Merge pull request #165 from neobrain/viewport-scaling

Stretch emulation output to render window and be display density independent

11 files changed, 281 insertions, 83 deletions

diff --git a/src/citra/emu_window/emu_window_glfw.cpp b/src/citra/emu_window/emu_window_glfw.cpp
index 0c774bbc..8efb39e2 100644
--- a/src/citra/emu_window/emu_window_glfw.cpp
+++ b/src/citra/emu_window/emu_window_glfw.cpp
@@ -2,6 +2,8 @@
 // Licensed under GPLv2
 // Refer to the license.txt file included.
 
+#include <GLFW/glfw3.h>
+
 #include "common/common.h"
 
 #include "video_core/video_core.h"
@@ -10,22 +12,21 @@
 
 #include "citra/emu_window/emu_window_glfw.h"
 
+EmuWindow_GLFW* EmuWindow_GLFW::GetEmuWindow(GLFWwindow* win) {
+    return static_cast<EmuWindow_GLFW*>(glfwGetWindowUserPointer(win));
+}
+
 /// Called by GLFW when a key event occurs
 void EmuWindow_GLFW::OnKeyEvent(GLFWwindow* win, int key, int scancode, int action, int mods) {
 
-    if (!VideoCore::g_emu_window) {
-        return;
-    }
-
-    int keyboard_id = ((EmuWindow_GLFW*)VideoCore::g_emu_window)->keyboard_id;
+    int keyboard_id = GetEmuWindow(win)->keyboard_id;
 
     if (action == GLFW_PRESS) {
         EmuWindow::KeyPressed({key, keyboard_id});
-    }
-
-    if (action == GLFW_RELEASE) {
+    } else if (action == GLFW_RELEASE) {
         EmuWindow::KeyReleased({key, keyboard_id});
     }
+
     HID_User::PadUpdateComplete();
 }
 
@@ -34,6 +35,23 @@ const bool EmuWindow_GLFW::IsOpen() {
     return glfwWindowShouldClose(m_render_window) == 0;
 }
 
+void EmuWindow_GLFW::OnFramebufferResizeEvent(GLFWwindow* win, int width, int height) {
+    _dbg_assert_(GUI, width > 0);
+    _dbg_assert_(GUI, height > 0);
+
+    GetEmuWindow(win)->NotifyFramebufferSizeChanged(std::pair<unsigned,unsigned>(width, height));
+}
+
+void EmuWindow_GLFW::OnClientAreaResizeEvent(GLFWwindow* win, int width, int height) {
+    _dbg_assert_(GUI, width > 0);
+    _dbg_assert_(GUI, height > 0);
+
+    // NOTE: GLFW provides no proper way to set a minimal window size.
+    //       Hence, we just ignore the corresponding EmuWindow hint.
+
+    GetEmuWindow(win)->NotifyClientAreaSizeChanged(std::pair<unsigned,unsigned>(width, height));
+}
+
 /// EmuWindow_GLFW constructor
 EmuWindow_GLFW::EmuWindow_GLFW() {
     keyboard_id = KeyMap::NewDeviceId();
@@ -50,19 +68,31 @@ EmuWindow_GLFW::EmuWindow_GLFW() {
     // GLFW on OSX requires these window hints to be set to create a 3.2+ GL context.
     glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
     glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
-	
-    m_render_window = glfwCreateWindow(VideoCore::kScreenTopWidth, 
-        (VideoCore::kScreenTopHeight + VideoCore::kScreenBottomHeight), 
-        m_window_title.c_str(), NULL, NULL);
+
+    std::string window_title = Common::StringFromFormat("Citra | %s-%s", Common::g_scm_branch, Common::g_scm_desc);
+    m_render_window = glfwCreateWindow(VideoCore::kScreenTopWidth,
+        (VideoCore::kScreenTopHeight + VideoCore::kScreenBottomHeight),
+        window_title.c_str(), NULL, NULL);
 
     if (m_render_window == NULL) {
         printf("Failed to create GLFW window! Exiting...");
         exit(1);
     }
-    
-    // Setup callbacks
+
     glfwSetWindowUserPointer(m_render_window, this);
+
+    // Notify base interface about window state
+    int width, height;
+    glfwGetFramebufferSize(m_render_window, &width, &height);
+    OnFramebufferResizeEvent(m_render_window, width, height);
+
+    glfwGetWindowSize(m_render_window, &width, &height);
+    OnClientAreaResizeEvent(m_render_window, width, height);
+
+    // Setup callbacks
     glfwSetKeyCallback(m_render_window, OnKeyEvent);
+    glfwSetFramebufferSizeCallback(m_render_window, OnFramebufferResizeEvent);
+    glfwSetWindowSizeCallback(m_render_window, OnClientAreaResizeEvent);
 
