libobs: Add function to enumerate video adapters

The gs_enum_adapters function is an optional implementation to allow
enumeration of available graphics adapters that can be used with the
program.  The ID associated with the adapter can be an index or a hash
depending on the implementation.

libobs/graphics/device-exports.h

@@ -25,6 +25,9 @@ extern "C" {
 
 EXPORT const char *device_get_name(void);
 EXPORT int device_get_type(void);
+EXPORT bool device_enum_adapters(
+		bool (*callback)(void *param, const char *name, uint32_t id),
+		void *param);
 EXPORT const char *device_preprocessor_name(void);
 EXPORT int device_create(gs_device_t **device, const struct gs_init_data *data);
 EXPORT void device_destroy(gs_device_t *device);

libobs/graphics/graphics-imports.c

@@ -42,6 +42,7 @@ bool load_graphics_imports(struct gs_exports *exports, void *module,
 
 	GRAPHICS_IMPORT(device_get_name);
 	GRAPHICS_IMPORT(device_get_type);
+	GRAPHICS_IMPORT_OPTIONAL(device_enum_adapters);
 	GRAPHICS_IMPORT(device_preprocessor_name);
 	GRAPHICS_IMPORT(device_create);
 	GRAPHICS_IMPORT(device_destroy);

libobs/graphics/graphics-internal.h

@@ -26,6 +26,9 @@
 struct gs_exports {
 	const char *(*device_get_name)(void);
 	int (*device_get_type)(void);
+	bool (*device_enum_adapters)(
+			bool (*callback)(void*, const char*, uint32_t),
+			void*);
 	const char *(*device_preprocessor_name)(void);
 	int (*device_create)(gs_device_t **device,
 			const struct gs_init_data *data);

libobs/graphics/graphics.c

@@ -36,6 +36,24 @@ static __thread graphics_t *thread_graphics = NULL;
 
 #define IMMEDIATE_COUNT 512
 
+void gs_enum_adapters(
+		bool (*callback)(void *param, const char *name, uint32_t id),
+		void *param)
+{
+	graphics_t *graphics = thread_graphics;
+
+	if (graphics && graphics->exports.device_enum_adapters) {
+		if (graphics->exports.device_enum_adapters(callback, param)) {
+			return;
+		}
+	}
+
+	/* If the subsystem does not currently support device enumeration of
+	 * adapters or fails to enumerate adapters, just set it to one adapter
+	 * named "Default" */
+	callback(param, "Default", 0);
+}
+
 extern void gs_init_image_deps(void);
 extern void gs_free_image_deps(void);
 

libobs/graphics/graphics.h

@@ -447,6 +447,9 @@ struct gs_init_data {
 
 EXPORT const char *gs_get_device_name(void);
 EXPORT int gs_get_device_type(void);
+EXPORT void gs_enum_adapters(
+		bool (*callback)(void *param, const char *name, uint32_t id),
+		void *param);
 
 EXPORT int gs_create(graphics_t **graphics, const char *module,
 		const struct gs_init_data *data);