diff --git a/data/pref.xml b/data/pref.xml
index 87f4d9133..dbc557525 100644
--- a/data/pref.xml
+++ b/data/pref.xml
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <!-- Aseprite -->
-<!-- Copyright (C) 2018-2023  Igara Studio S.A. -->
+<!-- Copyright (C) 2018-2024  Igara Studio S.A. -->
 <!-- Copyright (C) 2014-2018  David Capello -->
 <preferences>
 
@@ -133,6 +133,10 @@
       <value id="BILINEAR_MIPMAP" value="2" />
       <value id="TRILINEAR_MIPMAP" value="3" />
     </enum>
+    <enum id="AlphaRange">
+      <value id="EIGHT_BIT" value="0" />
+      <value id="PERCENTAGE" value="1" />
+    </enum>
   </types>
 
   <global>
@@ -431,6 +435,10 @@
       <option id="window_profile" type="WindowColorProfile" default="WindowColorProfile::MONITOR" />
       <option id="window_profile_name" type="std::string" />
     </section>
+    <section id="range">
+      <option id="alpha" type="AlphaRange" default="AlphaRange::EIGHT_BIT" />
+      <option id="opacity" type="AlphaRange" default="AlphaRange::PERCENTAGE" />
+    </section>
     <section id="canvas_size">
       <option id="trim_outside" type="bool" default="false" />
     </section>
diff --git a/data/strings/en.ini b/data/strings/en.ini
index a157d51af..1ea1b13bc 100644
--- a/data/strings/en.ini
+++ b/data/strings/en.ini
@@ -1,5 +1,5 @@
 # Aseprite
-# Copyright (C) 2018-2023  Igara Studio S.A.
+# Copyright (C) 2018-2024  Igara Studio S.A.
 # Copyright (C) 2016-2018  David Capello
 #
 # This work is licensed under the Creative Commons Attribution 4.0
@@ -1470,6 +1470,11 @@ use_embedded_cs = Use embedded profile
 convert_cs = Convert to working RGB space
 assign_cs = Assign working RGB space
 ask_cs = Ask
+alpha_and_opacity = Alpha && Opacity
+alpha_range = Alpha Range:
+opacity_range = Opacity Range:
+8bit_value = 0-255
+percentage = 0%-100%
 available_themes = Available Themes
 extension_themes = Extension Themes
 select_theme = &Select
diff --git a/data/widgets/cel_properties.xml b/data/widgets/cel_properties.xml
index 3e61262bb..519a84d38 100644
--- a/data/widgets/cel_properties.xml
+++ b/data/widgets/cel_properties.xml
@@ -1,11 +1,11 @@
 <!-- Aseprite -->
-<!-- Copyright (C) 2020-2023 by Igara Studio S.A. -->
+<!-- Copyright (C) 2020-2024 by Igara Studio S.A. -->
 <!-- Copyright (C) 2001-2016 by David Capello -->
 <gui>
 <window id="cel_properties" text="@.title">
   <grid id="properties_grid" columns="4">
     <label text="@.opacity" />
-    <slider min="0" max="255" id="opacity" cell_align="horizontal" width="128" cell_hspan="2" />
+    <opacityslider id="opacity" cell_align="horizontal" width="128" cell_hspan="2" />
     <button id="user_data" icon="icon_user_data" tooltip="@.user_data_tooltip" />
 
     <label text="@.zindex" />
diff --git a/data/widgets/layer_properties.xml b/data/widgets/layer_properties.xml
index 6a7033edb..4ab12279d 100644
--- a/data/widgets/layer_properties.xml
+++ b/data/widgets/layer_properties.xml
@@ -14,7 +14,7 @@
       <button id="tileset" icon="tiles" tooltip="@.tileset_tooltip" />
 
       <label text="@.opacity" />
-      <slider id="opacity" min="0" max="255" width="128" cell_align="horizontal" cell_hspan="2" />
+      <opacityslider id="opacity" width="128" cell_align="horizontal" cell_hspan="2" />
     </grid>
   </vbox>
 </window>
diff --git a/data/widgets/options.xml b/data/widgets/options.xml
index 3e3a3c22f..58dfbde81 100644
--- a/data/widgets/options.xml
+++ b/data/widgets/options.xml
@@ -1,5 +1,5 @@
 <!-- Aseprite -->
-<!-- Copyright (C) 2018-2023  Igara Studio S.A. -->
+<!-- Copyright (C) 2018-2024  Igara Studio S.A. -->
 <!-- Copyright (C) 2001-2018  David Capello -->
 <gui>
   <window id="options" text="@.title">
@@ -192,7 +192,7 @@
           <separator text="@.section_color" horizontal="true" />
           <check text="@.color_management" id="color_management" pref="color.manage" />
 
-	  <grid columns="2">
+          <grid columns="2">
             <label text="@.window_cs" id="window_cs_label" />
             <combobox id="window_cs">
               <listitem text="@.use_monitor_cs" />
@@ -213,20 +213,34 @@
               <listitem text="@.convert_cs" />
               <listitem text="@.assign_cs" />
               <listitem text="@.ask_cs" />
-	    </combobox>
+            </combobox>
 
