SetVsyncEnabled(false) + SetScreenClearedEveryFrame(false) consumes more CPU than expected on desktops

[hajimehoshi]

Ebitengine Version

v2.6.4 and main (006f14a)

Operating System

• Windows
• macOS
• Linux
• FreeBSD
• OpenBSD
• Android
• iOS
• Nintendo Switch
• PlayStation 5
• Xbox
• Web Browsers

Go Version (go version)

go version go1.21.6 windows/arm64

What steps will reproduce the problem?

Run this program and see the CPU usage on the task manager:

package main

import (
	"sync"

	"github.com/hajimehoshi/ebiten/v2"
)

type Game struct {
	once sync.Once
}

func (g *Game) Update() error {
	return nil
}

func (g *Game) Draw(screen *ebiten.Image) {
}

func (g *Game) Layout(width, height int) (int, int) {
	return width, height
}

func main() {
	ebiten.SetScreenClearedEveryFrame(false)
	ebiten.SetVsyncEnabled(false)
	if err := ebiten.RunGame(&Game{}); err != nil {
		panic(err)
	}
}

What is the expected result?

The CPU usage should be low (less than 5% or so)

What happens instead?

The CPU usage was about 50%

Anything else you feel useful to add?

This was found at #2889 (CC @erexo)

Let's check Linux too.

[hajimehoshi]

Even on macOS, this optimization doesn't work with OpenGL.

[erexo]

thanks ❤