improve unit conversions

6 files changed, 76 insertions, 86 deletions

diff --git a/compressor/compressor.go b/compressor/compressor.go
index ca5a0af..9e03cbb 100644
--- a/compressor/compressor.go
+++ b/compressor/compressor.go
@@ -93,7 +93,7 @@ func init() {
 		if err != nil {
 			return err
 		}
-		c.MaxFlow = mass.FlowRate{flow.FlowVal, u}
+		c.MaxFlow = mass.NewFlowRate(flow.FlowVal, u)
 
 		compressors[man][ser][mod] = c
 
diff --git a/main.go b/main.go
index b7d3206..83368dc 100644
--- a/main.go
+++ b/main.go
@@ -7,7 +7,6 @@ import (
 	"image/draw"
 	_ "image/jpeg"
 	"os"
-	"time"
 
 	"github.com/sam-anthony/volute/compressor"
 	"github.com/sam-anthony/volute/mass"
@@ -26,21 +25,21 @@ const (
 var numPoints = 1
 
 var (
-	displacement = volume.Volume{2000, volume.CubicCentimetre}
-	// selectedVolumeUnit is used to index volume.UnitStrings().
-	selectedVolumeUnit = volume.DefaultUnitIndex
+	displacement = volume.New(2000, volume.CubicCentimetre)
+	// volumeUnitIndex is used to index volume.UnitStrings().
+	volumeUnitIndex = volume.DefaultUnitIndex
 
 	engineSpeed = []int32{2000}
 
 	volumetricEfficiency = []int32{80}
 
 	intakeAirTemperature = []temperature.Temperature{{25, temperature.Celcius}}
-	// selectedTemperatureUnit is used to index temperature.UnitStrings().
-	selectedTemperatureUnit = temperature.DefaultUnitIndex
+	// temperatureUnitIndex is used to index temperature.UnitStrings().
+	temperatureUnitIndex = temperature.DefaultUnitIndex
 
-	manifoldPressure = []pressure.Pressure{{100, pressure.DefaultUnit}}
-	// selectedPressureUnit is used to index pressure.UnitStrings().
-	selectedPressureUnit = pressure.DefaultUnitIndex
+	manifoldPressure = []pressure.Pressure{pressure.Atmospheric()}
+	// pressureUnitIndex is used to index pressure.UnitStrings().
+	pressureUnitIndex = pressure.DefaultUnitIndex
 )
 
 var pressureRatio []float32
@@ -74,13 +73,7 @@ func massFlowRateAt(point int) mass.FlowRate {
 
 	kgPerMin := molsPerMin * airMolarMass
 
-	massPerMin := mass.Mass{kgPerMin, mass.Kilogram}
-
-	u, err := mass.FlowRateUnitFromString(mass.FlowRateUnitStrings()[selectedMassFlowRateUnit])
-	util.Check(err)
-
-	mfr, err := mass.NewFlowRate(massPerMin, time.Minute, u)
-	util.Check(err)
+	mfr := mass.NewFlowRate(kgPerMin/60.0, mass.KilogramsPerSecond)
 	return mfr
 }
 func init() {
diff --git a/mass/mass.go b/mass/mass.go
index 29ecbd5..6e9f670 100644
--- a/mass/mass.go
+++ b/mass/mass.go
@@ -3,7 +3,6 @@ package mass
 import (
 	"errors"
 	"fmt"
-	"time"
 )
 
 type unit float32
@@ -15,13 +14,15 @@ const (
 )
 
 type Mass struct {
-	Val  float32
-	Unit unit
+	val float32
+}
+
+func New(i float32, u unit) Mass {
+	return Mass{i * float32(u)}
 }
 
 func (m Mass) AsUnit(u unit) float32 {
-	g := m.Val * float32(m.Unit) // Convert to grams.
-	return g / float32(u)        // Convert to desired unit.
+	return m.val / float32(u)
 }
 
 type flowRateUnit float32
@@ -53,34 +54,18 @@ func FlowRateUnitFromString(s string) (flowRateUnit, error) {
 		return PoundsPerMinute, nil
 	default:
 		return *new(flowRateUnit), errors.New(
-			fmt.Sprintf("invalid massFlowRateUnit: '%s'", s))
+			fmt.Sprintf("invalid mass flow rate unit: '%s'", s))
 	}
 }
 
