x/mobile: fix x/mobile/gl just like c opengl or go-gl

[fastfading]

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

1.7

What operating system and processor architecture are you using (go env)?

mac os

What did you do?

migrate a program from pc to mobile
go get -u github.com/go-gl/glfw/v3.2/glfw --> golang.org/x/mobile/app
go get -u github.com/go-gl/gl/v2.1/gl --> golang.org/x/mobile/gl
go get -u github.com/timshannon/go-openal/openal --> golang.org/x/mobile/exp/audio/al
I wish to do the above change

What did you expect to see?

[golang.org/x/mobile/gl] act just like [github.com/go-gl/gl/v2.1/gl ]

What did you see instead?

There is lot of differences ,

//not implemented
gl.TexImage1D
gl.Begin(gl.TRIANGLE_STRIP)
gl.End()
gl.PushMatrix()
gl.PopMatrix()
gl.MatrixMode(gl.PROJECTION)
gl.TexCoord2f(1, 1)
gl.Vertex2f(x2, y2)
gl.Color4f(r, g, b, a)
gl.LoadIdentity()
gl.Ortho(0, float64(sys.scrrect[2]), 0, float64(sys.scrrect[3]), -1, 1)
gl.Translated(0, float64(sys.scrrect[3]), 0)

//interface/behaviour change
gl.GenTextures(1, &paltex) -->CreateTexture
gl.DeleteTextures(1, &paltex) --> DeleteTexture

//unclear
gl.Str(src) -->GetString(pname Enum) string ???
gl.DeleteObjectARB(fragObj) --> DeleteShader ????
gl.GetInfoLogARB -->GetProgramInfoLog| GetShaderInfoLog ????

[strangebug]

Hello,

The name of the package might be misleading, 'golang.org/x/mobile/gl' is built upon OpenGL ES 2.0 (w/ optional support for OpenGL 3.0) not the "desktop" OpenGL. OpenGL ES 2.0 dropped the support for the fixed pipeline so porting your code will a bit harder.

My two cents