diff --git a/cmd/math/main.go b/cmd/math/main.go
new file mode 100644
index 0000000..19625fc
--- /dev/null
+++ b/cmd/math/main.go
@@ -0,0 +1,39 @@
+package main
+
+import (
+	"vultras.su/core/gg"
+	"fmt"
+	"encoding/json"
+)
+type Float = gg.Float
+
+func EdgesFromVals(vals ...Float) gg.Edges {
+	ret := gg.Edges{}
+	for i:=0 ; i<len(vals) ; i += 4 {
+		ret = append(
+			ret,
+			gg.Edge{
+				gg.Point{
+					vals[i], vals[i+1],
+				},
+				gg.Point{
+					vals[i+2], vals[i+3],
+				},
+			},
+		)
+	}
+	return ret
+}
+
+func main() {
+	e1 := EdgesFromVals(
+		0, 0, 5, 5,
+	)
+	e2 := EdgesFromVals(
+		0, 1, 5, 0,
+		0, 0, 5, 5,
+	)
+	val, ok := e1.CrossWithEdges(e2)
+	bts, _ := json.MarshalIndent(val, "", "\t")
+	fmt.Println(string(bts), ok)
+}
diff --git a/cmd/test/debug.go b/cmd/test/debug.go
index 365f3fe..36a681b 100644
--- a/cmd/test/debug.go
+++ b/cmd/test/debug.go
@@ -9,6 +9,17 @@ import (
 
 type Debug struct {
 	gg.Object
+	gg.Visibility
+}
+
+func (d *Debug) Update(c *Context) {
+	for _, e := range c.Events { switch ec := e.(type) {
+	case *gg.KeyDown :
+		switch ec.Key {
+		case gg.KeyF11 :
+			d.Visible = !d.Visible
+		}
+	}}
 }
 
 func (d *Debug) Draw(c *Context) []gg.EVertex {
@@ -87,4 +98,3 @@ func (d *Debug) Draw(c *Context) []gg.EVertex {
 	return nil
 }
 
-func (d *Debug) IsVisible() bool { return true }
diff --git a/cmd/test/player.go b/cmd/test/player.go
index 963d206..ba72227 100644
--- a/cmd/test/player.go
+++ b/cmd/test/player.go
@@ -50,6 +50,13 @@ func (p *Player) Draw(c *Context) []gg.EVertex {
 }
 
 func (p *Player) Update(c *Context) {
+	/*r := gg.Rectangle{
+		Transform: gg.T(),
+	}
+	r.Width = 150
+	r.Height = 150
+	col, _ := gg.Collide(p, r)
+	fmt.Println(col.Crosses)*/
 	//p.SetPosition(p.Position().Sub(gg.Y(2)))
 	p.Move(gg.Y(1))
 	if p.Spawned {
@@ -71,7 +78,7 @@ func (p *Player) Update(c *Context) {
 				),
 			)
 		case gg.KeyW:
-			p.Move(gg.Y(-p.MoveSpeed * dt *10))
+			p.Move(gg.Y(-p.MoveSpeed * dt ))
 			walking = true
 			p.Animate(Walk)
 		case gg.KeyA:
@@ -80,7 +87,7 @@ func (p *Player) Update(c *Context) {
 			walking = true
 			p.Animate(Walk)
 		case gg.KeyS:
-			p.Move(gg.X(-p.MoveSpeed * dt))
+			p.Move(gg.Y(p.MoveSpeed * dt))
 			//p.Position.Y -= p.MoveSpeed * dt
 			walking = true
 			p.Animate(Walk)
@@ -160,8 +167,11 @@ func (p *Player) GetCollisionInterest() []gg.CollisionType {
 
 func (p *Player) Resolve(c *Context) {
 	col := c.Collisions[0]
-	if !p.Spawned {
-		fmt.Printf("frame[%d]: the col[0] len(%d): %T, %T\n", c.Frame(), len(c.Collisions), col.What, col.With)
+	if !p.Spawned && false {
+		fmt.Printf(
+			"frame[%d]: the col[0] len(%d): %T, %T, %d %d\n",
+			c.Frame(), len(c.Collisions), col.What, col.With, len(col.Crosses), len(col.Points),
+		)
 	}
 	for _, col := range c.Collisions {switch col.Type{
 	case gg.CollisionStaticPhysics :
diff --git a/cmd/test/rect.go b/cmd/test/rect.go
index 4832e01..8887222 100644
--- a/cmd/test/rect.go
+++ b/cmd/test/rect.go
@@ -8,7 +8,7 @@ type Rect struct {
 
