diff --git a/android/CMakeLists.txt b/android/CMakeLists.txt
index 2599bcd..38b70c7 100644
--- a/android/CMakeLists.txt
+++ b/android/CMakeLists.txt
@@ -40,6 +40,7 @@ add_library(
 	../engine/brush.cpp
 	../engine/canvas.cpp
 	../engine/log.cpp
+	../engine/action.cpp
 )
 
 target_include_directories(native-lib PRIVATE
diff --git a/android/src/main/cpp/main.cpp b/android/src/main/cpp/main.cpp
index b8e9406..8bedff9 100755
--- a/android/src/main/cpp/main.cpp
+++ b/android/src/main/cpp/main.cpp
@@ -26,7 +26,7 @@
 
 #include "pch.h"
 #include "app.h"
-#include "..\..\..\..\engine\asset.h"
+#include "../../../../engine/asset.h"
 
 typedef void (*GLDEBUGPROC)(GLenum source,
     GLenum type,
diff --git a/data/layout.xml b/data/layout.xml
index fa9c48c..40d2143 100644
--- a/data/layout.xml
+++ b/data/layout.xml
@@ -371,6 +371,7 @@
           </button-custom>-->
 
           <button id="btn-switch" width="50" height="50" margin="0 0 5 0" text="Switch"/>
+          <button id="btn-undo" width="50" height="50" margin="0 0 5 0" text="Undo"/>
           <button id="btn-close" width="50" height="50" margin="0 0 5 0" text="Clear"/>
           <button-custom id="btn-bucket" width="50" height="50" margin="0 0 5 0" thickness="1" border-color=".1" pad="2">
             <image path="data/ui/bucket.png" width="100%" height="100%" align="center" justify="flex-end"/>
diff --git a/engine.xcodeproj/project.pbxproj b/engine.xcodeproj/project.pbxproj
index 6b077b8..ea7fbfe 100644
--- a/engine.xcodeproj/project.pbxproj
+++ b/engine.xcodeproj/project.pbxproj
@@ -7,6 +7,7 @@
 	objects = {
 
 /* Begin PBXBuildFile section */
+		AD29CC621EA2B214008C8BFA /* action.cpp in Sources */ = {isa = PBXBuildFile; fileRef = AD29CC601EA2B214008C8BFA /* action.cpp */; };
 		AD3B1EC01E3B8B7600E918E3 /* layout.cpp in Sources */ = {isa = PBXBuildFile; fileRef = AD3B1EBE1E3B8B7600E918E3 /* layout.cpp */; };
 		AD4C08D91E89BD0F0051D85F /* asset.cpp in Sources */ = {isa = PBXBuildFile; fileRef = AD4C08CF1E89BD0F0051D85F /* asset.cpp */; };
 		AD4C08DA1E89BD0F0051D85F /* bezier.cpp in Sources */ = {isa = PBXBuildFile; fileRef = AD4C08D11E89BD0F0051D85F /* bezier.cpp */; };
@@ -48,6 +49,8 @@
 /* End PBXCopyFilesBuildPhase section */
 
