Index: ps/trunk/source/gui/CSlider.cpp
===================================================================
--- ps/trunk/source/gui/CSlider.cpp	(revision 22163)
+++ ps/trunk/source/gui/CSlider.cpp	(revision 22164)
@@ -1,141 +1,147 @@
-/* Copyright (C) 2017 Wildfire Games.
+/* Copyright (C) 2019 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. 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 2 of the License, or
  * (at your option) any later version.
  *
  * 0 A.D. 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 0 A.D.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 #include "precompiled.h"
 #include "CSlider.h"
 #include "GUI.h"
 #include "lib/ogl.h"
 #include "ps/CLogger.h"
 
 
 CSlider::CSlider()
 	: m_IsPressed(false), m_ButtonSide(0)
 {
 	AddSetting(GUIST_float, "value");
 	AddSetting(GUIST_float, "min_value");
 	AddSetting(GUIST_float, "max_value");
 	AddSetting(GUIST_int, "cell_id");
 	AddSetting(GUIST_CGUISpriteInstance, "sprite");
 	AddSetting(GUIST_CGUISpriteInstance, "sprite_bar");
 	AddSetting(GUIST_float, "button_width");
 
 	GUI<float>::GetSetting(this, "value", m_Value);
 	GUI<float>::GetSetting(this, "min_value", m_MinValue);
 	GUI<float>::GetSetting(this, "max_value", m_MaxValue);
 	GUI<float>::GetSetting(this, "button_width", m_ButtonSide);
 	m_Value = Clamp(m_Value, m_MinValue, m_MaxValue);
 }
 
 CSlider::~CSlider()
 {
 }
 
+float CSlider::GetSliderRatio() const
+{
+	return (m_MaxValue - m_MinValue) / (m_CachedActualSize.GetWidth() - m_ButtonSide);
+}
+
+void CSlider::IncrementallyChangeValue(const float difference)
+{
+	m_Value = Clamp(m_Value + difference, m_MinValue, m_MaxValue);
+	UpdateValue();
+}
+
 void CSlider::HandleMessage(SGUIMessage& Message)
 {
 	switch (Message.type)
 	{
 	case GUIM_SETTINGS_UPDATED:
 	{
 		GUI<float>::GetSetting(this, "value", m_Value);
 		GUI<float>::GetSetting(this, "min_value", m_MinValue);
 		GUI<float>::GetSetting(this, "max_value", m_MaxValue);
 		GUI<float>::GetSetting(this, "button_width", m_ButtonSide);
 		m_Value = Clamp(m_Value, m_MinValue, m_MaxValue);
 		break;
 	}
 	case GUIM_MOUSE_WHEEL_DOWN:
 	{
 		if (m_IsPressed)
 			break;
-		m_Value = std::max(m_Value - 0.01f, m_MinValue);
-		UpdateValue();
+		IncrementallyChangeValue(-0.01f);
 		break;
 	}
 	case GUIM_MOUSE_WHEEL_UP:
 	{
 		if (m_IsPressed)
 			break;
-		m_Value = std::min(m_Value + 0.01f, m_MaxValue);
-		UpdateValue();
+		IncrementallyChangeValue(0.01f);
 		break;
 	}
 	case GUIM_MOUSE_PRESS_LEFT:
 	{
-		if (GetButtonRect().PointInside(GetMousePos()))
-		{
-			m_Mouse = GetMousePos();
-			m_IsPressed = true;
-		}
+		m_Mouse = GetMousePos();
+		m_IsPressed = true;
+
+		IncrementallyChangeValue((m_Mouse.x - GetButtonRect().CenterPoint().x) * GetSliderRatio());
 		break;
 	}
 	case GUIM_MOUSE_RELEASE_LEFT:
 	{
 		m_IsPressed = false;
 		break;
 	}
 	case GUIM_MOUSE_MOTION:
 	{
 		if (!MouseOver())
 			m_IsPressed = false;
 		if (m_IsPressed)
 		{
-			float ratio = (m_MaxValue - m_MinValue) / (m_CachedActualSize.GetWidth() - m_ButtonSide);
-			float difference = float(GetMousePos().x - m_Mouse.x) * ratio;
+			float difference = float(GetMousePos().x - m_Mouse.x) * GetSliderRatio();
 			m_Mouse = GetMousePos();
-			m_Value = Clamp(m_Value + difference, m_MinValue, m_MaxValue);
-			UpdateValue();
+			IncrementallyChangeValue(difference);
 		}
 		break;
 	}
 	default:
 		break;
 	}
 }
 
 void CSlider::Draw()
 {
 	if (!GetGUI())
 		return;
 
 	CGUISpriteInstance* sprite;
 	CGUISpriteInstance* sprite_button;
 	int cell_id;
 	GUI<CGUISpriteInstance>::GetSettingPointer(this, "sprite_bar", sprite);
 	GUI<CGUISpriteInstance>::GetSettingPointer(this, "sprite", sprite_button);
 	GUI<int>::GetSetting(this, "cell_id", cell_id);
 
 	CRect slider_line(m_CachedActualSize);
 	slider_line.left += m_ButtonSide / 2.0f;
 	slider_line.right -= m_ButtonSide / 2.0f;
 	float bz = GetBufferedZ();
 	GetGUI()->DrawSprite(*sprite, cell_id, bz, slider_line);
 	GetGUI()->DrawSprite(*sprite_button, cell_id, bz, GetButtonRect());
 }
 
 void CSlider::UpdateValue()
-{	
+{
 	GUI<float>::SetSetting(this, "value", m_Value);
 	ScriptEvent("valuechange");
 }
 
 CRect CSlider::GetButtonRect()
 {
 	float ratio = m_MaxValue > m_MinValue ? (m_Value - m_MinValue) / (m_MaxValue - m_MinValue) : 0.0f;
 	float x = m_CachedActualSize.left + ratio * (m_CachedActualSize.GetWidth() - m_ButtonSide);
 	float y = m_CachedActualSize.top + (m_CachedActualSize.GetHeight() - m_ButtonSide) / 2.0;
 	return CRect(x, y, x + m_ButtonSide, y + m_ButtonSide);
 }
Index: ps/trunk/source/gui/CSlider.h
===================================================================
--- ps/trunk/source/gui/CSlider.h	(revision 22163)
+++ ps/trunk/source/gui/CSlider.h	(revision 22164)
@@ -1,58 +1,65 @@
-/* Copyright (C) 2017 Wildfire Games.
+/* Copyright (C) 2019 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. 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 2 of the License, or
  * (at your option) any later version.
  *
  * 0 A.D. 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 0 A.D.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 #ifndef INCLUDED_CSLIDER
 #define INCLUDED_CSLIDER
 
 #include "GUI.h"
 
 
 class CSlider : public IGUIObject
 {
 	GUI_OBJECT(CSlider)
 
 public:
 	CSlider();
 	virtual ~CSlider();
 
 protected:
 
 	/**
 	 * @see IGUIObject#HandleMessage()
 	 */
 	virtual void HandleMessage(SGUIMessage& Message);
 
 	virtual void Draw();
 
 	/**
 	 * Change settings and send the script event
 	 */
 	void UpdateValue();
 
 	CRect GetButtonRect();
 
+	/**
+	 * @return ratio between the value of the slider and its actual size in the GUI
+	 */
+	float GetSliderRatio() const;
+
+	void IncrementallyChangeValue(const float value);
+
 	float m_MinValue, m_MaxValue, m_Value;
 
 private:
 	bool m_IsPressed;
 
 	CPos m_Mouse;
 
 	float m_ButtonSide;
 };
 
 #endif // INCLUDED_CSLIDER