ShaderView.kt

private const val OPENGL_VERSION = 3

class ShaderView @JvmOverloads constructor(
   context: Context,
   attrs: AttributeSet? = null,
   defStyleAttr: Int = 0
) :
   GLTextureView(context, attrs, defStyleAttr) {

   init {
       // define OpenGL version
       setEGLContextClientVersion(OPENGL_VERSION)

       // load shader's source code from RAW files
       val vsh = context.resources.getRawTextFile(R.raw.vertex_shader)
       val fsh = context.resources.getRawTextFile(R.raw.fragment_shader)

       // set renderer
       setRenderer(QuadRender(vertexShaderSource = vsh, fragmentShaderSource = fsh))

       // set render mode RENDERMODE_WHEN_DIRTY or RENDERMODE_CONTINUOUSLY
       setRenderMode(GLSurfaceView.RENDERMODE_WHEN_DIRTY) // or GLSurfaceView.RENDERMODE_CONTINUOUSLY if we need to update it each frame
   }
}