 func NewRect() *Rect {
 	ret := &Rect{}
-	ret.SetScale(gg.V(200, 400))
+	ret.SetScale(gg.V(5, 5))
 	ret.Color = gg.Color{
 		gg.MaxColorV,
 		0,
diff --git a/cmd/test/trianlge.go b/cmd/test/trianlge.go
index 776cbda..8f57ed8 100644
--- a/cmd/test/trianlge.go
+++ b/cmd/test/trianlge.go
@@ -1,7 +1,7 @@
 package main
 
 import "vultras.su/core/gg"
-//import "fmt"
+import "fmt"
 
 var (
 	counter int
@@ -15,6 +15,7 @@ type Tri struct {
 func NewTri() *Tri {
 	ret := &Tri{}
 	ret.Transform = gg.T()
+	ret.SetPosition(gg.V(-100, -100))
 	ret.Triangles = gg.Triangles{
 		gg.Triangle{
 			gg.V(0, 10),
@@ -24,13 +25,27 @@ func NewTri() *Tri {
 	}
 	ret.Color = gg.Rgba(1, 1, 0, 1)
 	ret.Visible = true
+	ret.Collidable = true
+	ret.Type = gg.CollisionStaticPhysics
 	ret.Layer = TriangleL
-	ret.Connect(player)
+	//ret.Connect(player)
 
 	return ret
 }
 
 func (t *Tri) Update(c *Context) {
+	//redges := rect.Edges()
+	//tedges := t.Edges()
+	//crosses, ok := tedges.CrossWithEdges(redges)
+	//fmt.Println("shit:", crosses, ok)
+	
+	if false {
+		//fmt.Println("edges:", tedges)
+	}
+	col, hasCol := gg.Collide(t, rect)
+	if hasCol{
+		fmt.Println("col:", col)
+	}
 	dt := c.Dt().Seconds()
 	if !t.ContainedPoints(gg.Points{c.AbsCursorPosition()}).Empty() {
 		t.Color = gg.Rgba(0, 1, 0, 1)
diff --git a/collider.go b/collider.go
index 526cd20..4248a10 100644
--- a/collider.go
+++ b/collider.go
@@ -83,7 +83,7 @@ func (r Resolvability) GetCollisionInterest() []CollisionType {
 func Collide(c1, c2 Collider) (Collision, bool) {
 	vertices := c1.Vertices()
 	es1, es2 := c1.Edges(), c2.Edges()
-	crosses, doCross := es1.LineCrossWith(es2)
+	crosses, doCross := es1.CrossWithEdges(es2)
 	pts := c2.ContainedPoints(vertices)
 	return Collision{
 		Type: c2.CollisionType(),
@@ -91,7 +91,7 @@ func Collide(c1, c2 Collider) (Collision, bool) {
 		With: c2,
 		Points: pts,
 		Crosses: crosses,
-	}, len(pts) != 0 || doCross
+	}, len(pts) > 0 || doCross
 }
 
 func GetCollisions(c Collider, cs []Collider) []Collision {
diff --git a/edge.go b/edge.go
index fcc58ee..253a15e 100644
--- a/edge.go
+++ b/edge.go
@@ -2,7 +2,7 @@ package gg
 
 type Edges []Edge
 // Get crosses of edges.
-func (what Edges) LineCrossWith(with Edges) ([]LineCross, bool) {
+func (what Edges) CrossWithEdges(with Edges) ([]LineCross, bool) {
 	ret := []LineCross{}
 	for i := range what {
 		for j := range with {
@@ -13,11 +13,7 @@ func (what Edges) LineCrossWith(with Edges) ([]LineCross, bool) {
 		}
 	}
 	
-	if len(ret) == 0 {
-		return nil, false
-	}
-
-	return ret, true
+	return ret, len(ret) > 0
 }
 
 // The type represents a line segment. The name is for short.
@@ -25,13 +21,22 @@ type Edge [2]Vector
 
