feat(examples): add space example to measure fps and performance

This is a simple example that uses Lip Gloss and Bubble Tea to render a
moving color gradient.

examples/space/main.go

@@ -0,0 +1,153 @@
+package main
+
+import (
+	"fmt"
+	"image/color"
+	"math/rand"
+	"os"
+	"time"
+
+	tea "github.com/charmbracelet/bubbletea/v2"
+	"github.com/charmbracelet/lipgloss/v2"
+)
+
+type fps struct {
+	frameCount  int
+	lastInstant time.Time
+	fps         *float64
+}
+
+func (f *fps) tick() {
+	f.frameCount++
+	elapsed := time.Since(f.lastInstant)
+	// Update FPS every second if we have at least 2 frames
+	if elapsed > time.Second && f.frameCount > 2 {
+		fps := float64(f.frameCount) / elapsed.Seconds()
+		f.fps = &fps
+		f.frameCount = 0
+		f.lastInstant = time.Now()
+	}
+}
+
+type model struct {
+	colors     [][]color.Color
+	lastWidth  int
+	lastHeight int
+	fps        fps
+	frameCount int
+	width      int
+	height     int
+}
+
+func initialModel() model {
+	return model{
+		fps: fps{
+			lastInstant: time.Now(),
+		},
+	}
+}
+
+func (m model) Init() (tea.Model, tea.Cmd) {
+	return m, tea.Batch(
+		tea.EnterAltScreen,
+		tickCmd(),
+	)
+}
+
+func tickCmd() tea.Cmd {
+	return tea.Tick(time.Second/60, func(time.Time) tea.Msg {
+		return tickMsg{}
+	})
+}
+
+type tickMsg struct{}
+
+func (m model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
+	switch msg := msg.(type) {
+	case tea.KeyPressMsg:
+		switch msg.String() {
+		case "q", "ctrl+c":
+			return m, tea.Quit
+		}
+
+	case tea.WindowSizeMsg:
+		m.width = msg.Width
+		m.height = msg.Height
+		if m.width != m.lastWidth || m.height != m.lastHeight {
+			m.setupColors()
+			m.lastWidth = m.width
+			m.lastHeight = m.height
+		}
+
+	case tickMsg:
+		m.frameCount++
+		m.fps.tick()
+		return m, tickCmd()
+	}
+
+	return m, nil
+}
+
+func (m *model) setupColors() {
+	height := m.height * 2 // double height for half blocks
+	m.colors = make([][]color.Color, height)
+
+	for y := 0; y < height; y++ {
+		m.colors[y] = make([]color.Color, m.width)
+		randomnessFactor := float64(height-y) / float64(height)
+
+		for x := 0; x < m.width; x++ {
+			baseValue := randomnessFactor * (float64(height-y) / float64(height))
+			randomOffset := (rand.Float64() * 0.2) - 0.1
+			value := clamp(baseValue+randomOffset, 0, 1)
+
+			// Convert value to grayscale color (0-255)
+			gray := uint8(value * 255)
+			m.colors[y][x] = lipgloss.Color(fmt.Sprintf("#%02x%02x%02x", gray, gray, gray))
+		}
+	}
+}
+
+func clamp(value, min, max float64) float64 {
+	if value < min {
+		return min
+	}
+	if value > max {
+		return max
+	}
+	return value
+}
+
+func (m model) View() string {
+	// Title and FPS display
+	title := lipgloss.NewStyle().Bold(true).Render("Space ")
+	fpsText := ""
+	if m.fps.fps != nil {
+		fpsText = fmt.Sprintf("%.1f fps", *m.fps.fps)
+	}
+	header := lipgloss.JoinHorizontal(lipgloss.Center, title, fpsText)
+
+	// Color display
+	var s string
+	for y := 0; y < m.height; y++ {
+		for x := 0; x < m.width; x++ {
+			xi := (x + m.frameCount) % m.width
+			fg := m.colors[y*2][xi]
+			bg := m.colors[y*2+1][xi]
+			s += lipgloss.NewStyle().Foreground(fg).Background(bg).Render("▀")
+		}
+		s += "\n"
+	}
+
+	return lipgloss.JoinVertical(lipgloss.Left, header, s)
+}
+
+func main() {
+	p := tea.NewProgram(initialModel(), tea.WithAltScreen())
+
+	_, err := p.Run()
+	if err != nil {
+		fmt.Printf("Error running program: %v", err)
+		os.Exit(1)
+	}
+}