--- /dev/null
+package jalview.renderer.seqfeatures;
+
+import jalview.api.FeatureRenderer;
+import jalview.api.FeaturesDisplayedI;
+import jalview.datamodel.SequenceI;
+import jalview.viewmodel.seqfeatures.FeatureRendererModel;
+
+import java.awt.Color;
+import java.awt.Graphics;
+import java.awt.image.BufferedImage;
+
+/**
+ * A helper class to find feature colour using an associated FeatureRenderer
+ *
+ * @author gmcarstairs
+ *
+ */
+public class FeatureColourFinder
+{
+ /*
+ * the class we delegate feature finding to
+ */
+ private FeatureRenderer featureRenderer;
+
+ /*
+ * a 1-pixel image on which features can be drawn, for the case where
+ * transparency allows 'see-through' of multiple feature colours
+ */
+ private BufferedImage offscreenImage;
+
+ /**
+ * Constructor
+ *
+ * @param fr
+ */
+ public FeatureColourFinder(FeatureRenderer fr)
+ {
+ featureRenderer = fr;
+ offscreenImage = new BufferedImage(1, 1, BufferedImage.TYPE_INT_ARGB);
+ }
+
+ /**
+ * Answers the feature colour to show for the given sequence and column
+ * position. This delegates to the FeatureRenderer to find the colour, which
+ * will depend on feature location, visibility, ordering, colour scheme, and
+ * whether or not transparency is applied. For feature rendering with
+ * transparency, this class provides a dummy 'offscreen' graphics context
+ * where multiple feature colours can be overlaid and the combined colour read
+ * back.
+ * <p>
+ * This method is not thread-safe when transparency is applied, since a shared
+ * BufferedImage would be used by all threads to hold the composite colour at
+ * a position. Each thread should use a separate instance of this class.
+ *
+ * @param defaultColour
+ * @param seq
+ * @param column
+ * alignment column position (base zero)
+ * @return
+ */
+ public Color findFeatureColour(Color defaultColour, SequenceI seq,
+ int column)
+ {
+ if (noFeaturesDisplayed())
+ {
+ return defaultColour;
+ }
+
+ Graphics g = null;
+
+ /*
+ * if transparency applies, provide a notional 1x1 graphics context
+ * that has been primed with the default colour
+ */
+ if (featureRenderer.getTransparency() != 1f)
+ {
+ g = offscreenImage.getGraphics();
+ if (defaultColour != null)
+ {
+ offscreenImage.setRGB(0, 0, defaultColour.getRGB());
+ }
+ }
+
+ Color c = featureRenderer.findFeatureColour(seq, column, g);
+ if (c == null)
+ {
+ return defaultColour;
+ }
+
+ if (g != null)
+ {
+ c = new Color(offscreenImage.getRGB(0, 0));
+ }
+ return c;
+ }
+
+ /**
+ * Answers true if feature display is turned off, or there are no features
+ * configured to be visible
+ *
+ * @return
+ */
+ boolean noFeaturesDisplayed()
+ {
+ if (featureRenderer == null
+ || !featureRenderer.getViewport().isShowSequenceFeatures())
+ {
+ return true;
+ }
+
+ if (!((FeatureRendererModel) featureRenderer).hasRenderOrder())
+ {
+ return true;
+ }
+
+ FeaturesDisplayedI displayed = featureRenderer.getFeaturesDisplayed();
+ if (displayed == null || displayed.getVisibleFeatureCount() == 0)
+ {
+ return true;
+ }
+
+ return false;
+ }
+}