Fade disabled button icon when resource is a bitmap (#6217) by mohsenm4 · Pull Request #6381 · fyne-io/fyne

mohsenm4 · 2026-06-28T07:28:45Z

Summary

Buttons with bitmap (PNG/JPEG) icons stayed at full opacity when Disable()d, even though SVG-icon buttons were correctly grayed out via NewDisabledResource. There was no visual cue that the button was disabled.
Bitmap resources cannot be recolored the way themed SVGs can. When the button is disabled and the icon resource is not an SVG, we now apply a Translucency fade to the canvas.Image to give a visual disabled cue. SVG behaviour is unchanged.
Resolves the existing // TODO support disabling bitmap resource not just SVG in widget/button.go.

Scope / not closing #6217

The original report (#6217) mixes two related problems:

Bitmap icon resource (Button.Icon) not faded on Disable() — fixed here.
Bitmap-emoji text content (e.g. 🔝) not faded on Disable() — not addressed here, the fix would live in the text/painter pipeline rather than the button renderer. Tracked as #6383.

So this PR intentionally uses Refs #6217 rather than Fixes #6217, to avoid auto-closing the original report before the emoji part is solved.

Note on the translucency constant

disabledIconTranslucency = 0.5 is a fixed value because we can't recolor a raster image with theme.ColorNameDisabled the way SVGs are recolored. The choice is documented inline — happy to switch to a theme-derived value (e.g. derived from the alpha ratio between ColorNameDisabled and ColorNameForeground) if you prefer.

Test plan

go build ./...
go test ./widget/ -run TestButton -count=1 — all existing button tests pass plus the new TestButton_DisabledBitmapIcon (covers enable → disable → re-enable for a PNG resource).
Reviewer: visually confirm with a button that has a PNG Icon set that the icon now fades on Disable() and restores on Enable().

Refs #6217
Refs #6383

coveralls · 2026-06-28T07:36:13Z

coverage: 59.835% (-0.06%) from 59.89% — mohsenm4:fix/6217-disabled-bitmap-icon into fyne-io:develop

Buttons with SVG icons were already grayed out on Disable() via NewDisabledResource, but bitmap resources (PNG, JPEG, ...) cannot be recolored that way and stayed at full opacity, leaving no visual cue that the button is disabled. Apply a translucency to the icon image when the button is disabled and the resource is not an SVG; reset it when the button is enabled again. The chosen translucency is a fixed value and documented inline — the emoji-text rendering aspect from the original report is tracked separately and is not addressed here. Refs fyne-io#6217 (partial — Button.Icon only) Refs fyne-io#6383 (follow-up for emoji text)

andydotxyz

Thanks for looking at this. However translucency feels like a workaround. bitmap images absolutely can be recoloured. In this case it should be sufficient to reduce saturation to make it appear greyscale.

andydotxyz · 2026-06-28T12:36:11Z

 	ButtonIconTrailingText
 )

+// disabledIconTranslucency is the alpha-fade applied to bitmap icons (PNG, JPEG, ...)


Please don't commit walls of comment. A comment should be added when its public API or where the code is not clear without it.

andydotxyz · 2026-06-28T12:36:56Z

+			if svg.IsResourceSVG(icon) {
+				icon = theme.NewDisabledResource(icon)
+			} else {
+				// Bitmap resources cannot be recolored, so fade them instead


Yes, bitmaps can be recoloured. Not in the same way but it is not impossible.
Remove the colour saturation to be greyscale and then apply colour (if the desired outcome is not grey)

Per review feedback on fyne-io#6381: translucency was a workaround. Bitmap resources can be recoloured by reducing saturation so the icon appears greyscale, matching how SVGs are recoloured to ColorNameDisabled. Extend theme.DisabledResource.Content() to decode non-SVG resources, convert each pixel to its ITU-R BT.601 luminance (alpha preserved), and return the result as PNG. SVG content keeps its existing colorize path. Drop the IsResourceSVG branching in widget/button.go — NewDisabledResource now handles both kinds. Removes the disabledIconTranslucency constant and the Translucency field manipulation introduced earlier on this branch.

mohsenm4 · 2026-06-28T13:06:04Z

Thanks for the feedback — you're right, translucency was hiding the real fix.

In cf066e59b I moved the work into theme.DisabledResource.Content(): when the wrapped resource is a bitmap, it now decodes the image, converts each pixel to its ITU-R BT.601 luminance (alpha preserved), and returns the result as PNG. SVG content keeps its existing colorize path. The button renderer no longer needs the IsResourceSVG branch or the Translucency workaround — it just calls NewDisabledResource for all icons.

Side effect: every other call site of NewDisabledResource (entry_password.go, select.go, menu_item.go if its own SVG guard is later dropped) gets the bitmap support for free.

Pushed as a follow-up commit, no force-push, so the diff against your previous review should be just cf066e59b.

andydotxyz

A couple of notes inline. Plus the static check errors would need to be addressed

andydotxyz · 2026-06-28T19:35:30Z

-// Content returns the disabled style content of the correct resource for the current theme
+// Content returns the disabled style content of the correct resource for the current theme.
+// SVG resources are recolored with the theme's disabled color; bitmap resources (PNG, JPEG, ...)
+// are desaturated to greyscale since they cannot be recolored.


I don't think that "since they cannot be recolored" in the docs is required - focus on behaviour in public docs.

Fixed in e558fb3 — dropped the implementation reason, kept only the behaviour.

andydotxyz · 2026-06-28T19:36:19Z

+// desaturateLogError returns a PNG-encoded greyscale copy of the given image bytes,
+// preserving the alpha channel. If decoding or encoding fails, the original bytes are
+// returned so the caller can still render something.
+func desaturateLogError(src []byte) []byte {


As an internal API I would think that returning the error instead of logging it makes more sense.

Done in e558fb3 — desaturate now returns ([]byte, error); Content() logs and falls back to the original bytes.

andydotxyz · 2026-06-28T19:38:14Z

+			// Convert via NRGBA so the luminance is computed on unpremultiplied
+			// channels — otherwise partially-transparent pixels go too dark.
+			n := color.NRGBAModel.Convert(img.At(x, y)).(color.NRGBA)
+			lum := uint8((299*uint32(n.R) + 587*uint32(n.G) + 114*uint32(n.B)) / 1000)


What are these magic numbers?

ITU-R BT.601 luma coefficients. Replaced with named constants (lumaWeightR/G/B, lumaScale) in e558fb3. Same commit also resolves the gosec G115 lint by clamping before the uint8 cast.

…ec G115

mohsenm4 force-pushed the fix/6217-disabled-bitmap-icon branch from f4c155b to 92ef4b5 Compare June 28, 2026 07:32

mohsenm4 mentioned this pull request Jun 28, 2026

Disabled button does not fade emoji (bitmap glyph) text content #6383

Open

mohsenm4 force-pushed the fix/6217-disabled-bitmap-icon branch from 92ef4b5 to 008f894 Compare June 28, 2026 08:02

andydotxyz requested changes Jun 28, 2026

View reviewed changes

Address review: name luma constants, return desaturate error, fix gos…

e558fb3

…ec G115

andydotxyz added the after-release For when an ongoing release is finished. label Jun 30, 2026

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Summary

Scope / not closing #6217

Note on the translucency constant

Test plan

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mohsenm4 commented Jun 28, 2026

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mohsenm4 commented Jun 28, 2026 •

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coveralls commented Jun 28, 2026 •

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