Made ownership of textures more explicit

backend.go

@@ -19,7 +19,7 @@ type Backend interface {
 
 	// NewTexture creates a new texture from an image. The backend must
 	// reject any texture that was not made by it.
-	NewTexture (image.Image) canvas.Texture
+	NewTexture (image.Image) canvas.TextureCloser
 
 	// Run runs the event loop until Stop() is called, or the backend
 	// experiences a fatal error.

canvas/texture.go

@@ -5,26 +5,16 @@ import "image"
 
 // Texture is a handle that points to a 2D raster image managed by the backend.
 type Texture interface {
-	io.Closer
 	image.Image
 
 	// Clip returns a smaller section of this texture, pointing to the same
-	// internal data. Becaue of this, closing a clipped section will close
-	// the original texture as well.
+	// internal data.
 	Clip (image.Rectangle) Texture
 }
 
-type protectedTexture struct {
+// TextureCloser is a texture that can be closed. Anything that receives a
+// TextureCloser must close it after use.
+type TextureCloser interface {
 	Texture
-}
-
-func (protectedTexture) Close () error {
-	return nil
-}
-
-// Protect makes the Close() method of a texture do nothing. This is useful if
-// several of the same texture are given out to different objects, but only one
-// has the responsibility of closing it.
-func Protect (texture Texture) Texture {
-	return protectedTexture { Texture: texture }
+	io.Closer
 }

tomo.go

@@ -83,7 +83,7 @@ func NewContainerBox () ContainerBox {
 
 // NewTexture creates a new texture from an image. When no longer in use, it
 // must be freed using Close().
-func NewTexture (source image.Image) canvas.Texture {
+func NewTexture (source image.Image) canvas.TextureCloser {
 	assertBackend()
 	return backend.NewTexture(source)
 }