Update dynamic colors to new spec, conforming to contrast requirements.

PiperOrigin-RevId: 542477500

Author: Material Eng

cpp/dynamiccolor/contrast_curve.h

@@ -0,0 +1,69 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_DYNAMICCOLOR_CONTRAST_CURVE_H_
+#define CPP_DYNAMICCOLOR_CONTRAST_CURVE_H_
+
+#include "cpp/utils/utils.h"
+
+namespace material_color_utilities {
+
+/**
+ * Documents a constraint between two DynamicColors, in which their tones must
+ * have a certain distance from each other.
+ */
+struct ContrastCurve {
+  double low;
+  double normal;
+  double medium;
+  double high;
+
+  /**
+   * Creates a `ContrastCurve` object.
+   *
+   * @param low Contrast requirement for contrast level -1.0
+   * @param normal Contrast requirement for contrast level 0.0
+   * @param medium Contrast requirement for contrast level 0.5
+   * @param high Contrast requirement for contrast level 1.0
+   */
+  ContrastCurve(double low, double normal, double medium, double high)
+      : low(low), normal(normal), medium(medium), high(high) {}
+
+  /**
+   * Returns the contrast ratio at a given contrast level.
+   *
+   * @param contrastLevel The contrast level. 0.0 is the default (normal);
+   * -1.0 is the lowest; 1.0 is the highest.
+   * @return The contrast ratio, a number between 1.0 and 21.0.
+   */
+  double getContrast(double contrastLevel) {
+    if (contrastLevel <= -1.0) {
+      return low;
+    } else if (contrastLevel < 0.0) {
+      return Lerp(low, normal, (contrastLevel - (-1)) / 1);
+    } else if (contrastLevel < 0.5) {
+      return Lerp(normal, medium, (contrastLevel - 0) / 0.5);
+    } else if (contrastLevel < 1.0) {
+      return Lerp(medium, high, (contrastLevel - 0.5) / 0.5);
+    } else {
+      return high;
+    }
+  }
+};
+
+}  // namespace material_color_utilities
+
+#endif  // CPP_DYNAMICCOLOR_CONTRAST_CURVE_H_