From a494211e737eb47ffb135400f757a44fae16016f Mon Sep 17 00:00:00 2001
From: Paul Davis <paul@linuxaudiosystems.com>
Date: Fri, 19 Dec 2014 09:53:26 -0500
Subject: [PATCH] add ArdourCanvas::change_alpha()

Time to move away from rgba macros
---
 libs/canvas/canvas/colors.h | 2 ++
 libs/canvas/colors.cc       | 6 ++++++
 2 files changed, 8 insertions(+)

diff --git a/libs/canvas/canvas/colors.h b/libs/canvas/canvas/colors.h
index 526eb991e2..87901b4586 100644
--- a/libs/canvas/canvas/colors.h
+++ b/libs/canvas/canvas/colors.h
@@ -31,6 +31,8 @@ namespace ArdourCanvas
 struct LIBCANVAS_API HSV;
 struct LIBCANVAS_API HSVA;
 
+extern LIBCANVAS_API Color change_alpha (Color, double alpha);
+
 extern LIBCANVAS_API Color hsva_to_color (double h, double s, double v, double a = 1.0);
 extern LIBCANVAS_API void  color_to_hsva (Color color, double& h, double& s, double& v, double& a);
 extern LIBCANVAS_API void  color_to_hsv (Color color, double& h, double& s, double& v);
diff --git a/libs/canvas/colors.cc b/libs/canvas/colors.cc
index b96c609a85..d83c471c2f 100644
--- a/libs/canvas/colors.cc
+++ b/libs/canvas/colors.cc
@@ -35,6 +35,12 @@ using namespace ArdourCanvas;
 using std::max;
 using std::min;
 
+ArdourCanvas::Color
+change_alpha (Color c, double a)
+{
+	return ((c & ~0xff) | (lrintf (a*255.0) & 0xff));
+}
+
 void
 ArdourCanvas::color_to_hsv (Color color, double& h, double& s, double& v)
 {