Move all engine stuff to GoRetro. Still many interactions between game and engine code that there should not be.

element.go

@@ -0,0 +1,95 @@
+package GoRetro
+
+import (
+	"fmt"
+	"reflect"
+
+	"github.com/veandco/go-sdl2/sdl"
+)
+
+type component interface {
+	onUpdate() error
+	onDraw() error
+	onCollision(other *Element) error
+}
+
+type Element struct {
+	Renderer       *sdl.Renderer
+	Position       Vector
+	Rotation       float64
+	Active         bool
+	Delete         bool
+	Collisions     []Circle
+	components     []component
+	parentElement  *Element
+	ZIndex         int
+	CollisionLayer int
+}
+
+var Elements []*Element
+
+func (elem *Element) Draw() error {
+	for _, comp := range elem.components {
+		err := comp.onDraw()
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func (elem *Element) Update() error {
+	for _, comp := range elem.components {
+		err := comp.onUpdate()
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func (elem *Element) collision(other *Element) error {
+	for _, comp := range elem.components {
+		err := comp.onCollision(other)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func (elem *Element) AddComponent(new component) {
+	for _, existing := range elem.components {
+		if reflect.TypeOf(new) == reflect.TypeOf(existing) {
+			panic(fmt.Sprintf(
+				"attempt to add new component with existing type %v",
+				reflect.TypeOf(new)))
+		}
+	}
+	elem.components = append(elem.components, new)
+}
+
+func (elem *Element) getComponent(withType component) component {
+	typ := reflect.TypeOf(withType)
+	for _, comp := range elem.components {
+		if reflect.TypeOf(comp) == typ {
+			return comp
+		}
+	}
+
+	panic(fmt.Sprintf("no component with type %v", reflect.TypeOf(withType)))
+}
+
+func (elem *Element) checkComponentIsPresent(withType component) bool {
+	typ := reflect.TypeOf(withType)
+	for _, comp := range elem.components {
+		if reflect.TypeOf(comp) == typ {
+			return true
+		}
+	}
+
+	return false
+}