     DoneCurrent();
 }
@@ -110,3 +140,15 @@ void EmuWindow_GLFW::ReloadSetKeymaps() {
     KeyMap::SetKeyMapping({Settings::values.pad_sup_key,    keyboard_id}, HID_User::PAD_CIRCLE_UP);
     KeyMap::SetKeyMapping({Settings::values.pad_sdown_key,  keyboard_id}, HID_User::PAD_CIRCLE_DOWN);
 }
+
+void EmuWindow_GLFW::OnMinimalClientAreaChangeRequest(const std::pair<unsigned,unsigned>& minimal_size) {
+    std::pair<int,int> current_size;
+    glfwGetWindowSize(m_render_window, &current_size.first, &current_size.second);
+
+    _dbg_assert_(GUI, (int)minimal_size.first > 0 && (int)minimal_size.second > 0);
+    int new_width  = std::max(current_size.first,  (int)minimal_size.first);
+    int new_height = std::max(current_size.second, (int)minimal_size.second);
+
+    if (current_size != std::make_pair(new_width, new_height))
+        glfwSetWindowSize(m_render_window, new_width, new_height);
+}
diff --git a/src/citra/emu_window/emu_window_glfw.h b/src/citra/emu_window/emu_window_glfw.h
index 7c307214..61cef4e6 100644
--- a/src/citra/emu_window/emu_window_glfw.h
+++ b/src/citra/emu_window/emu_window_glfw.h
@@ -4,10 +4,10 @@
 
 #pragma once
 
-#include <GLFW/glfw3.h>
-
 #include "common/emu_window.h"
 
+struct GLFWwindow;
+
 class EmuWindow_GLFW : public EmuWindow {
 public:
     EmuWindow_GLFW();
@@ -21,7 +21,7 @@ public:
 
     /// Makes the graphics context current for the caller thread
     void MakeCurrent() override;
-    
+
     /// Releases (dunno if this is the "right" word) the GLFW context from the caller thread
     void DoneCurrent() override;
 
@@ -30,9 +30,17 @@ public:
     /// Whether the window is still open, and a close request hasn't yet been sent
     const bool IsOpen();
 
+    static void OnClientAreaResizeEvent(GLFWwindow* win, int width, int height);
+
+    static void OnFramebufferResizeEvent(GLFWwindow* win, int width, int height);
+
     void ReloadSetKeymaps() override;
 
 private:
+    void OnMinimalClientAreaChangeRequest(const std::pair<unsigned,unsigned>& minimal_size) override;
+
+    static EmuWindow_GLFW* GetEmuWindow(GLFWwindow* win);
+
     GLFWwindow* m_render_window; ///< Internal GLFW render window
 
     /// Device id of keyboard for use with KeyMap
diff --git a/src/citra_qt/bootmanager.cpp b/src/citra_qt/bootmanager.cpp
index 20824692..758f71fd 100644
--- a/src/citra_qt/bootmanager.cpp
+++ b/src/citra_qt/bootmanager.cpp
@@ -2,6 +2,12 @@
 #include <QKeyEvent>
 #include <QApplication>
 
+#if QT_VERSION >= QT_VERSION_CHECK(5, 0, 0)
+// Required for screen DPI information
+#include <QScreen>
+#include <QWindow>
+#endif
+
 #include "common/common.h"
 #include "bootmanager.hxx"
 
@@ -82,20 +88,20 @@ void EmuThread::Stop()
 class GGLWidgetInternal : public QGLWidget
 {
 public:
-    GGLWidgetInternal(QGLFormat fmt, GRenderWindow* parent) : QGLWidget(fmt, parent)
-    {
-        parent_ = parent;
+    GGLWidgetInternal(QGLFormat fmt, GRenderWindow* parent)
+                     : QGLWidget(fmt, parent), parent(parent) {
     }
 
