use projectm_pcm_get_max_samples to set buffer size

README.md

@@ -22,9 +22,12 @@ generate the PCM stream, then pipe to milkbucket, like so:
 ```
 ffmpeg -i $audio -ar 44100 -f s16le - | ./milkbucket -p $preset
 ```
+Note that you can pass in multiple presets with multiple `-p` flags, then use
+the arrow keys to cycle through the presets while running.
 
-Note that neither of these commands will output any audio! If you want to hear
-the audio at the same time (and assuming your machine uses pipewire), run:
+Note that neither of these commands (ffmpeg or milkbucket) will output any
+audio! If you want to hear the audio at the same time (and assuming your
+machine uses pipewire), run:
 ```
 ffmpeg -i $audio -ar 44100 -f s16le - | tee >(pw-play --rate=44100 --format=s16 -) | ./milkbucket -p $preset
 ```

cmd/root.go

@@ -17,6 +17,9 @@ along with this program. If not, see <http://www.gnu.org/licenses/>.
 package cmd
 
 import (
+	"encoding/binary"
+	"errors"
+	"io"
 	"log"
 	"os"
 
@@ -27,6 +30,41 @@ import (
 var presets []string
 var transition bool
 
+/*
+ * checkStdin checks if any data has been passed in through stdin and returns
+ * an error if we don't believe so.
+ */
+func checkStdin() error {
+	stat, err := os.Stdin.Stat()
+	if err != nil {
+		return err
+	} else if (stat.Mode() & os.ModeCharDevice) != 0 {
+		return errors.New("nothing to read from stdin")
+	}
+
+	return nil
+}
+
+/*
+ * validatePresets performs some basic checks on the presets passed in and
+ * returns an error if it finds a problem.
+ */
+func validatePresets() error {
+	for _, p := range presets {
+		info, err := os.Stat(p)
+		if err != nil {
+			return err
+		} else if info.IsDir() {
+			return errors.New("preset " + p + " is a directory")
+		}
+	}
+
+	return nil
+}
+
+/*
+ * handleWindowEvent handles window events like resizing.
+ */
 func handleWindowEvent(event *sdl.WindowEvent, m *milkDropWindow) {
 	switch event.Event {
 	case sdl.WINDOWEVENT_RESIZED:
@@ -35,6 +73,9 @@ func handleWindowEvent(event *sdl.WindowEvent, m *milkDropWindow) {
 	}
 }
 
+/*
+ * handleKeyboardEvent handles keyboard inputs.
+ */
 func handleKeyboardEvent(event *sdl.KeyboardEvent, m *milkDropWindow) {
 	scancode := event.Keysym.Scancode
 	if event.Type == sdl.KEYDOWN && scancode == sdl.SCANCODE_RIGHT && event.Repeat == 0 {
@@ -44,6 +85,10 @@ func handleKeyboardEvent(event *sdl.KeyboardEvent, m *milkDropWindow) {
 	}
 }
 
+/*
+ * handleEvent passes the event to a more specific function based on its type.
+ * It returns false if the program should quit, true otherwise.
+ */
 func handleEvent(event sdl.Event, m *milkDropWindow) bool {
 	switch event.(type) {
 	case *sdl.QuitEvent:
@@ -59,32 +104,55 @@ func handleEvent(event sdl.Event, m *milkDropWindow) bool {
 	return true
 }
 
+/*
+ * update handles events and renders new frames of the visualization. It
+ * returns a bool indicating whether the program should keep running and an
+ * error, if any.
+ */
+func update(m *milkDropWindow) (bool, error) {
+	for event := sdl.PollEvent(); event != nil; event = sdl.PollEvent() {
+		keepRunning := handleEvent(event, m)
+		if !keepRunning {
+			return false, nil
+		}
+	}
+
+	audioData := make([]int16, maxSamples(2, 2))
+
+	err := binary.Read(os.Stdin, binary.LittleEndian, audioData)
+	if err == io.ErrUnexpectedEOF {
+		return false, nil
+	} else if err != nil {
+		return true, err
+	}
+
+	m.render(audioData)
+	return true, nil
+}
+
+/*
+ * milkbucket sets up the program and starts a rendering loop.
+ */
 func milkbucket(cmd *cobra.Command, args []string) {
-	stat, err := os.Stdin.Stat()
+	err := checkStdin()
 	if err != nil {
-		panic(err)
-	} else if (stat.Mode() & os.ModeCharDevice) != 0 {
-		log.Fatal("nothing to read from stdin")
+		log.Fatal(err)
 	}
 
 	err = sdl.Init(sdl.INIT_VIDEO)
 	if err != nil {
-		panic(err)
+		log.Fatal(err)
 	}
 	defer sdl.Quit()
 
-	for _, p := range presets {
-		info, err := os.Stat(p)
+	err = validatePresets()
 	if err != nil {
-			panic(err)
-		} else if info.IsDir() {
-			panic("preset " + p + " is a directory")
-		}
+		log.Fatal(err)
 	}
 
 	m, err := newMilkDropWindow(800, 600, presets)
 	if err != nil {
-		panic(err)
+		log.Fatal(err)
 	}
 	defer m.destroy()
 