 /* Begin PBXFileReference section */
+		AD29CC601EA2B214008C8BFA /* action.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = action.cpp; sourceTree = "<group>"; };
+		AD29CC611EA2B214008C8BFA /* action.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = action.h; sourceTree = "<group>"; };
 		AD3B1EBE1E3B8B7600E918E3 /* layout.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = layout.cpp; sourceTree = "<group>"; };
 		AD3B1EBF1E3B8B7600E918E3 /* layout.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = layout.h; sourceTree = "<group>"; };
 		AD4C08CF1E89BD0F0051D85F /* asset.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = asset.cpp; sourceTree = "<group>"; };
@@ -133,6 +136,8 @@
 		AD58E0511E107411006ACC15 /* engine */ = {
 			isa = PBXGroup;
 			children = (
+				AD29CC601EA2B214008C8BFA /* action.cpp */,
+				AD29CC611EA2B214008C8BFA /* action.h */,
 				AD8CF71F1E913F0500083FFD /* log.cpp */,
 				AD8CF7201E913F0500083FFD /* log.h */,
 				AD4C08CF1E89BD0F0051D85F /* asset.cpp */,
@@ -235,6 +240,7 @@
 			buildActionMask = 2147483647;
 			files = (
 				AD58E0791E342205006ACC15 /* tinyxml2.cpp in Sources */,
+				AD29CC621EA2B214008C8BFA /* action.cpp in Sources */,
 				AD58E06F1E2A80BC006ACC15 /* shape.cpp in Sources */,
 				AD58E0651E2A76FD006ACC15 /* shader.cpp in Sources */,
 				AD4C08DA1E89BD0F0051D85F /* bezier.cpp in Sources */,
diff --git a/engine/action.cpp b/engine/action.cpp
new file mode 100644
index 0000000..084943c
--- /dev/null
+++ b/engine/action.cpp
@@ -0,0 +1,4 @@
+#include "pch.h"
+#include "action.h"
+
+ActionManager ActionManager::I;
diff --git a/engine/action.h b/engine/action.h
new file mode 100644
index 0000000..b8e902f
--- /dev/null
+++ b/engine/action.h
@@ -0,0 +1,24 @@
+#pragma once
+
+class Action
+{
+public:
+    virtual void run() = 0;
+    virtual void undo() = 0;
+};
+
+class ActionManager
+{
+public:
+    static ActionManager I;
+    std::stack<std::unique_ptr<Action>> m_actions;
+    static void add(Action* action)
+    {
+        I.m_actions.emplace(action);
+    }
+    static void undo()
+    {
+        I.m_actions.top()->undo();
+        I.m_actions.pop();
+    }
+};
diff --git a/engine/app.cpp b/engine/app.cpp
index 3faa1af..f0bc32d 100644
--- a/engine/app.cpp
+++ b/engine/app.cpp
@@ -420,6 +420,12 @@ void App::initLayout()
             };
             button->m_text->set_text("NORM");
         }
+        if (auto* button = layout[main_id]->find<NodeButton>("btn-undo"))
+        {
+            button->on_click = [this,button](Node*) {
+                ActionManager::undo();
+            };
+        }
         if (auto* button = layout[main_id]->find<NodeButton>("btn-close"))
         {
             button->on_click = [this](Node*) { 
diff --git a/engine/canvas.cpp b/engine/canvas.cpp
index e45c1d5..1e75c91 100644
--- a/engine/canvas.cpp
+++ b/engine/canvas.cpp
@@ -100,7 +100,7 @@ void ui::Canvas::stroke_draw()
                 bb_max = glm::min({ m_width, m_height }, glm::max(bb_max, P2[i].xy()));
             }
             auto bb_sz = bb_max - bb_min;
-
+            
             glm::vec2 pad(1);
             glm::ivec2 tex_pos = glm::clamp(glm::floor(bb_min) - pad , { 0, 0 }, { m_width, m_height });
             glm::ivec2 tex_sz  = glm::clamp(glm::ceil(bb_sz ) + pad*2.f, { 0, 0 }, (glm::vec2)(glm::ivec2(m_width, m_height) - tex_pos));
@@ -108,6 +108,9 @@ void ui::Canvas::stroke_draw()
                 tex_pos.x, tex_pos.y,
                 tex_pos.x, tex_pos.y,
                 tex_sz.x, tex_sz.y);
+            
+            m_box.xy = glm::min(m_box.xy(), (glm::vec2)tex_pos);
+            m_box.zw = glm::max(m_box.zw(), (glm::vec2)(tex_pos + tex_sz));
 
