7GUIs Circle Drawer

Note

This page describes an example listed in 7GUIs.

Undo, redo, dialog control.

Challenges: undo/redo, custom drawing, dialog control.

The task is to build a frame containing an undo and redo button as well as a canvas area underneath. Left-clicking inside an empty area inside the canvas will create an unfilled circle with a fixed diameter whose center is the left-clicked point. The circle nearest to the mouse pointer such that the distance from its center to the pointer is less than its radius, if it exists, is filled with the color gray. The gray circle is the selected circle C. Right-clicking C will make a popup menu appear with one entry “Adjust diameter..”. Clicking on this entry will open another frame with a slider inside that adjusts the diameter of C. Changes are applied immediately. Closing this frame will mark the last diameter as significant for the undo/redo history. Clicking undo will undo the last significant change (i.e. circle creation or diameter adjustment). Clicking redo will reapply the last undoed change unless new changes were made by the user in the meantime.

Circle Drawer’s goal is, among other things, to test how good the common challenge of implementing an undo/redo functionality for a GUI application can be solved. In an ideal solution the undo/redo functionality comes for free resp. just comes out as a natural consequence of the language / toolkit / paradigm. Moreover, Circle Drawer tests how dialog control, i.e. keeping the relevant context between several successive GUI interaction steps, is achieved in the source code. Last but not least, the ease of custom drawing is tested.

/*
 * AUI Framework - Declarative UI toolkit for modern C++20
 * Copyright (C) 2020-2024 Alex2772 and Contributors
 *
 * SPDX-License-Identifier: MPL-2.0
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */
 
#include <AUI/Platform/Entry.h>
#include <AUI/Platform/AWindow.h>
#include <AUI/Util/UIBuildingHelpers.h>
#include "AUI/View/AProgressBar.h"
#include "AUI/View/ASlider.h"
#include "AUI/View/AButton.h"
 
using namespace declarative;
 
struct Circle {
   glm::vec2 position;
   float radius = 10_dp;
};
 
class IAction {   // IAction: candidate to be committed to the framework
public:
   virtual ~IAction() = default;
   virtual void undo() = 0;
   virtual void redo() = 0;
};
 
class UndoStack {
public:
   using Container = std::list<_unique<IAction>>;
   using Iterator = Container::const_iterator;
private:
   Container mStack;
 
public:
 
   void undo() {
       if (nextAction == mStack.begin()) {
           return;
       }
       nextAction = std::prev(*nextAction);
       (**nextAction)->undo();
   }
 
   void redo() {
       if (nextAction == mStack.end()) {
           return;
       }
       (**nextAction)->redo();
       nextAction = std::next(*nextAction);
   }
 
   void add(_unique<IAction> action) {
       action->redo();
       nextAction = std::next(mStack.insert(mStack.erase(*nextAction, mStack.end()), std::move(action)));
       nextAction.notify();
   }
 
   Iterator begin() const {
       return mStack.begin();
   }
 
   Iterator end() const {
       return mStack.end();
   }
 
   AProperty<Iterator> nextAction = mStack.end();
};
 
struct State {
   AProperty<std::list<Circle>> circles;
   UndoStack history;
};
 
static constexpr auto MAX_RADIUS = 128.f;
 
class CircleDrawArea : public AView {
public:
   CircleDrawArea(_<State> state) : mState(std::move(state)) {
       setCustomStyle({
         Expanding(),
         BackgroundSolid(AColor::WHITE),
         Border(1_px, AColor::GRAY),
         AOverflow::HIDDEN_FROM_THIS,
       });
       connect(mState->circles.changed, me::redraw);
       connect(mHoveredCircle.changed, me::redraw);
   }
 
   void render(ARenderContext ctx) override {
       AView::render(ctx);
 
       for (const auto& circle : *mState->circles) {
           if (&circle == mHoveredCircle) {
               ctx.render.roundedRectangle(
                   ASolidBrush { AColor::GRAY }, circle.position - circle.radius, glm::vec2(circle.radius * 2.f),
                   circle.radius);
           }
           ctx.render.roundedRectangleBorder(
               ASolidBrush { AColor::BLACK }, circle.position - circle.radius, glm::vec2(circle.radius * 2.f),
               circle.radius, 1);
       }
   }
 
