style: unit conversion

Implemented the golang.org/x/exp/shiny/unit.Converter interface on
style.Style.

1 files changed, 202 insertions, 0 deletions

diff --git a/style/style_test.go b/style/style_test.go
new file mode 100644
index 0000000..14f00e2
--- /dev/null
+++ b/style/style_test.go
@@ -0,0 +1,202 @@
+package style
+
+import (
+	"testing"
+
+	"golang.org/x/exp/shiny/unit"
+	"golang.org/x/image/font/gofont/gomono"
+	"golang.org/x/image/math/fixed"
+)
+
+const (
+	dpi     = 150.0
+	epsilon = 0.5 // TODO: optimize precision
+)
+
+var (
+	fontTtf = gomono.TTF
+	units   = []unit.Unit{unit.Px, unit.Dp, unit.Pt, unit.Mm, unit.In, unit.Em, unit.Ex, unit.Ch}
+)
+
+func TestConvert(t *testing.T) {
+	t.Parallel()
+
+	s, err := New(Font(fontTtf), Dpi(dpi))
+	if err != nil {
+		t.Error(err)
+	}
+	defer func() {
+		if err := s.Close(); err != nil {
+			t.Fatal(err)
+		}
+	}()
+
+	// Trivial
+	for _, from := range units {
+		for _, to := range units {
+			testConvert(t, s, unit.Value{0, from}, to, 0)
+		}
+	}
+
+	pxPerEm := fixed26ToFloat(s.face.Metrics().Height)
+	pxPerEx := fixed26ToFloat(s.face.Metrics().XHeight)
+	advance, ok := s.face.GlyphAdvance('0')
+	if !ok {
+		t.Fail()
+	}
+	pxPerCh := fixed26ToFloat(advance)
+
+	// px → all
+	px := 123.4
+	in := px / dpi
+	from := unit.Value{px, unit.Px}
+	testConvert(t, s, from, unit.Px, px)
+	testConvert(t, s, from, unit.Dp, in*160)
+	testConvert(t, s, from, unit.Pt, in*72)
+	testConvert(t, s, from, unit.Mm, in*25.4)
+	testConvert(t, s, from, unit.In, in)
+	testConvert(t, s, from, unit.Em, px/pxPerEm)
+	testConvert(t, s, from, unit.Ex, px/pxPerEx)
+	testConvert(t, s, from, unit.Ch, px/pxPerCh)
+
+	// dp → all
+	dp := 123.4
+	in = dp / 160
+	px = in * dpi
+	from = unit.Value{dp, unit.Dp}
+	testConvert(t, s, from, unit.Px, px)
+	testConvert(t, s, from, unit.Dp, dp)
+	testConvert(t, s, from, unit.Pt, in*72)
+	testConvert(t, s, from, unit.Mm, in*25.4)
+	testConvert(t, s, from, unit.In, in)
+	testConvert(t, s, from, unit.Em, px/pxPerEm)
+	testConvert(t, s, from, unit.Ex, px/pxPerEx)
+	testConvert(t, s, from, unit.Ch, px/pxPerCh)
+
+	// Pt → all
+	pt := 123.4
+	in = pt / 72
+	px = in * dpi
+	from = unit.Value{pt, unit.Pt}
+	testConvert(t, s, from, unit.Px, px)
+	testConvert(t, s, from, unit.Dp, in*160)
+	testConvert(t, s, from, unit.Pt, pt)
+	testConvert(t, s, from, unit.Mm, in*25.4)
+	testConvert(t, s, from, unit.In, in)
+	testConvert(t, s, from, unit.Em, px/pxPerEm)
+	testConvert(t, s, from, unit.Ex, px/pxPerEx)
+	testConvert(t, s, from, unit.Ch, px/pxPerCh)
+
+	// Mm → all
+	mm := 123.4
+	in = mm / 25.4
+	px = in * dpi
+	from = unit.Value{mm, unit.Mm}
+	testConvert(t, s, from, unit.Px, px)
+	testConvert(t, s, from, unit.Dp, in*160)
+	testConvert(t, s, from, unit.Pt, in*72)
+	testConvert(t, s, from, unit.Mm, mm)
+	testConvert(t, s, from, unit.In, in)
+	testConvert(t, s, from, unit.Em, px/pxPerEm)
+	testConvert(t, s, from, unit.Ex, px/pxPerEx)
+	testConvert(t, s, from, unit.Ch, px/pxPerCh)
+
+	// In → all
+	in = 123.4
+	px = in * dpi
+	from = unit.Value{in, unit.In}
+	testConvert(t, s, from, unit.Px, px)
