use CheckErr

README.md

@@ -20,16 +20,16 @@ milkbucket reads a PCM stream from standard input to generate visualizations.
 If you have an audio file and a preset in mind, you can use `ffmpeg` to
 generate the PCM stream, then pipe to milkbucket, like so:
 ```
-ffmpeg -i $audio -ar 44100 -f s16le - | ./milkbucket -p $preset
+ffmpeg -i $audio -ar 44100 -f s16le - | ./milkbucket $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 you can pass in multiple presets, then use the arrow keys to cycle
+through the presets while running.
 
 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
+ffmpeg -i $audio -ar 44100 -f s16le - | tee >(pw-play --rate=44100 --format=s16 -) | ./milkbucket $preset
 ```
 (If you don't use pipewire try using `aplay` instead of `pw-play`, or some
 other command for playing PCM streams.)
@@ -37,5 +37,5 @@ other command for playing PCM streams.)
 You can also generate a visualization from your system sound. Assuming pipewire
 again, and that you have audio coming from Firefox, run:
 ```
-pw-record --target Firefox - | ./milkbucket -p $preset
+pw-record --target Firefox - | ./milkbucket $preset
 ```

cmd/root.go

@@ -20,14 +20,12 @@ import (
 	"encoding/binary"
 	"errors"
 	"io"
-	"log"
 	"os"
 
 	"github.com/spf13/cobra"
 	"github.com/veandco/go-sdl2/sdl"
 )
 
-var presets []string
 var transition bool
 
 /*
@@ -46,16 +44,29 @@ func checkStdin() error {
 }
 
 /*
- * validatePresets performs some basic checks on the presets passed in and
+ * validatePreset performs some basic checks on the preset passed in and
  * returns an error if it finds a problem.
  */
-func validatePresets() error {
-	for _, p := range presets {
-		info, err := os.Stat(p)
+func validatePreset(preset string) error {
+	info, err := os.Stat(preset)
 	if err != nil {
 		return err
 	} else if info.IsDir() {
-			return errors.New("preset " + p + " is a directory")
+		return errors.New("preset " + preset + " is a directory")
+	}
+
+	return nil
+}
+
+/*
+ * validatePresets validates each preset passed in and returns an error if it
+ * finds a problem.
+ */
+func validatePresets(cmd *cobra.Command, args []string) error {
+	for _, p := range args {
+		err := validatePreset(p)
+		if err != nil {
+			return err
 		}
 	}
 
@@ -136,45 +147,43 @@ func update(m *milkDropWindow) (bool, error) {
 func milkbucket(cmd *cobra.Command, args []string) {
 	err := checkStdin()
 	if err != nil {
-		log.Fatal(err)
+		cobra.CheckErr(err)
 	}
 
 	err = sdl.Init(sdl.INIT_VIDEO)
 	if err != nil {
-		log.Fatal(err)
+		cobra.CheckErr(err)
 	}
 	defer sdl.Quit()
 
-	err = validatePresets()
+	m, err := newMilkDropWindow(800, 600, args)
 	if err != nil {
-		log.Fatal(err)
-	}
-
-	m, err := newMilkDropWindow(800, 600, presets)
-	if err != nil {
-		log.Fatal(err)
+		cobra.CheckErr(err)
 	}
 	defer m.destroy()
 
+	if len(args) > 0 {
 		m.loadPreset(false)
+	}
 
 	running := true
 	for running {
 		running, err = update(m)
 		if err != nil {
-			log.Fatal(err)
+			cobra.CheckErr(err)
 		}
 	}
 }
 
 // rootCmd represents the base command when called without any subcommands
 var rootCmd = &cobra.Command{
-	Use:   "milkbucket",
+	Use:   "milkbucket [presets]",
 	Short: "Audio visualizer",
 	Long: `milkbucket is an audio visualizer.
 
 It uses Milkdrop preset files to generate visualizations from standard input.`,
 	Run:  milkbucket,
+	Args: validatePresets,
 }
 
 // Execute adds all child commands to the root command and sets flags appropriately.
@@ -194,6 +203,4 @@ func init() {
 	// Cobra also supports local flags, which will only run
 	// when this action is called directly.
 	rootCmd.Flags().BoolVarP(&transition, "transition", "t", false, "smoothly transition between presets")
-
-	rootCmd.Flags().StringArrayVarP(&presets, "presets", "p", []string{}, "preset files to use")
 }

cmd/window.go

@@ -67,18 +67,22 @@ func (m *milkDropWindow) setupPresets(presets []string) {
  * preset.
  */
 func (m *milkDropWindow) nextPreset(smooth bool) {
+	if m.preset.Len() > 0 {
 		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) {
+	if m.preset.Len() > 0 {
 		m.preset = m.preset.Prev()
 		m.loadPreset(smooth)
 	}
+}
 
 /*
  * newMilkDropWindow returns a new milkDropWindow with the given width and