Gui Only Render (#949)

* Add `RunGuiOnly` to `interpreter` to run ImGui interface without game commands.

* clang

* Add `RunGuiOnly` to `Window.h` and override with `Fast3dWindow`.

include/fast/Fast3dWindow.h

@@ -16,6 +16,7 @@ class Fast3dWindow : public Ship::Window {
 
     void Init() override;
     void Close() override;
+    void RunGuiOnly() override;
     void StartFrame() override;
     void EndFrame() override;
     bool IsFrameReady() override;

include/fast/interpreter.h

@@ -363,6 +363,7 @@ class Interpreter {
     void GetDimensions(uint32_t* width, uint32_t* height, int32_t* posX, int32_t* posY);
     GfxRenderingAPI* GetCurrentRenderingAPI();
     void StartFrame();
+    void RunGuiOnly();
     void Run(Gfx* commands, const std::unordered_map<Mtx*, MtxF>& mtx_replacements);
     void EndFrame();
     void HandleWindowEvents();

include/ship/window/Window.h

@@ -35,6 +35,7 @@ class Window {
 
     virtual void Init() = 0;
     virtual void Close() = 0;
+    virtual void RunGuiOnly() = 0;
     virtual void StartFrame() = 0;
     virtual void EndFrame() = 0;
     virtual bool IsFrameReady() = 0;

src/fast/Fast3dWindow.cpp

@@ -166,6 +166,10 @@ void Fast3dWindow::Close() {
     mWindowManagerApi->Close();
 }
 
+void Fast3dWindow::RunGuiOnly() {
+    mInterpreter->RunGuiOnly();
+}
+
 void Fast3dWindow::StartFrame() {
     mInterpreter->StartFrame();
 }

src/fast/interpreter.cpp

@@ -4301,6 +4301,46 @@ void Interpreter::StartFrame() {
 
 GfxExecStack g_exec_stack = {};
 
+void Interpreter::RunGuiOnly() {
+    SpReset();
+
+    mGetPixelDepthPending.clear();
+    mGetPixelDepthCached.clear();
+
+    mRapi->UpdateFramebufferParameters(0, mGfxCurrentWindowDimensions.width, mGfxCurrentWindowDimensions.height, 1,
+                                       false, true, true, !mRendersToFb);
+    mRapi->StartFrame();
+    mRapi->StartDrawToFramebuffer(mRendersToFb ? mGameFb : 0, (float)mCurDimensions.height / mNativeDimensions.height);
+    mRapi->ClearFramebuffer(false, true);
+    mRdp->viewport_or_scissor_changed = true;
+    mRenderingState.viewport = {};
+    mRenderingState.scissor = {};
+
+    Flush();
+    mGfxFrameBuffer = 0;
+
+    if (mRendersToFb) {
+        mRapi->StartDrawToFramebuffer(0, 1);
+        mRapi->ClearFramebuffer(true, true);
+        if (mMsaaLevel > 1) {
+            if (!ViewportMatchesRendererResolution()) {
+                mRapi->ResolveMSAAColorBuffer(mGameFbMsaaResolved, mGameFb);
+                mGfxFrameBuffer = (uintptr_t)mRapi->GetFramebufferTextureId(mGameFbMsaaResolved);
+            } else {
+                mRapi->ResolveMSAAColorBuffer(0, mGameFb);
+            }
+        } else {
+            mGfxFrameBuffer = (uintptr_t)mRapi->GetFramebufferTextureId(mGameFb);
+        }
+    } else if (mFbActive) {
+        // Failsafe reset to main framebuffer to prevent softlocking the renderer
+        mFbActive = 0;
+        mRapi->StartDrawToFramebuffer(0, 1);
+
+        assert(0 && "active framebuffer was never reset back to original");
+    }
+}
+
 void Interpreter::Run(Gfx* commands, const std::unordered_map<Mtx*, MtxF>& mtx_replacements) {
     SpReset();