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

3 files changed, 30 insertions, 29 deletions

diff --git a/source/blender/nodes/intern/node_geometry_exec.cc b/source/blender/nodes/intern/node_geometry_exec.cc
index 73a702c753a..188d198e159 100644
--- a/source/blender/nodes/intern/node_geometry_exec.cc
+++ b/source/blender/nodes/intern/node_geometry_exec.cc
@@ -104,9 +104,10 @@ GVArrayPtr GeoNodeExecParams::get_input_attribute(const StringRef name,
     return std::make_unique<fn::GVArray_For_SingleValue>(*cpp_type, domain_size, buffer);
   }
   if (found_socket->type == SOCK_RGBA) {
-    const Color4f value = this->get_input<Color4f>(found_socket->identifier);
+    const ColorGeometry4f value = this->get_input<ColorGeometry4f>(found_socket->identifier);
     BUFFER_FOR_CPP_TYPE_VALUE(*cpp_type, buffer);
-    conversions.convert_to_uninitialized(CPPType::get<Color4f>(), *cpp_type, &value, buffer);
+    conversions.convert_to_uninitialized(
+        CPPType::get<ColorGeometry4f>(), *cpp_type, &value, buffer);
     return std::make_unique<fn::GVArray_For_SingleValue>(*cpp_type, domain_size, buffer);
   }
   BLI_assert(false);
diff --git a/source/blender/nodes/intern/node_socket.cc b/source/blender/nodes/intern/node_socket.cc
index ce2848b52a0..783a7a9b3d8 100644
--- a/source/blender/nodes/intern/node_socket.cc
+++ b/source/blender/nodes/intern/node_socket.cc
@@ -637,9 +637,9 @@ static bNodeSocketType *make_socket_type_vector(PropertySubType subtype)
 static bNodeSocketType *make_socket_type_rgba()
 {
   bNodeSocketType *socktype = make_standard_socket_type(SOCK_RGBA, PROP_NONE);
-  socktype->get_cpp_type = []() { return &blender::fn::CPPType::get<blender::Color4f>(); };
+  socktype->get_cpp_type = []() { return &blender::fn::CPPType::get<blender::ColorGeometry4f>(); };
   socktype->get_cpp_value = [](const bNodeSocket &socket, void *r_value) {
-    *(blender::Color4f *)r_value = ((bNodeSocketValueRGBA *)socket.default_value)->value;
+    *(blender::ColorGeometry4f *)r_value = ((bNodeSocketValueRGBA *)socket.default_value)->value;
   };
   return socktype;
 }
diff --git a/source/blender/nodes/intern/type_conversions.cc b/source/blender/nodes/intern/type_conversions.cc
index 63f7b8a9ee8..220e5ea9046 100644
--- a/source/blender/nodes/intern/type_conversions.cc
+++ b/source/blender/nodes/intern/type_conversions.cc
@@ -66,9 +66,9 @@ static bool float_to_bool(const float &a)
 {
   return a > 0.0f;
 }
-static Color4f float_to_color(const float &a)
+static ColorGeometry4f float_to_color(const float &a)
 {
-  return Color4f(a, a, a, 1.0f);
+  return ColorGeometry4f(a, a, a, 1.0f);
 }
 
 static float3 float2_to_float3(const float2 &a)
@@ -87,9 +87,9 @@ static bool float2_to_bool(const float2 &a)
 {
   return !is_zero_v2(a);
 }
-static Color4f float2_to_color(const float2 &a)
+static ColorGeometry4f float2_to_color(const float2 &a)
 {
-  return Color4f(a.x, a.y, 0.0f, 1.0f);
+  return ColorGeometry4f(a.x, a.y, 0.0f, 1.0f);
 }
 
 static bool float3_to_bool(const float3 &a)
@@ -108,9 +108,9 @@ static float2 float3_to_float2(const float3 &a)
 {
   return float2(a);
 }
-static Color4f float3_to_color(const float3 &a)
+static ColorGeometry4f float3_to_color(const float3 &a)
 {
-  return Color4f(a.x, a.y, a.z, 1.0f);
+  return ColorGeometry4f(a.x, a.y, a.z, 1.0f);
 }
 
 static bool int_to_bool(const int32_t &a)
@@ -129,9 +129,9 @@ static float3 int_to_float3(const int32_t &a)
 {
   return float3((float)a);
 }
-static Color4f int_to_color(const int32_t &a)
+static ColorGeometry4f int_to_color(const int32_t &a)
 {
-  return Color4f((float)a, (float)a, (float)a, 1.0f);
+  return ColorGeometry4f((float)a, (float)a, (float)a, 1.0f);
 }
 
 static float bool_to_float(const bool &a)
@@ -150,28 +150,28 @@ static float3 bool_to_float3(const bool &a)
 {
   return (a) ? float3(1.0f) : float3(0.0f);
 }
-static Color4f bool_to_color(const bool &a)
+static ColorGeometry4f bool_to_color(const bool &a)
 {
-  return (a) ? Color4f(1.0f, 1.0f, 1.0f, 1.0f) : Color4f(0.0f, 0.0f, 0.0f, 1.0f);
+  return (a) ? ColorGeometry4f(1.0f, 1.0f, 1.0f, 1.0f) : ColorGeometry4f(0.0f, 0.0f, 0.0f, 1.0f);
 }
 
