Fix #23926: Extend GPS legend for time information, improve design (p…

…atch by Pauline, modified)

Modifications are as follows:
* Reduction of code duplication
* Addition of functions in ColorHelper to calculate contrast ratios

git-svn-id: https://josm.openstreetmap.de/svn/trunk@19236 0c6e7542-c601-0410-84e7-c038aed88b3b

src/org/openstreetmap/josm/gui/layer/gpx/GpxDrawHelper.java

@@ -236,24 +236,30 @@ public class GpxDrawHelper implements SoMChangeListener, MapViewPaintable.LayerP
     // The heat map was invalidated since the last draw.
     private boolean gpxLayerInvalidated;
 
+    /** minTime saves the start time of the track as epoch seconds */
+    private double minTime;
+    /** maxTime saves the end time of the track as epoch seconds */
+    private double maxTime;
+
+
     private void setupColors() {
         hdopAlpha = Config.getPref().getInt("hdop.color.alpha", -1);
         velocityScale = ColorScale.createHSBScale(256);
         /* Colors (without custom alpha channel, if given) for HDOP painting. */
         hdopScale = ColorScale.createHSBScale(256).makeReversed().addTitle(tr("HDOP"));
         qualityScale = ColorScale.createFixedScale(rtkLibQualityColors).addTitle(tr("Quality")).addColorBarTitles(rtkLibQualityNames);
-        fixScale = ColorScale.createFixedScale(gpsFixQualityColors).addTitle(tr("GPS fix")).addColorBarTitles(gpsFixQualityNames);
-        refScale = ColorScale.createCyclicScale(1).addTitle(tr("GPS ref"));
-        dateScale = ColorScale.createHSBScale(256).addTitle(tr("Time"));
-        directionScale = ColorScale.createCyclicScale(256).setIntervalCount(4).addTitle(tr("Direction"));
+        fixScale = ColorScale.createFixedScale(gpsFixQualityColors).addTitle(tr("GPS fix value")).addColorBarTitles(gpsFixQualityNames);
+        refScale = ColorScale.createCyclicScale(1).addTitle(tr("GPS Ref-ID"));
+        dateScale = ColorScale.createHSBScale(256).addTitle(tr("Track date"));
+        directionScale = ColorScale.createCyclicScale(256).setIntervalCount(4).addTitle(tr("Direction [°]"));
 
         systemOfMeasurementChanged(null, null);
     }
 
     @Override
     public void systemOfMeasurementChanged(String oldSoM, String newSoM) {
         SystemOfMeasurement som = SystemOfMeasurement.getSystemOfMeasurement();
-        velocityScale.addTitle(tr("Velocity, {0}", som.speedName));
+        velocityScale.addTitle(tr("Velocity [{0}]", som.speedName));
         layer.invalidate();
     }
 
@@ -622,6 +628,9 @@ public void calculateColors() {
             Interval interval = data.getMinMaxTimeForAllTracks().orElse(new Interval(Instant.EPOCH, Instant.now()));
             minval = interval.getStart().getEpochSecond();
             maxval = interval.getEnd().getEpochSecond();
+            this.minTime = minval;
+            this.maxTime = maxval;
+
             dateScale.setRange(minval, maxval);
         }
 
@@ -641,7 +650,7 @@ public void calculateColors() {
             if (!refs.isEmpty()) {
                 Collections.sort(refs);
                 String[] a = {};
-                refScale = ColorScale.createCyclicScale(refs.size()).addTitle(tr("GPS ref")).addColorBarTitles(refs.toArray(a));
+                refScale = ColorScale.createCyclicScale(refs.size()).addTitle(tr("GPS ref ID")).addColorBarTitles(refs.toArray(a));
                 refScale.setRange(0, refs.size());
             }
         }
@@ -1618,18 +1627,20 @@ public void drawColorBar(Graphics2D g, MapView mv) {
         g.setComposite(AlphaComposite.SrcOver.derive(1.00f));
 
