libwebp in VB 6.0 programs.

[Александр Рощупкин]

Hello!
I want to use part of the libwebp library to view images in a program written in VB 6.0 on 32-bit systems (Windows XP x86).
I've declared declarations for two library functions:
Public Declare Function WebPGetDecoderVersion Lib "libwebp.dll" () As Long
Public Declare Function WebPGetInfo Lib "libwebp.dll" (ByRef Arr As Any, _
ByVal data_size As Long, ByRef Wwidth As Long, _
ByRef Wheight As Long) As Long
The first function works fine when called:
Label4.Caption = WebPGetDecoderVersion
The second function, when called:
Addr = WebPGetInfo(bRead(0), FSize - 1, ImgW, ImgH)
raises an error: "Bad DLL calling convention".
I tried compiling the parts I needed from the libwebp library. The decode.h file contains prototypes of the functions I need, but I couldn't find the functions themselves.
What should I do to find them?

[James Zern]

Hi,

On Wed, Oct 22, 2025 at 1:49 AM Александр Рощупкин <arosch...@gmail.com> wrote:

Hello!
I want to use part of the libwebp library to view images in a program written in VB 6.0 on 32-bit systems (Windows XP x86).
I've declared declarations for two library functions:
Public Declare Function WebPGetDecoderVersion Lib "libwebp.dll" () As Long
Public Declare Function WebPGetInfo Lib "libwebp.dll" (ByRef Arr As Any, _
ByVal data_size As Long, ByRef Wwidth As Long, _
ByRef Wheight As Long) As Long 

The first function works fine when called:
Label4.Caption = WebPGetDecoderVersion
The second function, when called:
Addr = WebPGetInfo(bRead(0), FSize - 1, ImgW, ImgH)
raises an error: "Bad DLL calling convention".

https://learn.microsoft.com/en-us/dotnet/visual-basic/language-reference/error-messages/bad-dll-calling-convention has some guidance around this error. I'm not sure if the types are aligned correctly, but haven't tried this myself.

 

I tried compiling the parts I needed from the libwebp library. The decode.h file contains prototypes of the functions I need, but I couldn't find the functions themselves.
What should I do to find them?

If you're working from a git repository, you can use `git grep WebPGetInfo`. Otherwise something like `grep -R WebPGetInfo` can work. This function is defined in src/dec/webp_dec.c:

https://chromium.googlesource.com/webm/libwebp/+/refs/tags/v1.6.0/src/dec/webp_dec.c#718

 

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