change platform to be a singleton

platform/platform.go

@@ -1,38 +1,52 @@
 package platform
 
 import (
+	"errors"
+
+	"github.com/FooSoft/imgui-go"
 	"github.com/go-gl/gl/v2.1/gl"
 	"github.com/veandco/go-sdl2/sdl"
 )
 
-type Platform interface {
-	CreateWindow(title string, width, height int) (Window, error)
-	Destroy() error
-}
+var (
+	platformIsInit       bool
+	platformImguiContext *imgui.Context
+	platformWindows      []Window
+)
 
-var globalPlatformInit bool
-
-type platform struct {
-	windows []Window
-}
-
-func New() (*Platform, error) {
-	if !globalPlatformInit {
-		if err := sdl.Init(sdl.INIT_VIDEO); err != nil {
-			return nil, err
-		}
-
-		if err := gl.Init(); err != nil {
-			return nil, err
-		}
-
-		globalPlatformInit = true
+func Init() error {
+	if platformIsInit {
+		return errors.New("platform is already initialized")
 	}
 
-	return nil, nil
+	if err := sdl.Init(sdl.INIT_VIDEO); err != nil {
+		return err
+	}
+
+	if err := gl.Init(); err != nil {
+		return err
+	}
+
+	platformImguiContext = imgui.CreateContext(nil)
+	return nil
 }
 
-func (p *platform) CreateWindow(title string, width, height int) (Window, error) {
+func Shutdown() error {
+	if !platformIsInit {
+		return errors.New("platform is not yet initialized")
+	}
+
+	for _, w := range platformWindows {
+		if err := w.Destroy(); err != nil {
+			return err
+		}
+	}
+
+	platformWindows = nil
+	return nil
+}
+
+func CreateWindow(title string, width, height int) (Window, error) {
 	window, err := newWindow(title, width, height)
 	if err != nil {
 		return nil, err
@@ -40,14 +54,3 @@ func (p *platform) CreateWindow(title string, width, height int) (Window, error)
 
 	return window, err
 }
-
-func (p *platform) Destroy() error {
-	for _, w := range p.windows {
-		if err := w.Destroy(); err != nil {
-			return err
-		}
-	}
-
-	p.windows = nil
-	return nil
-}