Issue #212: Add possibility to configure alpha of description text. (#…

…213)

* Issue #212: Add possibility to configure alpha of description text.

* Add possibility to configure alpha of description text.

taptargetview/src/main/java/com/getkeepsafe/taptargetview/TapTarget.java

@@ -82,6 +82,7 @@ public class TapTarget {
   boolean cancelable = true;
   boolean tintTarget = true;
   boolean transparentTarget = false;
+  float descriptionTextAlpha = 0.54f;
 
   /**
    * Return a tap target for the overflow button from the given toolbar
@@ -330,6 +331,15 @@ public TapTarget titleTextDimen(@DimenRes int dimen) {
     return this;
   }
 
+  /** Specify the alpha value [0.0, 1.0] of the description text **/
+  public TapTarget descriptionTextAlpha(float descriptionTextAlpha) {
+    if (descriptionTextAlpha < 0 || descriptionTextAlpha > 1f) {
+      throw new IllegalArgumentException("Given an invalid alpha value: " + descriptionTextAlpha);
+    }
+    this.descriptionTextAlpha = descriptionTextAlpha;
+    return this;
+  }
+
   /**
    * Specify the text size for the description via a dimen resource
    * <p>
@@ -414,7 +424,6 @@ public TapTarget targetRadius(int targetRadius) {
     return this;
   }
 
-
   /** Return the id associated with this tap target **/
   public int id() {
     return id;

taptargetview/src/main/java/com/getkeepsafe/taptargetview/TapTargetView.java

@@ -665,7 +665,7 @@ protected void onDraw(Canvas c) {
 
       if (descriptionLayout != null && titleLayout != null) {
         c.translate(0, titleLayout.getHeight() + TEXT_SPACING);
-        descriptionPaint.setAlpha((int) (0.54f * textAlpha));
+        descriptionPaint.setAlpha((int) (target.descriptionTextAlpha * textAlpha));
         descriptionLayout.draw(c);
       }
     }