Bug fix: matrices' elements should be copied when assigning

colormatrix.go

@@ -30,12 +30,12 @@ const ColorMatrixDim = 5
 //
 // The initial value is identity.
 type ColorMatrix struct {
-	// es represents elements.
+	initialized bool
-	es *[ColorMatrixDim - 1][ColorMatrixDim]float64
+	es          [ColorMatrixDim - 1][ColorMatrixDim]float64
 }
 
-func colorMatrixEsI() *[ColorMatrixDim - 1][ColorMatrixDim]float64 {
+func colorMatrixEsI() [ColorMatrixDim - 1][ColorMatrixDim]float64 {
-	return &[ColorMatrixDim - 1][ColorMatrixDim]float64{
+	return [ColorMatrixDim - 1][ColorMatrixDim]float64{
 		{1, 0, 0, 0, 0},
 		{0, 1, 0, 0, 0},
 		{0, 0, 1, 0, 0},
@@ -49,7 +49,7 @@ func (c ColorMatrix) dim() int {
 
 // Element returns a value of a matrix at (i, j).
 func (c ColorMatrix) Element(i, j int) float64 {
-	if c.es == nil {
+	if !c.initialized {
 		if i == j {
 			return 1
 		}
@@ -60,8 +60,9 @@ func (c ColorMatrix) Element(i, j int) float64 {
 
 // Concat multiplies a color matrix with the other color matrix.
 func (c *ColorMatrix) Concat(other ColorMatrix) {
-	if c.es == nil {
+	if !c.initialized {
 		c.es = colorMatrixEsI()
+		c.initialized = true
 	}
 	result := ColorMatrix{}
 	mul(&other, c, &result)
@@ -70,8 +71,9 @@ 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 {
+	if !c.initialized {
 		c.es = colorMatrixEsI()
+		c.initialized = true
 	}
 	result := ColorMatrix{}
 	add(&other, c, &result)
@@ -80,8 +82,9 @@ 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 {
+	if !c.initialized {
 		c.es = colorMatrixEsI()
+		c.initialized = true
 	}
 	c.es[i][j] = element
 }
@@ -92,7 +95,8 @@ func Monochrome() ColorMatrix {
 	const g = 23434.0 / 32768.0
 	const b = 2366.0 / 32768.0
 	return ColorMatrix{
-		&[ColorMatrixDim - 1][ColorMatrixDim]float64{
+		initialized: true,
+		es: [ColorMatrixDim - 1][ColorMatrixDim]float64{
 			{r, g, b, 0, 0},
 			{r, g, b, 0, 0},
 			{r, g, b, 0, 0},
@@ -104,7 +108,8 @@ 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{
+		initialized: true,
+		es: [ColorMatrixDim - 1][ColorMatrixDim]float64{
 			{r, 0, 0, 0, 0},
 			{0, g, 0, 0, 0},
 			{0, 0, b, 0, 0},
@@ -116,7 +121,8 @@ 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{
+		initialized: true,
+		es: [ColorMatrixDim - 1][ColorMatrixDim]float64{
 			{1, 0, 0, 0, r},
 			{0, 1, 0, 0, g},
 			{0, 0, 1, 0, b},
@@ -132,7 +138,8 @@ 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{
+		initialized: true,
+		es: [ColorMatrixDim - 1][ColorMatrixDim]float64{
 			{v1, v2, v3, 0, 0},
 			{v3, v1, v2, 0, 0},
 			{v2, v3, v1, 0, 0},

colormatrix_test.go

@@ -48,3 +48,14 @@ func TestColorInit(t *testing.T) {
 		}
 	}
 }
+
+func TestColorAssign(t *testing.T) {
+	m := ScaleColor(1, 1, 1, 1) // Create elements explicitly
+	m2 := m
+	m.SetElement(0, 0, 0)
+	got := m2.Element(0, 0)
+	want := 1.0
+	if want != got {
+		t.Errorf("m2.Element(%d, %d) = %f, want %f", 0, 0, got, want)
+	}
+}

geometrymatrix.go

@@ -25,12 +25,12 @@ const GeometryMatrixDim = 3
 //
 // The initial value is identity.
 type GeometryMatrix struct {
-	// es represents elements.
+	initialized bool
-	es *[GeometryMatrixDim - 1][GeometryMatrixDim]float64
+	es          [GeometryMatrixDim - 1][GeometryMatrixDim]float64
 }
 
