Add system capabilities variable that tracks individual features instead of broad emulator support (#907)

Also implements check for FBE.

* start implementing selftest

* add some more

* gSupportsLibpl destroyed

* SYS_SUPPORTS -> SYSCAP

* add emux check

* make it compile

* play around with it until it writes the ASM i want

* format

* explain what im doing

* hopefully guard emux

* one feedback

* two feedback

* better libpl check

* better comment

* resolve some feedbackg

* add FBE check

* dont need to skip this check if its only for the first frame'

* skip framebuffer check if on a system that we know supports it.

* document that nothing in the repo has emux yet

* goodbye emux

* feed1

* various detectable

---------

Co-authored-by: someone2639 <someone2639@gmail.com>

src/game/emutest.c

@@ -23,7 +23,7 @@ extern void __osPiGetAccess(void);
 extern void __osPiRelAccess(void);
 
 u8 gEmulator = EMU_CONSOLE;
-u8 gSupportsLibpl = FALSE;
+u32 gSystemCapabilities = 0;
 
 static inline u32 get_pj64_version() {
     // When calling this function, we know that the emulator is some version of Project 64,
@@ -74,21 +74,37 @@ static u8 check_cache_emulation() {
     return cacheEmulated;
 }
 
+// Tests various system quirks and initializes gEmulator to the detected emulator(s).
+//  Also initializes gSystemCapabilities.
 u32 detect_emulator() {
-    // Test to see if the libpl emulator extension is present.
     u32 magic;
+    // Test to see if the libpl emulator extension is present.
+#ifdef LIBPL
+    // We have libpl downloaded as a submodule, just use the API call.
+    if (libpl_is_supported(LPL_ABI_VERSION_CURRENT)) {
+        const lpl_plugin_info *plugin_info = libpl_get_graphics_plugin();
+
+        // We can query framebuffer emulation from libpl
+        if (plugin_info->capabilities & LPL_FRAMEBUFFER_EMULATION) {
+            gSystemCapabilities |= SUPPORTS_SOFTWARE_FRAMEBUFFER;
+        }
+#else // LIBPL
+    // libpl interacts with the hardware register at 0x1FFB0000,
+    //  so we can still _detect_ it by clearing the register and
+    //  seeing if we get a specific value back.
     osPiWriteIo(0x1ffb0000u, 0u);
     osPiReadIo(0x1ffb0000u, &magic);
     if (magic == 0x00500000u) {
-        // libpl is supported. Must be ParallelN64
-#ifdef LIBPL
-        gSupportsLibpl = libpl_is_supported(LPL_ABI_VERSION_CURRENT);
-#endif
+#endif // LIBPL
+        gSystemCapabilities |= SUPPORTS_LIBPL;
+        // If libpl is supported, we're on Parallel Launcher
         return EMU_PARALLEL_LAUNCHER;
     }
 
     // If DPC registers are emulated, this is either console or a very accurate emulator
     if ((u32)IO_READ(DPC_PIPEBUSY_REG) | (u32)IO_READ(DPC_TMEM_REG) | (u32)IO_READ(DPC_BUFBUSY_REG)) {
+        // Assume we have the ability to manipulate the framebuffer too.
+        gSystemCapabilities |= SUPPORTS_SOFTWARE_FRAMEBUFFER;
         return EMU_CONSOLE;
     }
     
@@ -106,11 +122,14 @@ u32 detect_emulator() {
     if (1.0f != round_double_to_float(0.9999999999999999)) {
         fcr_set_rounding_mode(roundingMode);
         return EMU_WIIVC;
+    } else {
+        gSystemCapabilities |= SUPPORTS_FLOAT_ROUNDING_MODE;
     }
     fcr_set_rounding_mode(roundingMode);
 
     // If cache is emulated, then this is likely Simple64, or some other accurate emulator.
     if (check_cache_emulation()) {
+        gSystemCapabilities |= SUPPORTS_CACHING;
         return EMU_OTHER;
     }
 

src/game/emutest.h

@@ -14,10 +14,34 @@ enum Emulator {
     EMU_OTHER                = (1 << 6), // Any other emulator
 };
 
