WindowServer: Add a more generic mechanism for animations

This patch adds the WindowServer::Animation class, which represents
a simple animation driven by the compositor.

An animation has a length (in milliseconds) and two hooks:

- on_update: called whenever the animation should render something.
- on_stop: called when the animation is finished and/or stopped.

This patch also ports the window minimization animation to this new
mechanism. :^)

7 files changed, 171 insertions, 70 deletions

diff --git a/Userland/Services/WindowServer/Animation.cpp b/Userland/Services/WindowServer/Animation.cpp
new file mode 100644
index 0000000000..bb35691b4d
--- /dev/null
+++ b/Userland/Services/WindowServer/Animation.cpp
@@ -0,0 +1,53 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "Animation.h"
+#include "Compositor.h"
+#include <AK/Badge.h>
+
+namespace WindowServer {
+
+Animation::Animation()
+{
+    Compositor::the().register_animation({}, *this);
+}
+
+Animation::~Animation()
+{
+    Compositor::the().unregister_animation({}, *this);
+}
+
+void Animation::set_length(int length_in_ms)
+{
+    m_length = length_in_ms;
+}
+
+void Animation::start()
+{
+    m_running = true;
+    m_timer.start();
+}
+
+void Animation::stop()
+{
+    m_running = false;
+    if (on_stop)
+        on_stop();
+}
+
+void Animation::update(Badge<Compositor>, Gfx::Painter& painter, Screen& screen, Gfx::DisjointRectSet& flush_rects)
+{
+    int elapsed_ms = m_timer.elapsed();
+    float progress = min((float)elapsed_ms / (float)m_length, 1.0f);
+
+    if (on_update)
+        on_update(progress, painter, screen, flush_rects);
+
+    if (progress >= 1.0f)
+        stop();
+}
+
+}
diff --git a/Userland/Services/WindowServer/Animation.h b/Userland/Services/WindowServer/Animation.h
new file mode 100644
index 0000000000..6bd0072b61
--- /dev/null
+++ b/Userland/Services/WindowServer/Animation.h
@@ -0,0 +1,48 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Forward.h>
+#include <AK/Function.h>
+#include <AK/NonnullRefPtr.h>
+#include <AK/RefCounted.h>
+#include <LibCore/ElapsedTimer.h>
+#include <LibGfx/Forward.h>
+
+namespace WindowServer {
+
+class Compositor;
+class Screen;
+
+class Animation : public RefCounted<Animation> {
+public:
+    static NonnullRefPtr<Animation> create() { return adopt_ref(*new Animation); }
+
+    ~Animation();
+
+    bool is_running() const { return m_running; }
+
+    void start();
+    void stop();
+
+    void set_length(int length_in_ms);
+    int length() const { return m_length; }
+
+    void update(Badge<Compositor>, Gfx::Painter&, Screen&, Gfx::DisjointRectSet& flush_rects);
+
+    Function<void(float progress, Gfx::Painter&, Screen&, Gfx::DisjointRectSet& flush_rects)> on_update;
+    Function<void()> on_stop;
+
+private:
+    Animation();
+
+    Core::ElapsedTimer m_timer;
+    int m_length { 0 };
+    bool m_running { false };
+};
+
+}
diff --git a/Userland/Services/WindowServer/CMakeLists.txt b/Userland/Services/WindowServer/CMakeLists.txt
index 3dd7c0be51..b0fd2f652e 100644
--- a/Userland/Services/WindowServer/CMakeLists.txt
+++ b/Userland/Services/WindowServer/CMakeLists.txt
@@ -10,6 +10,7 @@ compile_ipc(WindowManagerServer.ipc WindowManagerServerEndpoint.h)
 compile_ipc(WindowManagerClient.ipc WindowManagerClientEndpoint.h)
 
 set(SOURCES
+    Animation.cpp
     AppletManager.cpp
     Button.cpp
     ClientConnection.cpp
diff --git a/Userland/Services/WindowServer/Compositor.cpp b/Userland/Services/WindowServer/Compositor.cpp
index af5b9dc3c7..554895eee6 100644
--- a/Userland/Services/WindowServer/Compositor.cpp
+++ b/Userland/Services/WindowServer/Compositor.cpp
@@ -1,10 +1,11 @@
 /*
- * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
 #include "Compositor.h"
+#include "Animation.h"
 #include "ClientConnection.h"
 #include "Event.h"
 #include "EventLoop.h"
@@ -527,10 +528,9 @@ void Compositor::compose()
     m_invalidated_window = false;
     m_invalidated_cursor = false;
 
-    bool did_render_animation = false;
     Screen::for_each([&](auto& screen) {
         auto& screen_data = m_screen_data[screen.index()];
-        did_render_animation |= render_animation_frame(screen, screen_data.m_flush_special_rects);
+        update_animations(screen, screen_data.m_flush_special_rects);
         return IterationDecision::Continue;
     });
 
