unit: add PxToDp and PxToSp

PxToDp and PxToSp are useful when you are trying to calculate
text-size or widget size based on dynamically sized container.

Signed-off-by: Egon Elbre <egonelbre@gmail.com>

unit/unit.go

@@ -60,6 +60,16 @@ func (c Metric) SpToDp(v Sp) Dp {
 	return Dp(float32(v) * nonZero(c.PxPerSp) / nonZero(c.PxPerDp))
 }
 
+// PxToSp converts v px to sp.
+func (c Metric) PxToSp(v int) Sp {
+	return Sp(float32(v) / nonZero(c.PxPerSp))
+}
+
+// PxToDp converts v px to dp.
+func (c Metric) PxToDp(v int) Dp {
+	return Dp(float32(v) / nonZero(c.PxPerDp))
+}
+
 func nonZero(v float32) float32 {
 	if v == 0. {
 		return 1

unit/unit_test.go

@@ -29,4 +29,20 @@ func TestMetric_DpToSp(t *testing.T) {
 			t.Errorf("SpToDp conversion mismatch %v != %v", exp, got)
 		}
 	}
+
+	{
+		exp := unit.Dp(5)
+		got := m.PxToDp(m.Dp(5))
+		if got != exp {
+			t.Errorf("PxToDp conversion mismatch %v != %v", exp, got)
+		}
+	}
+
+	{
+		exp := unit.Sp(5)
+		got := m.PxToSp(m.Sp(5))
+		if got != exp {
+			t.Errorf("PxToSp conversion mismatch %v != %v", exp, got)
+		}
+	}
 }