Make the elements of matrices optional

affine.go

@@ -43,7 +43,8 @@ func add(lhs, rhs, result affine) {
 
 	for i := 0; i < dim-1; i++ {
 		for j := 0; j < dim; j++ {
-			result.SetElement(i, j, lhs.Element(i, j)+rhs.Element(i, j))
+			v := lhs.Element(i, j) + rhs.Element(i, j)
+			result.SetElement(i, j, v)
 		}
 	}
 }

colormatrix.go

@@ -29,32 +29,45 @@ const ColorMatrixDim = 5
 // the color is multiplied again.
 type ColorMatrix struct {
 	// es represents elements.
-	es [ColorMatrixDim - 1][ColorMatrixDim]float64
+	es *[ColorMatrixDim - 1][ColorMatrixDim]float64
+}
+
+func colorMatrixEsI() *[ColorMatrixDim - 1][ColorMatrixDim]float64 {
+	return &[ColorMatrixDim - 1][ColorMatrixDim]float64{
+		{1, 0, 0, 0, 0},
+		{0, 1, 0, 0, 0},
+		{0, 0, 1, 0, 0},
+		{0, 0, 0, 1, 0},
+	}
 }
 
 // NewColorMatrix returns an identity color matrix.
 func NewColorMatrix() ColorMatrix {
 	return ColorMatrix{
-		[ColorMatrixDim - 1][ColorMatrixDim]float64{
-			{1, 0, 0, 0, 0},
-			{0, 1, 0, 0, 0},
-			{0, 0, 1, 0, 0},
-			{0, 0, 0, 1, 0},
-		},
+		es: colorMatrixEsI(),
 	}
 }
 
-func (c *ColorMatrix) dim() int {
+func (c ColorMatrix) dim() int {
 	return ColorMatrixDim
 }
 
 // Element returns a value of a matrix at (i, j).
-func (c *ColorMatrix) Element(i, j int) float64 {
+func (c ColorMatrix) Element(i, j int) float64 {
+	if c.es == nil {
+		if i == j {
+			return 1
+		}
+		return 0
+	}
 	return c.es[i][j]
 }
 
 // Concat multiplies a color matrix with the other color matrix.
 func (c *ColorMatrix) Concat(other ColorMatrix) {
+	if c.es == nil {
+		c.es = colorMatrixEsI()
+	}
 	result := ColorMatrix{}
 	mul(&other, c, &result)
 	*c = result
@@ -62,6 +75,9 @@ func (c *ColorMatrix) Concat(other ColorMatrix) {
 
 // Add adds a color matrix with the other color matrix.
 func (c *ColorMatrix) Add(other ColorMatrix) {
+	if c.es == nil {
+		c.es = colorMatrixEsI()
+	}
 	result := ColorMatrix{}
 	add(&other, c, &result)
 	*c = result
@@ -69,6 +85,9 @@ func (c *ColorMatrix) Add(other ColorMatrix) {
 
 // SetElement sets an element at (i, j).
 func (c *ColorMatrix) SetElement(i, j int, element float64) {
+	if c.es == nil {
+		c.es = colorMatrixEsI()
+	}
 	c.es[i][j] = element
 }
 
@@ -78,7 +97,7 @@ func Monochrome() ColorMatrix {
 	const g = 23434.0 / 32768.0
 	const b = 2366.0 / 32768.0
 	return ColorMatrix{
-		[ColorMatrixDim - 1][ColorMatrixDim]float64{
+		&[ColorMatrixDim - 1][ColorMatrixDim]float64{
 			{r, g, b, 0, 0},
 			{r, g, b, 0, 0},
 			{r, g, b, 0, 0},
@@ -90,7 +109,7 @@ func Monochrome() ColorMatrix {
 // ScaleColor returns a color matrix that scales a color matrix by the given color (r, g, b, a).
 func ScaleColor(r, g, b, a float64) ColorMatrix {
 	return ColorMatrix{
-		[ColorMatrixDim - 1][ColorMatrixDim]float64{
+		&[ColorMatrixDim - 1][ColorMatrixDim]float64{
 			{r, 0, 0, 0, 0},
 			{0, g, 0, 0, 0},
 			{0, 0, b, 0, 0},
@@ -102,7 +121,7 @@ func ScaleColor(r, g, b, a float64) ColorMatrix {
 // TranslateColor returns a color matrix that translates a color matrix by the given color (r, g, b, a).
 func TranslateColor(r, g, b, a float64) ColorMatrix {
 	return ColorMatrix{
-		[ColorMatrixDim - 1][ColorMatrixDim]float64{
+		&[ColorMatrixDim - 1][ColorMatrixDim]float64{
 			{1, 0, 0, 0, r},
 			{0, 1, 0, 0, g},
 			{0, 0, 1, 0, b},
@@ -118,7 +137,7 @@ func RotateHue(theta float64) ColorMatrix {
 	v2 := (1.0/3.0)*(1.0-cos) - math.Sqrt(1.0/3.0)*sin
 	v3 := (1.0/3.0)*(1.0-cos) + math.Sqrt(1.0/3.0)*sin
 	return ColorMatrix{
-		[ColorMatrixDim - 1][ColorMatrixDim]float64{
+		&[ColorMatrixDim - 1][ColorMatrixDim]float64{
 			{v1, v2, v3, 0, 0},
 			{v3, v1, v2, 0, 0},
 			{v2, v3, v1, 0, 0},

colormatrix_test.go

@@ -13,3 +13,38 @@
 // limitations under the License.
 