             <label text="@.missing_cs" id="missing_cs_label" />
             <combobox id="missing_cs">
               <listitem text="@.disable_cs" />
               <listitem text="@.assign_cs" />
               <listitem text="@.ask_cs" />
-	    </combobox>
-	  </grid>
+            </combobox>
+          </grid>
 
-	  <hbox>
-	    <hbox expansive="true" />
+          <hbox>
+            <hbox expansive="true" />
             <button id="reset_color_management" text="@general.reset" minwidth="60" />
-	  </hbox>
+          </hbox>
+
+          <separator text="@.alpha_and_opacity" horizontal="true" />
+          <grid columns="2">
+            <label text="@.alpha_range" id="alpha_range_label" />
+            <combobox id="alpha">
+              <listitem text="@.8bit_value" />
+              <listitem text="@.percentage" />
+            </combobox>
+            <label text="@.opacity_range" id="opacity_range_label" />
+            <combobox id="opacity">
+              <listitem text="@.8bit_value" />
+              <listitem text="@.percentage" />
+            </combobox>
+          </grid>
         </vbox>
 
         <!-- Editor -->
diff --git a/data/widgets/timeline_conf.xml b/data/widgets/timeline_conf.xml
index 6fa4c737e..8f2261430 100644
--- a/data/widgets/timeline_conf.xml
+++ b/data/widgets/timeline_conf.xml
@@ -43,10 +43,10 @@
     </hbox>
 
     <label text="@.opacity" />
-    <slider min="0" max="255" id="opacity" cell_align="horizontal" width="128" />
+    <opacityslider id="opacity" cell_align="horizontal" width="128" />
 
     <label text="@.opacity_step" />
-    <slider min="0" max="255" id="opacity_step" cell_align="horizontal" width="128" />
+    <opacityslider id="opacity_step" cell_align="horizontal" width="128" />
 
     <check id="loop_tag" text="@.loop_tags" cell_hspan="2" />
     <check id="current_layer" text="@.current_layer" cell_hspan="2" />
diff --git a/src/app/CMakeLists.txt b/src/app/CMakeLists.txt
index 8efd9ff4f..7d48cddd6 100644
--- a/src/app/CMakeLists.txt
+++ b/src/app/CMakeLists.txt
@@ -1,5 +1,5 @@
 # Aseprite
-# Copyright (C) 2018-2023  Igara Studio S.A.
+# Copyright (C) 2018-2024  Igara Studio S.A.
 # Copyright (C) 2001-2018  David Capello
 
 # Generate a ui::Widget for each widget in a XML file
@@ -336,6 +336,8 @@ if(ENABLE_UI)
     file_selector.cpp
     modules/gfx.cpp
     modules/gui.cpp
+    ui/alpha_entry.cpp
+    ui/alpha_slider.cpp
     ui/app_menuitem.cpp
     ui/backup_indicator.cpp
     ui/browser_view.cpp
diff --git a/src/app/commands/cmd_options.cpp b/src/app/commands/cmd_options.cpp
index d8f5d6117..19ea43383 100644
--- a/src/app/commands/cmd_options.cpp
+++ b/src/app/commands/cmd_options.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2018-2023  Igara Studio S.A.
+// Copyright (C) 2018-2024  Igara Studio S.A.
 // Copyright (C) 2001-2018  David Capello
 //
 // This program is distributed under the terms of
@@ -776,6 +776,9 @@ public:
     }
     update_windows_color_profile_from_preferences();
 
+    m_pref.range.alpha(static_cast<app::gen::AlphaRange>(alpha()->getSelectedItemIndex()));
+    m_pref.range.opacity(static_cast<app::gen::AlphaRange>(opacity()->getSelectedItemIndex()));
+
     // Change sprite grid bounds
     if (m_context &&
         m_context->activeDocument() &&
@@ -1073,6 +1076,9 @@ private:
     filesWithCs()->setEnabled(state);
     missingCsLabel()->setEnabled(state);
     missingCs()->setEnabled(state);
+
+    alpha()->setSelectedItemIndex(static_cast<int>(m_pref.range.alpha()));
+    opacity()->setSelectedItemIndex(static_cast<int>(m_pref.range.opacity()));
   }
 