         if (colored == ColorMode.HDOP) {
-            hdopScale.drawColorBar(g, w-30, 50, 20, 100, 1.0);
+            hdopScale.drawColorBar(g, w-10, 50, 20, 100, 1.0);
         } else if (colored == ColorMode.QUALITY) {
-            qualityScale.drawColorBar(g, w-30, 50, 20, 100, 1.0);
+            qualityScale.drawColorBar(g, w-10, 50, 20, 100, 1.0);
         } else if (colored == ColorMode.FIX) {
-            fixScale.drawColorBar(g, w-30, 50, 20, 175, 1.0);
+            fixScale.drawColorBar(g, w-10, 50, 20, 175, 1.0);
         } else if (colored == ColorMode.REF) {
-            refScale.drawColorBar(g, w-30, 50, 20, 175, 1.0);
+            refScale.drawColorBar(g, w-10, 50, 20, 175, 1.0);
         } else if (colored == ColorMode.VELOCITY) {
             SystemOfMeasurement som = SystemOfMeasurement.getSystemOfMeasurement();
-            velocityScale.drawColorBar(g, w-30, 50, 20, 100, som.speedValue);
+            velocityScale.drawColorBar(g, w-10, 50, 20, 100, som.speedValue);
         } else if (colored == ColorMode.DIRECTION) {
-            directionScale.drawColorBar(g, w-30, 50, 20, 100, 180.0/Math.PI);
+            directionScale.drawColorBar(g, w-10, 50, 20, 100, 180.0/Math.PI);
+        } else if (colored == ColorMode.TIME) {
+            dateScale.drawColorBarTime(g, w-10, 50, 20, 100, this.minTime, this.maxTime);
         }
     }
 

src/org/openstreetmap/josm/tools/ColorHelper.java

@@ -73,9 +73,13 @@ public static String color2html(Color color, boolean withAlpha) {
      */
     public static Color getForegroundColor(Color bg) {
         // http://stackoverflow.com/a/3943023/2257172
-        return bg == null ? null :
-              (bg.getRed()*0.299 + bg.getGreen()*0.587 + bg.getBlue()*0.114) > 186 ?
-                  Color.BLACK : Color.WHITE;
+        if (bg == null) {
+            return null;
+        }
+        if (calculateContrastRatio(Color.WHITE, bg) > calculateContrastRatio(Color.BLACK, bg)) {
+            return Color.WHITE;
+        }
+        return Color.BLACK;
     }
 
     /**
@@ -128,4 +132,44 @@ public static Color alphaMultiply(Color color, float alphaFactor) {
     public static Color complement(Color clr) {
         return new Color(255 - clr.getRed(), 255 - clr.getGreen(), 255 - clr.getBlue(), clr.getAlpha());
     }
+
+    /**
+     * Calculate the relative "luminance" of a color. This is mostly useful for choosing background/foreground colours
+     * @see <a href="https://stackoverflow.com/questions/9733288/how-to-programmatically-calculate-the-contrast-ratio-between-two-colors">
+     *     constrast ratio</a>
+     */
+    private static double calculateLuminance(Color color) {
+        final double rs = color.getRed() / 255.0;
+        final double gs = color.getGreen() / 255.0;
+        final double bs = color.getBlue() / 255.0;
+        final double r = calculateLuminanceStepFunction(rs);
+        final double g = calculateLuminanceStepFunction(gs);
+        final double b = calculateLuminanceStepFunction(bs);
+        return 0.2126 * r + 0.7152 * g + 0.0722 * b;
+    }
+
+    /**
+     * This is a step function for {@link #calculateLuminance(Color)}
+     * @param color The color to get the values for
+     * @return The value to use when calculating relative luminance
+     */
+    private static double calculateLuminanceStepFunction(double color) {
+        if (color <= 0.03928) {
+            return color / 12.92;
+        }
+        return Math.pow((color + 0.055) / 1.055, 2.4);
+    }
+
+    /**
+     * Calculate the contrast between two colors (e.g. {@link Color#black} and {@link Color#white}).
+     * @param first The first color to use
+     * @param second The second color to use
+     * @return The contrast ratio ((L1 + 0.05)/(L2 + 0.05))
+     * @since 19236
+     */
+    public static double calculateContrastRatio(Color first, Color second) {
+        final double fL = calculateLuminance(first);
+        final double sL = calculateLuminance(second);
+        return (Math.max(fL, sL) + 0.05) / (Math.min(fL, sL) + 0.05);
+    }
 }