Added fade helpers to help clean code in game objects

src/util/fade_helper.cpp

@@ -0,0 +1,74 @@
+//  SuperTux
+//  Copyright (C) 2021 A. Semphris <[email protected]>
+//
+//  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 3 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, see <http://www.gnu.org/licenses/>.
+
+#include "util/fade_helper.hpp"
+
+FadeHelper::FadeHelper(float time, float target_value,
+                       float start_value, easing ease) :
+  m_value(nullptr),
+  m_start(start_value),
+  m_target(target_value),
+  m_time(0.f),
+  m_total_time(time),
+  m_ease(ease)
+{
+}
+
+FadeHelper::FadeHelper(float* value, float time,
+                       float target_value, easing ease) :
+  m_value(value),
+  m_start(*value),
+  m_target(target_value),
+  m_time(0.f),
+  m_total_time(time),
+  m_ease(ease)
+{
+}
+
+float
+FadeHelper::update(float dt_sec)
+{
+  m_time += dt_sec;
+
+  if (completed())
+  {
+    m_time = m_total_time;
+    if (m_value)
+      *m_value = m_target;
+    return m_target;
+  }
+  else
+  {
+    // FLOAT/DOUBLE CONVERSION
+    // If at some point in development, floats are changed to doubles, or the
+    // ease funciton return type change from double to float, remove the casts
+    // here (it takes a lot of space).               ~ Semphris
+    float progress = static_cast<float>(m_ease(static_cast<double>(
+                        m_start + (m_target - m_start) * (m_time / m_total_time)
+                        )));
+    if (m_value)
+      *m_value = progress;
+    return progress;
+  }
+}
+
+bool
+FadeHelper::completed() const
+{
+  return m_time >= m_total_time;
+}
+
+/* EOF */

src/util/fade_helper.hpp

@@ -0,0 +1,58 @@
+//  SuperTux
+//  Copyright (C) 2021 A. Semphris <[email protected]>
+//
+//  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 3 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, see <http://www.gnu.org/licenses/>.
+
+#ifndef HEADER_SUPERTUX_UTIL_FADE_HELPER_HPP
+#define HEADER_SUPERTUX_UTIL_FADE_HELPER_HPP
+
+#include "math/easing.hpp"
+
+class FadeHelper
+{
+public:
+  /** Initialize FadeHelper without binding to a value */
+  FadeHelper(float time, float target_value,
+             float start_value = 0.f, easing ease = LinearInterpolation);
+
+  /** Initialize FadeHelper, binding to @c value */
+  FadeHelper(float* value, float time,
+             float target_value, easing ease = LinearInterpolation);
+
+
+  /**
+   * Increases the internal timer of the FadeHelper.
+   * 
+   * @param dt_sec The increase in time since last call to update().
+   * @returns The new value for the internal value.
+   */
+  float update(float dt_sec);
+
+  /** @returns true if the FadeHelper has completed fading. */
+  bool completed() const;
+
+private:
+  float* m_value;
+  float m_start, m_target,
+        m_time, m_total_time;
+  easing m_ease;
+
+private:
+  FadeHelper(const FadeHelper&) = delete;
+  FadeHelper& operator=(const FadeHelper&) = delete;
+};
+
+#endif
+
+/* EOF */