From 9d2b0b667b9bfb2d8b6969ade0ff0bd8d646d7d7 Mon Sep 17 00:00:00 2001
From: inmarket <andrewh@inmarket.com.au>
Date: Thu, 1 Aug 2013 14:52:28 +1000
Subject: [PATCH] Add color blending to GDISP

---
 include/gdisp/gdisp.h | 13 +++++++++++++
 src/gdisp/gdisp.c     | 21 +++++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/include/gdisp/gdisp.h b/include/gdisp/gdisp.h
index ac741d3b..ca1844fd 100644
--- a/include/gdisp/gdisp.h
+++ b/include/gdisp/gdisp.h
@@ -800,6 +800,19 @@ void gdispDrawBox(coord_t x, coord_t y, coord_t cx, coord_t cy, color_t color);
 	void gdispFillRoundedBox(coord_t x, coord_t y, coord_t cx, coord_t cy, coord_t radius, color_t color);
 #endif
 
+
+/**
+ * @brief   Blend 2 colors according to the alpha
+ * @return	The combined color
+ *
+ * @param[in] fg		The foreground color
+ * @param[in] bg		The background color
+ * @param[in] alpha		The alpha value (0-255). 0 is all background, 255 is all foreground.
+ *
+ * @api
+ */
+color_t gdispBlendColor(color_t fg, color_t bg, uint8_t alpha);
+
 /* Support routine for packed pixel formats */
 #if !defined(gdispPackPixels) || defined(__DOXYGEN__)
 	/**
diff --git a/src/gdisp/gdisp.c b/src/gdisp/gdisp.c
index 4c005079..b59b571d 100644
--- a/src/gdisp/gdisp.c
+++ b/src/gdisp/gdisp.c
@@ -990,6 +990,27 @@ void gdispDrawBox(coord_t x, coord_t y, coord_t cx, coord_t cy, color_t color) {
 	}
 #endif
 
+color_t gdispBlendColor(color_t fg, color_t bg, uint8_t alpha)
+{
+	uint16_t fg_ratio = alpha + 1;
+	uint16_t bg_ratio = 256 - alpha;
+	uint16_t r, g, b;
+
+	r = RED_OF(fg) * fg_ratio;
+	g = GREEN_OF(fg) * fg_ratio;
+	b = BLUE_OF(fg) * fg_ratio;
+
+	r += RED_OF(bg) * bg_ratio;
+	g += GREEN_OF(bg) * bg_ratio;
+	b += BLUE_OF(bg) * bg_ratio;
+
+	r /= 256;
+	g /= 256;
+	b /= 256;
+
+	return RGB2COLOR(r, g, b);
+}
+
 #if (!defined(gdispPackPixels) && !defined(GDISP_PIXELFORMAT_CUSTOM))
 	void gdispPackPixels(pixel_t *buf, coord_t cx, coord_t x, coord_t y, color_t color) {
 		/* No mutex required as we only read static data */