graphics: option to include subscreens in screenshot (#866)

## Link to GitHub Issue or related Pull Request, if one exists
#0

## Description of change
Adds `-screenshotsub`. Off by default. When on, screenshots include the
subscreens. All subscreens are captured, even if they are hidden from
view. Works for all four screens of gitadora arena model as well.

This should also fix an issue with API / companion app not capturing
gitadora subscreen correctly.

Note: only done for DX9... DX11 will need another PR to make this work.

Unrelated to this PR, there seems to be a bug with gitadora not
accepting mouse or api touch input.

## Testing

src/spice2x/hooks/graphics/backends/d3d9/d3d9_device.cpp

@@ -23,6 +23,11 @@
 #include "shaders/vertex_shader.h"
 #endif
 
+// maps arena's cached additional swap chains (SMALL, LEFT, RIGHT) to screen numbers.
+// MAIN is the implicit swap chain, is not in those slots, and is always screen 0.
+// screen 1 is the subscreen for every other game, so SMALL takes that number here too.
+static constexpr int GFDM_ARENA_SLOT_SCREENS[] { 1, 2, 3 };
+
 #define CHECK_RESULT_FMT(x, fmt, ...) \
     HRESULT __ret = (x); \
     if (GRAPHICS_LOG_HRESULT && FAILED(__ret)) [[unlikely]] { \
@@ -336,20 +341,25 @@ HRESULT STDMETHODCALLTYPE WrappedIDirect3DDevice9::CreateAdditionalSwapChain(
     int index = 0;
     bool create_swap_chain = false;
     bool create_fake_swap_chain = false;
+    bool arena_slot = false;
     if (avs::game::is_model({"LDJ", "KFC", "M39"})) {
         create_swap_chain = true;
 
     } else if (games::gitadora::is_arena_model() &&
-        (GRAPHICS_PREVENT_SECONDARY_WINDOWS || GRAPHICS_GITADORA_HIDE_SIDE_WINDOWS)) {
+        (GRAPHICS_SCREENSHOT_SUBSCREENS ||
+         GRAPHICS_PREVENT_SECONDARY_WINDOWS ||
+         GRAPHICS_GITADORA_HIDE_SIDE_WINDOWS)) {
 
         if (pPresentationParameters->BackBufferWidth == 800) {
             // SMALL (subscreen)
             create_swap_chain = true;
+            arena_slot = true;
             index = 0;
 
         } else if (pPresentationParameters->BackBufferWidth == 1080) {
             // LEFT/RIGHT
             create_swap_chain = true;
+            arena_slot = true;
             index = 1;
             if (sub_swapchain[index] || fake_sub_swapchain[index]) {
                 index = 2;
@@ -361,6 +371,11 @@ HRESULT STDMETHODCALLTYPE WrappedIDirect3DDevice9::CreateAdditionalSwapChain(
         }
     }
 
+    // the api lists screens from this registry, so arena heads need their logical numbers in it
+    if (arena_slot) {
+        graphics_screens_register(GFDM_ARENA_SLOT_SCREENS[index]);
+    }
+
     if (create_fake_swap_chain) {
         if (!fake_sub_swapchain[index]) {
             log_info(
@@ -539,6 +554,64 @@ UINT STDMETHODCALLTYPE WrappedIDirect3DDevice9::GetNumberOfSwapChains() {
     return n;
 }
 
+void WrappedIDirect3DDevice9::get_screenshot_screens(std::vector<int> &screens) const {
+    if (games::gitadora::is_arena_model()) {
+        screens.push_back(0);
+
+        // every head the game renders into, whether or not it reaches a display
+        for (int slot = 0; slot < 3; slot++) {
+            if (sub_swapchain[slot] != nullptr || fake_sub_swapchain[slot] != nullptr) {
+                screens.push_back(GFDM_ARENA_SLOT_SCREENS[slot]);
+            }
+        }
+        return;
+    }
+
+    graphics_screens_get(screens);
+
+    // the sub screen is only registered once the game asks for it by index
+    if (sub_swapchain[0] != nullptr &&
+        avs::game::is_model({"LDJ", "KFC", "M39"}) &&
+        std::find(screens.begin(), screens.end(), 1) == screens.end())
+    {
+        screens.push_back(1);
+    }
+}
+
+HRESULT WrappedIDirect3DDevice9::get_screenshot_swap_chain(
+        UINT iSwapChain,
+        IDirect3DSwapChain9 **ppSwapChain)
+{
+    if (ppSwapChain == nullptr) {
+        return D3DERR_INVALIDCALL;
+    }
+
+    // the game numbers the two-head SMALL head itself; keep screen 1 meaning SMALL
+    if (games::gitadora::is_arena_model() && is_gfdm_two_head_exclusive() && iSwapChain == 1) {
+        return GetSwapChain(gfdm_logical_small_swapchain, ppSwapChain);
+    }
+
+    if (games::gitadora::is_arena_model()) {
+        for (int slot = 0; slot < 3; slot++) {
+            if (GFDM_ARENA_SLOT_SCREENS[slot] != (int) iSwapChain) {
+                continue;
+            }
+            if (sub_swapchain[slot] != nullptr) {
+                sub_swapchain[slot]->AddRef();
+                *ppSwapChain = sub_swapchain[slot];
+                return D3D_OK;
+            }
+            if (fake_sub_swapchain[slot] != nullptr) {
+                fake_sub_swapchain[slot]->AddRef();
+                *ppSwapChain = fake_sub_swapchain[slot];
+                return D3D_OK;
+            }
+        }
+    }
+
+    return GetSwapChain(iSwapChain, ppSwapChain);
+}
+
 HRESULT STDMETHODCALLTYPE WrappedIDirect3DDevice9::Reset(
         D3DPRESENT_PARAMETERS *pPresentationParameters)
 {