Use dep to vendor things

vendor/github.com/faiface/pixel/drawer.go

@@ -0,0 +1,96 @@
+package pixel
+
+// Drawer glues all the fundamental interfaces (Target, Triangles, Picture) into a coherent and the
+// only intended usage pattern.
+//
+// Drawer makes it possible to draw any combination of Triangles and Picture onto any Target
+// efficiently.
+//
+// To create a Drawer, just assign it's Triangles and Picture fields:
+//
+//   d := pixel.Drawer{Triangles: t, Picture: p}
+//
+// If Triangles is nil, nothing will be drawn. If Picture is nil, Triangles will be drawn without a
+// Picture.
+//
+// Whenever you change the Triangles, call Dirty to notify Drawer that Triangles changed. You don't
+// need to notify Drawer about a change of the Picture.
+//
+// Note, that Drawer caches the results of MakePicture from Targets it's drawn to for each Picture
+// it's set to. What it means is that using a Drawer with an unbounded number of Pictures leads to a
+// memory leak, since Drawer caches them and never forgets. In such a situation, create a new Drawer
+// for each Picture.
+type Drawer struct {
+	Triangles Triangles
+	Picture   Picture
+
+	targets map[Target]*drawerTarget
+	inited  bool
+}
+
+type drawerTarget struct {
+	tris  TargetTriangles
+	pics  map[Picture]TargetPicture
+	clean bool
+}
+
+func (d *Drawer) lazyInit() {
+	if !d.inited {
+		d.targets = make(map[Target]*drawerTarget)
+		d.inited = true
+	}
+}
+
+// Dirty marks the Triangles of this Drawer as changed. If not called, changes will not be visible
+// when drawing.
+func (d *Drawer) Dirty() {
+	d.lazyInit()
+
+	for _, t := range d.targets {
+		t.clean = false
+	}
+}
+
+// Draw efficiently draws Triangles with Picture onto the provided Target.
+//
+// If Triangles is nil, nothing will be drawn. If Picture is nil, Triangles will be drawn without a
+// Picture.
+func (d *Drawer) Draw(t Target) {
+	d.lazyInit()
+
+	if d.Triangles == nil {
+		return
+	}
+
+	dt := d.targets[t]
+	if dt == nil {
+		dt = &drawerTarget{
+			pics: make(map[Picture]TargetPicture),
+		}
+		d.targets[t] = dt
+	}
+
+	if dt.tris == nil {
+		dt.tris = t.MakeTriangles(d.Triangles)
+		dt.clean = true
+	}
+
+	if !dt.clean {
+		dt.tris.SetLen(d.Triangles.Len())
+		dt.tris.Update(d.Triangles)
+		dt.clean = true
+	}
+
+	if d.Picture == nil {
+		dt.tris.Draw()
+		return
+	}
+
+	pic := dt.pics[d.Picture]
+	if pic == nil {
+		pic = t.MakePicture(d.Picture)
+		dt.pics[d.Picture] = pic
+	}
+
+	pic.Draw(dt.tris)
+}