From 3eb8564fd92ae2939275a40ea67c3475dadd431b Mon Sep 17 00:00:00 2001
From: Apaczer <94932128+Apaczer@users.noreply.github.com>
Date: Mon, 10 Feb 2025 21:28:33 +0100
Subject: [PATCH 3/3] LIBRETRO: add "Framerate cap" option to reduce audio
 stutter

via MM+ and: https://github.com/StupidHoroscope/libretro-scummvm-miyoo-backend/commit/6c3954f916bf430e7756afd8ca74618d48b56744
---
 backends/platform/libretro/libretro.cpp       | 32 +++++++++++++++++--
 .../platform/libretro/libretro_core_options.h | 19 +++++++++++
 2 files changed, 48 insertions(+), 3 deletions(-)

diff --git a/backends/platform/libretro/libretro.cpp b/backends/platform/libretro/libretro.cpp
index 3a5bf84b4bc..1668182774b 100644
--- a/backends/platform/libretro/libretro.cpp
+++ b/backends/platform/libretro/libretro.cpp
@@ -55,6 +55,10 @@ static bool analog_response_is_quadratic = false;
 static float mouse_speed = 1.0f;
 
 static bool speed_hack_is_enabled = false;
+static int cap_fps=50u;
+
+static size_t audio_buffer_length = 0;
+static uint32* audio_buffer = NULL;
 
 char cmd_params[20][200];
 char cmd_params_num;
@@ -144,6 +148,11 @@ void retro_init (void)
 
 void retro_deinit(void)
 {
+   if (audio_buffer != NULL)
+   {
+      delete [] audio_buffer;
+      audio_buffer = NULL;
+   }
 }
 
 void parse_command_params(char* cmdline)
@@ -258,6 +267,13 @@ static void update_variables(void)
 		if (strcmp(var.value, "enabled") == 0)
 			speed_hack_is_enabled = true;
 	}
+   var.key = "scummvm_audio_cap_fps";
+   var.value = NULL;
+   cap_fps = 50u;
+   if (environ_cb(RETRO_ENVIRONMENT_GET_VARIABLE, &var) && var.value)
+   {
+      cap_fps = (int)atof(var.value);
+	}
 }
 
 static int retro_device = RETRO_DEVICE_JOYPAD;
@@ -463,8 +479,18 @@ void retro_run (void)
       video_cb(screen.pixels, screen.w, screen.h, screen.pitch);
 
       /* Upload audio */
-      static uint32 buf[735];
-      int count = ((Audio::MixerImpl*)g_system->getMixer())->mixCallback((byte*)buf, 735*4);
+   // HACK: Reduce audio buffer under-run by capping framerate to lower value.
+   int samples_per_frame = 44100u / (cap_fps);
+   if (audio_buffer == NULL || samples_per_frame != audio_buffer_length)
+   {
+      if (audio_buffer != NULL)
+      {
+         delete [] audio_buffer;
+      }
+      audio_buffer_length = samples_per_frame;
+      audio_buffer = new uint32[audio_buffer_length];
+   }
+   int count = ((Audio::MixerImpl*)g_system->getMixer())->mixCallback((byte*)audio_buffer, audio_buffer_length*4);
 #if defined(_3DS)
       /* Hack: 3DS will produce static noise
        * unless we manually send a zeroed
@@ -478,7 +504,7 @@ void retro_run (void)
       }
       else
 #endif
-         audio_batch_cb((int16_t*)buf, count);
+         audio_batch_cb((int16_t*)audio_buffer, count);
    }
 
 #if defined(USE_LIBCO)
diff --git a/backends/platform/libretro/libretro_core_options.h b/backends/platform/libretro/libretro_core_options.h
index 0fbd01e86d8..a32c0e37529 100644
--- a/backends/platform/libretro/libretro_core_options.h
+++ b/backends/platform/libretro/libretro_core_options.h
@@ -138,6 +138,25 @@ struct retro_core_option_definition option_defs_us[] = {
       "disabled"
 #endif
    },
+   {
+      "scummvm_audio_cap_fps",
+      "Framerate cap",
+      "Lock max framerate on resource-intensive games, to reduce audio crackling",
+      {
+         { "15", NULL },
+         { "20", NULL },
+         { "25", NULL },
+         { "30", NULL },
+         { "35", NULL },
+         { "40", NULL },
+         { "45", NULL },
+         { "50", NULL },
+         { "55", NULL },
+         { "60", NULL },
+         { NULL, NULL },
+      },
+      "50"
+   },
    { NULL, NULL, NULL, {{0}}, NULL },
 };
 
-- 
2.45.2.windows.1