   void onResetColorManagement() {
diff --git a/src/app/script/values.cpp b/src/app/script/values.cpp
index 10e019339..70c91d7e5 100644
--- a/src/app/script/values.cpp
+++ b/src/app/script/values.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2019-2023  Igara Studio S.A.
+// Copyright (C) 2019-2024  Igara Studio S.A.
 //
 // This program is distributed under the terms of
 // the End-User License Agreement for Aseprite.
@@ -334,6 +334,7 @@ FOR_ENUM(app::gen::SymmetryMode)
 FOR_ENUM(app::gen::TimelinePosition)
 FOR_ENUM(app::gen::ToGrayAlgorithm)
 FOR_ENUM(app::gen::WindowColorProfile)
+FOR_ENUM(app::gen::AlphaRange)
 FOR_ENUM(app::tools::ColorFromTo)
 FOR_ENUM(app::tools::DynamicSensor)
 FOR_ENUM(app::tools::FreehandAlgorithm)
diff --git a/src/app/ui/alpha_entry.cpp b/src/app/ui/alpha_entry.cpp
new file mode 100644
index 000000000..546bf2a0f
--- /dev/null
+++ b/src/app/ui/alpha_entry.cpp
@@ -0,0 +1,67 @@
+// Aseprite UI Library
+// Copyright (C) 2024  Igara Studio S.A.
+//
+// This file is released under the terms of the MIT license.
+// Read LICENSE.txt for more information.
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include "app/pref/preferences.h"
+#include "app/ui/alpha_entry.h"
+#include "base/scoped_value.h"
+#include "gfx/rect.h"
+#include "gfx/region.h"
+#include "os/font.h"
+#include "ui/fit_bounds.h"
+#include "ui/manager.h"
+#include "ui/message.h"
+#include "ui/popup_window.h"
+#include "ui/scale.h"
+#include "ui/size_hint_event.h"
+#include "ui/slider.h"
+#include "ui/system.h"
+#include "ui/theme.h"
+
+#include <algorithm>
+#include <cmath>
+
+namespace app {
+
+using namespace gfx;
+
+AlphaEntry::AlphaEntry(AlphaSlider::Type type)
+  : IntEntry(0, 255)
+{
+  m_slider = std::make_unique<AlphaSlider>(0, type);
+  m_slider->setFocusStop(false); // In this way the IntEntry doesn't lost the focus
+  m_slider->setTransparent(true);
+  m_slider->Change.connect([this] { this->onChangeSlider(); });
+}
+
+int AlphaEntry::getValue() const
+{
+  int value = m_slider->convertTextToValue(text());
+  if (static_cast<AlphaSlider*>(m_slider.get())->getAlphaRange() == app::gen::AlphaRange::PERCENTAGE)
+    value = std::round(((double)m_slider->getMaxValue())*((double)value)/((double)100));
+
+  return std::clamp(value, m_min, m_max);
+}
+
+void AlphaEntry::setValue(int value)
+{
+  value = std::clamp(value, m_min, m_max);
+
+  if (m_popupWindow && !m_changeFromSlider)
+    m_slider->setValue(value);
+
+  if (static_cast<AlphaSlider*>(m_slider.get())->getAlphaRange() == app::gen::AlphaRange::PERCENTAGE)
+    value = std::round(((double)100)*((double)value)/((double)m_slider->getMaxValue()));
+
+  setText(m_slider->convertValueToText(value));
+
+  onValueChange();
+}
+
+} // namespace app
diff --git a/src/app/ui/alpha_entry.h b/src/app/ui/alpha_entry.h
new file mode 100644
index 000000000..9cc03005f
--- /dev/null
+++ b/src/app/ui/alpha_entry.h
@@ -0,0 +1,36 @@
+// Aseprite UI Library
+// Copyright (C) 2024  Igara Studio S.A.
+//
+// This file is released under the terms of the MIT license.
+// Read LICENSE.txt for more information.
+
+#ifndef APP_UI_ALPHA_ENTRY_H_INCLUDED
+#define APP_UI_ALPHA_ENTRY_H_INCLUDED
+#pragma once
+
+#include "ui/int_entry.h"
+#include "app/ui/alpha_slider.h"
+
+#include <memory>
+
+using namespace ui;
+
+
+namespace ui {
+  class CloseEvent;
+  class PopupWindow;
+}
+
+namespace app {
+
+  class AlphaEntry : public IntEntry {
+  public:
+    AlphaEntry(AlphaSlider::Type type);
+
+    int getValue() const override;
+    void setValue(int value) override;
+  };
+
+} // namespace ui
+
+#endif
diff --git a/src/app/ui/alpha_slider.cpp b/src/app/ui/alpha_slider.cpp
new file mode 100644
index 000000000..a426a38c5
--- /dev/null
+++ b/src/app/ui/alpha_slider.cpp
@@ -0,0 +1,69 @@
+// Aseprite
+// Copyright (C) 2024  Igara Studio S.A.
+//
+// This program is distributed under the terms of
+// the End-User License Agreement for Aseprite.
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include "app/ui/alpha_slider.h"
+#include "ui/message.h"
+
+#include <algorithm>
+
+using namespace ui;
+using namespace app::gen;
+
+namespace app {
+
+AlphaSlider::AlphaSlider(int value, Type type)
+  : ui::Slider(0, 255, value, this)
+  , m_type(type)
+{
+}
+
+void AlphaSlider::getSliderThemeInfo(int* min, int* max, int* value) const
+{
+  switch (getAlphaRange()) {
+    case AlphaRange::PERCENTAGE:
+      if (min) *min = 0;
+      if (max) *max = 100;
+      if (value) *value = std::round(((double)100)*((double)getValue())/((double)getMaxValue()));
+
+      return;
+    case AlphaRange::EIGHT_BIT:
+      return Slider::getSliderThemeInfo(min, max, value);
+  }
+}
+
+void AlphaSlider::updateValue(int value)
+{
+  if (getAlphaRange() == AlphaRange::PERCENTAGE)
+    value = std::round(((double)getMaxValue())*((double)value)/((double)100));
+
+  setValue(value);
+}
+
+std::string AlphaSlider::onGetTextFromValue(int value)
+{
+  char buf[128];
+  const char *format = "%d";
+  if (getAlphaRange() == AlphaRange::PERCENTAGE)
+      format = "%d%%";
+
+  std::snprintf(buf, sizeof(buf), format, value);
+  return buf;
+}
+
+int AlphaSlider::onGetValueFromText(const std::string& text)
+{
+  std::string str = text;
+  if (getAlphaRange() == AlphaRange::PERCENTAGE)
+      str.erase(std::remove(str.begin(), str.end(), '%'), str.end());
+
+  return std::strtol(str.c_str(), nullptr, 10);
+}
+
+}  // namespace app
diff --git a/src/app/ui/alpha_slider.h b/src/app/ui/alpha_slider.h
new file mode 100644
index 000000000..06edc9e11
--- /dev/null
+++ b/src/app/ui/alpha_slider.h
@@ -0,0 +1,42 @@
+// Aseprite
+// Copyright (C) 2024  Igara Studio S.A.
+//
+// This program is distributed under the terms of
+// the End-User License Agreement for Aseprite.
+
+#ifndef APP_UI_ALPHA_SLIDER_H_INCLUDED
+#define APP_UI_ALPHA_SLIDER_H_INCLUDED
+#pragma once
+
+#include "app/pref/preferences.h"
+#include "ui/slider.h"
+
+namespace app {
+
+class AlphaSlider : public ui::Slider,
+                    ui::SliderDelegate
+{
+public:
+  enum Type {ALPHA, OPACITY};
+
+  AlphaSlider(int value, Type type);
+
+  void getSliderThemeInfo(int* min, int* max, int* value) const override;
+  void updateValue(int value) override;
+
+  app::gen::AlphaRange getAlphaRange() const {
+    return (m_type == ALPHA ? Preferences::instance().range.alpha()
+                            : Preferences::instance().range.opacity());
+  }
+
+private:
+  // ui::SliderDelegate impl
+  std::string onGetTextFromValue(int value) override;
+  int onGetValueFromText(const std::string& text) override;
+
+  Type m_type;
+};
+
+}
+
+#endif
diff --git a/src/app/ui/color_sliders.cpp b/src/app/ui/color_sliders.cpp
index 1581459bd..d4efe31cc 100644
--- a/src/app/ui/color_sliders.cpp
+++ b/src/app/ui/color_sliders.cpp
@@ -13,6 +13,8 @@
 #include "app/color_spaces.h"
 #include "app/color_utils.h"
 #include "app/modules/gfx.h"
+#include "app/ui/alpha_entry.h"
+#include "app/ui/alpha_slider.h"
 #include "app/ui/color_sliders.h"
 #include "app/ui/expr_entry.h"
 #include "app/ui/skin/skin_slider_property.h"
@@ -141,19 +143,25 @@ namespace {
 
