feat(runner): add fps_real builtin and fix fps builtin

src/runner.c

@@ -2296,6 +2296,11 @@ Runner* Runner_create(DataWin* dataWin, VMContext* vm, Renderer* renderer, FileS
     runner->fileSystem = fileSystem;
     runner->audioSystem = audioSystem;
     runner->frameCount = 0;
+    double initialFps = (double)dataWin->gen8.gms2FPS;
+    runner->fps = initialFps;
+    runner->fpsReal = initialFps;
+    runner->fpsWindowStartFrame = 0;
+    runner->fpsWindowStartNanos = nowNanos();
     runner->osType = OS_WINDOWS;
     runner->keyboard = RunnerKeyboard_create();
     runner->gamepads = RunnerGamepad_create();
@@ -3833,7 +3838,7 @@ void Runner_step(Runner* runner) {
             if (entry->units == 1) {
                 entry->elapsed += (double)1.0;
             } else {
-                entry->elapsed += runner->deltaTime / (double)1000000.0;
+                entry->elapsed += (double)runner->deltaTime / (double)1000000.0;
             }
 
             if (entry->elapsed >= entry->period) {
@@ -4094,6 +4099,18 @@ void Runner_step(Runner* runner) {
     Runner_cleanupDestroyedInstances(runner);
     Runner_sweepDeadStructs(runner);
 
+    // Measure fps builtin
+    if (nowNanos() - runner->fpsWindowStartNanos >= (uint64_t)1000000000) {
+        runner->fps = (double)(runner->frameCount - runner->fpsWindowStartFrame);
+        runner->fpsWindowStartFrame = runner->frameCount;
+        runner->fpsWindowStartNanos = nowNanos();
+    }
+
+    // Measure fps_real builtin
+    if (runner->deltaTime > 0.0) {
+        runner->fpsReal = (double)(1000000.0 / runner->deltaTime);
+    }
+
     runner->frameCount++;
 }
 

src/runner.h

@@ -549,7 +549,13 @@ struct Runner {
     Instance** structInstances;
     int32_t forcedDepth;
     // The time between the last frame and the current frame, stored in microseconds.
-    double deltaTime;
+    GMLReal deltaTime;
+    // Current frame rate (capped at room speed)
+    double fps;                   // last measured frames-per-second value returned to GML
+    uint64_t fpsWindowStartNanos;  // nowNanos() at the start of the measurement window
+    int fpsWindowStartFrame;   // runner->frameCount at the start of the measurement window
+    // Real-time measured frame rate for the "fps_real" builtin, computed from deltaTime.
+    double fpsReal;
     char* windowTitle;
 
     // ===[ Builtin function state ]===

src/vm_builtins.c

@@ -323,6 +323,7 @@ static const BuiltinVarEntry BUILTIN_VAR_TABLE[] = {
     { "direction", BUILTIN_VAR_DIRECTION },
     { "false", BUILTIN_VAR_FALSE },
     { "fps", BUILTIN_VAR_FPS },
+    { "fps_real", BUILTIN_VAR_FPS_REAL },
     { "friction", BUILTIN_VAR_FRICTION },
     { "gp_axislh", BUILTIN_VAR_GP_AXIS_LH },
     { "gp_axislv", BUILTIN_VAR_GP_AXIS_LV },
@@ -1283,7 +1284,9 @@ RValue VMBuiltins_getVariable(VMContext* ctx, Instance* inst, int16_t builtinVar
             return RValue_makeReal((GMLReal) INSTANCE_NOONE);
         }
         case BUILTIN_VAR_FPS:
-            return RValue_makeReal(ctx->dataWin->gen8.gms2FPS);
+            return RValue_makeReal(runner->fps);
+        case BUILTIN_VAR_FPS_REAL:
+            return RValue_makeReal(runner->fpsReal);
         case BUILTIN_VAR_DEBUG_MODE:
             return RValue_makeBool(false);
         case BUILTIN_VAR_DELTA_TIME:
@@ -5674,7 +5677,7 @@ static RValue builtin_ds_queue_read(VMContext* ctx, RValue* args, MAYBE_UNUSED i
     if (s.error || 0 > last) { free(bytes); return RValue_makeBool(false); }
 
     // Replace queue contents.
-    {    
+    {
     repeat(arrlen(q->items), i) {
         RValue_free(&q->items[i]);
     }
@@ -18221,7 +18224,7 @@ void VMBuiltins_registerAll(VMContext* ctx) {
     VM_registerBuiltin(ctx, "tile_set_empty", builtin_tile_set_empty);
     VM_registerBuiltin(ctx, "tile_set_mirror", builtin_tile_set_mirror);
     VM_registerBuiltin(ctx, "tile_set_flip", builtin_tile_set_flip);
-    VM_registerBuiltin(ctx, "tile_set_rotate", builtin_tile_set_rotate);    
+    VM_registerBuiltin(ctx, "tile_set_rotate", builtin_tile_set_rotate);
     VM_registerBuiltin(ctx, "tilemap_set", builtin_tilemap_set);
     VM_registerBuiltin(ctx, "tilemap_set_at_pixel", builtin_tilemap_set_at_pixel);
 #endif

src/vm_builtins.h

@@ -238,6 +238,7 @@ typedef enum {
     BUILTIN_VAR_INSTANCE_COUNT,
     BUILTIN_VAR_INSTANCE_ID,
     BUILTIN_VAR_FPS,
+    BUILTIN_VAR_FPS_REAL,
     BUILTIN_VAR_DEBUG_MODE,
     BUILTIN_VAR_DELTA_TIME,