@@ -546,9 +546,6 @@ void Compositor::compose()
         flush(screen);
         return IterationDecision::Continue;
     });
-
-    if (did_render_animation)
-        step_animations();
 }
 
 void Compositor::flush(Screen& screen)
@@ -709,60 +706,6 @@ void Compositor::ScreenData::flip_buffers(Screen& screen)
     m_buffers_are_flipped = !m_buffers_are_flipped;
 }
 
-static const int minimize_animation_steps = 10;
-
-bool Compositor::render_animation_frame(Screen& screen, Gfx::DisjointRectSet& flush_rects)
-{
-    bool did_render_any = false;
-    auto& painter = *m_screen_data[screen.index()].m_back_painter;
-    Gfx::PainterStateSaver saver(painter);
-    painter.set_draw_op(Gfx::Painter::DrawOp::Invert);
-
-    WindowManager::the().window_stack().for_each_window([&](Window& window) {
-        if (window.in_minimize_animation()) {
-            int animation_index = window.minimize_animation_index();
-
-            auto from_rect = window.is_minimized() ? window.frame().rect() : window.taskbar_rect();
-            auto to_rect = window.is_minimized() ? window.taskbar_rect() : window.frame().rect();
-
-            float x_delta_per_step = (float)(from_rect.x() - to_rect.x()) / minimize_animation_steps;
-            float y_delta_per_step = (float)(from_rect.y() - to_rect.y()) / minimize_animation_steps;
-            float width_delta_per_step = (float)(from_rect.width() - to_rect.width()) / minimize_animation_steps;
-            float height_delta_per_step = (float)(from_rect.height() - to_rect.height()) / minimize_animation_steps;
-
-            Gfx::IntRect rect {
-                from_rect.x() - (int)(x_delta_per_step * animation_index),
-                from_rect.y() - (int)(y_delta_per_step * animation_index),
-                from_rect.width() - (int)(width_delta_per_step * animation_index),
-                from_rect.height() - (int)(height_delta_per_step * animation_index)
-            };
-
-            dbgln_if(MINIMIZE_ANIMATION_DEBUG, "Minimize animation from {} to {} frame# {} {} on screen #{}", from_rect, to_rect, animation_index, rect, screen.index());
-
-            painter.draw_rect(rect, Color::Transparent); // Color doesn't matter, we draw inverted
-            flush_rects.add(rect.intersected(screen.rect()));
-            invalidate_screen(rect);
-
-            did_render_any = true;
-        }
-        return IterationDecision::Continue;
-    });
-
-    return did_render_any;
-}
-
-void Compositor::step_animations()
-{
-    WindowManager::the().window_stack().for_each_window([&](Window& window) {
-        if (window.in_minimize_animation()) {
-            window.step_minimize_animation();
-            if (window.minimize_animation_index() >= minimize_animation_steps)
-                window.end_minimize_animation();
-        }
-        return IterationDecision::Continue;
-    });
-}
-
 void Compositor::screen_resolution_changed()
 {
     // Screens may be gone now, invalidate any references to them
@@ -1260,4 +1203,24 @@ void Compositor::recompute_occlusions()
     });
 }
 
+void Compositor::register_animation(Badge<Animation>, Animation& animation)
+{
+    auto result = m_animations.set(&animation);
+    VERIFY(result == AK::HashSetResult::InsertedNewEntry);
+}
+
+void Compositor::unregister_animation(Badge<Animation>, Animation& animation)
+{
+    bool was_removed = m_animations.remove(&animation);
+    VERIFY(was_removed);
+}
+
+void Compositor::update_animations(Screen& screen, Gfx::DisjointRectSet& flush_rects)
+{
+    auto& painter = *m_screen_data[screen.index()].m_back_painter;
+    for (RefPtr<Animation> animation : m_animations) {
+        animation->update({}, painter, screen, flush_rects);
+    }
+}
+
 }
diff --git a/Userland/Services/WindowServer/Compositor.h b/Userland/Services/WindowServer/Compositor.h
index ef1d76d6c3..75a046f481 100644
--- a/Userland/Services/WindowServer/Compositor.h
+++ b/Userland/Services/WindowServer/Compositor.h
@@ -16,6 +16,7 @@
 
 namespace WindowServer {
 
+class Animation;
 class ClientConnection;
 class Cursor;
 class MultiScaleBitmaps;
@@ -95,11 +96,12 @@ public:
     const Gfx::Bitmap* cursor_bitmap_for_screenshot(Badge<ClientConnection>, Screen&) const;
     const Gfx::Bitmap& front_bitmap_for_screenshot(Badge<ClientConnection>, Screen&) const;
 
+    void register_animation(Badge<Animation>, Animation&);
+    void unregister_animation(Badge<Animation>, Animation&);
+
 private:
     Compositor();
     void init_bitmaps();
-    bool render_animation_frame(Screen&, Gfx::DisjointRectSet&);
-    void step_animations();
     void invalidate_current_screen_number_rects();
     void overlays_theme_changed();
 