             ShaderManager::u_mat4(kShaderUniform::MVP, mvp);
             ShaderManager::u_float(kShaderUniform::Alpha, s.flow);
@@ -136,7 +139,12 @@ void ui::Canvas::stroke_commit()
     m_dirty = false;
 
     m_layers[m_current_layer_idx].m_rtt.bindFramebuffer();
-
+    
+    // save image before commit
+    glm::vec2 box_sz = m_box.zw() - m_box.xy();
+    auto image = std::make_unique<uint8_t[]>(box_sz.x * box_sz.y * 4);
+    glReadPixels(m_box.x, m_box.y, box_sz.x, box_sz.y, GL_RGBA, GL_UNSIGNED_BYTE, image.get());
+    
     // copy to tmp2 for layer blending
     m_tex2.bind();
     glCopyTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, 0, 0, m_width, m_height);
@@ -181,6 +189,15 @@ void ui::Canvas::stroke_commit()
     glClearColor(cc[0], cc[1], cc[2], cc[3]);
 
     m_layers[m_current_layer_idx].m_rtt.unbindFramebuffer();
+    
+    // save history
+    auto action = new ActionStroke;
+    action->m_image = std::move(image);
+    action->m_box = m_box;
+    action->m_layer_idx = m_current_layer_idx;
+    action->m_canvas = this;
+    action->m_stroke = std::move(m_current_stroke);
+    ActionManager::add(action);
 }
 void ui::Canvas::stroke_update(glm::vec2 point, float pressure)
 {
@@ -188,10 +205,11 @@ void ui::Canvas::stroke_update(glm::vec2 point, float pressure)
 }
 void ui::Canvas::stroke_start(glm::vec2 point, float pressure, const ui::Brush& brush)
 {
-    m_strokes.emplace_back();
-    m_strokes.back().start(brush);
-    m_strokes.back().add_point(point, pressure);
-    m_current_stroke = &m_strokes.back();
+    m_current_stroke = std::make_unique<Stroke>();
+    m_current_stroke->start(brush);
+    m_current_stroke->add_point(point, pressure);
+    
+    m_box = glm::vec4(m_width, m_height, 0, 0); // reset bounding box
     
     if (m_erase)
     {
diff --git a/engine/canvas.h b/engine/canvas.h
index ac4c6f5..27cf9db 100644
--- a/engine/canvas.h
+++ b/engine/canvas.h
@@ -4,6 +4,7 @@
 #include "shader.h"
 #include "shape.h"
 #include "brush.h"
+#include "action.h"
 
 NS_START
 
@@ -15,14 +16,14 @@ class Canvas
 public:
     bool m_erase = false;
     glm::mat4 m_mvp;
+    glm::vec4 m_box;
     int m_width;
     int m_height;
     bool m_use_instanced = false;
     int m_current_layer_idx = 0;
-    Stroke* m_current_stroke = nullptr;
+    std::unique_ptr<Stroke> m_current_stroke;
     bool m_show_tmp = false;
     std::vector<Layer> m_layers;
-    std::vector<Stroke> m_strokes;
     std::vector<int> m_order;
     RTT m_tmp;
     Texture2D m_tex;
@@ -42,4 +43,28 @@ public:
     void clear(const glm::vec4& color = { 1, 1, 1, 1 });
 };
 
+
+class ActionStroke : public Action
+{
+public:
+    std::unique_ptr<Stroke> m_stroke;
+    std::unique_ptr<uint8_t[]> m_image;
+    glm::ivec4 m_box;
+    int m_layer_idx;
+    Canvas* m_canvas;
+    virtual void run() override
+    {
+        
+    }
+    virtual void undo() override
+    {
+        m_canvas->m_layers[m_stroke->m_layer].m_rtt.bindTexture();
+
+        glm::vec2 box_sz = m_box.zw() - m_box.xy();
+        glTexSubImage2D(GL_TEXTURE_2D, 0, m_box.x, m_box.y, box_sz.x, box_sz.y, GL_RGBA, GL_UNSIGNED_BYTE, m_image.get());
+
+        m_canvas->m_layers[m_stroke->m_layer].m_rtt.unbindTexture();
+    }
+};
+
 NS_END
diff --git a/engine/pch.h b/engine/pch.h
index d922bfb..7215e66 100644
--- a/engine/pch.h
+++ b/engine/pch.h
@@ -46,6 +46,7 @@
 #include <stack>
 #include <regex>
 #include <mutex>
+#include <queue>
 #include <memory>
 #include <string>
 #include <vector>