   private:
     int minValue() const {
-      if (m_absSlider->isVisible())
-        return m_absSlider->getMinValue();
-      else if (m_relSlider->isVisible())
-        return m_relSlider->getMinValue();
+      auto slider = (m_absSlider->isVisible() ? m_absSlider : m_relSlider);
+
+      if (slider->isVisible()) {
+        int min;
+        slider->getSliderThemeInfo(&min, nullptr, nullptr);
+        return min;
+      }
       else
         return 0;
     }
 
     int maxValue() const {
-      if (m_absSlider->isVisible())
-        return m_absSlider->getMaxValue();
-      else if (m_relSlider->isVisible())
-        return m_relSlider->getMaxValue();
+      auto slider = (m_absSlider->isVisible() ? m_absSlider : m_relSlider);
+
+      if (slider->isVisible()) {
+        int max;
+        slider->getSliderThemeInfo(nullptr, &max, nullptr);
+        return max;
+      }
       else
         return 0;
     }
@@ -373,7 +381,9 @@ void ColorSliders::addSlider(const Channel channel,
   ASSERT(!item.label);
   item.label     = new Label(labelText);
   item.box       = new HBox();
-  item.absSlider = new Slider(absMin, absMax, 0);
+  item.absSlider = (channel != Channel::Alpha
+                   ? new Slider(absMin, absMax, 0)
+                   : new AlphaSlider(0, AlphaSlider::Type::ALPHA));
   item.relSlider = new Slider(relMin, relMax, 0);
   item.entry     = new ColorEntry(item.absSlider, item.relSlider);
 