@@ -92,20 +160,9 @@ func milkbucket(cmd *cobra.Command, args []string) {
 
 	running := true
 	for running {
-		for event := sdl.PollEvent(); event != nil; event = sdl.PollEvent() {
-			running = handleEvent(event, m)
-			if !running {
-				break
-			}
-		}
-
-		if !running {
-			break
-		}
-
-		running, err = m.render()
+		running, err = update(m)
 		if err != nil {
-			panic(err)
+			log.Fatal(err)
 		}
 	}
 }

cmd/window.go

@@ -25,17 +25,25 @@ import "C"
 
 import (
 	"container/ring"
-	"encoding/binary"
 	"errors"
-	"io"
-	"os"
 	"unsafe"
 
 	"github.com/veandco/go-sdl2/sdl"
 )
 
-const bufSize uint = 2048
+/*
+ * maxSamples returns the maximum number of audio samples stored by projectm
+ * when passing it audio data, given the number of bytes in one sample and the
+ * number of channels.
+ */
+func maxSamples(bytesPerSample uint, numChannels uint) uint {
+	// NOTE: not 100% sure about this, but I think
+	// projectm_pcm_get_max_samples assumes 4 bytes per sample, so we
+	// multiply by 4/bytesPerSample to convert
+	return 4 / bytesPerSample * numChannels * uint(C.projectm_pcm_get_max_samples())
+}
 
+// milkDropWindow represents the window projectm will render visualizations in.
 type milkDropWindow struct {
 	window  *sdl.Window
 	context sdl.GLContext
@@ -43,6 +51,9 @@ type milkDropWindow struct {
 	preset  *ring.Ring
 }
 
+/*
+ * setupPresets initializes a ring to store the passed presets in.
+ */
 func (m *milkDropWindow) setupPresets(presets []string) {
 	m.preset = ring.New(len(presets))
 	for _, preset := range presets {
@@ -51,16 +62,28 @@ func (m *milkDropWindow) setupPresets(presets []string) {
 	}
 }
 
+/*
+ * prevPreset sets the milkDropWindow's preset to the one after the current
+ * preset.
+ */
 func (m *milkDropWindow) nextPreset(smooth bool) {
 	m.preset = m.preset.Next()
 	m.loadPreset(smooth)
 }
 
+/*
+ * prevPreset sets the milkDropWindow's preset to the one before the current
+ * preset.
+ */
 func (m *milkDropWindow) prevPreset(smooth bool) {
 	m.preset = m.preset.Prev()
 	m.loadPreset(smooth)
 }
 
+/*
+ * newMilkDropWindow returns a new milkDropWindow with the given width and
+ * height, and sets presets available to the window.
+ */
 func newMilkDropWindow(width, height int32, presets []string) (*milkDropWindow, error) {
 	var m milkDropWindow
 	var err error
@@ -87,12 +110,20 @@ func newMilkDropWindow(width, height int32, presets []string) (*milkDropWindow,
 	return &m, nil
 }
 
+/*
+ * destroy handles cleanup of the milkDropWindow.
+ */
 func (m *milkDropWindow) destroy() {
 	C.projectm_destroy(m.handle)
 	sdl.GLDeleteContext(m.context)
 	m.window.Destroy()
 }
 
+/*
+ * loadPreset loads the preset file currently pointed to by m.preset. smooth
+ * determines whether there is a smooth transition between the current preset
+ * and the new preset.
+ */
 func (m *milkDropWindow) loadPreset(smooth bool) {
 	preset := m.preset.Value.(string)
 	cPreset := C.CString(preset)
@@ -100,24 +131,20 @@ func (m *milkDropWindow) loadPreset(smooth bool) {
 	C.projectm_load_preset_file(m.handle, cPreset, C.bool(smooth))
 }
 
-func (m *milkDropWindow) render() (bool, error) {
-	var audioData [bufSize]int16
-
-	err := binary.Read(os.Stdin, binary.LittleEndian, &audioData)
-	if err == io.ErrUnexpectedEOF {
-		return false, nil
-	} else if err != nil {
-		return true, err
-	}
-
-	C.projectm_pcm_add_int16(m.handle, (*C.int16_t)(&audioData[0]), C.uint(bufSize), C.PROJECTM_STEREO)
+/*
+ * render passes data to projectm for rendering. It returns a bool for if the
+ * program should keep running and an error.
+ */
+func (m *milkDropWindow) render(data []int16) {
+	C.projectm_pcm_add_int16(m.handle, (*C.int16_t)(&data[0]), C.uint(len(data)), C.PROJECTM_STEREO)
 
 	C.projectm_opengl_render_frame(m.handle)
 	m.window.GLSwap()
-
-	return true, nil
 }
 
+/*
+ * resize informs projectm of the new window size.
+ */
 func (m *milkDropWindow) resize(w, h int32) {
 	C.projectm_set_window_size(m.handle, C.ulong(w), C.ulong(h))
 }