IDEA-187834 Replace translucent text rendering in tab pane with opaque

Used premultiplied alpha and srcOver rules to replace translucent text

platform/platform-api/src/com/intellij/ui/SimpleColoredComponent.java

@@ -830,7 +830,7 @@ public class SimpleColoredComponent extends JComponent implements Accessible, Co
 
       if (!secondPass) {
         if (shouldDrawMacShadow()) {
-          g.setColor(SHADOW_COLOR);
+          g.setColor(ColorUtil.srcOver(SHADOW_COLOR, getBackground()));
           doDrawString(g, i, offset, textBaseline + 1);
         }
 

platform/platform-api/src/com/intellij/ui/tabs/impl/singleRow/MoreTabsIcon.java

@@ -52,7 +52,7 @@ public abstract class MoreTabsIcon {
                                         iconX + AllIcons.General.MoreTabs.getIconWidth() + 2,
                                         iconY + AllIcons.General.MoreTabs.getIconHeight() - 5,
                                         JBColor.BLACK,
-                                        ColorUtil.withAlpha(JBColor.WHITE, .9));
+                                        ColorUtil.withPreAlpha(JBColor.WHITE, .9));
     } finally {
       g.dispose();
     }

platform/util/src/com/intellij/ui/ColorUtil.java

@@ -32,6 +32,7 @@ import java.lang.annotation.Annotation;
  * @author max
  * @author Konstantin Bulenkov
  */
+@SuppressWarnings("UseJBColor")
 public class ColorUtil {
   private ColorUtil() {
   }
@@ -126,6 +127,26 @@ public class ColorUtil {
     return toAlpha(c, (int)(255 * a));
   }
 
+  public static Color srcOver(Color c, Color b) {
+    float [] rgba = new float[4];
+    float [] brgba = new float[4];
+
+    rgba = c.getRGBComponents(rgba);
+    brgba = b.getRGBComponents(brgba);
+    float dsta = 1.0f - rgba[3];
+    // Applying SrcOver rule
+    return new Color(rgba[0]*rgba[3] + dsta*brgba[0],
+                     rgba[1]*rgba[3] + dsta*brgba[1],
+                     rgba[2]*rgba[3] + dsta*brgba[2], 1.0f);
+  }
+
+  public static Color withPreAlpha(Color c, double a) {
+    float [] rgba = new float[4];
+
+    rgba = withAlpha(c, a).getRGBComponents(rgba);
+    return new Color(rgba[0]*rgba[3], rgba[1]*rgba[3], rgba[2]*rgba[3], 1.0f);
+  }
+
   public static Color toAlpha(Color color, int a) {
     Color c = color != null ? color : Color.black;
     return new Color(c.getRed(), c.getGreen(), c.getBlue(), a);