@@ -468,8 +478,7 @@ void ColorSliders::onEntryChange(const Channel i)
   Slider* slider = (m_mode == Mode::Absolute ?
                     m_items[i].absSlider:
                     m_items[i].relSlider);
-  value = std::clamp(value, slider->getMinValue(), slider->getMaxValue());
-  slider->setValue(value);
+  slider->updateValue(value);
 
   onControlChange(i);
 }
@@ -494,7 +503,10 @@ void ColorSliders::updateEntryText(const Channel i)
   Slider* slider = (m_mode == Mode::Absolute ? m_items[i].absSlider:
                                                m_items[i].relSlider);
 
-  m_items[i].entry->setTextf("%d", slider->getValue());
+  int value;
+  slider->getSliderThemeInfo(nullptr, nullptr, &value);
+
+  m_items[i].entry->setTextf("%d", value);
   if (m_items[i].entry->hasFocus())
     m_items[i].entry->selectAllText();
 }
diff --git a/src/app/ui/context_bar.cpp b/src/app/ui/context_bar.cpp
index 1fd6281ea..500375919 100644
--- a/src/app/ui/context_bar.cpp
+++ b/src/app/ui/context_bar.cpp
@@ -34,6 +34,7 @@
 #include "app/tools/tool.h"
 #include "app/tools/tool_box.h"
 #include "app/tools/tool_loop_modifiers.h"
+#include "app/ui/alpha_entry.h"
 #include "app/ui/brush_popup.h"
 #include "app/ui/button_set.h"
 #include "app/ui/color_button.h"
@@ -710,9 +711,9 @@ private:
   obs::scoped_connection m_conn;
 };
 
-class ContextBar::InkOpacityField : public IntEntry {
+class ContextBar::InkOpacityField : public AlphaEntry {
 public:
-  InkOpacityField() : IntEntry(0, 255) {
+  InkOpacityField() : AlphaEntry(AlphaSlider::Type::OPACITY) {
   }
 
 protected:
@@ -720,7 +721,7 @@ protected:
     if (g_updatingFromCode)
       return;
 
-    IntEntry::onValueChange();
+    AlphaEntry::onValueChange();
     base::ScopedValue lockFlag(g_updatingFromCode, true);
 
     int newValue = getValue();
@@ -1914,6 +1915,8 @@ ContextBar::ContextBar(TooltipManager* tooltipManager,
     [this]{ onFgOrBgColorChange(doc::Brush::ImageColor::MainColor); });
   m_bgColorConn = pref.colorBar.bgColor.AfterChange.connect(
     [this]{ onFgOrBgColorChange(doc::Brush::ImageColor::BackgroundColor); });
+  m_alphaRangeConn = pref.range.opacity.AfterChange.connect(
+    [this]{ onOpacityRangeChange(); });
   m_keysConn = KeyboardShortcuts::instance()->UserChange.connect(
     [this, tooltipManager]{ setupTooltips(tooltipManager); });
   m_dropPixelsConn = m_dropPixels->DropPixels.connect(&ContextBar::onDropPixels, this);
@@ -2056,6 +2059,11 @@ void ContextBar::onFgOrBgColorChange(doc::Brush::ImageColor imageColor)
   }
 }
 
+void ContextBar::onOpacityRangeChange()
+{
+  updateForActiveTool();
+}
+
 void ContextBar::onDropPixels(ContextBarObserver::DropAction action)
 {
   notify_observers(&ContextBarObserver::onDropPixels, action);
@@ -2143,7 +2151,7 @@ void ContextBar::updateForTool(tools::Tool* tool)
     m_contiguous->setSelected(toolPref->contiguous());
 
     m_inkType->setInkTypeIcon(toolPref->ink());
-    m_inkOpacity->setTextf("%d", toolPref->opacity());
+    m_inkOpacity->setValue(toolPref->opacity());
 
     hasInkWithOpacity =
       ((isPaint && tools::inkHasOpacity(toolPref->ink())) ||
diff --git a/src/app/ui/context_bar.h b/src/app/ui/context_bar.h
index 4cbc322ab..de0d147f7 100644
--- a/src/app/ui/context_bar.h
+++ b/src/app/ui/context_bar.h
@@ -123,6 +123,7 @@ namespace app {
     void onBrushAngleChange();
     void onSymmetryModeChange();
     void onFgOrBgColorChange(doc::Brush::ImageColor imageColor);
+    void onOpacityRangeChange();
     void onDropPixels(ContextBarObserver::DropAction action);
     void updateSliceFields(const Site& site);
 