 // Returns corresponding to the segment Line.
 func (l Edge) Line() Line {
+	var (
+		x Float
+		vertical bool
+	)
+
 	p0 := l[0]
 	p1 := l[1]
 	
 	k := (p0.Y - p1.Y) / (p0.X - p1.X)
 	c := p0.Y - p0.X*k 
-	
-	return Line{k, c}
+	if p0.X == p1.X {
+		vertical = true
+		x = p0.X
+	}
+
+	return Line{k, c, x, vertical}
 }
 
 func (l Edge) ContainedPoints(pts Points) (Points) {
@@ -51,11 +56,11 @@ func (l Edge) ContainsPoint(p Point) bool {
 		return false
 	}
 	
-	xMax := Max(l[0].X, l[1].X)	
-	xMin := Min(l[0].X, l[1].X)	
+	xMax := Max(l[0].X, l[1].X)
+	xMin := Min(l[0].X, l[1].X)
 	
-	yMax := Max(l[0].Y, l[1].Y)	
-	yMin := Min(l[0].Y, l[1].Y)	
+	yMax := Max(l[0].Y, l[1].Y)
+	yMin := Min(l[0].Y, l[1].Y)
 	
 	if !(xMin < p.X && p.X < xMax) ||
 		!(yMin < p.Y && p.Y < yMax) {
diff --git a/fmt.go b/fmt.go
new file mode 100644
index 0000000..bdd5b07
--- /dev/null
+++ b/fmt.go
@@ -0,0 +1,13 @@
+package gg
+
+import (
+	"fmt"
+)
+
+func Println(v ...any) {
+	fmt.Println(v...)
+}
+
+func Printf(format string, v ...any) {
+	fmt.Printf(format, v...)
+}
diff --git a/line.go b/line.go
index e89664b..b2a08ce 100644
--- a/line.go
+++ b/line.go
@@ -1,8 +1,11 @@
 package gg
 
+//import "fmt"
+
 // The type represents mathematical equation of line and line itself.
 type Line struct {
-	K, C Float
+	K, C, X Float
+	Vertical bool
 }
 
 // Returns the line itself. Made to implement the Liner interface.
@@ -11,22 +14,32 @@ func (l Line) Line() Line {
 }
 
 func (l Line) ContainsPoint(p Point) bool {
-	buf := Line{0, p.Y}
+	buf := Line{0, p.Y, 0, false}
 	pc, ok := l.crossesLine(buf)
 	if !ok {
 		return false
 	}
 	
-	return pc == p 
+	return Neq(pc.X, p.X) && Neq(pc.Y, p.Y)
 }
 
 func (l1 Line) crossesLine(l2 Line) (Point, bool) {
+	var x, y Float
 	if LinersParallel(l1, l2) {
 		return Point{}, false
 	}
-	
-	x := (l1.C - l2.C) / (l2.K - l1.K)
-	y := l1.K*x + l1.C
+
+	if l1.Vertical {
+		x = l1.X
+		y = l2.K*x + l2.C
+	} else if l2.Vertical {
+		x = l2.X
+		y = l1.K*x + l1.C
+	} else {
+		x = (l1.C - l2.C) / (l2.K - l1.K)
+		y = l1.K*x + l1.C
+	}
+
 	return Point{x, y}, true
 }
 
diff --git a/liner.go b/liner.go
index 965511e..7892002 100644
--- a/liner.go
+++ b/liner.go
@@ -22,16 +22,15 @@ func LinersCross(lp1, lp2 LinerPointContainer) (LineCross, bool) {
 	l2 := lp2.Line()
 	
 	crossPt, doCross := l1.crossesLine(l2)
-	if !doCross ||
-			len(lp1.ContainedPoints([]Point{crossPt}))==0 ||
+	if len(lp1.ContainedPoints([]Point{crossPt}))==0 ||
 			len(lp2.ContainedPoints([]Point{crossPt}))==0 {
-		return LineCross{}, false
+		doCross = false
 	}
 	
 	return LineCross{
 		Pair: [2]Line{l1, l2},
 		Point: crossPt,
-	}, true
+	}, doCross
 }
 
 // Check whether the liner is parallel to the other liner.
@@ -39,7 +38,7 @@ func LinersParallel(first, second Liner) bool {
 	l1 := first.Line()
 	l2 := second.Line()
 	
-	return l1.K == l2.K
+	return l1.K == l2.K || l1.Vertical && l2.Vertical
 }
 
 // Returns angle between liners in radians.
diff --git a/math.go b/math.go
index 98a67bf..1f3e124 100644
--- a/math.go
+++ b/math.go
@@ -13,8 +13,17 @@ const (
 	Pi = math.Pi
 	RadDegrees = 57.2958
 	//PiRad = Pi * Rad
+	EqualityThreshold = 1e-9
 )
 
