ui,ui/app: convert Config to an interface

To keep the interface slim, remove the helper methods and shorten
the essential method, Pixels, to Px.

Add and use unexported Config implementation in the app package.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

ui/ui.go

@@ -11,41 +11,13 @@ import (
 	"gioui.org/ui/internal/ops"
 )
 
-// Config contains the essential configuration for
+// Config represents the essential configuration for
 // updating and drawing a user interface.
-type Config struct {
-	// Device pixels per dp.
-	PxPerDp float32
-	// Device pixels per sp.
-	PxPerSp float32
-	// The current time for animation.
-	Now time.Time
-}
-
-// Dp converts a value in dp units to pixels.
-func (c *Config) Dp(dp float32) int {
-	return c.Pixels(Dp(dp))
-}
-
-// Sp converts a value in sp units to pixels.
-func (c *Config) Sp(sp float32) int {
-	return c.Pixels(Sp(sp))
-}
-
-// Pixels converts a value to pixels.
-func (c *Config) Pixels(v Value) int {
-	var r float32
-	switch v.U {
-	case UnitPx:
-		r = v.V
-	case UnitDp:
-		r = c.PxPerDp * v.V
-	case UnitSp:
-		r = c.PxPerSp * v.V
-	default:
-		panic("unknown unit")
-	}
-	return int(math.Round(float64(r)))
+type Config interface {
+	// Now returns the current animation time.
+	Now() time.Time
+	// Px converts a Value to pixels.
+	Px(v Value) int
 }
 
 // LayerOp represents a semantic layer of UI.