x/mobile: graphics quality with OpenGL ES

[star-tek-mb]

Please answer these questions before submitting your issue. Thanks!

1. What version of Go are you using (go version)?
   go version go1.6 linux/386
   gomobile version +0ee7f82 Thu Mar 3 05:14:23 2016 +0000 (android); androidSDK=/home/startek/android-sdk/platforms/android-23
2. What operating system and processor architecture are you using (go env)?
   GOARCH="386"
   GOBIN=""
   GOEXE=""
   GOHOSTARCH="386"
   GOHOSTOS="linux"
   GOOS="linux"
   GOPATH="/home/startek/go/dev"
   GORACE=""
   GOROOT="/home/startek/go"
   GOTOOLDIR="/home/startek/go/pkg/tool/linux_386"
   GO15VENDOREXPERIMENT="1"
   CC="gcc"
   GOGCCFLAGS="-fPIC -m32 -pthread -fmessage-length=0"
   CXX="g++"
   CGO_ENABLED="1"
3. What did you do?
   (Use play.golang.org to provide a runnable example, if possible.)
   Draw arc with OpenGL ES.
4. What did you expect to see?
   Smooth arc.
5. What did you see instead?
   Unsmooth arc.

Please, change configuration of context creation. From this in android.c (also in x11.c and others):

const EGLint RGB_888[] = {
    EGL_RENDERABLE_TYPE, EGL_OPENGL_ES2_BIT,
    EGL_SURFACE_TYPE, EGL_WINDOW_BIT,
    EGL_BLUE_SIZE, 8,
    EGL_GREEN_SIZE, 8,
    EGL_RED_SIZE, 8,
    EGL_DEPTH_SIZE, 16,
    EGL_CONFIG_CAVEAT, EGL_NONE,
    EGL_NONE
};

to:

const EGLint RGB_888[] = {
    EGL_RENDERABLE_TYPE, EGL_OPENGL_ES2_BIT,
    EGL_SURFACE_TYPE, EGL_WINDOW_BIT,
    EGL_BLUE_SIZE, 8,
    EGL_GREEN_SIZE, 8,
    EGL_RED_SIZE, 8,
    EGL_DEPTH_SIZE, 16,
    EGL10.EGL_SAMPLE_BUFFERS, 1,
    EGL10.EGL_SAMPLES, 4,  // This is for 4x MSAA.
    EGL_CONFIG_CAVEAT, EGL_NONE,
    EGL_NONE
};

I know, some devices may not support this configuration - but many devices on Android uses modern hardware, and now supports OpenGL ES 3.0.