 package ebiten_test
+
+import (
+	. "."
+	"testing"
+)
+
+func TestColorInit(t *testing.T) {
+	var m ColorMatrix
+	for i := 0; i < ColorMatrixDim-1; i++ {
+		for j := 0; j < ColorMatrixDim; j++ {
+			got := m.Element(i, j)
+			want := 0.0
+			if i == j {
+				want = 1
+			}
+			if want != got {
+				t.Errorf("m.Element(%d, %d) = %f, want %f", i, j, got, want)
+			}
+		}
+	}
+
+	m.Add(m)
+	for i := 0; i < ColorMatrixDim-1; i++ {
+		for j := 0; j < ColorMatrixDim; j++ {
+			got := m.Element(i, j)
+			want := 0.0
+			if i == j {
+				want = 2
+			}
+			if want != got {
+				t.Errorf("m.Element(%d, %d) = %f, want %f", i, j, got, want)
+			}
+		}
+	}
+}

geometrymatrix.go

@@ -24,30 +24,43 @@ const GeometryMatrixDim = 3
 // A GeometryMatrix represents a matrix to transform geometry when rendering an image.
 type GeometryMatrix struct {
 	// es represents elements.
-	es [GeometryMatrixDim - 1][GeometryMatrixDim]float64
+	es *[GeometryMatrixDim - 1][GeometryMatrixDim]float64
+}
+
+func geometryMatrixEsI() *[GeometryMatrixDim - 1][GeometryMatrixDim]float64 {
+	return &[GeometryMatrixDim - 1][GeometryMatrixDim]float64{
+		{1, 0, 0},
+		{0, 1, 0},
+	}
 }
 
 // NewGeometryMatrix returns an identity geometry matrix.
 func NewGeometryMatrix() GeometryMatrix {
 	return GeometryMatrix{
-		[GeometryMatrixDim - 1][GeometryMatrixDim]float64{
-			{1, 0, 0},
-			{0, 1, 0},
-		},
+		es: geometryMatrixEsI(),
 	}
 }
 
-func (g *GeometryMatrix) dim() int {
+func (g GeometryMatrix) dim() int {
 	return GeometryMatrixDim
 }
 
 // Element returns a value of a matrix at (i, j).
-func (g *GeometryMatrix) Element(i, j int) float64 {
+func (g GeometryMatrix) Element(i, j int) float64 {
+	if g.es == nil {
+		if i == j {
+			return 1
+		}
+		return 0
+	}
 	return g.es[i][j]
 }
 
 // Concat multiplies a geometry matrix with the other geometry matrix.
 func (g *GeometryMatrix) Concat(other GeometryMatrix) {
+	if g.es == nil {
+		g.es = geometryMatrixEsI()
+	}
 	result := GeometryMatrix{}
 	mul(&other, g, &result)
 	*g = result
@@ -55,6 +68,9 @@ func (g *GeometryMatrix) Concat(other GeometryMatrix) {
 
 // Add adds a geometry matrix with the other geometry matrix.
 func (g *GeometryMatrix) Add(other GeometryMatrix) {
+	if g.es == nil {
+		g.es = geometryMatrixEsI()
+	}
 	result := GeometryMatrix{}
 	add(&other, g, &result)
 	*g = result
@@ -62,13 +78,16 @@ func (g *GeometryMatrix) Add(other GeometryMatrix) {
 
 // SetElement sets an element at (i, j).
 func (g *GeometryMatrix) SetElement(i, j int, element float64) {
+	if g.es == nil {
+		g.es = geometryMatrixEsI()
+	}
 	g.es[i][j] = element
 }
 
 // ScaleGeometry returns a matrix that scales a geometry matrix by (x, y).
 func ScaleGeometry(x, y float64) GeometryMatrix {
 	return GeometryMatrix{
-		[2][3]float64{
+		es: &[2][3]float64{
 			{x, 0, 0},
 			{0, y, 0},
 		},
@@ -78,7 +97,7 @@ func ScaleGeometry(x, y float64) GeometryMatrix {
 // TranslateGeometry returns a matrix taht translates a geometry matrix by (tx, ty).
 func TranslateGeometry(tx, ty float64) GeometryMatrix {
 	return GeometryMatrix{
-		[2][3]float64{
+		es: &[2][3]float64{
 			{1, 0, tx},
 			{0, 1, ty},
 		},
@@ -89,7 +108,7 @@ func TranslateGeometry(tx, ty float64) GeometryMatrix {
 func RotateGeometry(theta float64) GeometryMatrix {
 	sin, cos := math.Sincos(theta)
 	return GeometryMatrix{
-		[2][3]float64{
+		es: &[2][3]float64{
 			{cos, -sin, 0},
 			{sin, cos, 0},
 		},

geometrymatrix_test.go

@@ -19,6 +19,36 @@ import (
 	"testing"
 )
 
+func TestGeometryInit(t *testing.T) {
+	var m GeometryMatrix
+	for i := 0; i < GeometryMatrixDim-1; i++ {
+		for j := 0; j < GeometryMatrixDim; j++ {
+			got := m.Element(i, j)
+			want := 0.0
+			if i == j {
+				want = 1
+			}
+			if want != got {
+				t.Errorf("m.Element(%d, %d) = %f, want %f", i, j, got, want)
+			}
+		}
+	}
+
+	m.Add(m)
+	for i := 0; i < GeometryMatrixDim-1; i++ {
+		for j := 0; j < GeometryMatrixDim; j++ {
+			got := m.Element(i, j)
+			want := 0.0
+			if i == j {
+				want = 2
+			}
+			if want != got {
+				t.Errorf("m.Element(%d, %d) = %f, want %f", i, j, got, want)
+			}
+		}
+	}
+}
+
 func TestGeometryConcat(t *testing.T) {
 	matrix1 := ScaleGeometry(2, 2)
 	matrix2 := TranslateGeometry(1, 1)