-    void paintEvent(QPaintEvent* ev) override
-    {
+    void paintEvent(QPaintEvent* ev) override {
     }
+
     void resizeEvent(QResizeEvent* ev) override {
-        parent_->SetClientAreaWidth(size().width());
-        parent_->SetClientAreaHeight(size().height());
+        parent->OnClientAreaResized(ev->size().width(), ev->size().height());
+        parent->OnFramebufferSizeChanged();
     }
+
 private:
-    GRenderWindow* parent_;
+    GRenderWindow* parent;
 };
 
 EmuThread& GRenderWindow::GetEmuThread()
@@ -105,6 +111,9 @@ EmuThread& GRenderWindow::GetEmuThread()
 
 GRenderWindow::GRenderWindow(QWidget* parent) : QWidget(parent), emu_thread(this), keyboard_id(0)
 {
+    std::string window_title = Common::StringFromFormat("Citra | %s-%s", Common::g_scm_branch, Common::g_scm_desc);
+    setWindowTitle(QString::fromStdString(window_title));
+
     keyboard_id = KeyMap::NewDeviceId();
     ReloadSetKeymaps();
 
@@ -114,16 +123,25 @@ GRenderWindow::GRenderWindow(QWidget* parent) : QWidget(parent), emu_thread(this
     fmt.setProfile(QGLFormat::CoreProfile);
     // Requests a forward-compatible context, which is required to get a 3.2+ context on OS X
     fmt.setOption(QGL::NoDeprecatedFunctions);
-    
+
     child = new GGLWidgetInternal(fmt, this);
     QBoxLayout* layout = new QHBoxLayout(this);
     resize(VideoCore::kScreenTopWidth, VideoCore::kScreenTopHeight + VideoCore::kScreenBottomHeight);
     layout->addWidget(child);
     layout->setMargin(0);
     setLayout(layout);
-    QObject::connect(&emu_thread, SIGNAL(started()), this, SLOT(moveContext()));
+    connect(&emu_thread, SIGNAL(started()), this, SLOT(moveContext()));
+
+    OnMinimalClientAreaChangeRequest(GetActiveConfig().min_client_area_size);
+
+    OnFramebufferSizeChanged();
+    NotifyClientAreaSizeChanged(std::pair<unsigned,unsigned>(child->width(), child->height()));
 
     BackupGeometry();
+
+#if QT_VERSION >= QT_VERSION_CHECK(5, 0, 0)
+    connect(this->windowHandle(), SIGNAL(screenChanged(QScreen*)), this, SLOT(OnFramebufferSizeChanged()));
+#endif
 }
 
 void GRenderWindow::moveContext()
@@ -166,14 +184,28 @@ void GRenderWindow::DoneCurrent()
 }
 
 void GRenderWindow::PollEvents() {
-    // TODO(ShizZy): Does this belong here? This is a reasonable place to update the window title
-    //  from the main thread, but this should probably be in an event handler...
-    /*
-    static char title[128];
-    sprintf(title, "%s (FPS: %02.02f)", window_title_.c_str(), 
-        video_core::g_renderer->current_fps());
-    setWindowTitle(title);
-    */
+}
+
+// On Qt 5.0+, this correctly gets the size of the framebuffer (pixels).
+//
+// Older versions get the window size (density independent pixels),
+// and hence, do not support DPI scaling ("retina" displays).
+// The result will be a viewport that is smaller than the extent of the window.
+void GRenderWindow::OnFramebufferSizeChanged()
+{
+    // Screen changes potentially incur a change in screen DPI, hence we should update the framebuffer size
+#if QT_VERSION >= QT_VERSION_CHECK(5, 0, 0)
+    // windowHandle() might not be accessible until the window is displayed to screen.
+    auto pixel_ratio = windowHandle() ? (windowHandle()->screen()->devicePixelRatio()) : 1.0;
+
+    unsigned width = child->QPaintDevice::width() * pixel_ratio;
+    unsigned height = child->QPaintDevice::height() * pixel_ratio;
+#else
+    unsigned width = child->QPaintDevice::width();
+    unsigned height = child->QPaintDevice::height();
+#endif
+
+    NotifyFramebufferSizeChanged(std::make_pair(width, height));
 }
 
 void GRenderWindow::BackupGeometry()
@@ -236,3 +268,11 @@ void GRenderWindow::ReloadSetKeymaps()
     KeyMap::SetKeyMapping({Settings::values.pad_sdown_key,  keyboard_id}, HID_User::PAD_CIRCLE_DOWN);
 }
 