+	testConvert(t, s, from, unit.Dp, in*160)
+	testConvert(t, s, from, unit.Pt, in*72)
+	testConvert(t, s, from, unit.Mm, in*25.4)
+	testConvert(t, s, from, unit.In, in)
+	testConvert(t, s, from, unit.Em, px/pxPerEm)
+	testConvert(t, s, from, unit.Ex, px/pxPerEx)
+	testConvert(t, s, from, unit.Ch, px/pxPerCh)
+
+	// Em → all
+	em := 123.4
+	px = em * pxPerEm
+	in = px / dpi
+	from = unit.Value{em, unit.Em}
+	testConvert(t, s, from, unit.Px, px)
+	testConvert(t, s, from, unit.Dp, in*160)
+	testConvert(t, s, from, unit.Pt, in*72)
+	testConvert(t, s, from, unit.Mm, in*25.4)
+	testConvert(t, s, from, unit.In, in)
+	testConvert(t, s, from, unit.Em, em)
+	testConvert(t, s, from, unit.Ex, px/pxPerEx)
+	testConvert(t, s, from, unit.Ch, px/pxPerCh)
+
+	// Ex → all
+	ex := 123.4
+	px = ex * pxPerEx
+	in = px / dpi
+	from = unit.Value{ex, unit.Ex}
+	testConvert(t, s, from, unit.Px, px)
+	testConvert(t, s, from, unit.Dp, in*160)
+	testConvert(t, s, from, unit.Pt, in*72)
+	testConvert(t, s, from, unit.Mm, in*25.4)
+	testConvert(t, s, from, unit.In, in)
+	testConvert(t, s, from, unit.Em, px/pxPerEm)
+	testConvert(t, s, from, unit.Ex, ex)
+	testConvert(t, s, from, unit.Ch, px/pxPerCh)
+
+	// Ch → all
+	ch := 123.4
+	px = ch * pxPerCh
+	in = px / dpi
+	from = unit.Value{ch, unit.Ch}
+	testConvert(t, s, from, unit.Px, px)
+	testConvert(t, s, from, unit.Dp, in*160)
+	testConvert(t, s, from, unit.Pt, in*72)
+	testConvert(t, s, from, unit.Mm, in*25.4)
+	testConvert(t, s, from, unit.In, in)
+	testConvert(t, s, from, unit.Em, px/pxPerEm)
+	testConvert(t, s, from, unit.Ex, px/pxPerEx)
+	testConvert(t, s, from, unit.Ch, ch)
+}
+
+func testConvert(t *testing.T, s *Style, from unit.Value, to unit.Unit, want float64) {
+	out := s.Convert(from, to)
+	if out.U != to || out.F < want-epsilon || out.F > want+epsilon {
+		t.Errorf("Convert(%v, %v) = %v; want %v", from, to, out, unit.Value{want, to})
+	}
+}
+
+func TestPixels(t *testing.T) {
+	t.Parallel()
+
+	s, err := New(Font(fontTtf), Dpi(dpi))
+	if err != nil {
+		t.Error(err)
+	}
+	defer func() {
+		if err := s.Close(); err != nil {
+			t.Fatal(err)
+		}
+	}()
+
+	for _, u := range units {
+		testPixels(t, s, unit.Value{0, u}, 0)
+	}
+	testPixels(t, s, unit.Value{123.4, unit.Px}, floatToFixed26(123.4))
+	testPixels(t, s, unit.Value{123.4, unit.Dp}, floatToFixed26(123.4/160*dpi))
+	testPixels(t, s, unit.Value{123.4, unit.Pt}, floatToFixed26(123.4/72*dpi))
+	testPixels(t, s, unit.Value{123.4, unit.Mm}, floatToFixed26(123.4/25.4*dpi))
+	testPixels(t, s, unit.Value{123.4, unit.In}, floatToFixed26(123.4*dpi))
+	testPixels(t, s, unit.Value{123.4, unit.Em}, floatToFixed26(123.4).Mul(s.face.Metrics().Height))
+	testPixels(t, s, unit.Value{123.4, unit.Ex}, floatToFixed26(123.4).Mul(s.face.Metrics().XHeight))
+	if advance, ok := s.face.GlyphAdvance('0'); ok {
+		testPixels(t, s, unit.Value{123.4, unit.Ch}, floatToFixed26(123.4).Mul(advance))
+	} else {
+		t.Fail()
+	}
+}
+
+func testPixels(t *testing.T, s *Style, in unit.Value, want fixed.Int26_6) {
+	out := s.Pixels(in)
+	if out != want {
+		t.Errorf("Pixels(%#v) = %v; want %v", in, out, want)
+	}
+}