From aca0abf4ea289f0389c8bdbd504da4d8bb368048 Mon Sep 17 00:00:00 2001
From: SaschaZorn <Sascha.Zorn@gmail.com>
Date: Mon, 30 May 2016 11:56:36 +0200
Subject: [PATCH] Define gamma independent color conversions static

Define gamma independent color conversions static and make use
of C++11 constexpr to support constructs like:
class Colors {
  static const uint16_t RED = RGBmatrixPanel::Color333(7,0,0);
  static const uint16_t GREEN = RGBmatrixPanel::Color333(0,6,0);
  static const uint16_t WHITE = RGBmatrixPanel::Color333(7, 7, 7);
}
---
 RGBmatrixPanel.cpp | 22 ----------------------
 RGBmatrixPanel.h   | 33 ++++++++++++++++++++++++++++++---
 2 files changed, 30 insertions(+), 25 deletions(-)

diff --git a/RGBmatrixPanel.cpp b/RGBmatrixPanel.cpp
index 0ddaedd..57130e2 100644
--- a/RGBmatrixPanel.cpp
+++ b/RGBmatrixPanel.cpp
@@ -191,28 +191,6 @@ void RGBmatrixPanel::begin(void) {
 // needed when drawing.  These next functions are mostly here for the
 // benefit of older code using one of the original color formats.
 
-// Promote 3/3/3 RGB to Adafruit_GFX 5/6/5
-uint16_t RGBmatrixPanel::Color333(uint8_t r, uint8_t g, uint8_t b) {
-  // RRRrrGGGgggBBBbb
-  return ((r & 0x7) << 13) | ((r & 0x6) << 10) |
-         ((g & 0x7) <<  8) | ((g & 0x7) <<  5) |
-         ((b & 0x7) <<  2) | ((b & 0x6) >>  1);
-}
-
-// Promote 4/4/4 RGB to Adafruit_GFX 5/6/5
-uint16_t RGBmatrixPanel::Color444(uint8_t r, uint8_t g, uint8_t b) {
-  // RRRRrGGGGggBBBBb
-  return ((r & 0xF) << 12) | ((r & 0x8) << 8) |
-         ((g & 0xF) <<  7) | ((g & 0xC) << 3) |
-         ((b & 0xF) <<  1) | ((b & 0x8) >> 3);
-}
-
-// Demote 8/8/8 to Adafruit_GFX 5/6/5
-// If no gamma flag passed, assume linear color
-uint16_t RGBmatrixPanel::Color888(uint8_t r, uint8_t g, uint8_t b) {
-  return ((uint16_t)(r & 0xF8) << 8) | ((uint16_t)(g & 0xFC) << 3) | (b >> 3);
-}
-
 // 8/8/8 -> gamma -> 5/6/5
 uint16_t RGBmatrixPanel::Color888(
   uint8_t r, uint8_t g, uint8_t b, boolean gflag) {
diff --git a/RGBmatrixPanel.h b/RGBmatrixPanel.h
index 4bdc7f5..fd1ee88 100644
--- a/RGBmatrixPanel.h
+++ b/RGBmatrixPanel.h
@@ -6,6 +6,12 @@
 #endif
 #include "Adafruit_GFX.h"
 
+#if __cplusplus >= 201103L
+ #define CONSTEXPR constexpr
+#else
+ #define CONSTEXPR const
+#endif
+
 class RGBmatrixPanel : public Adafruit_GFX {
 
  public:
@@ -27,13 +33,33 @@ class RGBmatrixPanel : public Adafruit_GFX {
     dumpMatrix(void);
   uint8_t
     *backBuffer(void);
+    
   uint16_t
-    Color333(uint8_t r, uint8_t g, uint8_t b),
-    Color444(uint8_t r, uint8_t g, uint8_t b),
-    Color888(uint8_t r, uint8_t g, uint8_t b),
     Color888(uint8_t r, uint8_t g, uint8_t b, boolean gflag),
     ColorHSV(long hue, uint8_t sat, uint8_t val, boolean gflag);
 
+  // Promote 3/3/3 RGB to Adafruit_GFX 5/6/5
+  static CONSTEXPR uint16_t Color333(uint8_t r, uint8_t g, uint8_t b) {
+    // RRRrrGGGgggBBBbb
+    return ((r & 0x7) << 13) | ((r & 0x6) << 10) |
+           ((g & 0x7) <<  8) | ((g & 0x7) <<  5) |
+           ((b & 0x7) <<  2) | ((b & 0x6) >>  1);
+  }
+
+  // Promote 4/4/4 RGB to Adafruit_GFX 5/6/5
+  static CONSTEXPR uint16_t Color444(uint8_t r, uint8_t g, uint8_t b) {
+    // RRRRrGGGGggBBBBb
+    return ((r & 0xF) << 12) | ((r & 0x8) << 8) |
+           ((g & 0xF) <<  7) | ((g & 0xC) << 3) |
+           ((b & 0xF) <<  1) | ((b & 0x8) >> 3);
+  }
+
+  // Demote 8/8/8 to Adafruit_GFX 5/6/5
+  // If no gamma flag passed, assume linear color
+  static CONSTEXPR uint16_t Color888(uint8_t r, uint8_t g, uint8_t b) {
+    return ((uint16_t)(r & 0xF8) << 8) | ((uint16_t)(g & 0xFC) << 3) | (b >> 3);
+  };
+
  private:
 
   uint8_t         *matrixbuff[2];
@@ -58,3 +84,4 @@ class RGBmatrixPanel : public Adafruit_GFX {
   volatile uint8_t *buffptr;
 };
 
+#undef CONSTEXPR