downgrade OpenGL from 4.1 to 3.3

[pchampio]

fixes #248
downgrading from 4.x to 3.3 enable us target more devices without any cost.

[pchampio]

@nzlov has reported that the OpenGL 3.3 was working and OpenGL 4.1 not

[nzlov]

I'm not sure if downgrading is necessary because I'm running win10 on a virtual machine and can't update the OpenGL driver.

[pchampio]

I don't want to maintain the 'gl-3.3' branch forever.
Either we merge it or drop it.
If we drop p it, you wouldn't ne able to run on windows 10? Am I understanding correctly?

[nzlov]

Yes,I need gl-3.3.

[pchampio]

see: #258

[ekasetiawans]

is this means we need computer that supported opengl version 3.3 or above on graphics card, to run our applications? @Drakirus

[pchampio]

$ hover build --help 
Flags:
      --opengl string       The OpenGL version specified here is only relevant for external texture plugin (i.e. video_plugin).
                            If 'none' is provided, texture won't be supported. Note: the Flutter Engine still needs a OpenGL compatible context. (default "3.3")

OpenGL is used in 2 way.

• One through GLFW, used to draw your flutter app handle event, etc..
• Two through OpenGL-bindings directly, ONLY for textures (as the above flag description says).
  But the OpenGL-bindings version used here affect GLFW internally.

By default, we use GLFW/3.2 and OpenGL-bindings 3.3, so your system must be compatible with those versions (at least OpenGL 3.3 or above).

But if you don't have support for OpenGL 3.3. you could use the --opengl=none flag.
This flag will use OpenGL in one way:

• through GLFW, used to draw your flutter app handle event, etc..
• Texture plugin won't be supported and panic the app.

GLFW will internally choose the min OpenGL version to use.

[lmx01]

I got this error while run "hover run -b '@gl-3.3':
go get github.com/go-flutter-desktop/go-flutter@gl-3.3: github.com/go-flutter-desktop/go-flutter@gl-3.3: invalid version: unknown revision gl-3.3
Can U help me?Thanks.

[pchampio]

This branch does not exist anymore, that's why you have this error.
Please read the hover help page about -b.

[lmx01]

thanks @pchampio