affine: Add more tests for (*ColorM).Invert

colorm.go

@@ -104,11 +104,7 @@ func (c *ColorM) ChangeHSV(hueTheta float64, saturationScale float64, valueScale
 
 // Element returns a value of a matrix at (i, j).
 func (c *ColorM) Element(i, j int) float64 {
-	b, t := c.impl.UnsafeElements()
-	if j < ColorMDim-1 {
-		return float64(b[i+j*(ColorMDim-1)])
-	}
-	return float64(t[i])
+	return float64(c.impl.Element(i, j))
 }
 
 // SetElement sets an element at (i, j).

internal/affine/colorm.go

@@ -319,6 +319,15 @@ func (c *ColorM) Invert() *ColorM {
 	return m
 }
 
+// Element returns a value of a matrix at (i, j).
+func (c *ColorM) Element(i, j int) float32 {
+	b, t := c.UnsafeElements()
+	if j < ColorMDim-1 {
+		return b[i+j*(ColorMDim-1)]
+	}
+	return t[i]
+}
+
 // SetElement sets an element at (i, j).
 func (c *ColorM) SetElement(i, j int, element float32) *ColorM {
 	newC := &ColorM{

internal/affine/colorm_test.go

@@ -136,6 +136,26 @@ func arrayToColorM(es [4][5]float32) *ColorM {
 	return a
 }
 
+func abs(x float32) float32 {
+	if x < 0 {
+		return -x
+	}
+	return x
+}
+
+func equalWithDelta(a, b *ColorM, delta float32) bool {
+	for j := 0; j < 5; j++ {
+		for i := 0; i < 4; i++ {
+			ea := a.Element(i, j)
+			eb := b.Element(i, j)
+			if abs(ea-eb) > delta {
+				return false
+			}
+		}
+	}
+	return true
+}
+
 func TestColorMInvert(t *testing.T) {
 	cases := []struct {
 		In  *ColorM
@@ -159,10 +179,24 @@ func TestColorMInvert(t *testing.T) {
 				{7, -4, -2, 1, 0},
 			}),
 		},
+		{
+			In: arrayToColorM([4][5]float32{
+				{1, 2, 3, 4, 5},
+				{5, 1, 2, 3, 4},
+				{4, 5, 1, 2, 3},
+				{3, 4, 5, 1, 2},
+			}),
+			Out: arrayToColorM([4][5]float32{
+				{-6 / 35.0, 3 / 14.0, 1 / 70.0, 1 / 70.0, -1 / 14.0},
+				{1 / 35.0, -13 / 70.0, 3 / 14.0, 1 / 70.0, -1 / 14.0},
+				{1 / 35.0, 1 / 70.0, -13 / 70.0, 3 / 14.0, -1 / 14.0},
+				{9 / 35.0, 1 / 35.0, 1 / 35.0, -6 / 35.0, -8 / 7.0},
+			}),
+		},
 	}
 
 	for _, c := range cases {
-		if got, want := c.In.Invert(), c.Out; !got.Equals(want) {
+		if got, want := c.In.Invert(), c.Out; !equalWithDelta(got, want, 1e-6) {
 			t.Errorf("got: %v, want: %v", got, want)
 		}
 	}