-func geometryMatrixEsI() *[GeometryMatrixDim - 1][GeometryMatrixDim]float64 {
+func geometryMatrixEsI() [GeometryMatrixDim - 1][GeometryMatrixDim]float64 {
-	return &[GeometryMatrixDim - 1][GeometryMatrixDim]float64{
+	return [GeometryMatrixDim - 1][GeometryMatrixDim]float64{
 		{1, 0, 0},
 		{0, 1, 0},
 	}
@@ -42,7 +42,7 @@ func (g GeometryMatrix) dim() int {
 
 // Element returns a value of a matrix at (i, j).
 func (g GeometryMatrix) Element(i, j int) float64 {
-	if g.es == nil {
+	if !g.initialized {
 		if i == j {
 			return 1
 		}
@@ -53,8 +53,9 @@ func (g GeometryMatrix) Element(i, j int) float64 {
 
 // Concat multiplies a geometry matrix with the other geometry matrix.
 func (g *GeometryMatrix) Concat(other GeometryMatrix) {
-	if g.es == nil {
+	if !g.initialized {
 		g.es = geometryMatrixEsI()
+		g.initialized = true
 	}
 	result := GeometryMatrix{}
 	mul(&other, g, &result)
@@ -63,8 +64,9 @@ 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 {
+	if !g.initialized {
 		g.es = geometryMatrixEsI()
+		g.initialized = true
 	}
 	result := GeometryMatrix{}
 	add(&other, g, &result)
@@ -73,8 +75,9 @@ 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 {
+	if !g.initialized {
 		g.es = geometryMatrixEsI()
+		g.initialized = true
 	}
 	g.es[i][j] = element
 }
@@ -82,7 +85,8 @@ func (g *GeometryMatrix) SetElement(i, j int, element float64) {
 // ScaleGeometry returns a matrix that scales a geometry matrix by (x, y).
 func ScaleGeometry(x, y float64) GeometryMatrix {
 	return GeometryMatrix{
-		es: &[2][3]float64{
+		initialized: true,
+		es: [2][3]float64{
 			{x, 0, 0},
 			{0, y, 0},
 		},
@@ -92,7 +96,8 @@ 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{
-		es: &[2][3]float64{
+		initialized: true,
+		es: [2][3]float64{
 			{1, 0, tx},
 			{0, 1, ty},
 		},
@@ -103,7 +108,8 @@ func TranslateGeometry(tx, ty float64) GeometryMatrix {
 func RotateGeometry(theta float64) GeometryMatrix {
 	sin, cos := math.Sincos(theta)
 	return GeometryMatrix{
-		es: &[2][3]float64{
+		initialized: true,
+		es: [2][3]float64{
 			{cos, -sin, 0},
 			{sin, cos, 0},
 		},

geometrymatrix_test.go

@@ -49,6 +49,17 @@ func TestGeometryInit(t *testing.T) {
 	}
 }
 
+func TestGeometryAssign(t *testing.T) {
+	m := ScaleGeometry(1, 1) // Create elements explicitly
+	m2 := m
+	m.SetElement(0, 0, 0)
+	got := m2.Element(0, 0)
+	want := 1.0
+	if want != got {
+		t.Errorf("m2.Element(%d, %d) = %f, want %f", 0, 0, got, want)
+	}
+}
+
 func TestGeometryConcat(t *testing.T) {
 	matrix1 := ScaleGeometry(2, 2)
 	matrix2 := TranslateGeometry(1, 1)

image.go

@@ -152,7 +152,7 @@ func (i *Image) Fill(clr color.Color) (err error) {
 // The parts of the given image at the parts of the destination.
 // After determining parts to draw, this applies the geometry matrix and the color matrix.
 //
-// If options is nil or its members are nil, the default values are used.
+// Here are the default values:
 //     DstParts:       (0, 0) - (source width, source height)
 //     SrcParts:       (0, 0) - (source width, source height) (i.e. the whole source image)
 //     GeometryMatrix: Identity matrix