ebiten/example/blocks/scenemanager.go

package blocks

import (
	"github.com/hajimehoshi/ebiten/graphics"
	"github.com/hajimehoshi/ebiten/graphics/matrix"
)

func init() {
	renderTargetSizes["scene_manager_transition_from"] =
		Size{ScreenWidth, ScreenHeight}
	renderTargetSizes["scene_manager_transition_to"] =
		Size{ScreenWidth, ScreenHeight}
}

type Scene interface {
	Update(state *GameState)
	Draw(context graphics.Context, textures *Textures)
}

const transitionMaxCount = 20

type SceneManager struct {
	current         Scene
	next            Scene
	transitionCount int
}

func NewSceneManager(initScene Scene) *SceneManager {
	return &SceneManager{
		current:         initScene,
		transitionCount: -1,
	}
}

func (s *SceneManager) Update(state *GameState) {
	if s.transitionCount == -1 {
		s.current.Update(state)
		return
	}
	s.transitionCount++
	if transitionMaxCount <= s.transitionCount {
		s.current = s.next
		s.next = nil
		s.transitionCount = -1
	}
}

func (s *SceneManager) Draw(context graphics.Context, textures *Textures) {
	if s.transitionCount == -1 {
		s.current.Draw(context, textures)
		return
	}
	from := textures.GetRenderTarget("scene_manager_transition_from")
	context.SetOffscreen(from)
	context.Clear()
	s.current.Draw(context, textures)

	to := textures.GetRenderTarget("scene_manager_transition_to")
	context.SetOffscreen(to)
	context.Clear()
	s.next.Draw(context, textures)

	context.ResetOffscreen()
	color := matrix.ColorI()
	graphics.DrawWhole(
		context.RenderTarget(from),
		ScreenWidth,
		ScreenHeight,
		matrix.GeometryI(),
		color)

	alpha := float64(s.transitionCount) / float64(transitionMaxCount)
	color.Elements[3][3] = alpha
	graphics.DrawWhole(
		context.RenderTarget(to),
		ScreenWidth,
		ScreenHeight,
		matrix.GeometryI(),
		color)
}

func (s *SceneManager) GoTo(scene Scene) {
	s.next = scene
	s.transitionCount = 0
}