SDL: Support loading 2bpp .bmp files

From 8598f05b473be7ed6b41c72c3ad690d003e2ef8c Mon Sep 17 00:00:00 2001
From: Cameron Cawley <[EMAIL REDACTED]>
Date: Sat, 17 Sep 2022 21:45:08 +0100
Subject: [PATCH] Support loading 2bpp .bmp files

---
 src/video/SDL_bmp.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/src/video/SDL_bmp.c b/src/video/SDL_bmp.c
index cb220440a48..d52d6e84e41 100644
--- a/src/video/SDL_bmp.c
+++ b/src/video/SDL_bmp.c
@@ -328,15 +328,15 @@ SDL_LoadBMP_RW(SDL_RWops * src, int freesrc)
         goto done;
     }
 
-    /* Expand 1 and 4 bit bitmaps to 8 bits per pixel */
+    /* Expand 1, 2 and 4 bit bitmaps to 8 bits per pixel */
     switch (biBitCount) {
     case 1:
+    case 2:
     case 4:
         ExpandBMP = biBitCount;
         biBitCount = 8;
         break;
     case 0:
-    case 2:
     case 3:
     case 5:
     case 6:
@@ -473,6 +473,10 @@ SDL_LoadBMP_RW(SDL_RWops * src, int freesrc)
         bmpPitch = (biWidth + 7) >> 3;
         pad = (((bmpPitch) % 4) ? (4 - ((bmpPitch) % 4)) : 0);
         break;
+    case 2:
+        bmpPitch = (biWidth + 3) >> 2;
+        pad = (((bmpPitch) % 4) ? (4 - ((bmpPitch) % 4)) : 0);
+        break;
     case 4:
         bmpPitch = (biWidth + 1) >> 1;
         pad = (((bmpPitch) % 4) ? (4 - ((bmpPitch) % 4)) : 0);
@@ -489,6 +493,7 @@ SDL_LoadBMP_RW(SDL_RWops * src, int freesrc)
     while (bits >= top && bits < end) {
         switch (ExpandBMP) {
         case 1:
+        case 2:
         case 4:{
                 Uint8 pixel = 0;
                 int shift = (8 - ExpandBMP);