From 03d1482b296b3808dc201078480e41fa29939e67 Mon Sep 17 00:00:00 2001
From: ds22x <jrb22x@gmail.com>
Date: Wed, 17 Feb 2021 17:02:36 +0100
Subject: [PATCH] Add an option to remove left side border ( Sega Master
 System)

---
 core/vdp_ctrl.c     |  6 ++++++
 libretro/libretro.c | 16 ++++++++++++++++
 libretro/osd.h      |  1 +
 3 files changed, 23 insertions(+)

diff --git a/core/vdp_ctrl.c b/core/vdp_ctrl.c
index cc40063..be0f02c 100644
--- a/core/vdp_ctrl.c
+++ b/core/vdp_ctrl.c
@@ -330,6 +330,12 @@ void vdp_reset(void)
     bitmap.viewport.x = (config.overscan & 2) ? 14 : -48;
     bitmap.viewport.y = (config.overscan & 1) ? (24 * (vdp_pal + 1)) : -24;
   }
+  else if ((system_hw == SYSTEM_SMS || system_hw == SYSTEM_SMS2) && config.left_border)
+  {
+    /* Horizontal display area reduced to 240 when hiding the left border */
+    bitmap.viewport.x = (config.overscan & 2) ? 7 : -8;
+    bitmap.viewport.y = (config.overscan & 1) * 24 * (vdp_pal + 1);
+  }
   else
   {
     bitmap.viewport.x = (config.overscan & 2) * 7;
diff --git a/libretro/libretro.c b/libretro/libretro.c
index 902b149..3908260 100644
--- a/libretro/libretro.c
+++ b/libretro/libretro.c
@@ -621,6 +621,7 @@ static void config_default(void)
    config.ntsc     = 0;
    config.lcd      = 0;
    config.render   = 0;
+   config.left_border = 0;
 
    /* input options */
    input.system[0] = SYSTEM_GAMEPAD;
@@ -1384,6 +1385,18 @@ static void check_variables(void)
     else
       config.invert_mouse = 1;
   }
+  
+  var.key = "genesis_plus_gx_left_border";
+  environ_cb(RETRO_ENVIRONMENT_GET_VARIABLE, &var);
+  {
+    orig_value = config.left_border;
+    if (!var.value || !strcmp(var.value, "disabled"))
+      config.left_border = 0;
+    else if (var.value && !strcmp(var.value, "enabled"))
+      config.left_border = 1;
+    if (orig_value != config.left_border)
+      update_viewports = true;
+  }
 
 #ifdef HAVE_OVERCLOCK
   var.key = "genesis_plus_gx_overclock";
@@ -1432,6 +1445,8 @@ static void check_variables(void)
     bitmap.viewport.changed = 11;
     if ((system_hw == SYSTEM_GG) && !config.gg_extra)
       bitmap.viewport.x = (config.overscan & 2) ? 14 : -48;
+    else if ((system_hw == SYSTEM_SMS || system_hw == SYSTEM_SMS2) && config.left_border)
+	  bitmap.viewport.x = (config.overscan & 2) ? 7 : -8;
     else
       bitmap.viewport.x = (config.overscan & 2) * 7;
   }
@@ -1996,6 +2011,7 @@ void retro_set_environment(retro_environment_t cb)
       { "genesis_plus_gx_lcd_filter", "LCD Ghosting filter; disabled|enabled" },
       { "genesis_plus_gx_overscan", "Borders; disabled|top/bottom|left/right|full" },
       { "genesis_plus_gx_gg_extra", "Game Gear extended screen; disabled|enabled" },
+	  { "genesis_plus_gx_left_border", "Hide Master System Left Border; disabled|enabled" },
       { "genesis_plus_gx_aspect_ratio", "Core-provided aspect ratio; auto|NTSC PAR|PAL PAR" },
       { "genesis_plus_gx_render", "Interlaced mode 2 output; single field|double field" },
       { "genesis_plus_gx_gun_cursor", "Show Lightgun crosshair; disabled|enabled" },
diff --git a/libretro/osd.h b/libretro/osd.h
index 1ba4f61..8f83c83 100644
--- a/libretro/osd.h
+++ b/libretro/osd.h
@@ -123,6 +123,7 @@ typedef struct
   uint8 ntsc;
   uint8 lcd;
   uint8 gg_extra;
+  uint8 left_border;
   uint8 render;
   t_input_config input[MAX_INPUTS];
   uint8 invert_mouse;