gfx::ColorSpace::ToString() - print primaries ISO chromatic adaptation matrix

This CL changes the implementation of the said method to print out the
primaries coordinates instead of the Chromatic adaptation matrix, if
CUSTOM primaries are used.  The former is more informative than the
latter.

Example output with primaries triangle (edid and recalculated) can be
found in https://i.imgur.com/p5q9uyY.png (https://imgur.com/a/gdj62).

Bug: 821393
Change-Id: I690d2d6df1ece0ca75e4dcbbdb42bbd092eb234c
Reviewed-on: https://chromium-review.googlesource.com/985316
Commit-Queue: Miguel Casas <mcasas@chromium.org>
Reviewed-by: ccameron <ccameron@chromium.org>
Cr-Commit-Position: refs/heads/master@{#547083}

ui/gfx/color_space.cc

@@ -38,6 +38,10 @@ base::LazyInstance<SkColorSpaceCache>::Leaky g_sk_color_space_cache =
 base::LazyInstance<base::Lock>::Leaky g_sk_color_space_cache_lock =
     LAZY_INSTANCE_INITIALIZER;
 
+static bool IsAlmostZero(float value) {
+  return std::abs(value) < std::numeric_limits<float>::epsilon();
+}
+
 }  // namespace
 
 ColorSpace::ColorSpace() {}
@@ -306,7 +310,8 @@ size_t ColorSpace::GetHash() const {
 std::string ColorSpace::ToString() const {
   std::stringstream ss;
   ss << std::fixed << std::setprecision(4);
-  ss << "{primaries:";
+  if (primaries_ != PrimaryID::CUSTOM)
+    ss << "{primaries:";
   switch (primaries_) {
     PRINT_ENUM_CASE(PrimaryID, INVALID)
     PRINT_ENUM_CASE(PrimaryID, BT709)
@@ -324,14 +329,22 @@ std::string ColorSpace::ToString() const {
     PRINT_ENUM_CASE(PrimaryID, APPLE_GENERIC_RGB)
     PRINT_ENUM_CASE(PrimaryID, WIDE_GAMUT_COLOR_SPIN)
     case PrimaryID::CUSTOM:
-      ss << "[";
-      for (size_t i = 0; i < 3; ++i) {
-        ss << "[";
-        for (size_t j = 0; j < 3; ++j)
-          ss << custom_primary_matrix_[3 * i + j] << ",";
-        ss << "],";
-      }
-      ss << "]";
+      // |custom_primary_matrix_| is in column-major order.
+      const float sum_X = custom_primary_matrix_[0] +
+                          custom_primary_matrix_[3] + custom_primary_matrix_[6];
+      const float sum_Y = custom_primary_matrix_[1] +
+                          custom_primary_matrix_[4] + custom_primary_matrix_[7];
+      const float sum_Z = custom_primary_matrix_[2] +
+                          custom_primary_matrix_[5] + custom_primary_matrix_[8];
+      if (IsAlmostZero(sum_X) || IsAlmostZero(sum_Y) || IsAlmostZero(sum_Z))
+        break;
+
+      ss << "{primaries_d50_referred: [[" << (custom_primary_matrix_[0] / sum_X)
+         << ", " << (custom_primary_matrix_[3] / sum_X) << "], "
+         << " [" << (custom_primary_matrix_[1] / sum_Y) << ", "
+         << (custom_primary_matrix_[4] / sum_Y) << "], "
+         << " [" << (custom_primary_matrix_[2] / sum_Z) << ", "
+         << (custom_primary_matrix_[5] / sum_Z) << "]]";
       break;
   }
   ss << ", transfer:";