0;  /* keep going. */
}

void SDL_AppQuit(void *appstate)
{
    while (things) {
        DestroyThing(things);  /* make sure all the audio devices are closed, etc. */
    }

    DestroyTexture(physdev_texture);
    DestroyTexture(logdev_texture);
    DestroyTexture(audio_texture);
    DestroyTexture(trashcan_texture);
    DestroyTexture(soundboard_texture);
    DestroyTexture(soundboard_levels_texture);
    SDLTest_CommonQuit(state);
}