Demos: Add Eyes demo

This is a neat clone of xeyes. It demoes the new ellipse filling functionality,
as well as the existing global mouse cursor tracking functionality :^)

1 files changed, 129 insertions, 0 deletions

diff --git a/Demos/Eyes/EyesWidget.cpp b/Demos/Eyes/EyesWidget.cpp
new file mode 100644
index 0000000000..e7a229c33c
--- /dev/null
+++ b/Demos/Eyes/EyesWidget.cpp
@@ -0,0 +1,129 @@
+/*
+ * Copyright (c) 2020, Sergey Bugaev <bugaevc@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "EyesWidget.h"
+#include <LibGUI/Painter.h>
+#include <LibGUI/Window.h>
+#include <LibGUI/WindowServerConnection.h>
+#include <LibGfx/Palette.h>
+#include <math.h>
+
+EyesWidget::~EyesWidget()
+{
+}
+
+void EyesWidget::track_cursor_globally()
+{
+    ASSERT(window());
+    auto window_id = window()->window_id();
+    ASSERT(window_id >= 0);
+
+    set_global_cursor_tracking(true);
+    GUI::WindowServerConnection::the().send_sync<Messages::WindowServer::SetGlobalCursorTracking>(window_id, true);
+}
+
+void EyesWidget::mousemove_event(GUI::MouseEvent& event)
+{
+    m_mouse_position = event.position();
+    update();
+}
+
+void EyesWidget::paint_event(GUI::PaintEvent& event)
+{
+    GUI::Painter painter(*this);
+
+    painter.clear_rect(event.rect(), Gfx::Color());
+
+    for (int i = 0; i < m_num_eyes; i++)
+        render_eyeball(i, painter);
+}
+
+void EyesWidget::render_eyeball(int index, GUI::Painter& painter) const
+{
+    auto eye_width = width() / m_num_eyes;
+    Gfx::Rect bounds { index * eye_width, 0, eye_width, height() };
+    auto thickness = max((width() + height()) / 15, 1);
+
+    bounds.shrink(width() / 25, 0);
+    painter.fill_ellipse(bounds, palette().base_text());
+    bounds.shrink(thickness, thickness);
+    painter.fill_ellipse(bounds, palette().base());
+
+    Gfx::Point pupil_center = this->pupil_center(bounds);
+    Gfx::Size pupil_size {
+        bounds.width() / 5,
+        bounds.height() / 5
+    };
+    Gfx::Rect pupil {
+        pupil_center.x() - pupil_size.width() / 2,
+        pupil_center.y() - pupil_size.height() / 2,
+        pupil_size.width(),
+        pupil_size.height()
+    };
+
+    painter.fill_ellipse(pupil, palette().base_text());
+}
+
+Gfx::Point EyesWidget::pupil_center(Gfx::Rect& eyeball_bounds) const
+{
+    auto mouse_vector = m_mouse_position - eyeball_bounds.center();
+    double dx = mouse_vector.x();
+    double dy = mouse_vector.y();
+    double mouse_distance = sqrt(dx * dx + dy * dy);
+
+    if (mouse_distance == 0.0)
+        return eyeball_bounds.center();
+
+    double width_squared = eyeball_bounds.width() * eyeball_bounds.width();
+    double height_squared = eyeball_bounds.height() * eyeball_bounds.height();
+
+    double max_distance_along_this_direction;
+
+    if (dx != 0 && abs(dx) >= abs(dy)) {
+        double slope = dy / dx;
+        double slope_squared = slope * slope;
+        max_distance_along_this_direction = 0.25 * sqrt(
+            (slope_squared + 1) /
+            (1 / width_squared + slope_squared / height_squared)
+        );
+    } else if (dy != 0 && abs(dy) >= abs(dx)) {
+        double slope = dx / dy;
+        double slope_squared = slope * slope;
+        max_distance_along_this_direction = 0.25 * sqrt(
+            (slope_squared + 1) /
+            (slope_squared / width_squared + 1 / height_squared)
+        );
+    } else {
+        ASSERT_NOT_REACHED();
+    }
+
+    double scale = min(1.0, max_distance_along_this_direction / mouse_distance);
+
+    return {
+        eyeball_bounds.center().x() + int(dx * scale),
+        eyeball_bounds.center().y() + int(dy * scale)
+    };
+}