Added a texture interface

backend.go

@@ -16,6 +16,10 @@ type Backend interface {
 	NewCanvasBox    () CanvasBox
 	NewContainerBox () ContainerBox
 
+	// NewTexture creates a new texture from an image. The backend must
+	// reject any texture that was not made by it.
+	NewTexture (image.Image) Texture
+
 	// Run runs the event loop until Stop() is called, or the backend
 	// experiences a fatal error.
 	Run () error

object.go

@@ -238,6 +238,8 @@ type TextBox interface {
 	// SetSelectable sets whether or not the text content can be
 	// highlighted/selected.
 	SetSelectable (bool)
+	// SetDotColor sets the highlight color of the text selection.
+	SetDotColor   (color.Color)
 	// Select sets the text cursor or selection.
 	Select        (text.Dot)
 	// Dot returns the text cursor or selection.

texture.go

@@ -0,0 +1,14 @@
+package tomo
+
+import "io"
+import "image"
+
+// Texture is a handle that points to a 2D raster image managed by the backend.
+type Texture interface {
+	io.Closer
+
+	// 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.
+	Clip (image.Rectangle) Texture
+}

tomo.go

@@ -79,3 +79,10 @@ func NewContainerBox () ContainerBox {
 	assertBackend()
 	return backend.NewContainerBox()
 }
+
+// NewTexture creates a new texture from an image. When no longer in use, it
+// must be freed using Close().
+func NewTexture (source image.Image) Texture {
+	assertBackend()
+	return backend.NewTexture(source)
+}