-static bool color_to_bool(const Color4f &a)
+static bool color_to_bool(const ColorGeometry4f &a)
 {
   return rgb_to_grayscale(a) > 0.0f;
 }
-static float color_to_float(const Color4f &a)
+static float color_to_float(const ColorGeometry4f &a)
 {
   return rgb_to_grayscale(a);
 }
-static int32_t color_to_int(const Color4f &a)
+static int32_t color_to_int(const ColorGeometry4f &a)
 {
   return (int)rgb_to_grayscale(a);
 }
-static float2 color_to_float2(const Color4f &a)
+static float2 color_to_float2(const ColorGeometry4f &a)
 {
   return float2(a.r, a.g);
 }
-static float3 color_to_float3(const Color4f &a)
+static float3 color_to_float3(const ColorGeometry4f &a)
 {
   return float3(a.r, a.g, a.b);
 }
@@ -184,37 +184,37 @@ static DataTypeConversions create_implicit_conversions()
   add_implicit_conversion<float, float3, float_to_float3>(conversions);
   add_implicit_conversion<float, int32_t, float_to_int>(conversions);
   add_implicit_conversion<float, bool, float_to_bool>(conversions);
-  add_implicit_conversion<float, Color4f, float_to_color>(conversions);
+  add_implicit_conversion<float, ColorGeometry4f, float_to_color>(conversions);
 
   add_implicit_conversion<float2, float3, float2_to_float3>(conversions);
   add_implicit_conversion<float2, float, float2_to_float>(conversions);
   add_implicit_conversion<float2, int32_t, float2_to_int>(conversions);
   add_implicit_conversion<float2, bool, float2_to_bool>(conversions);
-  add_implicit_conversion<float2, Color4f, float2_to_color>(conversions);
+  add_implicit_conversion<float2, ColorGeometry4f, float2_to_color>(conversions);
 
   add_implicit_conversion<float3, bool, float3_to_bool>(conversions);
   add_implicit_conversion<float3, float, float3_to_float>(conversions);
   add_implicit_conversion<float3, int32_t, float3_to_int>(conversions);
   add_implicit_conversion<float3, float2, float3_to_float2>(conversions);
-  add_implicit_conversion<float3, Color4f, float3_to_color>(conversions);
+  add_implicit_conversion<float3, ColorGeometry4f, float3_to_color>(conversions);
 
   add_implicit_conversion<int32_t, bool, int_to_bool>(conversions);
   add_implicit_conversion<int32_t, float, int_to_float>(conversions);
   add_implicit_conversion<int32_t, float2, int_to_float2>(conversions);
   add_implicit_conversion<int32_t, float3, int_to_float3>(conversions);
-  add_implicit_conversion<int32_t, Color4f, int_to_color>(conversions);
+  add_implicit_conversion<int32_t, ColorGeometry4f, int_to_color>(conversions);
 
   add_implicit_conversion<bool, float, bool_to_float>(conversions);
   add_implicit_conversion<bool, int32_t, bool_to_int>(conversions);
   add_implicit_conversion<bool, float2, bool_to_float2>(conversions);
   add_implicit_conversion<bool, float3, bool_to_float3>(conversions);
-  add_implicit_conversion<bool, Color4f, bool_to_color>(conversions);
+  add_implicit_conversion<bool, ColorGeometry4f, bool_to_color>(conversions);
 
-  add_implicit_conversion<Color4f, bool, color_to_bool>(conversions);
-  add_implicit_conversion<Color4f, float, color_to_float>(conversions);
-  add_implicit_conversion<Color4f, int32_t, color_to_int>(conversions);
-  add_implicit_conversion<Color4f, float2, color_to_float2>(conversions);
-  add_implicit_conversion<Color4f, float3, color_to_float3>(conversions);
+  add_implicit_conversion<ColorGeometry4f, bool, color_to_bool>(conversions);
+  add_implicit_conversion<ColorGeometry4f, float, color_to_float>(conversions);
+  add_implicit_conversion<ColorGeometry4f, int32_t, color_to_int>(conversions);
+  add_implicit_conversion<ColorGeometry4f, float2, color_to_float2>(conversions);
+  add_implicit_conversion<ColorGeometry4f, float3, color_to_float3>(conversions);
 
   return conversions;
 }