docs(src): add examples alias and general cleanup (#2763)

src/input.h

@@ -1,6 +1,6 @@
 /**
  * @file src/input.h
- * @brief todo
+ * @brief Declarations for gamepad, keyboard, and mouse input handling.
  */
 #pragma once
 
@@ -42,6 +42,13 @@ namespace input {
     }
   };
 
+  /**
+   * @brief Scale the ellipse axes according to the provided size.
+   * @param val The major and minor axis pair.
+   * @param rotation The rotation value from the touch/pen event.
+   * @param scalar The scalar cartesian coordinate pair.
+   * @return The major and minor axis pair.
+   */
   std::pair<float, float>
   scale_client_contact_area(const std::pair<float, float> &val, uint16_t rotation, const std::pair<float, float> &scalar);
 }  // namespace input