 type FlowRate struct {
-	Val  float32
-	Unit flowRateUnit
+	val float32
 }
 
-func NewFlowRate(m Mass, t time.Duration, u flowRateUnit) (FlowRate, error) {
-	switch u {
-	case KilogramsPerSecond:
-		return FlowRate{
-			m.AsUnit(Kilogram) / float32(t.Seconds()),
-			u,
-		}, nil
-	case PoundsPerMinute:
-		return FlowRate{
-			m.AsUnit(Pound) / float32(t.Minutes()),
-			u,
-		}, nil
-	default:
-		return *new(FlowRate), errors.New(
-			fmt.Sprintf("invalid massFlowRateUnit: '%v'", u))
-	}
+func NewFlowRate(i float32, u flowRateUnit) FlowRate {
+	return FlowRate{i * float32(u)}
 }
 
 func (fr FlowRate) AsUnit(u flowRateUnit) float32 {
-	kgps := fr.Val * float32(fr.Unit) // Convert to kilogramsPerSecond.
-	return kgps / float32(u)          // Convert to desired unit.
+	return fr.val / float32(u)
 }
diff --git a/pressure/pressure.go b/pressure/pressure.go
index 2948c72..b3063cc 100644
--- a/pressure/pressure.go
+++ b/pressure/pressure.go
@@ -44,15 +44,17 @@ func UnitFromString(s string) (unit, error) {
 }
 
 type Pressure struct {
-	Val  float32
-	Unit unit
+	val float32
+}
+
+func New(i float32, u unit) Pressure {
+	return Pressure{i * float32(u)}
 }
 
 func (p Pressure) AsUnit(u unit) float32 {
-	pa := p.Val * float32(p.Unit) // Convert to pascals.
-	return pa / float32(u)        // Convert to desired unit.
+	return p.val / float32(u)
 }
 
 func Atmospheric() Pressure {
-	return Pressure{1, Bar}
+	return Pressure{float32(1 * Bar)}
 }
diff --git a/ui.go b/ui.go
index 1ee281d..f4b0a0d 100644
--- a/ui.go
+++ b/ui.go
@@ -21,9 +21,14 @@ func red() color.RGBA {
 }
 
 func engineDisplacementRow() *g.RowWidget {
+	s := volume.UnitStrings()[volumeUnitIndex]
+	unit, err := volume.UnitFromString(s)
+	util.Check(err)
+	engDisp := displacement.AsUnit(unit)
 	return g.Row(
 		g.Label("Engine Displacement"),
-		g.InputFloat(&displacement.Val).Format("%.2f").OnChange(func() {
+		g.InputFloat(&engDisp).Format("%.2f").OnChange(func() {
+			displacement = volume.New(engDisp, unit)
 			for i := 0; i < numPoints; i++ {
 				engineMassFlowRate[i] = massFlowRateAt(i)
 				go updateCompImg()
@@ -31,17 +36,14 @@ func engineDisplacementRow() *g.RowWidget {
 		}),
 		g.Combo(
 			"",
-			volume.UnitStrings()[selectedVolumeUnit],
+			volume.UnitStrings()[volumeUnitIndex],
 			volume.UnitStrings(),
-			&selectedVolumeUnit,
+			&volumeUnitIndex,
 		).OnChange(func() {
-			s := volume.UnitStrings()[selectedVolumeUnit]
-			u, err := volume.UnitFromString(s)
-			util.Check(err)
-			displacement = volume.Volume{
-				displacement.AsUnit(u),
-				u,
-			}
+			displacement = volume.New(
+				displacement.AsUnit(unit),
+				unit,
+			)
 		}),
 	)
 }
@@ -87,11 +89,11 @@ func intakeAirTemperatureRow() *g.TableRowWidget {
 		g.Label("Intake Air Temperature"),
 		g.Combo(
 			"",
-			temperature.UnitStrings()[selectedTemperatureUnit],
+			temperature.UnitStrings()[temperatureUnitIndex],
 			temperature.UnitStrings(),
-			&selectedTemperatureUnit,
+			&temperatureUnitIndex,
 		).OnChange(func() {
-			s := temperature.UnitStrings()[selectedTemperatureUnit]
+			s := temperature.UnitStrings()[temperatureUnitIndex]
 			u, err := temperature.UnitFromString(s)
 			util.Check(err)
 
