improved delta calculations for capped framrates

src/pc/pc_main.c

@@ -61,6 +61,8 @@
 #include "gfx_dimensions.h"
 #include "game/segment2.h"
 
+#include "engine/math_util.h"
+
 #ifdef DISCORD_SDK
 #include "pc/discord/discord.h"
 #endif
@@ -203,18 +205,16 @@ static s32 get_num_frames_to_draw(f64 t, u32 frameLimit) {
 static u32 get_refresh_rate() {
     if (configFramerateMode == RRM_MANUAL) { return configFrameLimit; }
     if (configFramerateMode == RRM_UNLIMITED) { return 3000; } // Has no effect
-#ifdef HAVE_SDL2
     static u32 refreshRate = 60;
+#ifdef HAVE_SDL2
     if (!refreshRate) {
         SDL_DisplayMode mode;
         if (SDL_GetCurrentDisplayMode(0, &mode) == 0) {
             refreshRate = (u32) mode.refresh_rate;
         }
     }
-    return refreshRate;
-#else
-    return 60;
 #endif
+    return refreshRate;
 }
 
 void produce_interpolation_frames_and_delay(void) {
@@ -229,15 +229,21 @@ void produce_interpolation_frames_and_delay(void) {
     f64 curTime = clock_elapsed_f64();
     f64 loopStartTime = curTime;
     f64 expectedTime = 0;
+    u16 frames = 0;
+    const f64 interpFrameTime = sFrameTime / (f64) numFramesToDraw;
 
     // interpolate and render
     // make sure to draw at least one frame to prevent the game from freezing completely
     // (including inputs and window events) if the game update duration is greater than 33ms
     do {
+        ++frames;
+
+        // when we know how many frames to draw, use a precise delta
+        f64 idealTime = configFramerateMode != RRM_UNLIMITED ? (sFrameTimeStart + interpFrameTime * frames) : curTime;
         f32 delta = (
             is30Fps ?
             1.0f :
-            MIN(MAX((curTime - sFrameTimeStart) / sFrameTime, 0.f), 1.f)
+            clamp((idealTime - sFrameTimeStart) / sFrameTime, 0.f, 1.f)
         );
         gRenderingDelta = delta;
 
@@ -248,7 +254,7 @@ void produce_interpolation_frames_and_delay(void) {
         gfx_end_frame_render();
 
         // delay if our framerate is capped
-        if (!configUncappedFramerate && !configWindow.vsync) {
+        if (configFramerateMode != RRM_UNLIMITED && !configWindow.vsync) {
             f64 now = clock_elapsed_f64();
             f64 elapsedTime = now - loopStartTime;
             expectedTime += (targetTime - curTime) / (f64) numFramesToDraw;