+void GRenderWindow::OnClientAreaResized(unsigned width, unsigned height)
+{
+    NotifyClientAreaSizeChanged(std::make_pair(width, height));
+}
+
+void GRenderWindow::OnMinimalClientAreaChangeRequest(const std::pair<unsigned,unsigned>& minimal_size) {
+	setMinimumSize(minimal_size.first, minimal_size.second);
+}
diff --git a/src/citra_qt/bootmanager.hxx b/src/citra_qt/bootmanager.hxx
index f8afc403..3eec1668 100644
--- a/src/citra_qt/bootmanager.hxx
+++ b/src/citra_qt/bootmanager.hxx
@@ -1,12 +1,16 @@
+#include <atomic>
+
 #include <QThread>
 #include <QGLWidget>
-#include <atomic>
+
 #include "common/common.h"
 #include "common/emu_window.h"
 
-class GRenderWindow;
+class QScreen;
 class QKeyEvent;
 
+class GRenderWindow;
+
 class EmuThread : public QThread
 {
     Q_OBJECT
@@ -74,7 +78,7 @@ private:
 signals:
     /**
      * Emitted when CPU when we've finished processing a single Gekko instruction
-     * 
+     *
      * @warning This will only be emitted when the CPU is not running (SetCpuRunning(false))
      * @warning When connecting to this signal from other threads, make sure to specify either Qt::QueuedConnection (invoke slot within the destination object's message thread) or even Qt::BlockingQueuedConnection (additionally block source thread until slot returns)
      */
@@ -100,7 +104,7 @@ public:
     void BackupGeometry();
     void RestoreGeometry();
     void restoreGeometry(const QByteArray& geometry); // overridden
-    QByteArray saveGeometry(); // overridden
+    QByteArray saveGeometry();  // overridden
 
     EmuThread& GetEmuThread();
 
@@ -109,10 +113,16 @@ public:
 
     void ReloadSetKeymaps() override;
 
+    void OnClientAreaResized(unsigned width, unsigned height);
+
+    void OnFramebufferSizeChanged();
+
 public slots:
-    void moveContext();
+    void moveContext();  // overridden
 
 private:
+    void OnMinimalClientAreaChangeRequest(const std::pair<unsigned,unsigned>& minimal_size) override;
+
     QGLWidget* child;
 
     EmuThread emu_thread;
diff --git a/src/citra_qt/main.cpp b/src/citra_qt/main.cpp
index 9a4e36ad..d5554d91 100644
--- a/src/citra_qt/main.cpp
+++ b/src/citra_qt/main.cpp
@@ -117,7 +117,8 @@ GMainWindow::GMainWindow()
     connect(GetHotkey("Main Window", "Load File", this), SIGNAL(activated()), this, SLOT(OnMenuLoadFile()));
     connect(GetHotkey("Main Window", "Start Emulation", this), SIGNAL(activated()), this, SLOT(OnStartGame()));
 
-    setWindowTitle(render_window->GetWindowTitle().c_str());
+    std::string window_title = Common::StringFromFormat("Citra | %s-%s", Common::g_scm_branch, Common::g_scm_desc);
+    setWindowTitle(window_title.c_str());
 
     show();
 
diff --git a/src/common/emu_window.h b/src/common/emu_window.h
index 6c2b598f..4cb94fed 100644
--- a/src/common/emu_window.h
+++ b/src/common/emu_window.h
@@ -9,17 +9,33 @@
 #include "common/string_util.h"
 #include "common/key_map.h"
 
