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affine: Add Skew function to GeoM

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Fixes #654
This commit is contained in:
Nathaniel Knight 2018-07-31 22:15:30 -07:00 committed by Hajime Hoshi
parent 5c201af311
commit 6f23029e4c
2 changed files with 76 additions and 0 deletions
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21
geom.go
View File

@ -162,6 +162,27 @@ func (g *GeoM) Rotate(theta float64) {
g.ty = ty
}
// Skew skews the matrix by (skewX, skewY). The unit is radian.
func (g *GeoM) Skew(skewX, skewY float64) {
sx64 := math.Tan(skewX)
sy64 := math.Tan(skewY)
sx, sy := float32(sx64), float32(sy64)
a := (g.a_1 + 1) + g.c*sx
b := g.b + (g.d_1+1)*sx
c := (g.a_1+1)*sy + g.c
d := g.b*sy + (g.d_1 + 1)
tx := g.tx + g.ty*sx
ty := g.ty + g.tx*sy
g.a_1 = a - 1
g.b = b
g.c = c
g.d_1 = d - 1
g.tx = tx
g.ty = ty
}
func (g *GeoM) det() float32 {
return (g.a_1+1)*(g.d_1+1) - g.b*g.c
}

55
geom_test.go
View File

@ -206,6 +206,9 @@ func TestGeoMIsInvert(t *testing.T) {
cpx2.Rotate(0.234)
cpx2.Translate(100, 100)
skew := GeoM{}
skew.Skew(1, 1)
cases := []struct {
GeoM GeoM
Invertible bool
@ -234,6 +237,10 @@ func TestGeoMIsInvert(t *testing.T) {
GeoM: cpx2,
Invertible: true,
},
{
GeoM: skew,
Invertible: true,
},
}
pts := []struct {
@ -279,6 +286,54 @@ func TestGeoMIsInvert(t *testing.T) {
}
}
func constructGeom(a, b, c, d, tx, ty float64) GeoM {
outp := GeoM{}
outp.SetElement(0, 0, a)
outp.SetElement(0, 1, b)
outp.SetElement(0, 2, tx)
outp.SetElement(1, 0, c)
outp.SetElement(1, 1, d)
outp.SetElement(1, 2, ty)
return outp
}
func TestGeomSkew(t *testing.T) {
testSkew := func(skewX, skewY float64, input, expected GeoM) {
input.Skew(skewX, skewY)
for i := 0; i < 2; i++ {
for j := 0; j < 3; j++ {
got := input.Element(i, j)
want := expected.Element(i, j)
if want != got {
t.Errorf("Geom{}.Skew(%f, %f): got %s, want: %s", skewX, skewY, input.String(), expected.String())
return
}
}
}
}
// skewX = 0.25
expectedX := constructGeom(1, math.Tan(0.25), math.Tan(0), 1, 0, 0)
testSkew(0.25, 0, GeoM{}, expectedX)
// skewY = 0.25
expectedY := constructGeom(1, math.Tan(0), math.Tan(0.5), 1, 0, 0)
testSkew(0, 0.5, GeoM{}, expectedY)
// skewX, skewY = 0.3, 0.8
expectedXY := constructGeom(1, math.Tan(0.3), math.Tan(0.8), 1, 0, 0)
testSkew(0.3, 0.8, GeoM{}, expectedXY)
// skewX, skewY = 0.4, -1.8 ; b, c = 2, 3
expectedOffDiag := constructGeom(1+3*math.Tan(0.4), 2+math.Tan(0.4), 3+math.Tan(-1.8), 1+2*math.Tan(-1.8), 0, 0)
inputOffDiag := constructGeom(1, 2, 3, 1, 0, 0)
testSkew(0.4, -1.8, inputOffDiag, expectedOffDiag)
// skewX, skewY = -1.5, 1.5 ; tx, ty = 5, 6
expectedTrn := constructGeom(1, math.Tan(-1.5), math.Tan(1.5), 1, 5+math.Tan(-1.5)*6, 6+5*math.Tan(1.5))
inputTrn := constructGeom(1, 0, 0, 1, 5, 6)
testSkew(-1.5, 1.5, inputTrn, expectedTrn)
}
func BenchmarkGeoM(b *testing.B) {
var m GeoM
for i := 0; i < b.N; i++ {