GrDirectContext::MakeGL functions undefined

[Alex Humphrey]

I'm attempting to compile a project that uses SDL2 & Skia on Ubuntu.

I am able to build Skia through gn with the following:
```
bin/gn gen out/shared --args='is_component_build=true is_debug=false is_official_build=true skia_use_system_expat=false skia_use_system_libjpeg_turbo=false skia_use_system_libpng=false skia_use_system_libwebp=false skia_use_system_zlib=false skia_use_system_icu=false skia_use_system_harfbuzz=false'

```

I have also attempted building skia with the following args added and achieved the same result:

```

--defines=["SK_GL"]

skia_use_gl=true

skia_enable_gpu=true

// I have also added '#define SK_GL' to the top of main.cpp

```

Skia appears to sucessfully build, however when I come to build my own project and link against the libs gn produced, I am told by the linker that the MakeGL functions in GrDirectContext are undefined. I am attempting to build using the following:
```
eval "g++ main.cpp -o out  -I ../skia -I ../skia/include -L ../skia/out/shared -lglut -lGLU -lGL -lSDL2"

```

The linker produces:

```

main.cpp: In function ‘int main(int, char**)’:
main.cpp:79:58: error: ‘MakeGL’ is not a member of ‘GrDirectContext’
                                         sk_sp<GrDirectContext> gr_context = GrDirectContext::MakeGL(interface);

```

The error appears whether I'm building on Ubuntu or through WSL. I am assuming there's an OpenGL flag missing somewhere as the function defs I'm missing are wrapped in an ifdef that looks for 'SK_GL', however even placing '#define SK_GL' at the top of my main.cpp before the includes is doing nothing, so I'm at a bit of a loss.

I'm new to working with UNIX systems so if I'm missing something very obvious I apologise in advance.

Any help greatly appreciated.

[William Candillon]

We've had a similar issue in the past, and I think we were missing the SK_GANESH flag (https://groups.google.com/g/skia-discuss/c/2hA_8Fcfih4/m/crPPJfiQAQAJ).

These are our preprocessor options for OpenGL.

-DSK_GL -DSK_GANESH

Kind regards,

William

[Alex Humphrey]

Could you specify exactly how you are passing these to gn? I tried adding them as defines and as c flags however neither changes anything, but I've likely got the syntax slightly wrong. Running gn args out/shared --list also shows that skia_enable_ganesh, skia_enable_gpu & skia_use_gl are all set to true.

[William Candillon]

This is after the gn step. When you include the Skia header files in
your code, you need the right preprocessor directives.

Kind regards,

William

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[Alex Humphrey]

This was indeed the issue. Thanks William, your help is greatly appreciated!