High CPU and sluggishness running a simple wasm app

[bogen85]

Checklist

• I have searched the issue tracker for open issues that relate to the same problem, before opening a new one.
• This issue only relates to a single bug. I will open new issues for any other problems.

Describe the bug

Example app when idling uses a lot of CPU.
When entering in text it feels sluggish.

With chromium running nothing, it is at very low CPU usage. See screenshots.
Just running https://get.webgl.org/?ref=colonist-blog around 14% and 8% (2 cores)
Just running the provided example code fyne serve --sourceDir client around 16 and 18% (2 cores)

Firefox shows similar results.
GPU acceleration is being used. See screenshots.

How to reproduce

fyne serve --sourceDir client with the provided example code in the directory client

Wait for app to load then look at CPU usage.

Type in text into the entry box and press enter (or press the button).

Screenshots

chromium idle

chromium just running https://get.webgl.org/?ref=colonist-blog

chromium just running the provided example fyne wasm app

GPU is being used

Chromium version 127

Example code

// client/main.go
package main

import (
        "fmt"
        "fyne.io/fyne/v2/app"
        "fyne.io/fyne/v2/container"
        "fyne.io/fyne/v2/widget"
)

func main() {
        a := app.NewWithID("go-fyne-wasm-app")
        w := a.NewWindow("Sample app")

        entry := widget.NewEntry()
        addButton := widget.NewButton("Add", func() {
                text := entry.Text
                if text != "" {
                        entry.SetText("")
                        fmt.Printf("Text: %s\n", text)
                }
        })

        entry.OnSubmitted = func(s string) {
                addButton.OnTapped()
        }

        w.SetContent(container.NewVBox(
                entry,
                addButton,
        ))

        w.ShowAndRun()
}

Fyne version

fyne version v2.5.0

Go compiler version

go version go1.23.0 linux/amd64

Operating system and version

AlmaLinux 9.4 x86_64

Additional Information

This might be related to #2803 but this is with an idling app.

chrome:://gpu shows:

*   WebGL: Hardware accelerated
*   WebGL2: Hardware accelerated

[bogen85]

I'm aware of #4641 as well, but as I said already, this issue is with an idling app.

[bogen85]

This uses very little CPU, when run as a wasm app, but it has no text input:

package main

import (
        "fmt"

        "fyne.io/fyne/v2"
        "fyne.io/fyne/v2/app"
        "fyne.io/fyne/v2/container"
        "fyne.io/fyne/v2/widget"
)

type customLayout struct {
        split *container.Split
}

func (c *customLayout) Layout(objects []fyne.CanvasObject, size fyne.Size) {
        c.split.Resize(size)
}

func (c *customLayout) MinSize(objects []fyne.CanvasObject) fyne.Size {
        return c.split.MinSize()
}

func main() {
        myApp := app.New()
        myWindow := myApp.NewWindow("Four Regions App")

        // Top region
        topRegion := widget.NewLabel("Top Region")
        topRegion.Alignment = fyne.TextAlignCenter

        // Middle resizable regions
        middleRegion1 := widget.NewLabel("Middle Region 1 (Resizable)")
        middleRegion1.Alignment = fyne.TextAlignCenter

        middleRegion2 := widget.NewLabel("Middle Region 2 (Resizable)")
        middleRegion2.Alignment = fyne.TextAlignCenter

        // Bottom region
        bottomRegion := widget.NewLabel("Bottom Region")
        bottomRegion.Alignment = fyne.TextAlignCenter

        // Create a split container for the middle resizable regions
        split := container.NewVSplit(
                container.NewVBox(middleRegion1),
                container.NewVBox(middleRegion2),
        )

        // Create a custom layout to wrap the split container
        customSplit := container.New(&customLayout{split: split}, split)

        // Set up the main container with all regions
        content := container.NewBorder(
                container.NewVBox(topRegion),
                container.NewVBox(bottomRegion),
                nil,
                nil,
                customSplit,
        )

        // Set minimum window size
        myWindow.Resize(fyne.NewSize(400, 300))

        myWindow.SetContent(content)

        // Common callback function to print dimensions
        printDimensions := func() {
                fmt.Printf("Window size: %v\n", myWindow.Canvas().Size())
                fmt.Printf("Top region size: %v\n", topRegion.Size())
                fmt.Printf("Middle region 1 size: %v\n", middleRegion1.Size())
                fmt.Printf("Middle region 2 size: %v\n", middleRegion2.Size())
                fmt.Printf("Bottom region size: %v\n", bottomRegion.Size())
                fmt.Println("------------------------")
        }

        // Callback for window resize
        myWindow.Canvas().SetOnTypedKey(func(ke *fyne.KeyEvent) {
                if ke.Name == fyne.KeyF11 {
                        fmt.Println("Window resized")
                        printDimensions()
                }
        })

        myWindow.ShowAndRun()
}

[bogen85]

Alright, this might be related to #4641 and therefore possibly a duplicate.
The text inputs on that demo feel like they may be sluggish as well.

[andydotxyz]

I'm guessing this is with the entry focused? There is a cursor animation that you could turn off to see if it's related (by disabling animations in the build).

[bogen85]

Yeah, that makes sense. Yes, that is with the entry focused. That explains why the app with no blinking cursor does not have the CPU usage at idle. I'll try disabling the cursor animation.

[bogen85]

Disabling the animations also made the cursor invisible for me (local x11, not in the browser). Offhand I don't see a way in fyne serve to apply the no_animations tag.

Removed the wasm directory, rebuilt it with fyne package --target web --tags no_animations --src client/.

Served it with

package main

import (
        "fmt"
        "net/http"
)

func main() {
        fs := http.FileServer(http.Dir("./wasm")) // Serve from the 'web' directory
        http.Handle("/", fs)

        fmt.Println("Server started at http://localhost:8080")
        http.ListenAndServe(":8080", nil)
}

The cursor in the web page is now no longer animated, but it is now not visible as well. Also, the cpu usage is very low, so it is the blinking cursor that was consuming the CPU.

[andydotxyz]

Offhand I don't see a way in fyne serve to apply the no_animations tag.

There is a PR open to fix this already :).

The cursor in the web page is now no longer animated, but it is now not visible as well.

That is fixed on the release branch in preparation for v2.5.1 coming soon.

[bogen85]

Alight, since I know what is going on, I'll close this. Especially with the mitigations you mentioned.