Improve GUI on Android, add OpenAsset function

raylib/platform_android.go

@@ -4,12 +4,21 @@ package raylib
 
 /*
 #include "raylib.h"
-#include "android_native_app_glue.h"
+#include <android/asset_manager.h>
+#include <android_native_app_glue.h>
 
 extern void android_main(struct android_app *app);
+
+AAssetManager* asset_manager;
+extern void init_asset_manager(void *state);
 */
 import "C"
-import "unsafe"
+
+import (
+	"errors"
+	"io"
+	"unsafe"
+)
 
 var callbackHolder func(unsafe.Pointer)
 
@@ -18,6 +27,7 @@ func InitWindow(width int32, height int32, app unsafe.Pointer) {
 	cwidth := (C.int)(width)
 	cheight := (C.int)(height)
 	C.InitWindow(cwidth, cheight, app)
+	C.init_asset_manager(app)
 }
 
 // Sets callback function
@@ -31,3 +41,34 @@ func androidMain(app *C.struct_android_app) {
 		callbackHolder(unsafe.Pointer(app))
 	}
 }
+
+// Open asset
+func OpenAsset(name string) (io.ReadCloser, error) {
+	cname := C.CString(name)
+	defer C.free(unsafe.Pointer(cname))
+
+	a := &asset{C.AAssetManager_open(C.asset_manager, cname, C.AASSET_MODE_UNKNOWN)}
+
+	if a.ptr == nil {
+		return nil, errors.New("asset file could not be opened")
+	}
+
+	return a, nil
+}
+
+type asset struct {
+	ptr *C.AAsset
+}
+
+func (a *asset) Read(p []byte) (n int, err error) {
+	n = int(C.AAsset_read(a.ptr, unsafe.Pointer(&p[0]), C.size_t(len(p))))
+	if n == 0 && len(p) > 0 {
+		return 0, io.EOF
+	}
+	return n, nil
+}
+
+func (a *asset) Close() error {
+	C.AAsset_close(a.ptr)
+	return nil
+}