   void onPointerMove(glm::vec2 pos, const APointerMoveEvent& event) override {
       AView::onPointerMove(pos, event);
       mHoveredCircle = [&] {
           Circle* result = nullptr;
           float nearestDistanceToCursor = std::numeric_limits<float>::max();
           for (auto& circle : mState->circles.raw) {
               float distanceToCursor = glm::distance2(circle.position, pos);
               if (distanceToCursor > nearestDistanceToCursor) {
                   continue;
               }
               if (distanceToCursor > circle.radius * circle.radius) {
                   continue;
               }
               result = &circle;
               nearestDistanceToCursor = distanceToCursor;
           }
           return result;
       }();
   }
 
protected:
   AMenuModel composeContextMenu() override {
       auto circle = *mHoveredCircle;
       if (circle == nullptr) {
           return {};
       }
       return {
           {},
           {
             .name = "Adjust radius...",
             .onAction =
                 [this, circle] {
 
 
                     auto radiusPopup = _new<AWindow>(
                         "", 200_dp, 50_dp, dynamic_cast<AWindow*>(AWindow::current()), WindowStyle::MODAL);
                     radiusPopup->setContents(Vertical {
                       Label { "Adjust diameter of circle at {}."_format(circle->position) },
                       _new<ASlider>() let {
                               it->setValue(circle->radius / MAX_RADIUS);
                               connect(
                                   it->valueChanging, [this, circle](aui::float_within_0_1 s) {
                                       circle->radius = s * MAX_RADIUS;
                                       mState->circles.notify();
                                   });
                           },
                     });
                     connect(radiusPopup->closed, [this, circle, oldRadius = circle->radius] {
                         if (oldRadius == circle->radius) {
                             return;
                         }
                         class ActionChangeRadius : public IAction {
                         public:
                             ActionChangeRadius(Circle* circle, float prevRadius, float newRadius)
                               : mCircle(circle), mPrevRadius(prevRadius), mNewRadius(newRadius) {}
 
                             ~ActionChangeRadius() override = default;
 
                             void undo() override {
                                 mCircle->radius = mPrevRadius;
                             }
 
                             void redo() override {
                                 mCircle->radius = mNewRadius;
                             }
 
                         private:
                             Circle* mCircle;
                             float mPrevRadius;
                             float mNewRadius;
                         };
                         mState->history.add(std::make_unique<ActionChangeRadius>(circle, oldRadius, circle->radius));
                     });
                     radiusPopup->show();
                 },
           },
       };
   }
 
public:
   void onPointerReleased(const APointerReleasedEvent& event) override {
       AView::onPointerReleased(event);
       if (event.asButton != AInput::LBUTTON) {
           return;
       }
       class ActionAddCircle : public IAction {
       public:
           ActionAddCircle(_<State> state, Circle circle) : mState(std::move(state)), mCircle(std::move(circle)) {}
           ~ActionAddCircle() override = default;
           void undo() override {
               mState->circles.writeScope()->pop_back();
           }
           void redo() override {
               mState->circles.writeScope()->push_back(mCircle);
           }
 
       private:
           _<State> mState;
           Circle mCircle;
       };
       mState->history.add(std::make_unique<ActionAddCircle>(mState, Circle { .position = event.position }));
   }
 
private:
   _<State> mState;
   AProperty<Circle*> mHoveredCircle = nullptr;
};
 
class CircleDrawerWindow : public AWindow {
public:
   CircleDrawerWindow() : AWindow("AUI - 7GUIs - Circle Drawer", 300_dp, 250_dp) {
       setContents(Vertical {
         Centered {
           Horizontal {
             Button { "Undo" } let {
                 connect(it->clicked, me::undo);
                 it & mState.history.nextAction.readProjected([&](UndoStack::Iterator i) { return i != mState.history.begin(); }) > &AView::setEnabled;
             },
             Button { "Redo" } let {
               connect(it->clicked, me::redo);
               it & mState.history.nextAction.readProjected([&](UndoStack::Iterator i) { return i != mState.history.end(); }) > &AView::setEnabled;
             },
           },
         },
         _new<CircleDrawArea>(aui::ptr::fake(&mState)),
       });
   }
 
private:
   State mState;
 
   void undo() {
       mState.history.undo();
   }
 
   void redo() {
       mState.history.redo();
   }
};
 
AUI_ENTRY {
   _new<CircleDrawerWindow>()->show();
   return 0;
}

Source Files#

• Repository
• src/main.cpp

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