layout,f32: add convenience functions for rectangles and points

layout.FRect, layout.FPt for converting from integer to floating point,
useful for drawing operations.

f32.Pt is a shorthand that mirrors image.Pt.

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

layout/layout.go

@@ -5,6 +5,7 @@ package layout
 import (
 	"image"
 
+	"gioui.org/f32"
 	"gioui.org/op"
 	"gioui.org/unit"
 )
@@ -66,6 +67,20 @@ func Exact(size image.Point) Constraints {
 	}
 }
 
+// FPt converts an point to a f32.Point.
+func FPt(p image.Point) f32.Point {
+	return f32.Point{
+		X: float32(p.X), Y: float32(p.Y),
+	}
+}
+
+// FRect converts a rectangle to a f32.Rectangle.
+func FRect(r image.Rectangle) f32.Rectangle {
+	return f32.Rectangle{
+		Min: FPt(r.Min), Max: FPt(r.Max),
+	}
+}
+
 // Constrain a size so each dimension is in the range [min;max].
 func (c Constraints) Constrain(size image.Point) image.Point {
 	if min := c.Min.X; size.X < min {