-// Abstraction class used to provide an interface between emulation code and the frontend (e.g. SDL, 
-//  QGLWidget, GLFW, etc...)
+/**
+ * Abstraction class used to provide an interface between emulation code and the frontend
+ * (e.g. SDL, QGLWidget, GLFW, etc...).
+ *
+ * Design notes on the interaction between EmuWindow and the emulation core:
+ * - Generally, decisions on anything visible to the user should be left up to the GUI.
+ *   For example, the emulation core should not try to dictate some window title or size.
+ *   This stuff is not the core's business and only causes problems with regards to thread-safety
+ *   anyway.
+ * - Under certain circumstances, it may be desirable for the core to politely request the GUI
+ *   to set e.g. a minimum window size. However, the GUI should always be free to ignore any
+ *   such hints.
+ * - EmuWindow may expose some of its state as read-only to the emulation core, however care
+ *   should be taken to make sure the provided information is self-consistent. This requires
+ *   some sort of synchronization (most of this is still a TODO).
+ * - DO NOT TREAT THIS CLASS AS A GUI TOOLKIT ABSTRACTION LAYER. That's not what it is. Please
+ *   re-read the upper points again and think about it if you don't see this.
+ */
 class EmuWindow
 {
-
 public:
-    /// Data structure to store an emuwindow configuration
+    /// Data structure to store emuwindow configuration
     struct WindowConfig {
         bool    fullscreen;
         int     res_width;
         int     res_height;
+        std::pair<unsigned,unsigned> min_client_area_size;
     };
 
     /// Swap buffers to display the next frame
@@ -42,52 +58,96 @@ public:
     /// Signals a key release action to the HID module
     static void KeyReleased(KeyMap::HostDeviceKey key);
 
-    WindowConfig GetConfig() const {
-        return m_config;
+    /**
+     * Returns currently active configuration.
+     * @note Accesses to the returned object need not be consistent because it may be modified in another thread
+     */
+    const WindowConfig& GetActiveConfig() const {
+        return active_config;
     }
 
+    /**
+     * Requests the internal configuration to be replaced by the specified argument at some point in the future.
+     * @note This method is thread-safe, because it delays configuration changes to the GUI event loop. Hence there is no guarantee on when the requested configuration will be active.
+     */
     void SetConfig(const WindowConfig& val) {
-        m_config = val;
-    }
-    
-    int GetClientAreaWidth() const { 
-        return m_client_area_width;
+        config = val;
     }
 
-    void SetClientAreaWidth(const int val) {
-        m_client_area_width = val;
+    /**
+      * Gets the framebuffer size in pixels.
+      * @note This method is thread-safe
+      */
+    const std::pair<unsigned,unsigned> GetFramebufferSize() const {
+        return framebuffer_size;
     }
 
-    int GetClientAreaHeight() const {
-        return m_client_area_height;
+    /**
+     * Gets window client area width in logical coordinates.
+     * @note For high-DPI systems, this is smaller than the framebuffer size.
+     * @note This method is thread-safe
+     */
+    std::pair<unsigned,unsigned> GetClientAreaSize() const {
+        return std::make_pair(client_area_width, client_area_height);
     }
 
-    void SetClientAreaHeight(const int val) {
-        m_client_area_height = val;
+protected:
+    EmuWindow()
+    {
+        // TODO: Find a better place to set this.
+        config.min_client_area_size = std::make_pair(400u, 480u);
+        active_config = config;
     }
+    virtual ~EmuWindow() {}
 
-    std::string GetWindowTitle() const { 
-        return m_window_title;
+    /**
+     * Processes any pending configuration changes from the last SetConfig call.
+     * This method invokes OnMinimalClientAreaChangeRequest if the corresponding configuration
+     * field changed.
+     * @note Implementations will usually want to call this from the GUI thread.
+     * @todo Actually call this in existing implementations.
+     */
+    void ProcessConfigurationChanges() {
+        // TODO: For proper thread safety, we should eventually implement a proper
+        // multiple-writer/single-reader queue...
+
+        if (config.min_client_area_size != active_config.min_client_area_size) {
+            OnMinimalClientAreaChangeRequest(config.min_client_area_size);
+            config.min_client_area_size = active_config.min_client_area_size;
+        }
     }
-    
-    void SetWindowTitle(std::string val) {
-        m_window_title = val;
+
+    /**
+     * Update internal framebuffer size with the given parameter.
+     * @note EmuWindow implementations will usually use this in window resize event handlers.
+     */
+    void NotifyFramebufferSizeChanged(const std::pair<unsigned,unsigned>& size) {
+        framebuffer_size = size;
     }
 
