Sprites layering

1 files changed, 67 insertions, 0 deletions

diff --git a/engine/Components/Layering.go b/engine/Components/Layering.go
new file mode 100644
index 0000000..3e42b44
--- /dev/null
+++ b/engine/Components/Layering.go
@@ -0,0 +1,67 @@
+package components
+
+type LayeringElement interface {
+	Draw()
+	// returnt Y-index of the element
+	GetYIndex() float32
+}
+
+// Stores elements by their Y-layer ordered in decreasing order.
+// Used to draw objects in the correct order on screen
+type layering struct {
+	ObjectCount int
+	firstLayer *layer
+}
+
+func (base *layering) Insert(new LayeringElement) {
+	base.ObjectCount += 1
+	var y = new.GetYIndex()
+	var newLayer = layer {
+		Index: y,
+		Objects: []LayeringElement { new },
+	}
+	if base.firstLayer == nil {
+		base.firstLayer = &newLayer
+		return
+	}
+
+	// The first layer is greater than the current first layer
+	if base.firstLayer.Index > y {
+		newLayer.next = base.firstLayer
+		base.firstLayer = &newLayer
+		return
+	}
+
+	var current = base.firstLayer
+	var next *layer
+	for {
+		if current == nil {
+			break
+		}
+		next = current.Next()
+		if current.Index == y {
+			current.Objects = append(current.Objects, new)
+			return
+		}
+		if y < current.Index && y > next.Index {
+			newLayer.next = next
+			current.next = &newLayer
+			return
+		}
+		if current.Next() == nil {
+			current.next = &newLayer
+			return
+		}
+		next = current
+	}
+}
+
+type layer struct {
+	Index float32
+	Objects []LayeringElement
+	next *layer
+}
+
+func (base *layer) Next() *layer {
+	return base.next
+}