feat(examples): add splash example

This is ported from Textualize splash.py example.

examples/splash/main.go

@@ -0,0 +1,177 @@
+package main
+
+import (
+	"fmt"
+	"image/color"
+	"math"
+	"strings"
+	"time"
+
+	tea "github.com/charmbracelet/bubbletea/v2"
+	"github.com/charmbracelet/lipgloss/v2"
+)
+
+// Colors matching the Python version
+var colors = []color.Color{
+	lipgloss.Color("#881177"),
+	lipgloss.Color("#aa3355"),
+	lipgloss.Color("#cc6666"),
+	lipgloss.Color("#ee9944"),
+	lipgloss.Color("#eedd00"),
+	lipgloss.Color("#99dd55"),
+	lipgloss.Color("#44dd88"),
+	lipgloss.Color("#22ccbb"),
+	lipgloss.Color("#00bbcc"),
+	lipgloss.Color("#0099cc"),
+	lipgloss.Color("#3366bb"),
+	lipgloss.Color("#663399"),
+}
+
+type model struct {
+	width  int
+	height int
+	rate   int64
+}
+
+func (m model) Init() (tea.Model, tea.Cmd) {
+	m.rate = 90
+	return m, tick
+}
+
+func (m model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
+	switch msg := msg.(type) {
+	case tea.KeyPressMsg:
+		return m, tea.Quit
+	case tea.WindowSizeMsg:
+		m.width = msg.Width
+		m.height = msg.Height
+	case tickMsg:
+		return m, tick
+	}
+	return m, nil
+}
+
+func (m model) View() string {
+	if m.width == 0 {
+		return "Initializing..."
+	}
+
+	return m.gradient()
+}
+
+func (m model) gradient() string {
+	// Time-based angle for animation
+	t := float64(time.Now().UnixNano()*m.rate) / float64(time.Second)
+	angleRadians := -t * math.Pi / 180.0
+	sinAngle := math.Sin(angleRadians)
+	cosAngle := math.Cos(angleRadians)
+
+	centerX := float64(m.width) / 2
+	centerY := float64(m.height)
+
+	var output strings.Builder
+
+	for lineY := 0; lineY < m.height; lineY++ {
+		pointY := float64(lineY)*2 - centerY
+		pointX := 0.0 - centerX
+
+		x1 := (centerX + (pointX*cosAngle - pointY*sinAngle)) / float64(m.width)
+		x2 := (centerX + (pointX*cosAngle - (pointY+1.0)*sinAngle)) / float64(m.width)
+		pointX = float64(m.width) - centerX
+		endX1 := (centerX + (pointX*cosAngle - pointY*sinAngle)) / float64(m.width)
+		deltaX := (endX1 - x1) / float64(m.width)
+
+		if math.Abs(deltaX) < 0.0001 {
+			// Special case for verticals
+			color1 := getGradientColor(x1)
+			color2 := getGradientColor(x2)
+			style := lipgloss.NewStyle().
+				Foreground(color1).
+				Background(color2)
+			output.WriteString(style.Render(strings.Repeat("▀", m.width)))
+		} else {
+			// Render each column in the row
+			for x := 0; x < m.width; x++ {
+				pos1 := x1 + float64(x)*deltaX
+				pos2 := x2 + float64(x)*deltaX
+				color1 := getGradientColor(pos1)
+				color2 := getGradientColor(pos2)
+				style := lipgloss.NewStyle().
+					Foreground(color1).
+					Background(color2)
+				output.WriteString(style.Render("▀"))
+			}
+		}
+		output.WriteString("\n")
+	}
+
+	return output.String()
+}
+
+func getGradientColor(position float64) color.Color {
+	// Normalize position to [0,1]
+	if position <= 0 {
+		position = 0
+	}
+	if position >= 1 {
+		position = 1
+	}
+
+	// Calculate the color index
+	idx := position * float64(len(colors)-1)
+	i1 := int(math.Floor(idx))
+	i2 := int(math.Ceil(idx))
+
+	// Ensure indices are within bounds
+	i1 = i1 % len(colors)
+	i2 = i2 % len(colors)
+	if i1 < 0 {
+		i1 += len(colors)
+	}
+	if i2 < 0 {
+		i2 += len(colors)
+	}
+
+	// Interpolate between colors
+	t := idx - float64(i1)
+	return interpolateColors(colors[i1], colors[i2], t)
+}
+
+func interpolateColors(color1, color2 color.Color, t float64) color.Color {
+	// Parse hex colors
+	r1, g1, b1, _ := color1.RGBA()
+	r1, g1, b1 = r1>>8, g1>>8, b1>>8
+	r2, g2, b2, _ := color2.RGBA()
+	r2, g2, b2 = r2>>8, g2>>8, b2>>8
+
+	// Interpolate
+	r := int(float64(r1)*(1-t) + float64(r2)*t)
+	g := int(float64(g1)*(1-t) + float64(g2)*t)
+	b := int(float64(b1)*(1-t) + float64(b2)*t)
+
+	return color.RGBA{uint8(r), uint8(g), uint8(b), 255}
+}
+
+type tickMsg time.Time
+
+func tick() tea.Msg {
+	return tickMsg(time.Now())
+}
+
+func abs(i int) int {
+	if i < 0 {
+		return -i
+	}
+	return i
+}
+
+func main() {
+	p := tea.NewProgram(
+		model{},
+		tea.WithAltScreen(),
+	)
+
+	if _, err := p.Run(); err != nil {
+		fmt.Printf("Error running program: %v", err)
+	}
+}