-protected:
-    EmuWindow():
-        m_window_title(Common::StringFromFormat("Citra | %s-%s", Common::g_scm_branch, Common::g_scm_desc)),
-        m_client_area_width(640),
-        m_client_area_height(480)
-    {}
-    virtual ~EmuWindow() {}
+    /**
+     * Update internal client area size with the given parameter.
+     * @note EmuWindow implementations will usually use this in window resize event handlers.
+     */
+    void NotifyClientAreaSizeChanged(const std::pair<unsigned,unsigned>& size) {
+        client_area_width = size.first;
+        client_area_height = size.second;
+    }
 
-    std::string m_window_title;     ///< Current window title, should be used by window impl.
+private:
+    /**
+     * Handler called when the minimal client area was requested to be changed via SetConfig.
+     * For the request to be honored, EmuWindow implementations will usually reimplement this function.
+     */
+    virtual void OnMinimalClientAreaChangeRequest(const std::pair<unsigned,unsigned>& minimal_size) {
+        // By default, ignore this request and do nothing.
+    }
 
-    int m_client_area_width;        ///< Current client width, should be set by window impl.
-    int m_client_area_height;       ///< Current client height, should be set by window impl.
+    std::pair<unsigned,unsigned> framebuffer_size;
 
-private:
-    WindowConfig m_config;                ///< Internal configuration
+    unsigned client_area_width;    ///< Current client width, should be set by window impl.
+    unsigned client_area_height;   ///< Current client height, should be set by window impl.
 
+    WindowConfig config;         ///< Internal configuration (changes pending for being applied in ProcessConfigurationChanges)
+    WindowConfig active_config;  ///< Internal active configuration
 };
diff --git a/src/common/log.h b/src/common/log.h
index bfd73f8a..822cd21e 100644
--- a/src/common/log.h
+++ b/src/common/log.h
@@ -69,6 +69,7 @@ enum LOG_TYPE {
     HW,
     TIME,
     NETPLAY,
+    GUI,
 
     NUMBER_OF_LOGS // Must be last
 };
diff --git a/src/common/log_manager.cpp b/src/common/log_manager.cpp
index 4d590d98..687f4e33 100644
--- a/src/common/log_manager.cpp
+++ b/src/common/log_manager.cpp
@@ -75,6 +75,7 @@ LogManager::LogManager()
     m_Log[LogTypes::ACTIONREPLAY]       = new LogContainer("ActionReplay",      "ActionReplay");
     m_Log[LogTypes::MEMCARD_MANAGER]    = new LogContainer("MemCard Manager",   "MemCard Manager");
     m_Log[LogTypes::NETPLAY]            = new LogContainer("NETPLAY",           "Netplay");
+    m_Log[LogTypes::GUI]                = new LogContainer("GUI",               "GUI");
 
     m_fileLog = new FileLogListener(FileUtil::GetUserPath(F_MAINLOG_IDX).c_str());
     m_consoleLog = new ConsoleListener();
diff --git a/src/common/math_util.h b/src/common/math_util.h
index b32e7bb1..b10a25c1 100644
--- a/src/common/math_util.h
+++ b/src/common/math_util.h
@@ -7,6 +7,7 @@
 #include "common/common.h"
 
 #include <algorithm>
+#include <type_traits>
 #include <vector>
 
 namespace MathUtil
@@ -109,11 +110,11 @@ struct Rectangle
     Rectangle(T theLeft, T theTop, T theRight, T theBottom)
         : left(theLeft), top(theTop), right(theRight), bottom(theBottom)
     { }
-    
+
     bool operator==(const Rectangle& r) { return left==r.left && top==r.top && right==r.right && bottom==r.bottom; }
 
-    T GetWidth() const { return abs(right - left); }
-    T GetHeight() const { return abs(bottom - top); }
+    T GetWidth() const { return std::abs(static_cast<typename std::make_signed<T>::type>(right - left)); }
+    T GetHeight() const { return std::abs(static_cast<typename std::make_signed<T>::type>(bottom - top)); }
 
     // If the rectangle is in a coordinate system with a lower-left origin, use
     // this Clamp.
@@ -127,7 +128,7 @@ struct Rectangle
 
