Blenlib: Explicit Colors.

Colors are often thought of as being 4 values that make up that can make any color.
But that is of course too limited. In C we didn’t spend time to annotate what we meant
when using colors.

Recently `BLI_color.hh` was made to facilitate color structures in CPP. CPP has possibilities to
enforce annotating structures during compilation and can adds conversions between them using
function overloading and explicit constructors.

The storage structs can hold 4 channels (r, g, b and a).

Usage:

Convert a theme byte color to a linearrgb premultiplied.
```
ColorTheme4b theme_color;
ColorSceneLinear4f<eAlpha::Premultiplied> linearrgb_color =
    BLI_color_convert_to_scene_linear(theme_color).premultiply_alpha();
```

The API is structured to make most use of inlining. Most notable are space
conversions done via `BLI_color_convert_to*` functions.

- Conversions between spaces (theme <=> scene linear) should always be done by
  invoking the `BLI_color_convert_to*` methods.
- Encoding colors (compressing to store colors inside a less precision storage)
  should be done by invoking the `encode` and `decode` methods.
- Changing alpha association should be done by invoking `premultiply_alpha` or
  `unpremultiply_alpha` methods.

# Encoding.

Color encoding is used to store colors with less precision as in using `uint8_t` in
stead of `float`. This encoding is supported for `eSpace::SceneLinear`.
To make this clear to the developer the `eSpace::SceneLinearByteEncoded`
space is added.

# Precision

Colors can be stored using `uint8_t` or `float` colors. The conversion
between the two precisions are available as methods. (`to_4b` and
`to_4f`).

# Alpha conversion

Alpha conversion is only supported in SceneLinear space.

Extending:
- This file can be extended with `ColorHex/Hsl/Hsv` for different representations
  of rgb based colors. `ColorHsl4f<eSpace::SceneLinear, eAlpha::Premultiplied>`
- Add non RGB spaces/storages ColorXyz.

Reviewed By: JacquesLucke, brecht

Differential Revision: https://developer.blender.org/D10978

1 files changed, 55 insertions, 0 deletions

diff --git a/source/blender/blenlib/intern/BLI_color.cc b/source/blender/blenlib/intern/BLI_color.cc
new file mode 100644
index 00000000000..6dcef4f4688
--- /dev/null
+++ b/source/blender/blenlib/intern/BLI_color.cc
@@ -0,0 +1,55 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+#include "BLI_color.hh"
+
+namespace blender {
+
+std::ostream &operator<<(std::ostream &stream, const eAlpha &space)
+{
+  switch (space) {
+    case eAlpha::Straight: {
+      stream << "Straight";
+      break;
+    }
+    case eAlpha::Premultiplied: {
+      stream << "Premultiplied";
+      break;
+    }
+  }
+  return stream;
+}
+
+std::ostream &operator<<(std::ostream &stream, const eSpace &space)
+{
+  switch (space) {
+    case eSpace::Theme: {
+      stream << "Theme";
+      break;
+    }
+    case eSpace::SceneLinear: {
+      stream << "SceneLinear";
+      break;
+    }
+    case eSpace::SceneLinearByteEncoded: {
+      stream << "SceneLinearByteEncoded";
+      break;
+    }
+  }
+  return stream;
+}
+
+}  // namespace blender