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Subject: Re: Cygwin fails to utilize Unicode replacement character
To: cygwin AT cygwin DOT com
References: <7942b18e-96bf-a824-4dac-82715d87af55 AT towo DOT net> <5b8bdcc4 DOT 1c69fb81 DOT 84d1a DOT e6b9 AT mx DOT google DOT com> <20180903124616 DOT GT6350 AT calimero DOT vinschen DOT de> <20180903145919 DOT GU6350 AT calimero DOT vinschen DOT de> <126ebbde-2432-f19b-6c5c-fe61f31e4647 AT towo DOT net> <20180903171659 DOT GY6350 AT calimero DOT vinschen DOT de>
From: Thomas Wolff <towo AT towo DOT net>
Message-ID: <e3207913-84d8-901a-b5ff-020dd86eed61@towo.net>
Date: Mon, 3 Sep 2018 19:56:33 +0200
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Am 03.09.2018 um 19:16 schrieb Corinna Vinschen:
> On Sep  3 18:34, Thomas Wolff wrote:
>> Am 03.09.2018 um 16:59 schrieb Corinna Vinschen:
>>> On Sep  3 14:46, Corinna Vinschen wrote:
>>>> On Sep  2 05:51, Steven Penny wrote:
>>>>> On Sun, 2 Sep 2018 10:07:10, Thomas Wolff wrote:
>>>>>> Actually, the width problem I suggested in my other response (and even
>>>>>> referring to the wrong character) does not apply as mintty enforces
>>>>>> proper width in that case.
>>>>>> Also, even with fonts that do not provide the glyph, you will usually
>>>>>> still see it by the Windows font fallback mechanism.
>>>>>> Shall I make it configurable?
>>>>> your call - here are the possible resolutions - in order of my preference:
>>>>>
>>>>> 1. Change the default to U+FFFD with no option
>>>>> 2. Change the default to U+FFFD with option to change
>>>>> 3. Leave default as is with option to change
>>>> Ideally we could check if the current font supports a visual
>>>> representation of 0xfffd and if not, fall back to 0x2592.
>>>>
>>>> Not sure how feasible that is, but it doesn't seem to be overly
>>>> complicated.  I'm just looking into a solution for the Cygwin
>>>> console.
>>> Only, I can't get this working.  In theory the GDI function
>>> GetGlyphIndicesW is supposed to allow checking if a certain character
>>> exists.  But I'm getting a weird result.  This code:
>>>
>>>     static const wchar_t replacement_char[2] =
>>>       {
>>>         0xfffd, /* REPLACEMENT CHARACTER */
>>>         0x2592  /* MEDIUM SHADE */
>>>       };
>>>     HWND cwnd = GetConsoleWindow ();
>>>     HDC cdc = GetDC (cwnd);
>>>     int rp_idx = 0;
>>>     WORD gi = 0;
>>>     DWORD ret = GetGlyphIndicesW (cdc, replacement_char, 1, &gi,
>>>                                   GGI_MARK_NONEXISTING_GLYPHS);
>>>     if (ret != GDI_ERROR && gi == 0xffff)
>>>       rp_idx = 1;
>>>
>>> always sets rp_idx to 1 when called from inside the Cygwin DLL,
>>> independently of the actual console font.  And, here's the really weird
>>> thing, it always sets rp_idx to 0 when called directly from an
>>> application, likewise independently of the actual console font.
>>>
>>> Does anybody have an idea what I'm doing wrong?
>> This works in mintty, just uploaded a patch. Maybe somehow the GetConsole
>> "dc" does not support this usage?
> ¯\_(ツ)_/¯
Dito; hold on, sorry, your code does *not* work inside mintty.
Mine looks a bit different and I thought to have manually verified it's 
functionally equivalent, but indeed there must be something fishy...

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