Empty but visible images consume high CPU on 2.4.x

[dweymouth]

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

A canvas.Image that is empty (no image.Image, fyne.Resource or file set) but not hidden will cause high CPU use as it causes constant texture cache misses and a new GL texture to be created for the "image" on every redraw. This is a regression from 2.3.x.

How to reproduce

Run the example app

Screenshots

Example code

package main

import (
	"fyne.io/fyne/v2"
	"fyne.io/fyne/v2/app"
	"fyne.io/fyne/v2/canvas"
)

func main() {

	myApp := app.New()
	myWindow := myApp.NewWindow("Empty image perf regression")

	myWindow.SetContent(canvas.NewImageFromImage(nil))
	myWindow.Resize(fyne.NewSize(400, 400))
	myWindow.ShowAndRun()
}

Fyne version

2.4.1

Go compiler version

go1.21.1

Operating system and version

macOS Ventura M2

Additional Information

No response

[dweymouth]

OK I've managed to work out that it's texture cache misses. newGlImageTexture which is in the pprof trace is only referenced here in drawImage, and print statements in getTexture (which is called by drawTextureWithDetails) reveal that on 2.3.x there are a handful of cache misses on startup (as expected), but then none until mousing over an image. On 2.4.x however it continues to have dozens of cache misses a second even when not interacting with the app

[andydotxyz]

Should we mark this as blocker for v2.4.3 (i.e. the point release after current work)?

[dweymouth]

Should we mark this as blocker for v2.4.3 (i.e. the point release after current work)?

I imagine this should be a quick fix to someone familiar with the image painter but I don't know what the fix is. On the other hand it has a very easy workaround (hide empty images) so personally I don't feel it needs to be high priority, unless others complain about it.

[andydotxyz]

I'm inclined to agree - unless there is a common case when images may be empty and developers won't know, or be able to tell?

[andydotxyz]

I wonder if the following is a good solution? It doesn't seem to take the CPU usage to 0 though...

--- a/internal/painter/gl/draw.go
+++ b/internal/painter/gl/draw.go
@@ -36,6 +36,9 @@ func (p *painter) drawGradient(o fyne.CanvasObject, texCreator func(fyne.CanvasO
 }
 
 func (p *painter) drawImage(img *canvas.Image, pos fyne.Position, frame fyne.Size) {
+       if img.Image == nil && img.File == "" && img.Resource == nil || img.Translucency == 1.0 {
+               return
+       }
        p.drawTextureWithDetails(img, p.newGlImageTexture, pos, img.Size(), frame, img.FillMode, float32(img.Alpha()), 0)
 }

[andydotxyz]

Resolved by #5290, I'm glad to have found a better solution than I proposed before - it helps when you identify the root cause ;)