@@ -118,32 +120,34 @@ func intakeAirTemperatureRow() *g.TableRowWidget {
 }
 
 func manifoldPressureRow() *g.TableRowWidget {
+	s := pressure.UnitStrings()[pressureUnitIndex]
+	unit, err := pressure.UnitFromString(s)
+	util.Check(err)
+
 	widgets := []g.Widget{
 		g.Label("Manifold Absolute Pressure"),
 		g.Combo(
 			"",
-			pressure.UnitStrings()[selectedPressureUnit],
+			pressure.UnitStrings()[pressureUnitIndex],
 			pressure.UnitStrings(),
-			&selectedPressureUnit,
+			&pressureUnitIndex,
 		).OnChange(func() {
-			s := pressure.UnitStrings()[selectedPressureUnit]
-			u, err := pressure.UnitFromString(s)
-			util.Check(err)
-
 			for i := 0; i < numPoints; i++ {
-				manifoldPressure[i] = pressure.Pressure{
-					manifoldPressure[i].AsUnit(u),
-					u,
-				}
+				manifoldPressure[i] = pressure.New(
+					manifoldPressure[i].AsUnit(unit),
+					unit,
+				)
 			}
 		}),
 	}
 	for i := 0; i < numPoints; i++ {
 		i := i
+		manPres := manifoldPressure[i].AsUnit(unit)
 		widgets = append(
 			widgets,
-			g.InputFloat(&manifoldPressure[i].Val).Format("%.2f").
+			g.InputFloat(&manPres).Format("%.2f").
 				OnChange(func() {
+					manifoldPressure[i] = pressure.New(manPres, unit)
 					pressureRatio[i] = pressureRatioAt(i)
 					engineMassFlowRate[i] = massFlowRateAt(i)
 					go updateCompImg()
@@ -169,6 +173,10 @@ func pressureRatioRow() *g.TableRowWidget {
 }
 
 func massFlowRateRow() *g.TableRowWidget {
+	s := mass.FlowRateUnitStrings()[selectedMassFlowRateUnit]
+	mfrUnit, err := mass.FlowRateUnitFromString(s)
+	util.Check(err)
+
 	widgets := []g.Widget{
 		g.Label("Mass Flow Rate"),
 		g.Combo(
@@ -177,21 +185,17 @@ func massFlowRateRow() *g.TableRowWidget {
 			mass.FlowRateUnitStrings(),
 			&selectedMassFlowRateUnit,
 		).OnChange(func() {
-			s := mass.FlowRateUnitStrings()[selectedMassFlowRateUnit]
-			u, err := mass.FlowRateUnitFromString(s)
-			util.Check(err)
-
 			for i := 0; i < numPoints; i++ {
-				engineMassFlowRate[i] = mass.FlowRate{
-					engineMassFlowRate[i].AsUnit(u),
-					u,
-				}
+				engineMassFlowRate[i] = mass.NewFlowRate(
+					engineMassFlowRate[i].AsUnit(mfrUnit),
+					mfrUnit,
+				)
 			}
 		}),
 	}
 	for i := 0; i < numPoints; i++ {
 		mfr := strconv.FormatFloat(
-			float64(engineMassFlowRate[i].Val),
+			float64(engineMassFlowRate[i].AsUnit(mfrUnit)),
 			'f',
 			3,
 			32,
@@ -321,15 +325,19 @@ func updateCompImg() {
 	for i := 0; i < numPoints; i++ {
 		min := selectedCompressor.MinX
 		max := selectedCompressor.MaxX
-		unit := selectedCompressor.MaxFlow.Unit
+
+		unit := mass.KilogramsPerSecond
 		mfr := engineMassFlowRate[i].AsUnit(unit)
 		maxMfr := selectedCompressor.MaxFlow.AsUnit(unit)
+
 		x := min + int(float32(max-min)*(mfr/maxMfr))
 
 		min = selectedCompressor.MinY
 		max = selectedCompressor.MaxY
+
 		pr := pressureRatio[i]
 		maxPr := selectedCompressor.MaxPR
+
 		y := min - int(float32((min-max))*((pr-1.0)/(maxPr-1.0)))
 
 		ps := m.Bounds().Dx() / 100 // Point size
diff --git a/volume/volume.go b/volume/volume.go
index 020d1a6..acec040 100644
--- a/volume/volume.go
+++ b/volume/volume.go
@@ -44,11 +44,13 @@ func UnitFromString(s string) (unit, error) {
 }
 
 type Volume struct {
-	Val  float32
-	Unit unit
+	val float32
+}
+
+func New(i float32, u unit) Volume {
+	return Volume{i * float32(u)}
 }
 
 func (v Volume) AsUnit(u unit) float32 {
-	cc := v.Val * float32(v.Unit) // Convert to cubic centimetres.
-	return cc / float32(u)        // Convert to desired unit.
+	return v.val / float32(u)
 }