@@ -114,6 +116,7 @@ private:
     bool any_opaque_window_above_this_one_contains_rect(const Window&, const Gfx::IntRect&);
     void change_cursor(const Cursor*);
     void flush(Screen&);
+    void update_animations(Screen&, Gfx::DisjointRectSet& flush_rects);
 
     RefPtr<Core::Timer> m_compose_timer;
     RefPtr<Core::Timer> m_immediate_compose_timer;
@@ -195,6 +198,8 @@ private:
 
     size_t m_show_screen_number_count { 0 };
     Optional<Gfx::Color> m_custom_background_color;
+
+    HashTable<Animation*> m_animations;
 };
 
 }
diff --git a/Userland/Services/WindowServer/Window.cpp b/Userland/Services/WindowServer/Window.cpp
index 3e5099a2dd..98a33c34e9 100644
--- a/Userland/Services/WindowServer/Window.cpp
+++ b/Userland/Services/WindowServer/Window.cpp
@@ -1,10 +1,11 @@
 /*
- * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
 #include "Window.h"
+#include "Animation.h"
 #include "AppletManager.h"
 #include "ClientConnection.h"
 #include "Compositor.h"
@@ -306,6 +307,21 @@ void Window::set_taskbar_rect(const Gfx::IntRect& rect)
     m_have_taskbar_rect = !m_taskbar_rect.is_empty();
 }
 
+static Gfx::IntRect interpolate_rect(Gfx::IntRect const& from_rect, Gfx::IntRect const& to_rect, float progress)
+{
+    auto dx = to_rect.x() - from_rect.x();
+    auto dy = to_rect.y() - from_rect.y();
+    auto dw = to_rect.width() - from_rect.width();
+    auto dh = to_rect.height() - from_rect.height();
+
+    return Gfx::IntRect {
+        from_rect.x() + ((float)dx * progress),
+        from_rect.y() + ((float)dy * progress),
+        from_rect.width() + ((float)dw * progress),
+        from_rect.height() + ((float)dh * progress),
+    };
+}
+
 void Window::start_minimize_animation()
 {
     if (!m_have_taskbar_rect) {
@@ -327,7 +343,26 @@ void Window::start_minimize_animation()
             return IterationDecision::Continue;
         });
     }
-    m_minimize_animation_step = 0;
+
+    m_animation = Animation::create();
+    m_animation->set_length(150);
+    m_animation->on_update = [this](float progress, Gfx::Painter& painter, Screen& screen, Gfx::DisjointRectSet& flush_rects) {
+        Gfx::PainterStateSaver saver(painter);
+        painter.set_draw_op(Gfx::Painter::DrawOp::Invert);
+
+        auto from_rect = is_minimized() ? frame().rect() : taskbar_rect();
+        auto to_rect = is_minimized() ? taskbar_rect() : frame().rect();
+
+        auto rect = interpolate_rect(from_rect, to_rect, progress);
+
+        painter.draw_rect(rect, Color::Transparent); // Color doesn't matter, we draw inverted
+        flush_rects.add(rect.intersected(screen.rect()));
+        Compositor::the().invalidate_screen(rect);
+    };
+    m_animation->on_stop = [this] {
+        m_animation = nullptr;
+    };
+    m_animation->start();
 }
 
 void Window::set_opacity(float opacity)
@@ -1071,5 +1106,4 @@ String Window::computed_title() const
         return String::formatted("{} (Not responding)", title);
     return title;
 }
-
 }
diff --git a/Userland/Services/WindowServer/Window.h b/Userland/Services/WindowServer/Window.h
index 129f7d7281..2eaa624985 100644
--- a/Userland/Services/WindowServer/Window.h
+++ b/Userland/Services/WindowServer/Window.h
@@ -20,6 +20,7 @@
 
 namespace WindowServer {
 
+class Animation;
 class ClientConnection;
 class Cursor;
 class KeyEvent;
@@ -256,11 +257,7 @@ public:
     Gfx::DisjointRectSet take_pending_paint_rects() { return move(m_pending_paint_rects); }
 
     bool has_taskbar_rect() const { return m_have_taskbar_rect; };
-    bool in_minimize_animation() const { return m_minimize_animation_step != -1; }
-    int minimize_animation_index() const { return m_minimize_animation_step; }
-    void step_minimize_animation() { m_minimize_animation_step += 1; }
     void start_minimize_animation();
-    void end_minimize_animation() { m_minimize_animation_step = -1; }
 
     Gfx::IntRect tiled_rect(Screen*, WindowTileType) const;
     void recalculate_rect();
@@ -408,10 +405,10 @@ private:
     MenuItem* m_window_menu_move_item { nullptr };
     MenuItem* m_window_menu_close_item { nullptr };
     MenuItem* m_window_menu_menubar_visibility_item { nullptr };
-    int m_minimize_animation_step { -1 };
     Optional<int> m_progress;
     bool m_should_show_menubar { true };
     WindowStack* m_outer_stack { nullptr };
+    RefPtr<Animation> m_animation;
 
 public:
     using List = IntrusiveList<Window, RawPtr<Window>, &Window::m_list_node>;