render: move render_world_helper, remove chunks drawn behind view

internal/util/itype/rect.go

@@ -14,12 +14,36 @@ type Rectf struct {
 	Width, Height float32
 }
 
+func (r Rectf) MinPoint() Vec2f {
+	return Vec2f{r.Left, r.Top}
+}
+
+func (r Rectf) MaxPoint() Vec2f {
+	return Vec2f{r.Left + r.Width, r.Top + r.Height}
+}
+
+func (r Rectf) Size() Vec2f {
+	return Vec2f{r.Width, r.Height}
+}
+
 // Rectd is a 2D rectangle with float64 coordinates.
 type Rectd struct {
 	Left, Top     float64
 	Width, Height float64
 }
 
+func (r Rectd) MinPoint() Vec2d {
+	return Vec2d{r.Left, r.Top}
+}
+
+func (r Rectd) MaxPoint() Vec2d {
+	return Vec2d{r.Left + r.Width, r.Top + r.Height}
+}
+
+func (r Rectd) Size() Vec2d {
+	return Vec2d{r.Width, r.Height}
+}
+
 // Boxi is a 3D box with int coordinates.
 type Boxi struct {
 	OffX, OffY, OffZ    int

internal/util/itype/vec.go

@@ -79,6 +79,10 @@ func (v Vec2f) ToFloat64() Vec2d {
 // Vec3f is a three-element float vector
 type Vec3f [3]float32
 
+func (v Vec3f) Negative() Vec3f {
+	return Vec3f{-v[0], -v[1], -v[2]}
+}
+
 func (v Vec3f) Add(add Vec3f) Vec3f {
 	return Vec3f{v[0] + add[0], v[1] + add[1], v[2] + add[2]}
 }