-// initializes gEmulator
+/**
+ * Various detectable system capabilities
+ */
+enum SystemCapabilities {
+    // Whether the system caches instructions and data
+    SUPPORTS_CACHING              = (1 << 0),
+
+    // Whether the system supports changing how floats get rounded
+    SUPPORTS_FLOAT_ROUNDING_MODE  = (1 << 1),
+
+    // Whether the system supports the `libpl` API on Parallel Launcher
+    SUPPORTS_LIBPL                = (1 << 2),
+
+    // Whether the system can edit the framebuffer in software
+    SUPPORTS_SOFTWARE_FRAMEBUFFER = (1 << 3),
+
+    // TODO: `emux` is a developing standard.
+    // SUPPORTS_EMULATOR_EXTENSIONS  = (1 << 4), // i.e. `emux`
+
+    // TODO: Figure out what these mean and implement them too
+    // SUPPORTS_DMA_TIMING = 0,
+    // SUPPORTS_RSP_PIPELINE_STALL_TIMING = 0,
+};
+
 extern u32 detect_emulator();
 
-/* gEmulator is an enum that identifies the current emulator.
+/**
+ * gEmulator is an enum that identifies the current emulator.
  * The enum values work as a bitfield, so you can use the & and | operators
  * to test for multiple emulators or versions at once.
  * 
@@ -34,8 +58,17 @@ extern u32 detect_emulator();
  */
 extern u8 gEmulator;
 
-// determines whether libpl is safe to use
-extern u8 gSupportsLibpl;
+/**
+ * Bitflag that lists all system capabilities, for more granular
+ * feature detection than gEmulator.
+ */
+extern u32 gSystemCapabilities;
+
+/**
+ * Whether the emulator supports libpl.
+ *  Left in for backwards compatibility.
+ */
+#define gSupportsLibpl (gSystemCapabilities & SUPPORTS_LIBPL)
 
 // Included for backwards compatibility when upgrading from HackerSM64 2.0
 #define gIsConsole ((gEmulator & EMU_CONSOLE) != 0)

src/game/game_init.c

@@ -408,6 +408,31 @@ void draw_reset_bars(void) {
     osRecvMesg(&gGameVblankQueue, &gMainReceivedMesg, OS_MESG_BLOCK);
 }
 
+/**
+ * Check if we are emulating the framebuffer
+ * 
+ * s32 frameIndex:
+ *  0: Write to the framebuffer, wait to process displaylist
+ *  1: Check whether the framebuffer write persisted
+ */
+static void check_fbe(s32 frameIndex) {
+    // NOTE: For whatever reason, checking against pixel index 12 fails on some versions of GlideN64 (pain).
+    // So apparently, this value being set to 13 actually matters...???
+    const s32 fbePixelOffset = 13;
+    const u16 fbePixelVal = 0xFF01;
+
+    if (frameIndex == 0) {
+        // Write pixel to the framebuffer
+        gFramebuffers[sRenderingFramebuffer][fbePixelOffset] = fbePixelVal;
+    } else {
+        // Check if pixel persisted in the framebuffer after executing the display list
+        //  that clears it (but before updating sRenderingFramebuffer!)
+        if (gFramebuffers[sRenderingFramebuffer][fbePixelOffset] != fbePixelVal) {
+            gSystemCapabilities |= SUPPORTS_SOFTWARE_FRAMEBUFFER;
+        }
+    }
+}
+
 /**
  * Initial settings for the first rendered frame.
  */
@@ -423,7 +448,23 @@ void render_init(void) {
     init_rcp(CLEAR_ZBUFFER);
     clear_framebuffer(0);
     end_master_display_list();
-    exec_display_list(&gGfxPool->spTask);
+
+    // Skip the FBE check if system is console,
+    //  or had already been determined to support framebuffer emulation.
+    if (gSystemCapabilities & SUPPORTS_SOFTWARE_FRAMEBUFFER) {
+        exec_display_list(&gGfxPool->spTask);
+    } else {
+        check_fbe(0);
+
+        exec_display_list(&gGfxPool->spTask);
+
+        // Wait for frame rendering to complete to prevent race condition with FBE check
+        osRecvMesg(&gGfxVblankQueue, &gMainReceivedMesg, OS_MESG_BLOCK);
+        check_fbe(1);
+
+        // Send message back to queue to prevent locking up
+        osSendMesg(&gGfxVblankQueue, gMainReceivedMesg, OS_MESG_BLOCK);
+    }
 
     // Skip incrementing the initial framebuffer index on certain emulators so that they display immediately as the Gfx task finishes
     // This will break accurate emulators, so only enable on Project64, Parallel Launcher and Mupen.