diff --git a/src/cmd/test/main.go b/src/cmd/test/main.go
index a6cab2b..2809c07 100644
--- a/src/cmd/test/main.go
+++ b/src/cmd/test/main.go
@@ -8,6 +8,7 @@ import (
 	"log"
 	"strings"
 	"fmt"
+	"math/rand"
 )
 
 type Player struct {
@@ -65,6 +66,7 @@ func NewPlayer() *Player {
 			},
 			Visible: true,
 			Shader: gx.SolidWhiteColorShader,
+			Uniforms: make(map[string] any),
 		},
 		MoveSpeed: 90.,
 		ScaleSpeed: .2,
@@ -85,7 +87,8 @@ func (p *Player) Update(e *gx.Engine) error {
 	dt := e.DT()
 	c := e.Camera()
 	keys := e.Keys()
-
+	
+	p.Uniforms["Random"] = any(rand.Float32())
 	for _, v := range keys {switch v {
 	case ebiten.KeyArrowUp :
 		c.T.P.Y += p.MoveSpeed * dt
diff --git a/src/gx/line-segment.go b/src/gx/line-segment.go
index 9a764c2..79c8e84 100644
--- a/src/gx/line-segment.go
+++ b/src/gx/line-segment.go
@@ -1,4 +1,17 @@
 package gx
 
+import (
+	"math"
+)
+
 type LineSegment [2]Point
 
+func (ls LineSegment) LenSqr() Float {
+	return Sqr(ls[0].X - ls[1].X) +
+		Sqr(ls[0].Y - ls[1].Y)
+}
+
+func (ls LineSegment) Len() Float {
+	return Sqrt(ls.LenSqr())
+}
+
diff --git a/src/gx/main.go b/src/gx/main.go
index e0e9a77..2ec580d 100644
--- a/src/gx/main.go
+++ b/src/gx/main.go
@@ -10,10 +10,6 @@ import (
 	"math"
 )
 
-// The type is used in all Engine interactions
-// where you need floating values.
-type Float = float64
-
 // The type represents order of drawing.
 type Layer int
 
diff --git a/src/gx/math.go b/src/gx/math.go
new file mode 100644
index 0000000..3578a0d
--- /dev/null
+++ b/src/gx/math.go
@@ -0,0 +1,15 @@
+package gx
+
+// The type is used in all Engine interactions
+// where you need floating values.
+type Float = float64
+
+const (
+	MaxFloat = math.MaxFloat64
+)
+
+// Returns square of the value.
+func Sqr(v Float) Float {
+	return v * v
+}
+
diff --git a/src/gx/shader.go b/src/gx/shader.go
index 8d10148..7e736fe 100644
--- a/src/gx/shader.go
+++ b/src/gx/shader.go
@@ -7,6 +7,7 @@ import (
 
 type Shader = ebiten.Shader
 type ShaderOptions struct {
+	Shader *Shader
 	Uniforms map[string] any
 	Images [4]*Image
 }
@@ -16,6 +17,8 @@ var (
 	SolidWhiteColorShader = MustNewShader([]byte(`
 		package main
 		
+		var Random float
+		
 		func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 			//ts := imageSrcTextureSize()
 			
@@ -37,14 +40,16 @@ var (
 				)
 			}*/
 			
-			ret := vec4(
+			/*ret := vec4(
 				0,
 				sin(position.x),
 				sin(position.y),
 				1,
 			)
 			
-			return imageSrc0UnsafeAt(texCoord) * (ret)
+			return imageSrc0UnsafeAt(texCoord) * (ret)*/
+			return imageSrc0UnsafeAt(texCoord) * 
+				vec4(1, 1, Random, Random)
 		}
 	`))
 )
diff --git a/src/gx/triangle.go b/src/gx/triangle.go
index 84c77bb..6a36bae 100644
--- a/src/gx/triangle.go
+++ b/src/gx/triangle.go
@@ -7,6 +7,10 @@ import (
 // The structure of a triangle. What more you want to hear?
 type Triangle [3]Point
 type Triangles []Triangle
+type DrawableTriangle struct {
+	Triangle
+	ShaderOptions
+}
 
 // Returns the area of the triangle.
 func (t Triangle) Area() Float {
@@ -21,4 +25,76 @@ func (t Triangle) Area() Float {
 	
 	return math.Abs( (x1*(y2-y3) + x2*(y3-y1) + x3*(y1-y2))/2)
 }
+func sqr(v Float) Float {
+	return v * v
+}
+// Return squares of lengths of sides of the triangle.
+func (t Triangle) SideLengthSquares() ([3]Float) {
+	
+	l1 := LineSegment{t[0], t[1]}.LenSqr()
+	l2 := LineSegment{t[1], t[2]}.LenSqr()
+	l2 := LineSegment{t[2], t[0]}.LenSqr()
+	
+	return [3]Float{l1, l2, l3}
+}
+
+// Check whether the point is in the triangle.
+func (t Triangle) PointIsIn(p Point) bool {
+	return false	
+}
+/*
+func (r *DrawableRectangle) Draw(
+	e *Engine,
+	i *Image,
+) {
+	t := r.T
+	
+	// Draw solid color if no shader.
+	if r.Shader == nil {
+		t.S.X *= r.W
+		t.S.Y *= r.H
+		
+		m := t.Matrix(e)
+		rm := e.Camera().RealMatrix(e, true)
+		
+		m.Concat(rm)
+		
+		opts := &ebiten.DrawImageOptions{
+			GeoM: m,
+		}
+		i.DrawTriangles(img, opts)
+		return
+	}
+	
+	// Use the Color as base image if no is provided.
+	var did bool
+	if r.Images[0] == nil {
+		r.Images[0] = NewImage(1, 1)
+		r.Images[0].Set(0, 0, r.Color)
+		did = true
+	} 
+	
+	w, h := r.Images[0].Size()
+	if !did {
+		t.S.X /= Float(w)
+		t.S.Y /= Float(h)
+		
+		t.S.X *= r.W
+		t.S.Y *= r.H
+	}
+	
+	
+	rm := e.Camera().RealMatrix(e, true)
+	m := t.Matrix(e)
+	m.Concat(rm)
+	
+	// Drawing with shader.
+	opts := &ebiten.DrawRectShaderOptions{
+		GeoM: m,
+		Images: r.Images,
+		Uniforms: r.Uniforms,
+	}
+	i.DrawRectShader(w, h, r.Shader, opts)
+}
+*/