graphics: Use float64 in GeoM

The reason why float32 was adopted was forgotten. Using float64
should not be problematic.

Fixes #883

geom.go

@@ -26,12 +26,12 @@ const GeoMDim = 3
 //
 // The initial value is identity.
 type GeoM struct {
-	a_1 float32 // The actual 'a' value minus 1
-	b   float32
-	c   float32
-	d_1 float32 // The actual 'd' value minus 1
-	tx  float32
-	ty  float32
+	a_1 float64 // The actual 'a' value minus 1
+	b   float64
+	c   float64
+	d_1 float64 // The actual 'd' value minus 1
+	tx  float64
+	ty  float64
 }
 
 // String returns a string representation of GeoM.
@@ -53,33 +53,28 @@ func (g *GeoM) Reset() {
 // In other words, Apply calculates GeoM * (x, y, 1)^T.
 // The return value is x and y values of the result vector.
 func (g *GeoM) Apply(x, y float64) (float64, float64) {
-	x2, y2 := g.apply32(float32(x), float32(y))
-	return float64(x2), float64(y2)
-}
-
-func (g *GeoM) apply32(x, y float32) (x2, y2 float32) {
 	return (g.a_1+1)*x + g.b*y + g.tx, g.c*x + (g.d_1+1)*y + g.ty
 }
 
-func (g *GeoM) elements() (a, b, c, d, tx, ty float32) {
-	return g.a_1 + 1, g.b, g.c, g.d_1 + 1, g.tx, g.ty
+func (g *GeoM) elements32() (a, b, c, d, tx, ty float32) {
+	return float32(g.a_1) + 1, float32(g.b), float32(g.c), float32(g.d_1) + 1, float32(g.tx), float32(g.ty)
 }
 
 // Element returns a value of a matrix at (i, j).
 func (g *GeoM) Element(i, j int) float64 {
 	switch {
 	case i == 0 && j == 0:
-		return float64(g.a_1) + 1
+		return g.a_1 + 1
 	case i == 0 && j == 1:
-		return float64(g.b)
+		return g.b
 	case i == 0 && j == 2:
-		return float64(g.tx)
+		return g.tx
 	case i == 1 && j == 0:
-		return float64(g.c)
+		return g.c
 	case i == 1 && j == 1:
-		return float64(g.d_1) + 1
+		return g.d_1 + 1
 	case i == 1 && j == 2:
-		return float64(g.ty)
+		return g.ty
 	default:
 		panic("ebiten: i or j is out of index")
 	}
@@ -116,25 +111,25 @@ func (g *GeoM) Add(other GeoM) {
 
 // Scale scales the matrix by (x, y).
 func (g *GeoM) Scale(x, y float64) {
-	a := (float64(g.a_1) + 1) * x
-	b := float64(g.b) * x
-	tx := float64(g.tx) * x
-	c := float64(g.c) * y
-	d := (float64(g.d_1) + 1) * y
-	ty := float64(g.ty) * y
+	a := (g.a_1 + 1) * x
+	b := g.b * x
+	tx := g.tx * x
+	c := g.c * y
+	d := (g.d_1 + 1) * y
+	ty := g.ty * y
 
-	g.a_1 = float32(a) - 1
-	g.b = float32(b)
-	g.c = float32(c)
-	g.d_1 = float32(d) - 1
-	g.tx = float32(tx)
-	g.ty = float32(ty)
+	g.a_1 = a - 1
+	g.b = b
+	g.c = c
+	g.d_1 = d - 1
+	g.tx = tx
+	g.ty = ty
 }
 
 // Translate translates the matrix by (tx, ty).
 func (g *GeoM) Translate(tx, ty float64) {
-	g.tx += float32(tx)
-	g.ty += float32(ty)
+	g.tx += tx
+	g.ty += ty
 }
 
 // Rotate rotates the matrix by theta.
@@ -144,8 +139,7 @@ func (g *GeoM) Rotate(theta float64) {
 		return
 	}
 
-	sin64, cos64 := math.Sincos(theta)
-	sin, cos := float32(sin64), float32(cos64)
+	sin, cos := math.Sincos(theta)
 
 	a := cos*(g.a_1+1) - sin*g.c
 	b := cos*g.b - sin*(g.d_1+1)
@@ -164,9 +158,8 @@ func (g *GeoM) Rotate(theta float64) {
 
 // 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)
+	sx := math.Tan(skewX)
+	sy := math.Tan(skewY)
 
 	a := (g.a_1 + 1) + g.c*sx
 	b := g.b + (g.d_1+1)*sx
@@ -183,7 +176,7 @@ func (g *GeoM) Skew(skewX, skewY float64) {
 	g.ty = ty
 }
 
-func (g *GeoM) det() float32 {
+func (g *GeoM) det() float64 {
 	return (g.a_1+1)*(g.d_1+1) - g.b*g.c
 }
 
@@ -218,7 +211,7 @@ func (g *GeoM) Invert() {
 
 // SetElement sets an element at (i, j).
 func (g *GeoM) SetElement(i, j int, element float64) {
-	e := float32(element)
+	e := element
 	switch {
 	case i == 0 && j == 0:
 		g.a_1 = e - 1

image.go

@@ -197,7 +197,7 @@ func (i *Image) DrawImage(img *Image, options *DrawImageOptions) error {
 		filter = driver.Filter(img.filter)
 	}
 
-	a, b, c, d, tx, ty := geom.elements()
+	a, b, c, d, tx, ty := geom.elements32()
 	i.buffered.DrawImage(img.buffered, img.Bounds(), a, b, c, d, tx, ty, options.ColorM.impl, mode, filter)
 	return nil
 }