@@ -203,6 +204,7 @@ namespace app {
     obs::scoped_connection m_symmModeConn;
     obs::scoped_connection m_fgColorConn;
     obs::scoped_connection m_bgColorConn;
+    obs::scoped_connection m_alphaRangeConn;
     obs::scoped_connection m_keysConn;
     obs::scoped_connection m_dropPixelsConn;
     obs::scoped_connection m_sizeConn;
diff --git a/src/app/widget_loader.cpp b/src/app/widget_loader.cpp
index 957d3c5fd..50c1b1718 100644
--- a/src/app/widget_loader.cpp
+++ b/src/app/widget_loader.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2019-2023  Igara Studio S.A.
+// Copyright (C) 2019-2024  Igara Studio S.A.
 // Copyright (C) 2001-2018  David Capello
 //
 // This program is distributed under the terms of
@@ -17,6 +17,7 @@
 #include "app/i18n/strings.h"
 #include "app/modules/gui.h"
 #include "app/resource_finder.h"
+#include "app/ui/alpha_slider.h"
 #include "app/ui/button_set.h"
 #include "app/ui/color_button.h"
 #include "app/ui/drop_down_button.h"
@@ -405,6 +406,13 @@ Widget* WidgetLoader::convertXmlElementToWidget(const TiXmlElement* elem, Widget
     widget = new Slider(min_value, max_value, min_value);
     static_cast<Slider*>(widget)->setReadOnly(readonly);
   }
+  else if (elem_name == "alphaslider" || elem_name == "opacityslider") {
+    const bool readonly = bool_attr(elem, "readonly", false);
+    widget = new AlphaSlider(0, (elem_name == "alphaslider"
+                                 ? AlphaSlider::Type::ALPHA
+                                 : AlphaSlider::Type::OPACITY));
+    static_cast<AlphaSlider*>(widget)->setReadOnly(readonly);
+  }
   else if (elem_name == "textbox") {
     const char* text = (elem->GetText() ? elem->GetText(): "");
     bool wordwrap = bool_attr(elem, "wordwrap", false);
diff --git a/src/gen/ui_class.cpp b/src/gen/ui_class.cpp
index c693cb268..6c16aae2e 100644
--- a/src/gen/ui_class.cpp
+++ b/src/gen/ui_class.cpp
@@ -1,5 +1,5 @@
 // Aseprite Code Generator
-// Copyright (c) 2021-2023 Igara Studio S.A.
+// Copyright (c) 2021-2024 Igara Studio S.A.
 // Copyright (c) 2014-2018 David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -157,6 +157,9 @@ static Item convert_to_item(TiXmlElement* elem)
   if (name == "slider")
     return item.typeIncl("ui::Slider",
                          "ui/slider.h");
+  if (name == "alphaslider" || name == "opacityslider")
+    return item.typeIncl("app::AlphaSlider",
+                         "app/ui/alpha_slider.h");
   if (name == "splitter")
     return item.typeIncl("ui::Splitter",
                          "ui/splitter.h");
diff --git a/src/ui/int_entry.cpp b/src/ui/int_entry.cpp
index ab9eed867..bb7462c9e 100644
--- a/src/ui/int_entry.cpp
+++ b/src/ui/int_entry.cpp
@@ -36,13 +36,13 @@ IntEntry::IntEntry(int min, int max, SliderDelegate* sliderDelegate)
   : Entry(int(std::floor(std::log10(double(max))))+1, "")
   , m_min(min)
   , m_max(max)
-  , m_slider(m_min, m_max, m_min, sliderDelegate)
   , m_popupWindow(nullptr)
   , m_changeFromSlider(false)
 {
-  m_slider.setFocusStop(false); // In this way the IntEntry doesn't lost the focus
-  m_slider.setTransparent(true);
-  m_slider.Change.connect(&IntEntry::onChangeSlider, this);
+  m_slider = std::make_unique<Slider>(m_min, m_max, m_min, sliderDelegate);
+  m_slider->setFocusStop(false); // In this way the IntEntry doesn't lost the focus
+  m_slider->setTransparent(true);
+  m_slider->Change.connect(&IntEntry::onChangeSlider, this);
   initTheme();
 }
 
@@ -53,7 +53,7 @@ IntEntry::~IntEntry()
 
 int IntEntry::getValue() const
 {
-  int value = m_slider.convertTextToValue(text());
+  int value = m_slider->convertTextToValue(text());
   return std::clamp(value, m_min, m_max);
 }
 
@@ -61,10 +61,10 @@ void IntEntry::setValue(int value)
 {
   value = std::clamp(value, m_min, m_max);
 
-  setText(m_slider.convertValueToText(value));
+  setText(m_slider->convertValueToText(value));
 
   if (m_popupWindow && !m_changeFromSlider)
-    m_slider.setValue(value);
+    m_slider->setValue(value);
 
   onValueChange();
 }
@@ -92,7 +92,7 @@ bool IntEntry::onProcessMessage(Message* msg)
         MouseMessage* mouseMsg = static_cast<MouseMessage*>(msg);
         Widget* pick = manager()->pickFromScreenPos(
           display()->nativeWindow()->pointToScreen(mouseMsg->position()));
-        if (pick == &m_slider) {
+        if (pick == m_slider.get()) {
           releaseMouse();
 
