From bfbe9e43e108f6816c17b9b7764b75284ac78313 Mon Sep 17 00:00:00 2001
From: Tavian Barnes <tavianator@gmail.com>
Date: Wed, 14 Dec 2011 19:27:22 -0500
Subject: Re-think colors.

Color is a property of light, and thus doesn't include information
about transparency.  But canvas pixels and object pigments represent
a color and a degree of transparency.  The new type dmnsn_tcolor/
TColor encapsulates that information.

Also, fix the transparent shadow implementation.
---
 libdimension/dimension/tcolor.h | 100 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 100 insertions(+)
 create mode 100644 libdimension/dimension/tcolor.h

(limited to 'libdimension/dimension/tcolor.h')

diff --git a/libdimension/dimension/tcolor.h b/libdimension/dimension/tcolor.h
new file mode 100644
index 0000000..d1b7338
--- /dev/null
+++ b/libdimension/dimension/tcolor.h
@@ -0,0 +1,100 @@
+/*************************************************************************
+ * Copyright (C) 2009-2011 Tavian Barnes <tavianator@tavianator.com>     *
+ *                                                                       *
+ * This file is part of The Dimension Library.                           *
+ *                                                                       *
+ * The Dimension Library is free software; you can redistribute it and/  *
+ * or modify it under the terms of the GNU Lesser General Public License *
+ * as published by the Free Software Foundation; either version 3 of the *
+ * License, or (at your option) any later version.                       *
+ *                                                                       *
+ * The Dimension Library is distributed in the hope that it will be      *
+ * useful, but WITHOUT ANY WARRANTY; without even the implied warranty   *
+ * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU  *
+ * Lesser General Public License for more details.                       *
+ *                                                                       *
+ * You should have received a copy of the GNU Lesser General Public      *
+ * License along with this program.  If not, see                         *
+ * <http://www.gnu.org/licenses/>.                                       *
+ *************************************************************************/
+
+/**
+ * @file
+ * Colors with transparency information.
+ */
+
+/** A transparent color. */
+typedef struct dmnsn_tcolor {
+  dmnsn_color c; /**< Color. */
+  double T;      /**< Transparency. */
+  double F;      /**< Proportion of filtered transparency. */
+} dmnsn_tcolor;
+
+/** Create a tcolor. */
+DMNSN_INLINE dmnsn_tcolor
+dmnsn_new_tcolor(dmnsn_color c, double T, double F)
+{
+  dmnsn_tcolor ret = { c, T, F };
+  return ret;
+}
+
+/** Convert a dmnsn_color into a dmnsn_tcolor. */
+#define DMNSN_TCOLOR(c) dmnsn_new_tcolor(c, 0.0, 0.0)
+
+/** Create a tcolor with individually-specified components. */
+DMNSN_INLINE dmnsn_tcolor
+dmnsn_new_tcolor5(double R, double G, double B, double T, double F)
+{
+  dmnsn_tcolor ret = { dmnsn_new_color(R, G, B), T, F };
+  return ret;
+}
+
+/** Return the color at \p n on a gradient from \p c1 at 0 to \p c2 at 1. */
+DMNSN_INLINE dmnsn_tcolor
+dmnsn_tcolor_gradient(dmnsn_tcolor c1, dmnsn_tcolor c2, double n)
+{
+  return dmnsn_new_tcolor(
+    dmnsn_color_gradient(c1.c, c2.c, n),
+    n*(c2.T - c1.T) + c1.T,
+    n*(c2.F - c1.F) + c1.F
+  );
+}
+
+/** Filter \p light through \p filter. */
+DMNSN_INLINE dmnsn_color
+dmnsn_tcolor_filter(dmnsn_color light, dmnsn_tcolor filter)
+{
+  dmnsn_color filtered =
+    dmnsn_color_mul(filter.T*filter.F, dmnsn_color_illuminate(light, filter.c));
+  dmnsn_color transmitted = dmnsn_color_mul(filter.T*(1.0 - filter.F), light);
+  return dmnsn_color_add(filtered, transmitted);
+}
+
+/** Remove the filtered component of a tcolor. */
+DMNSN_INLINE dmnsn_tcolor
+dmnsn_tcolor_remove_filter(dmnsn_tcolor tcolor)
+{
+  double intensity = dmnsn_color_intensity(tcolor.c);
+  double newtrans = (1.0 - (1.0 - intensity)*tcolor.F)*tcolor.T;
+  if (1.0 - newtrans >= dmnsn_epsilon) {
+    tcolor.c = dmnsn_color_mul((1.0 - tcolor.T)/(1.0 - newtrans), tcolor.c);
+  }
+  tcolor.T = newtrans;
+  tcolor.F = 0.0;
+  return tcolor;
+}
+
+/** Saturate the tcolor components to [0.0, 1.0]. */
+DMNSN_INLINE dmnsn_tcolor
+dmnsn_tcolor_saturate(dmnsn_tcolor tcolor)
+{
+  tcolor.c = dmnsn_color_saturate(tcolor.c);
+  tcolor.T = dmnsn_min(dmnsn_max(tcolor.T, 0.0), 1.0);
+  tcolor.F = dmnsn_min(dmnsn_max(tcolor.F, 0.0), 1.0);
+  return tcolor;
+}
+
+/* Standard tcolors */
+
+/** Clear. */
+#define dmnsn_clear dmnsn_new_tcolor5(0.0, 0.0, 0.0, 0.0, 0.0)
-- 
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