The language interop layer of libGimbal is primarily facilitated through its low-level, C-based meta type system. The type system has two primary goals, one of which is to provide the C (and C++) programming language(s) with higher-level object-oriented constructs, and the other is to use these constructs to create a common type system for cross-langauge interoperability.

Overview

At its core, the LibGimbal Type Framework utilizes a dynamic type system, provided by the GblType API (within gimbal_type.h). This system provides a runtime type registry maintaining all type information provided by builtin or user-registered types. This registry provides object-oriented concepts such as classes, objects, interfaces, poperties, signals, and an inheritance model to both the C programming language, and any langauge which can provide glue code to a C API.

Example

One of the things libGimabl's type system aims to do is endow C programmers with a powerful set of tools and constructs from higher-level object-oriented languages. Constructs such as inheritance, private member variables, virtual functions, interfaces, and even signals and properties become accessible to C programs. The following is an almost complete header from the ElysianVMU emulator, creating an object-oriented type for the piezoelectric Buzzer peripheral:

#ifndef EVMU_BUZZER_H
#define EVMU_BUZZER_H
 
#include <gimbal/meta.h>
 
// UUID associated with the given type 
#define EVMU_BUZZER_TYPE                (GBL_TYPEOF(EvmuBuzzer))
 
// Convenience function-style cast operators
#define EVMU_BUZZER(instance)           (GBL_INSTANCE_CAST(instance, EvmuBuzzer))
#define EVMU_BUZZER_CLASS(klass)        (GBL_CLASS_CAST(klass, EvmuBuzzer))
#define EVMU_BUZZER_GET_CLASS(instance) (GBL_INSTANCE_GET_CLASS(instance, EvmuBuzzer))
 
// Define the "self" or "this" type for its methods
#define GBL_SELF_TYPE EvmuBuzzer
 
// Declare everything extern "C"
GBL_DECLS_BEGIN
 
// Define a "type class" structure or vtable, containing overridable
// virtual functions, inheriting EvmuPeripheral's vtable.
GBL_CLASS_DERIVE(EvmuBuzzer, EvmuPeripheral)
    EVMU_RESULT (*pFnPlayPcm)  (GBL_SELF);
    EVMU_RESULT (*pFnStopPcm)  (GBL_SELF);
    EVMU_RESULT (*pFnBufferPcm)(GBL_SELF);
GBL_CLASS_END
 
// Define a "type instance" structure containing public members, 
// inheriting EvmuPeripheral's public instance members.
GBL_INSTANCE_DERIVE(EvmuBuzzer, EvmuPeripheral)
    GblBool pcmChanged;     
    GblBool enableFreqResp; 
GBL_INSTANCE_END
 
// Create a list of properties for the given type.
GBL_PROPERTIES(EvmuBuzzer,
    (enabled,        GBL_GENERIC, (READ, WRITE), GBL_BOOL_TYPE),
    (configured,     GBL_GENERIC, (READ),        GBL_BOOL_TYPE),
    (active,         GBL_GENERIC, (READ, WRITE), GBL_BOOL_TYPE),
    (period,         GBL_GENERIC, (READ, WRITE), GBL_UINT16_TYPE),
    (invPulseLength, GBL_GENERIC, (READ, WRITE), GBL_UINT8_TYPE),
    (frequency,      GBL_GENERIC, (READ),        GBL_UINT32_TYPE),
    (gain,           GBL_GENERIC, (READ),        GBL_FLOAT_TYPE)
)
 
// Define a list of signals on the type, which can be
// subscribed to with custom callback logic.
GBL_SIGNALS(EvmuBuzzer,
    (toneStart,  (GBL_INSTANCE_TYPE, pReceiver)),
    (toneStop,   (GBL_INSTANCE_TYPE, pReceiver)),
    (toneUpdate, (GBL_INSTANCE_TYPE, pReceiver),
                 (GBL_UINT16_TYPE,   period),
                 (GBL_UINT8_TYPE,    invPulseLength))
)
 
// Declare all public methods for the EvmuBuzzer type
EVMU_EXPORT GblType     EvmuBuzzer_type         (void)                  GBL_NOEXCEPT;
 
EVMU_EXPORT GblBool     EvmuBuzzer_isActive     (GBL_CSELF)             GBL_NOEXCEPT;
EVMU_EXPORT GblBool     EvmuBuzzer_isConfigured (GBL_CSELF)             GBL_NOEXCEPT;
EVMU_EXPORT GblBool     EvmuBuzzer_isEnabled    (GBL_CSELF)             GBL_NOEXCEPT;
 
EVMU_EXPORT void        EvmuBuzzer_setEnabled   (GBL_SELF,
                                                 GblBool enabled)       GBL_NOEXCEPT;
 
EVMU_EXPORT void        EvmuBuzzer_tone         (GBL_CSELF,
                                                 uint16_t* pPeriod,
                                                 uint8_t* pInvPulseLen) GBL_NOEXCEPT;
 
EVMU_EXPORT EVMU_RESULT EvmuBuzzer_setTone      (GBL_SELF,
                                                 uint16_t period,
                                                 uint8_t invPulseLen)   GBL_NOEXCEPT;
 
EVMU_EXPORT EVMU_RESULT EvmuBuzzer_playTone     (GBL_SELF)              GBL_NOEXCEPT;
EVMU_EXPORT EVMU_RESULT EvmuBuzzer_stopTone     (GBL_SELF)              GBL_NOEXCEPT;
 
EVMU_EXPORT const void* EvmuBuzzer_pcmBuffer    (GBL_CSELF)             GBL_NOEXCEPT;
EVMU_EXPORT GblSize     EvmuBuzzer_pcmSamples   (GBL_CSELF)             GBL_NOEXCEPT;
EVMU_EXPORT GblSize     EvmuBuzzer_pcmFrequency (GBL_CSELF)             GBL_NOEXCEPT;
EVMU_EXPORT float       EvmuBuzzer_pcmGain      (GBL_CSELF)             GBL_NOEXCEPT;
 
GBL_DECLS_END
 
#undef GBL_SELF_TYPE
 
#endif // EVMU_BUZZER_H

Table of Contents

Overview

Example