First run at basic structure

internal/hero/hero.go

@@ -0,0 +1,117 @@
+package hero
+
+import (
+	"image/color"
+	"math"
+
+	"github.com/hajimehoshi/ebiten/v2"
+	"github.com/hajimehoshi/ebiten/v2/vector"
+)
+
+// Direction flags from the controls.
+type Input struct {
+	Left  bool
+	Right bool
+	Up    bool
+	Down  bool
+}
+
+// Playfield limits for movement.
+type Bounds struct {
+	Width  float64
+	Height float64
+}
+
+// Player avatar data.
+type Hero struct {
+	X      float64
+	Y      float64
+	Radius float64
+	Speed  float64
+	Color  color.NRGBA
+}
+
+// Spawn settings for the avatar.
+type Config struct {
+	StartX float64
+	StartY float64
+	Radius float64
+	Speed  float64
+	Color  color.NRGBA
+}
+
+// Builds an avatar from the config with fallbacks.
+func New(cfg Config) *Hero {
+	if cfg.Radius <= 0 {
+		cfg.Radius = 24
+	}
+	if cfg.Speed <= 0 {
+		cfg.Speed = 180
+	}
+	if cfg.Color.A == 0 {
+		cfg.Color = color.NRGBA{R: 210, G: 220, B: 255, A: 255}
+	}
+
+	return &Hero{
+		X:      cfg.StartX,
+		Y:      cfg.StartY,
+		Radius: cfg.Radius,
+		Speed:  cfg.Speed,
+		Color:  cfg.Color,
+	}
+}
+
+// Applies movement input and clamps to the playfield.
+func (h *Hero) Update(input Input, dt float64, bounds Bounds) {
+	dx, dy := 0.0, 0.0
+
+	if input.Left {
+		dx -= 1
+	}
+	if input.Right {
+		dx += 1
+	}
+	if input.Up {
+		dy -= 1
+	}
+	if input.Down {
+		dy += 1
+	}
+
+	if dx != 0 || dy != 0 {
+		length := math.Hypot(dx, dy)
+		dx /= length
+		dy /= length
+	}
+
+	h.X += dx * h.Speed * dt
+	h.Y += dy * h.Speed * dt
+
+	maxX := math.Max(h.Radius, bounds.Width-h.Radius)
+	maxY := math.Max(h.Radius, bounds.Height-h.Radius)
+
+	h.X = clamp(h.X, h.Radius, maxX)
+	h.Y = clamp(h.Y, h.Radius, maxY)
+}
+
+// Renders the avatar as a filled circle.
+func (h *Hero) Draw(screen *ebiten.Image) {
+	vector.FillCircle(
+		screen,
+		float32(h.X),
+		float32(h.Y),
+		float32(h.Radius),
+		h.Color,
+		false,
+	)
+}
+
+func clamp(value, min, max float64) float64 {
+	if value < min {
+		return min
+	}
+	if value > max {
+		return max
+	}
+	return value
+}