     // If the rectangle is in a coordinate system with an upper-left origin,
     // use this Clamp.
-    void ClampUL(T x1, T y1, T x2, T y2) 
+    void ClampUL(T x1, T y1, T x2, T y2)
     {
         if (left < x1) left = x1;
         if (right > x2) right = x2;
diff --git a/src/video_core/renderer_opengl/renderer_opengl.cpp b/src/video_core/renderer_opengl/renderer_opengl.cpp
index 8483f79b..729e8e73 100644
--- a/src/video_core/renderer_opengl/renderer_opengl.cpp
+++ b/src/video_core/renderer_opengl/renderer_opengl.cpp
@@ -191,7 +191,8 @@ void RendererOpenGL::DrawSingleScreenRotated(const TextureInfo& texture, float x
  * Draws the emulated screens to the emulator window.
  */
 void RendererOpenGL::DrawScreens() {
-    glViewport(0, 0, resolution_width, resolution_height);
+    auto viewport_extent = GetViewportExtent();
+    glViewport(viewport_extent.left, viewport_extent.top, viewport_extent.GetWidth(), viewport_extent.GetHeight()); // TODO: Or bottom?
     glClear(GL_COLOR_BUFFER_BIT);
 
     glUseProgram(program_id);
@@ -228,6 +229,34 @@ void RendererOpenGL::SetWindow(EmuWindow* window) {
     render_window = window;
 }
 
+MathUtil::Rectangle<unsigned> RendererOpenGL::GetViewportExtent() {
+    unsigned framebuffer_width;
+    unsigned framebuffer_height;
+    std::tie(framebuffer_width, framebuffer_height) = render_window->GetFramebufferSize();
+
+    float window_aspect_ratio = static_cast<float>(framebuffer_height) / framebuffer_width;
+    float emulation_aspect_ratio = static_cast<float>(resolution_height) / resolution_width;
+
+    MathUtil::Rectangle<unsigned> viewport_extent;
+    if (window_aspect_ratio > emulation_aspect_ratio) {
+		// Window is narrower than the emulation content => apply borders to the top and bottom
+        unsigned viewport_height = emulation_aspect_ratio * framebuffer_width;
+        viewport_extent.left = 0;
+        viewport_extent.top = (framebuffer_height - viewport_height) / 2;
+        viewport_extent.right = viewport_extent.left + framebuffer_width;
+        viewport_extent.bottom = viewport_extent.top + viewport_height;
+    } else {
+        // Otherwise, apply borders to the left and right sides of the window.
+        unsigned viewport_width = framebuffer_height / emulation_aspect_ratio;
+        viewport_extent.left = (framebuffer_width - viewport_width) / 2;
+        viewport_extent.top = 0;
+        viewport_extent.right = viewport_extent.left + viewport_width;
+        viewport_extent.bottom = viewport_extent.top + framebuffer_height;
+    }
+
+    return viewport_extent;
+}
+
 /// Initialize the renderer
 void RendererOpenGL::Init() {
     render_window->MakeCurrent();
diff --git a/src/video_core/renderer_opengl/renderer_opengl.h b/src/video_core/renderer_opengl/renderer_opengl.h
index eed201a9..7fdcec73 100644
--- a/src/video_core/renderer_opengl/renderer_opengl.h
+++ b/src/video_core/renderer_opengl/renderer_opengl.h
@@ -4,13 +4,15 @@
 
 #pragma once
 
+#include <array>
+
 #include "generated/gl_3_2_core.h"
 
-#include "common/common.h"
+#include "common/math_util.h"
+
 #include "core/hw/gpu.h"
-#include "video_core/renderer_base.h"
 
-#include <array>
+#include "video_core/renderer_base.h"
 
 class EmuWindow;
 
@@ -52,6 +54,9 @@ private:
     static void LoadFBToActiveGLTexture(const GPU::Regs::FramebufferConfig& framebuffer,
                                         const TextureInfo& texture);
 
+    /// Computes the viewport rectangle
+    MathUtil::Rectangle<unsigned> GetViewportExtent();
+
     EmuWindow*  render_window;                    ///< Handle to render window
     u32         last_mode;                        ///< Last render mode