+func IsNan(v Float) bool {
+	return math.IsNaN(v)
+}
+
+func IsInf(f Float, sign int) bool {
+	return math.IsInf(f, sign)
+}
+
 func Degree(f Float) Float {
 	return (f/(2*Pi))*360
 }
@@ -64,6 +73,13 @@ func Min(v1, v2 Float) Float {
 	return v2
 }
 
+func Abs(v Float) Float {
+	if v >= 0 {
+		return v
+	}
+	return -v
+}
+
 func RadiansToDegrees(v Float) Float {
 	return v/Pi * 180
 }
@@ -72,4 +88,8 @@ func DeegresToRadians(v Float) Float {
 	return v
 }
 
+// Returns whether the two floats are nearly equal.
+func Neq(a, b Float) bool {
+	return Abs(a-b) <= EqualityThreshold
+}
 
diff --git a/polygon.go b/polygon.go
index 0f31c4a..6424aaa 100644
--- a/polygon.go
+++ b/polygon.go
@@ -28,6 +28,13 @@ func (p Polygon) MakeTriangles() Triangles {
 	return ret
 }
 
+func (p Polygon) Vertices() Vertices {
+	return p.MakeTriangles().Vertices()
+}
+func (p Polygon) Edges() Edges {
+	return p.MakeTriangles().Edges()
+}
+
 // Polygon that can be drawn.
 type DrawablePolygon struct {
 	Polygon
diff --git a/size.go b/size.go
index 02877ab..c06b113 100644
--- a/size.go
+++ b/size.go
@@ -6,7 +6,13 @@ type Size struct {
 	// The upper left corner position point.
 	Position Point
 	// Absolute width and height.
+	// Both must be positive values.
 	Width, Height Float
 }
 
+func (size Size) ContainsPoint(pt Point) bool {
+	return (size.Position.X < pt.X && (size.Position.X + size.Width) > pt.X ) &&
+		(size.Position.Y < pt.Y && (size.Position.Y + size.Height) > pt.Y )
+}
+
 //type (s Size) ContainsPoint
diff --git a/taskfile.yml b/taskfile.yml
index 1043de8..8ceccca 100644
--- a/taskfile.yml
+++ b/taskfile.yml
@@ -3,3 +3,6 @@ tasks:
   btest:
     cmds:
       - go build ./cmd/test/
+  bmath:
+    cmds:
+      - go build ./cmd/math/
diff --git a/transform.go b/transform.go
index 790845d..8b25878 100644
--- a/transform.go
+++ b/transform.go
@@ -43,6 +43,7 @@ func T() Transform {
 		scale: Vector{1, 1},
 		// Rotate around the center.
 		around: V(.5, .5),
+		rotation: EqualityThreshold,
 	}
 	return ret
 }
diff --git a/triangle.go b/triangle.go
index 4106f66..ea9983d 100644
--- a/triangle.go
+++ b/triangle.go
@@ -86,6 +86,14 @@ func (t Triangle) Sgn() Float {
 		(t[1].X - t[2].X) * (t[0].Y - t[2].Y)
 }
 
+func (t Triangle) Edges() Edges {
+	return Edges{
+		Edge{t[0], t[1]},
+		Edge{t[1], t[2]},
+		Edge{t[2], t[0]},
+	}
+}
+
 func (t Triangle) Vertices() Vertices {
 	return Vertices{
 		t[0], t[1], t[2],
@@ -103,6 +111,22 @@ func (ts Triangles) ContainedPoints(pts Points) (Points) {
 	return ret
 }
 
+func (ts Triangles) Vertices() Vertices {
+	ret := make(Vertices, 0, len(ts)*3)
+	for _, t := range ts {
+		ret = append(ret, t.Vertices()...)
+	}
+	return ret
+}
+
+func (ts Triangles) Edges() Edges {
+	ret := make(Edges, 0, len(ts)*3)
+	for _, t := range ts {
+		ret = append(ret, t.Edges()...)
+	}
+	return ret
+}
+
 func (r *DrawableTriangles) MakeEVertices(c *Context) []EVertex {
 	m := c.Camera.RealMatrix()
 	vs := make([]ebiten.Vertex, len(r.Triangles) * 3)
@@ -117,3 +141,4 @@ func (r *DrawableTriangles) MakeEVertices(c *Context) []EVertex {
 	return vs
 }
 
+