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wxWidgets: Fixed the types of pixel values. #10303

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wxWidgets: Fixed the types of pixel values. #10303

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@wallacegibbon wallacegibbon commented Oct 20, 2025 •
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The GetRed, GetBlue, GetGreen in wxWidgets return unsigned char, But the code in wxe_wrapper_4 is using char to receive the result and sign extending it into a int.

As a result, a pixel whose red is 250(16#FA) will be returned as 4294967290(16#FFFFFFFA) by wxImage:getRed/3.

This commit fixed this problem.

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// Erlang/OTP Github Action Bot

@wallacegibbon
wx: Fixed the types of pixel values.
49e92ca 
The GetRed, GetBlue, GetGreen in wxWidgets return `unsigned char`,
But the code in wxe_wrapper_4.cpp is using `char` to receive the result
and sign extending it into a int.

As a result, a pixel whose red is `250`(`16#FA`) will be returned as
`4294967290`(`16#FFFFFFFA`) by `wxImage:getRed/3`.

This commit fixed this problem.
@rickard-green rickard-green added the team:PS Assigned to OTP team PS label Oct 20, 2025
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wallacegibbon commented Oct 21, 2025 •
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Notes to test this feature.

We can use convert (or magick for newer version of imagemagick) to create a grey picture:

convert -size 128x128 xc:"rgb(250, 250, 250)" lightgrey.png

Then reading the red value of any pixel from this image should return 250 (0xFA)

I = wxImage:new("./lightgrey.png"),
P = wxImage:getRed(I, 0, 0),
io:format("first pixel: ~p (~.16B) ~n", [P, P]),

Before this commit:

first pixel: 4294967290 (FFFFFFFA)

After this commit:

first pixel: 250 (FA)

@dgud dgud mentioned this pull request Oct 21, 2025
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dgud commented Oct 21, 2025

Thanks for the great PR, only a testcase missing :-)
Since the wx code is generated, I have updated the code generator to fix this (and some stuff that was lagging behind).
I also added a variant of the testcase you provided, thanks.

Replaced by #10314

@dgud dgud closed this Oct 21, 2025
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