create error constants, hookup imgui_backend init and shutdown

platform/imgui_backend/imgui_backend.go

@@ -18,9 +18,14 @@ var (
 	imguiContext     *imgui.Context
 )
 
+var (
+	ErrAlreadyInit = errors.New("imgui backend is already initialized")
+	ErrWasNotInit  = errors.New("imgui backend was not initialized")
+)
+
 func Init() error {
 	if imguiIsInit {
-		return errors.New("imgui backend is already initialized")
+		return ErrAlreadyInit
 	}
 
 	imguiContext = imgui.CreateContext(nil)
@@ -56,14 +61,14 @@ func Init() error {
 	}
 
 	imguiFontTexture = createFontTexture()
-
 	imguiIsInit = true
+
 	return nil
 }
 
 func Shutdown() error {
 	if !imguiIsInit {
-		return errors.New("imgui backend was not initialized")
+		return ErrWasNotInit
 	}
 
 	imguiIsInit = false
@@ -79,7 +84,7 @@ func Shutdown() error {
 
 func NewFrame(windowSize math.Vec2i) error {
 	if !imguiIsInit {
-		return errors.New("imgui backend was not initialized")
+		return ErrWasNotInit
 	}
 
 	// Setup display size (every frame to accommodate for window resizing)
@@ -116,7 +121,7 @@ func NewFrame(windowSize math.Vec2i) error {
 // If you have multiple SDL events and some of them are not meant to be used by dear imgui, you may need to filter events based on their windowID field.
 func ProcessEvent(event sdl.Event) (bool, error) {
 	if !imguiIsInit {
-		return false, errors.New("imgui backend was not initialized")
+		return false, ErrWasNotInit
 	}
 
 	switch io := imgui.CurrentIO(); event.GetType() {
@@ -176,7 +181,7 @@ func ProcessEvent(event sdl.Event) (bool, error) {
 // Note that this implementation is little overcomplicated because we are saving/setting up/restoring every OpenGL state explicitly, in order to be able to run within any OpenGL engine that doesn't do so.
 func Render(windowSize, fbSize math.Vec2i, drawData imgui.DrawData) error {
 	if !imguiIsInit {
-		return errors.New("imgui backend was not initialized")
+		return ErrWasNotInit
 	}
 
 	drawData.ScaleClipRects(imgui.Vec2{

platform/platform.go

@@ -5,6 +5,7 @@ import (
 	"runtime"
 	"time"
 
+	"github.com/FooSoft/lazarus/platform/imgui_backend"
 	"github.com/go-gl/gl/v2.1/gl"
 	"github.com/veandco/go-sdl2/sdl"
 )
@@ -14,9 +15,14 @@ var (
 	platformWindows []Window
 )
 
+var (
+	ErrAlreadyInit = errors.New("platform is already initialized")
+	ErrWasNotInit  = errors.New("platform was not initialized")
+)
+
 func Init() error {
 	if platformIsInit {
-		return errors.New("platform is already initialized")
+		return ErrAlreadyInit
 	}
 
 	runtime.LockOSThread()
@@ -29,13 +35,38 @@ func Init() error {
 		return err
 	}
 
+	if err := imgui_backend.Init(); err != nil {
+		return err
+	}
+
 	platformIsInit = true
 	return nil
 }
 
+func Shutdown() error {
+	if !platformIsInit {
+		return ErrWasNotInit
+	}
+
+	for _, w := range platformWindows {
+		if err := w.Destroy(); err != nil {
+			return err
+		}
+	}
+
+	if err := imgui_backend.Shutdown(); err != nil {
+		return err
+	}
+
+	platformWindows = nil
+	platformIsInit = false
+
+	return nil
+}
+
 func ProcessEvents() error {
 	if !platformIsInit {
-		return errors.New("platform was not initialized")
+		return ErrWasNotInit
 	}
 
 	var terminate bool
@@ -54,26 +85,9 @@ func ProcessEvents() error {
 	return nil
 }
 
-func Shutdown() error {
-	if !platformIsInit {
-		return errors.New("platform was not initialized")
-	}
-
-	for _, w := range platformWindows {
-		if err := w.Destroy(); err != nil {
-			return err
-		}
-	}
-
-	platformWindows = nil
-	platformIsInit = false
-
-	return nil
-}
-
 func CreateWindow(title string, width, height int) (Window, error) {
 	if !platformIsInit {
-		return nil, errors.New("platform was not initialized")
+		return nil, ErrWasNotInit
 	}
 
 	window, err := newWindow(title, width, height)