style: unit conversion

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

1 files changed, 106 insertions, 3 deletions

diff --git a/style/style.go b/style/style.go
index 5b74952..fe10833 100644
--- a/style/style.go
+++ b/style/style.go
@@ -1,22 +1,125 @@
 package style
 
 import (
+	"fmt"
+
 	"golang.org/x/exp/shiny/unit"
+	"golang.org/x/image/font"
+	"golang.org/x/image/font/opentype"
 	"golang.org/x/image/math/fixed"
 )
 
-// TODO
+const (
+	DefaultFontSize = 12.0 // points (1/72")
+	DefaultDpi      = 72.0 // dots per inch
+	DefaultHinting  = font.HintingFull
+)
+
+// Style defines the colors and font faces that widgets are drawn with.
 type Style struct {
+	font     *opentype.Font
+	faceOpts opentype.FaceOptions
+	face     font.Face // for measurements
+
+	// TODO
+}
+
+// New returns a new Style with the given options.
+// The Style should be closed after use.
+func New(opts ...Option) (*Style, error) {
+	o := parseOpts(opts...)
+
+	fnt, err := opentype.Parse(o.font)
+	if err != nil {
+		return nil, err
+	}
+	face, err := opentype.NewFace(fnt, &o.FaceOptions)
+	if err != nil {
+		return nil, err
+	}
+
+	return &Style{
+		fnt,
+		o.FaceOptions,
+		face,
+	}, nil
+}
+
+func (s *Style) Close() error {
+	return s.face.Close()
+}
+
+// NewFace returns a new font.Face using the Style's Font and FaceOptions.
+func (s *Style) NewFace() (font.Face, error) {
+	return opentype.NewFace(s.font, &s.faceOpts)
 }
 
 // Convert implements the golang.org/x/exp/shiny/unit.Converter
 // interface.
 func (s *Style) Convert(v unit.Value, to unit.Unit) unit.Value {
-	// TODO
+	px := fixed26ToFloat(s.Pixels(v))
+	var f float64
+	switch to {
+	case unit.Px:
+		f = px
+	case unit.Dp:
+		f = s.pixelsToInches(px) * unit.DensityIndependentPixelsPerInch
+	case unit.Pt:
+		f = s.pixelsToInches(px) * unit.PointsPerInch
+	case unit.Mm:
+		f = s.pixelsToInches(px) * unit.MillimetresPerInch
+	case unit.In:
+		f = s.pixelsToInches(px)
+	case unit.Em:
+		f = px / fixed26ToFloat(s.face.Metrics().Height)
+	case unit.Ex:
+		f = px / fixed26ToFloat(s.face.Metrics().XHeight)
+	case unit.Ch:
+		f = px / fixed26ToFloat(s.zeroWidth())
+	default:
+		panic(fmt.Sprintf("unreachable: impossible %T: %v", to, to))
+	}
+	return unit.Value{f, to}
 }
 
 // Pixels implements the golang.org/x/exp/shiny/unit.Converter
 // interface.
 func (s *Style) Pixels(v unit.Value) fixed.Int26_6 {
-	// TODO
+	f := floatToFixed26(v.F)
+	switch v.U {
+	case unit.Px:
+		return f
+	case unit.Dp:
+		return s.inchesToPixels(v.F / unit.DensityIndependentPixelsPerInch)
+	case unit.Pt:
+		return s.inchesToPixels(v.F / unit.PointsPerInch)
+	case unit.Mm:
+		return s.inchesToPixels(v.F / unit.MillimetresPerInch)
+	case unit.In:
+		return s.inchesToPixels(v.F)
+	case unit.Em:
+		return f.Mul(s.face.Metrics().Height)
+	case unit.Ex:
+		return f.Mul(s.face.Metrics().XHeight)
+	case unit.Ch:
+		return f.Mul(s.zeroWidth())
+	default:
+		panic(fmt.Sprintf("unreachable: impossible %T: %v", v.U, v.U))
+	}
+}
+
+func (s *Style) pixelsToInches(px float64) (in float64) {
+	return px / s.faceOpts.DPI
+}
+
+func (s *Style) inchesToPixels(in float64) (px fixed.Int26_6) {
+	return floatToFixed26(in * s.faceOpts.DPI)
+}
+
+func (s *Style) zeroWidth() (px fixed.Int26_6) {
+	if advance, ok := s.face.GlyphAdvance('0'); ok {
+		return advance
+	} else {
+		return floatToFixed26(0.5).Mul(s.face.Metrics().Height) // 0.5em
+	}
 }