private static void CheckError(string operation)
{
int error;
int lastError = GLES20.GL_NO_ERROR;
while ((error = GLES20.GetError()) != GLES20.GL_NO_ERROR)
{
lastError = error;
}
if (lastError != GLES20.GL_NO_ERROR)
{
throw new Exception(operation + " produced error code " + lastError + ".");
}
}