gitadora: allow a landscape monitor to display subscreen (#899)

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

## Description of change
Arena Model's SMALL touch subscreen is a portrait (800x1280) panel -
however, it's common for people to set up a touch screen in landscape
orientation since IIDX/SDVX/popn all use landscape.

Add a new option, `-gdsublandscape`, which forces the subscreen to
launch at 1080p landscape. The image is rendered with black bars on the
sides. Touches will be unaligned initially; user needs to go into test
mode and recalibrate. In reality this option is just a short hand for
`-forceressub 1920,1080`.

Wire up `-forceressub` which previously didn't work for gitadora, so
that a resolution other than 1080p can be used in either orientation. In
other games `-forceressub` just forces the rendering resolution and
IIDX/SDVX/popn's game engine automatically stretches to fill... however
for gitadora it works differently since we want to keep the aspect ratio
of the original screen; it instead hijacks the back buffer and makes the
game draw to an intermediate buffer.

## Testing

src/spice2x/games/gitadora/gitadora.cpp

@@ -39,10 +39,38 @@ namespace games::gitadora {
     std::optional<socd::SocdAlgorithm> PICK_ALGO = socd::SocdAlgorithm::PreferRecent;
     std::optional<uint8_t> ARENA_WINDOW_COUNT = std::nullopt;
     bool ARENA_TWO_HEAD_EXCLUSIVE = false;
+    bool ARENA_SUBSCREEN_LANDSCAPE = false;
     std::optional<std::string> ASIO_DRIVER = std::nullopt;
     bool ALLOW_REALTEK_AUDIO = false;
     bool NATIVE_TOUCH = false;
 
+    std::pair<UINT, UINT> arena_subscreen_host_size() {
+        if (GRAPHICS_FS_CUSTOM_RESOLUTION_SUB.has_value()) {
+            return GRAPHICS_FS_CUSTOM_RESOLUTION_SUB.value();
+        }
+        if (ARENA_SUBSCREEN_LANDSCAPE) {
+            return { ARENA_SUBSCREEN_LANDSCAPE_WIDTH, ARENA_SUBSCREEN_LANDSCAPE_HEIGHT };
+        }
+        return { ARENA_SUBSCREEN_WIDTH, ARENA_SUBSCREEN_HEIGHT };
+    }
+
+    RECT arena_subscreen_content_rect(LONG host_width, LONG host_height) {
+        if (host_width <= 0 || host_height <= 0) {
+            return RECT {};
+        }
+
+        LONG width = MulDiv(host_height, ARENA_SUBSCREEN_WIDTH, ARENA_SUBSCREEN_HEIGHT);
+        LONG height = host_height;
+        if (width > host_width) {
+            width = host_width;
+            height = MulDiv(host_width, ARENA_SUBSCREEN_HEIGHT, ARENA_SUBSCREEN_WIDTH);
+        }
+
+        const LONG left = (host_width - width) / 2;
+        const LONG top = (host_height - height) / 2;
+        return RECT { left, top, left + width, top + height };
+    }
+
     /*
      * Prevent GitaDora from creating folders on F drive
      */
@@ -343,6 +371,23 @@ namespace games::gitadora {
                             "gitadora",
                             "arena model: unsupported window count: {}", count);
                 }
+
+                if (ARENA_SUBSCREEN_LANDSCAPE && !ARENA_TWO_HEAD_EXCLUSIVE) {
+                    log_warning(
+                        "gitadora",
+                        "arena model: landscape subscreen needs full screen two-window mode, ignoring");
+                    ARENA_SUBSCREEN_LANDSCAPE = false;
+                }
+                if (ARENA_TWO_HEAD_EXCLUSIVE) {
+                    const auto [host_width, host_height] = arena_subscreen_host_size();
+                    if (host_width != ARENA_SUBSCREEN_WIDTH
+                            || host_height != ARENA_SUBSCREEN_HEIGHT) {
+                        log_info(
+                            "gitadora",
+                            "arena model: SMALL head runs at {}x{}, subscreen is scaled to fit",
+                            host_width, host_height);
+                    }
+                }
             }
 
 #endif