           MouseMessage mouseMsg2(kMouseDownMessage,
@@ -140,7 +140,7 @@ bool IntEntry::onProcessMessage(Message* msg)
 void IntEntry::onInitTheme(InitThemeEvent& ev)
 {
   Entry::onInitTheme(ev);
-  m_slider.initTheme();       // The slider might not be in the popup window
+  m_slider->initTheme();       // The slider might not be in the popup window
   if (m_popupWindow)
     m_popupWindow->initTheme();
 }
@@ -150,8 +150,8 @@ void IntEntry::onSizeHint(SizeHintEvent& ev)
   int trailing = font()->textLength(getSuffix());
   trailing = std::max(trailing, 2*theme()->getEntryCaretSize(this).w);
 
-  int min_w = font()->textLength(m_slider.convertValueToText(m_min));
-  int max_w = font()->textLength(m_slider.convertValueToText(m_max)) + trailing;
+  int min_w = font()->textLength(m_slider->convertValueToText(m_min));
+  int max_w = font()->textLength(m_slider->convertValueToText(m_max)) + trailing;
 
   int w = std::max(min_w, max_w);
   int h = textHeight();
@@ -175,7 +175,7 @@ void IntEntry::onValueChange()
 
 void IntEntry::openPopup()
 {
-  m_slider.setValue(getValue());
+  m_slider->setValue(getValue());
 
   // We weren't able to reproduce it, but there are crash reports
   // where this openPopup() function is called and the popup is still
@@ -186,7 +186,7 @@ void IntEntry::openPopup()
 
   m_popupWindow = std::make_unique<TransparentPopupWindow>(PopupWindow::ClickBehavior::CloseOnClickInOtherWindow);
   m_popupWindow->setAutoRemap(false);
-  m_popupWindow->addChild(&m_slider);
+  m_popupWindow->addChild(m_slider.get());
   m_popupWindow->Close.connect(&IntEntry::onPopupClose, this);
 
   fit_bounds(
@@ -229,7 +229,7 @@ void IntEntry::closePopup()
 void IntEntry::onChangeSlider()
 {
   base::ScopedValue lockFlag(m_changeFromSlider, true);
-  setValue(m_slider.getValue());
+  setValue(m_slider->getValue());
   selectAllText();
 }
 
@@ -244,8 +244,8 @@ void IntEntry::onPopupClose(CloseEvent& ev)
 void IntEntry::removeSlider()
 {
   if (m_popupWindow &&
-      m_slider.parent() == m_popupWindow.get()) {
-    m_popupWindow->removeChild(&m_slider);
+      m_slider->parent() == m_popupWindow.get()) {
+    m_popupWindow->removeChild(m_slider.get());
   }
 }
 
diff --git a/src/ui/int_entry.h b/src/ui/int_entry.h
index 7e64332f3..74dde7b40 100644
--- a/src/ui/int_entry.h
+++ b/src/ui/int_entry.h
@@ -22,32 +22,33 @@ namespace ui {
   class IntEntry : public Entry {
   public:
     IntEntry(int min, int max, SliderDelegate* sliderDelegate = nullptr);
-    ~IntEntry();
+    virtual ~IntEntry();
 
-    int getValue() const;
-    void setValue(int value);
+    virtual int getValue() const;
+    virtual void setValue(int value);
 
   protected:
     bool onProcessMessage(Message* msg) override;
     void onInitTheme(InitThemeEvent& ev) override;
     void onSizeHint(SizeHintEvent& ev) override;
     void onChange() override;
+    virtual void onChangeSlider();
 
     // New events
     virtual void onValueChange();
 
+    int m_min;
+    int m_max;
+    std::unique_ptr<PopupWindow> m_popupWindow;
+    bool m_changeFromSlider;
+    std::unique_ptr<Slider> m_slider;
+
   private:
     void openPopup();
     void closePopup();
-    void onChangeSlider();
     void onPopupClose(CloseEvent& ev);
     void removeSlider();
 
-    int m_min;
-    int m_max;
-    Slider m_slider;
-    std::unique_ptr<PopupWindow> m_popupWindow;
-    bool m_changeFromSlider;
   };
 
 } // namespace ui
diff --git a/src/ui/slider.cpp b/src/ui/slider.cpp
index caa370375..a74eecf27 100644
--- a/src/ui/slider.cpp
+++ b/src/ui/slider.cpp
@@ -1,5 +1,5 @@
 // Aseprite UI Library
-// Copyright (C) 2019-2022  Igara Studio S.A.
+// Copyright (C) 2019-2024  Igara Studio S.A.
 // Copyright (C) 2001-2016  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -24,9 +24,9 @@
 
 namespace ui {
 
-static int slider_press_x;
-static int slider_press_value;
-static bool slider_press_left;
+int Slider::slider_press_x;
+int Slider::slider_press_value;
+bool Slider::slider_press_left;
 
 Slider::Slider(int min, int max, int value, SliderDelegate* delegate)
   : Widget(kSliderWidget)
@@ -75,6 +75,11 @@ void Slider::getSliderThemeInfo(int* min, int* max, int* value) const
   if (value) *value = m_value;
 }
 
