From c2e79038252dbf7bbbfbf5aaa09bb5450691186f Mon Sep 17 00:00:00 2001
From: James Rowe <jroweboy@gmail.com>
Date: Mon, 16 Sep 2019 20:36:16 -0600
Subject: [PATCH] Split graphics out of EmuWindow in preparation of shared
 contexts

---
 src/core/frontend/emu_window.cpp |  2 +
 src/core/frontend/emu_window.h   | 72 ++++++++++++++++++++++++++++----
 2 files changed, 65 insertions(+), 9 deletions(-)

diff --git a/src/core/frontend/emu_window.cpp b/src/core/frontend/emu_window.cpp
index 4fc285fee7..f393e4c764 100644
--- a/src/core/frontend/emu_window.cpp
+++ b/src/core/frontend/emu_window.cpp
@@ -10,6 +10,8 @@
 
 namespace Frontend {
 
+GraphicsContext::~GraphicsContext() = default;
+
 class EmuWindow::TouchState : public Input::Factory<Input::TouchDevice>,
                               public std::enable_shared_from_this<TouchState> {
 public:
diff --git a/src/core/frontend/emu_window.h b/src/core/frontend/emu_window.h
index f2878b202a..be868f5064 100644
--- a/src/core/frontend/emu_window.h
+++ b/src/core/frontend/emu_window.h
@@ -12,6 +12,54 @@
 
 namespace Frontend {
 
+struct Frame;
+/**
+ * For smooth Vsync rendering, we want to always present the latest frame that the core generates,
+ * but also make sure that rendering happens at the pace that the frontend dictates. This is a
+ * helper class that the renderer can define to sync frames between the render thread and the
+ * presentation thread
+ */
+class TextureMailbox {
+public:
+    virtual ~TextureMailbox() = default;
+
+    /**
+     * Retrieve a frame that is ready to be rendered into
+     */
+    virtual Frame& GetRenderFrame() = 0;
+
+    /**
+     * Mark this frame as ready to present
+     */
+    virtual void RenderComplete() = 0;
+
+    /**
+     * Retrieve the latest frame to present in the frontend
+     */
+    virtual Frame& GetPresentationFrame() = 0;
+
+    /**
+     * Mark the presentation frame as complete and set it for reuse
+     */
+    virtual void PresentationComplete() = 0;
+};
+
+/**
+ * Represents a graphics context that can be used for background computation or drawing. If the
+ * graphics backend doesn't require the context, then the implementation of these methods can be
+ * stubs
+ */
+class GraphicsContext {
+public:
+    virtual ~GraphicsContext();
+
+    /// Makes the graphics context current for the caller thread
+    virtual void MakeCurrent() = 0;
+
+    /// Releases (dunno if this is the "right" word) the context from the caller thread
+    virtual void DoneCurrent() = 0;
+};
+
 /**
  * Abstraction class used to provide an interface between emulation code and the frontend
  * (e.g. SDL, QGLWidget, GLFW, etc...).
@@ -30,7 +78,7 @@ namespace Frontend {
  * - 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 {
+class EmuWindow : public GraphicsContext {
 public:
     /// Data structure to store emuwindow configuration
     struct WindowConfig {
@@ -40,17 +88,21 @@ public:
         std::pair<unsigned, unsigned> min_client_area_size;
     };
 
-    /// Swap buffers to display the next frame
-    virtual void SwapBuffers() = 0;
-
     /// Polls window events
     virtual void PollEvents() = 0;
 
-    /// Makes the graphics context current for the caller thread
-    virtual void MakeCurrent() = 0;
-
-    /// Releases (dunno if this is the "right" word) the GLFW context from the caller thread
-    virtual void DoneCurrent() = 0;
+    /**
+     * Returns a GraphicsContext that the frontend provides that is shared with the emu window. This
+     * context can be used from other threads for background graphics computation. If the frontend
+     * is using a graphics backend that doesn't need anything specific to run on a different thread,
+     * then it can use a stubbed implemenation for GraphicsContext.
+     *
+     * If the return value is null, then the core should assume that the frontend cannot provide a
+     * Shared Context
+     */
+    virtual std::unique_ptr<GraphicsContext> CreateSharedContext() const {
+        return nullptr;
+    }
 
     /**
      * Signal that a touch pressed event has occurred (e.g. mouse click pressed)
@@ -102,6 +154,8 @@ public:
      */
     void UpdateCurrentFramebufferLayout(unsigned width, unsigned height);
 
+    std::unique_ptr<TextureMailbox> mailbox = nullptr;
+
 protected:
     EmuWindow();
     virtual ~EmuWindow();