QuadRender.kt

/**
* Create shader program from source code of vertex and fragment shader
*/
private fun createProgram(vertexSource: String, fragmentSource: String): Boolean {
   if (program != UNKNOWN_PROGRAM) {
       // delete program
       GLES30.glDeleteProgram(program)
       program = UNKNOWN_PROGRAM
   }
   // load vertex shader
   val vertexShader = loadShader(GLES30.GL_VERTEX_SHADER, vertexSource)
   if (vertexShader == UNKNOWN_PROGRAM) {
       return false
   }
   // load pixel shader
   val pixelShader = loadShader(GLES30.GL_FRAGMENT_SHADER, fragmentSource)
   if (pixelShader == UNKNOWN_PROGRAM) {
       return false
   }
   program = GLES30.glCreateProgram()
   if (program != UNKNOWN_PROGRAM) {
       GLES30.glAttachShader(program, vertexShader)
       checkGlError("glAttachShader: vertex")
       GLES30.glAttachShader(program, pixelShader)
       checkGlError("glAttachShader: pixel")
       return linkProgram()
   }
   return true
}

private fun linkProgram(): Boolean {
   if (program == UNKNOWN_PROGRAM) {
       return false
   }
   GLES30.glLinkProgram(program)
   val linkStatus = IntArray(1)
   GLES30.glGetProgramiv(program, GLES30.GL_LINK_STATUS, linkStatus, 0)
   if (linkStatus[0] != GLES30.GL_TRUE) {
       Log.e(TAG, "Could not link program: ")
       Log.e(TAG, GLES30.glGetProgramInfoLog(program))
       GLES30.glDeleteProgram(program)
       program = UNKNOWN_PROGRAM
       return false
   }
   return true
}

private fun loadShader(shaderType: Int, source: String): Int {
   var shader = GLES30.glCreateShader(shaderType)
   if (shader != UNKNOWN_PROGRAM) {
       GLES30.glShaderSource(shader, source)
       GLES30.glCompileShader(shader)
       val compiled = IntArray(1)
       GLES30.glGetShaderiv(shader, GLES30.GL_COMPILE_STATUS, compiled, 0)
       if (compiled[0] == UNKNOWN_PROGRAM) {
           Log.e(TAG, "Could not compile shader $shaderType:")
           Log.e(TAG, GLES30.glGetShaderInfoLog(shader))
           GLES30.glDeleteShader(shader)
           shader = UNKNOWN_PROGRAM
       }
   }
   return shader
}

private fun checkGlError(op: String) {
   var error: Int
   while (GLES30.glGetError().also { error = it } != GLES30.GL_NO_ERROR) {
       Log.e(TAG, "$op: glError $error")
       throw RuntimeException("$op: glError $error")
   }
}