affine: Add Reset function

colorm.go

@@ -33,6 +33,11 @@ type ColorM struct {
 	impl affine.ColorM
 }
 
+// Reset resets the ColorM as identity.
+func (c *ColorM) Reset() {
+	c.impl.Reset()
+}
+
 // Concat multiplies a color matrix with the other color matrix.
 // This is same as muptiplying the matrix other and the matrix c in this order.
 func (c *ColorM) Concat(other ColorM) {

examples/sprites/main.go

@@ -110,7 +110,7 @@ func update(screen *ebiten.Image) error {
 	}
 	for i := 0; i < sprites.num; i++ {
 		s := sprites.sprites[i]
-		op.GeoM = ebiten.GeoM{}
+		op.GeoM.Reset()
 		op.GeoM.Translate(float64(s.x), float64(s.y))
 		screen.DrawImage(ebitenImage, op)
 	}

geom.go

@@ -28,6 +28,11 @@ type GeoM struct {
 	impl affine.GeoM
 }
 
+// Reset resets the GeoM as identity.
+func (g *GeoM) Reset() {
+	g.impl.Reset()
+}
+
 // Element returns a value of a matrix at (i, j).
 func (g *GeoM) Element(i, j int) float64 {
 	a, b, c, d, tx, ty := g.impl.Elements()

internal/affine/colorm.go

@@ -44,6 +44,10 @@ type ColorM struct {
 	elements []float64
 }
 
+func (c *ColorM) Reset() {
+	c.elements = nil
+}
+
 func (c *ColorM) UnsafeElements() []float64 {
 	if c.elements == nil {
 		c.elements = colorMIdentityElements

internal/affine/geom.go

@@ -34,6 +34,10 @@ type GeoM struct {
 	inited bool
 }
 
+func (g *GeoM) Reset() {
+	g.inited = false
+}
+
 func (g *GeoM) Elements() (a, b, c, d, tx, ty float64) {
 	if !g.inited {
 		return 1, 0, 0, 1, 0, 0