From 4a4047fdd90aede6d16c020ddcd70c57ea4aa218 Mon Sep 17 00:00:00 2001
From: "Johan B. C. Engelen" <jbc.engelen@swissonline.ch>
Date: Mon, 21 Feb 2011 23:28:50 +0100
Subject: NEW: Grayscale color display mode. (toggle assigned keybinding:
 Shift+keypad5)

(bzr r10065)
---
 src/display/grayscale.cpp | 91 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 91 insertions(+)
 create mode 100644 src/display/grayscale.cpp

(limited to 'src/display/grayscale.cpp')

diff --git a/src/display/grayscale.cpp b/src/display/grayscale.cpp
new file mode 100644
index 000000000..af3a781b0
--- /dev/null
+++ b/src/display/grayscale.cpp
@@ -0,0 +1,91 @@
+/** \file
+ * Provide methods to calculate grayscale values (e.g. convert rgba value to grayscale rgba value)
+ */
+
+/*
+ * Author:
+ *   Johan Engelen <goejendaagh@zonnet.nl>
+ *
+ * Copyright (C) 2011 Author
+ *
+ * Released under GNU GPL
+ */
+
+#include "display/grayscale.h"
+#include "color.h"
+
+// for activeDesktopIsGrayscale:
+#include "display/rendermode.h"
+#include "inkscape.h"
+#include "desktop.h"
+
+namespace Grayscale {
+
+guint32 process(guint32 rgba) {
+    return process(SP_RGBA32_R_U(rgba), SP_RGBA32_G_U(rgba), SP_RGBA32_B_U(rgba), SP_RGBA32_A_U(rgba));
+}
+
+guint32 process(guchar r, guchar g, guchar b, guchar a) {
+    float red_factor = 0.3;
+    float green_factor = 0.59;
+    float blue_factor = 0.11;
+
+    /** To reduce banding in gradients, this calculation is tweaked a bit
+     *  by outputing blue+1 or red+1 or both. The luminance is calculated
+     *  times 4. Then last two bits are used to determine if red and/or blue
+     *  can be increased by one. Then these two bits are discarded.
+     *  So the output color it still looks gray, but has more than 256 steps.
+     *  The assumption is that the eye is most sensitive to green, then red, then blue.
+     *  (hope this trick works :-) Johan)
+     */
+
+    guint32 luminance = ( red_factor * (r << 3)
+                          + green_factor * (g << 3)
+                          + blue_factor * (b << 3) );
+    unsigned blue_plus_one = (luminance & 0x01) ? 1 : 0;
+    unsigned red_plus_one = (luminance & 0x02) ? 1 : 0;
+    unsigned green_plus_one = (luminance & 0x04) ? 1 : 0;
+    luminance = luminance >> 3;
+
+    if (luminance >= 0xff) {
+        return SP_RGBA32_U_COMPOSE(0xff, 0xff, 0xff, a);
+    } else {
+        return SP_RGBA32_U_COMPOSE(luminance + red_plus_one, luminance + green_plus_one, luminance + blue_plus_one, a);
+    }
+}
+
+guchar luminance(guchar r, guchar g, guchar b) {
+    guint32 luminance = ( red_factor * r
+                          + green_factor * g
+                          + blue_factor * b );
+    if (luminance > 0xff) {
+        luminance = 0xff;
+    }
+
+    return luminance & 0xff;
+}
+
+/** @brief  Use this method if there is no other way to find out if grayscale view or not
+ *
+ *  In some cases, the choice between normal or grayscale is so deep in the code hierarchy,
+ *  that it is not possible to determine whether grayscale is desired or not, without using
+ *  the global SP_ACTIVE_DESKTOP macro. Then use this method, so we know where the abuse is
+ *  happening...
+ */
+bool activeDesktopIsGrayscale() {
+    return (SP_ACTIVE_DESKTOP->getColorMode() == Inkscape::COLORRENDERMODE_GRAYSCALE);
+}
+    
+
+};
+
+/*
+  Local Variables:
+  mode:c++
+  c-file-style:"stroustrup"
+  c-file-offsets:((innamespace . 0)(inline-open . 0)(case-label . +))
+  indent-tabs-mode:nil
+  fill-column:99
+  End:
+*/
+// vim: filetype=cpp:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:fileencoding=utf-8:textwidth=99 :
-- 
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