+void Slider::updateValue(int value)
+{
+  setValue(value);
+}
+
 std::string Slider::convertValueToText(int value) const
 {
   if (m_delegate)
@@ -113,9 +118,11 @@ bool Slider::onProcessMessage(Message* msg)
       captureMouse();
 
       {
+        int value;
+        getSliderThemeInfo(nullptr, nullptr, &value);
         gfx::Point mousePos = static_cast<MouseMessage*>(msg)->position();
         slider_press_x = mousePos.x;
-        slider_press_value = m_value;
+        slider_press_value = value;
         slider_press_left = static_cast<MouseMessage*>(msg)->left();
       }
 
@@ -125,27 +132,33 @@ bool Slider::onProcessMessage(Message* msg)
 
     case kMouseMoveMessage:
       if (hasCapture()) {
-        int value, accuracy, range;
+        int min, max, value, range;
         gfx::Rect rc = childrenBounds();
         gfx::Point mousePos = static_cast<MouseMessage*>(msg)->positionForDisplay(display());
 
-        range = m_max - m_min + 1;
+        getSliderThemeInfo(&min, &max, &value);
+
+        range =  max - min + 1;
 
         // With left click
         if (slider_press_left) {
-          value = m_min + range * (mousePos.x - rc.x) / rc.w;
+          value = min + range * (mousePos.x - rc.x) / rc.w;
         }
         // With right click
         else {
-          accuracy = std::clamp(rc.w / range, 1, rc.w);
+          int w = rc.w;
+          if (rc.w == 0 || range > rc.w) {
+            w = 1;
+            range = 1;
+          }
 
           value = slider_press_value +
-            (mousePos.x - slider_press_x) / accuracy;
+            (mousePos.x - slider_press_x) * range / w;
         }
 
-        value = std::clamp(value, m_min, m_max);
-        if (m_value != value) {
-          setValue(value);
+        value = std::clamp(value, min, max);
+        if (getValue() != value) {
+          updateValue(value);
           onChange();
         }
 
@@ -172,22 +185,24 @@ bool Slider::onProcessMessage(Message* msg)
 
     case kKeyDownMessage:
       if (hasFocus() && !isReadOnly()) {
-        int value = m_value;
+        int min, max, value, oldValue;
+        getSliderThemeInfo(&min, &max, &value);
+        oldValue = value;
 
         switch (static_cast<KeyMessage*>(msg)->scancode()) {
           case kKeyLeft:     --value; break;
           case kKeyRight:    ++value; break;
-          case kKeyPageDown: value -= (m_max-m_min+1)/4; break;
-          case kKeyPageUp:   value += (m_max-m_min+1)/4; break;
-          case kKeyHome:     value = m_min; break;
-          case kKeyEnd:      value = m_max; break;
+          case kKeyPageDown: value -= (max-min+1)/4; break;
+          case kKeyPageUp:   value += (max-min+1)/4; break;
+          case kKeyHome:     value = min; break;
+          case kKeyEnd:      value = max; break;
           default:
             goto not_used;
         }
 
-        value = std::clamp(value, m_min, m_max);
-        if (m_value != value) {
-          setValue(value);
+        value = std::clamp(value, min, max);
+        if (oldValue != value) {
+          updateValue(value);
           onChange();
         }
 
@@ -204,7 +219,7 @@ bool Slider::onProcessMessage(Message* msg)
         value = std::clamp(value, m_min, m_max);
 
         if (m_value != value) {
-          this->setValue(value);
+          setValue(value);
           onChange();
         }
         return true;
diff --git a/src/ui/slider.h b/src/ui/slider.h
index c6de0c5e2..2cf47ca39 100644
--- a/src/ui/slider.h
+++ b/src/ui/slider.h
@@ -1,5 +1,5 @@
 // Aseprite UI Library
-// Copyright (C) 2020  Igara Studio S.A.
+// Copyright (C) 2020-2024  Igara Studio S.A.
 // Copyright (C) 2001-2016  David Capello
 //
 // This file is released under the terms of the MIT license.
@@ -35,7 +35,8 @@ namespace ui {
     bool isReadOnly() const { return m_readOnly; }
     void setReadOnly(bool readOnly) { m_readOnly = readOnly; }
 
-    void getSliderThemeInfo(int* min, int* max, int* value) const;
+    virtual void getSliderThemeInfo(int* min, int* max, int* value) const;
+    virtual void updateValue(int value);
 
     std::string convertValueToText(int value) const;
     int convertTextToValue(const std::string& text) const;
@@ -45,6 +46,10 @@ namespace ui {
     obs::signal<void()> SliderReleased;
 
   protected:
+    static int slider_press_x;
+    static int slider_press_value;
+    static bool slider_press_left;
+
     // Events
     bool onProcessMessage(Message* msg) override;
     void onPaint(PaintEvent& ev) override;