feat(ui): implement new ui system

game/ui/widgets/button.go

@@ -0,0 +1,48 @@
+package widgets
+
+import (
+	"tetris/engine/core"
+	"tetris/engine/render"
+	"tetris/game/ui/base"
+
+	rl "github.com/gen2brain/raylib-go/raylib"
+)
+
+type Button struct {
+	*base.WithFocus
+	Text     string
+	TextSize int32
+	Action   func()
+}
+
+func NewButton(text string, size int32, action func()) Button {
+	return Button{
+		WithFocus: &base.WithFocus{},
+		Text:      text,
+		TextSize:  size,
+		Action:    action,
+	}
+}
+
+func (b Button) Size() core.Vec2i {
+	s := int(b.TextSize)
+	return core.Vec2i{
+		X: len(b.Text) * s,
+		Y: s,
+	}
+}
+
+func (b Button) HandleInput() {
+	if rl.IsKeyPressed(rl.KeyEnter) {
+		b.Action()
+	}
+}
+
+func (b Button) Draw(x, y int32) {
+	// TODO: use a theme system here so colors are not hardcoded.
+	col := rl.White
+	if b.HasFocus() {
+		col = rl.Red
+	}
+	render.DrawTextCenter(x, y, b.TextSize, b.Text, col)
+}