From a75041e8dd820b89e746c737f58d0163e100a3e6 Mon Sep 17 00:00:00 2001
From: Sylvain <sylvain.becker@gmail.com>
Date: Thu, 10 Feb 2022 13:44:59 +0100
Subject: [PATCH] Fixed bug #2140: basic support to convert 16 colors palette
 PIXELFORMAT_INDEX4, to allow conversion to SDL_Texture

---
 src/video/SDL_blit_0.c   | 83 ++++++++++++++++++++++++++++++++++++++++
 src/video/SDL_fillrect.c | 22 ++++++++---
 2 files changed, 100 insertions(+), 5 deletions(-)

diff --git a/src/video/SDL_blit_0.c b/src/video/SDL_blit_0.c
index e2eecba7d..54882f8b1 100644
--- a/src/video/SDL_blit_0.c
+++ b/src/video/SDL_blit_0.c
@@ -452,11 +452,94 @@ static const SDL_BlitFunc colorkey_blit[] = {
     (SDL_BlitFunc) NULL, BlitBto1Key, BlitBto2Key, BlitBto3Key, BlitBto4Key
 };
 
+
+static void
+Blit4bto4(SDL_BlitInfo * info)
+{
+    int width = info->dst_w;
+    int height = info->dst_h;
+    Uint8 *src = info->src;
+    Uint32 *dst = (Uint32 *) info->dst;
+    int srcskip = info->src_skip;
+    int dstskip = info->dst_skip;
+    Uint32 *map = (Uint32 *) info->table;
+    int c;
+
+    /* Set up some basic variables */
+    srcskip += width - (width + 1) / 2;
+
+    while (height--) {
+        Uint8 byte = 0, bit;
+        for (c = 0; c < width; ++c) {
+            if ((c & 0x1) == 0) {
+                byte = *src++;
+            }
+            bit = (byte & 0xF0) >> 4;
+            if (1) {
+                *dst = map[bit];
+            }
+            byte <<= 4;
+            dst++;
+        }
+        src += srcskip;
+        dst = (Uint32 *) ((Uint8 *) dst + dstskip);
+    }
+}
+
+static void
+Blit4bto4Key(SDL_BlitInfo * info)
+{
+    int width = info->dst_w;
+    int height = info->dst_h;
+    Uint8 *src = info->src;
+    Uint32 *dst = (Uint32 *) info->dst;
+    int srcskip = info->src_skip;
+    int dstskip = info->dst_skip;
+    Uint32 ckey = info->colorkey;
+    Uint32 *map = (Uint32 *) info->table;
+    int c;
+
+    /* Set up some basic variables */
+    srcskip += width - (width + 1) / 2;
+
+    while (height--) {
+        Uint8 byte = 0, bit;
+        for (c = 0; c < width; ++c) {
+            if ((c & 0x1) == 0) {
+                byte = *src++;
+            }
+            bit = (byte & 0xF0) >> 4;
+            if (bit != ckey) {
+                *dst = map[bit];
+            }
+            byte <<= 4;
+            dst++;
+        }
+        src += srcskip;
+        dst = (Uint32 *) ((Uint8 *) dst + dstskip);
+    }
+}
+
 SDL_BlitFunc
 SDL_CalculateBlit0(SDL_Surface * surface)
 {
     int which;
 
+    /* 4bits to 32bits */
+    if (surface->format->BitsPerPixel == 4) {
+        if (surface->map->dst->format->BytesPerPixel == 4) {
+            switch (surface->map->info.flags & ~SDL_COPY_RLE_MASK) {
+                case 0:
+                    return Blit4bto4;
+
+                case SDL_COPY_COLORKEY:
+                    return Blit4bto4Key;
+            }
+        }
+        /* We don't fully support 4-bit packed pixel modes */
+        return NULL;
+    }
+
     if (surface->format->BitsPerPixel != 1) {
         /* We don't support sub 8-bit packed pixel modes */
         return (SDL_BlitFunc) NULL;
diff --git a/src/video/SDL_fillrect.c b/src/video/SDL_fillrect.c
index 0b40bb25c..13872d271 100644
--- a/src/video/SDL_fillrect.c
+++ b/src/video/SDL_fillrect.c
@@ -309,11 +309,6 @@ SDL_FillRects(SDL_Surface * dst, const SDL_Rect * rects, int count,
         return SDL_InvalidParamError("SDL_FillRects(): dst");
     }
 
-    /* This function doesn't work on surfaces < 8 bpp */
-    if (dst->format->BitsPerPixel < 8) {
-        return SDL_SetError("SDL_FillRects(): Unsupported surface format");
-    }
-
     /* Nothing to do */
     if (dst->w == 0 || dst->h == 0) {
         return 0;
@@ -328,6 +323,23 @@ SDL_FillRects(SDL_Surface * dst, const SDL_Rect * rects, int count,
         return SDL_InvalidParamError("SDL_FillRects(): rects");
     }
 
+    /* This function doesn't usually work on surfaces < 8 bpp
+     * Except: support for 4bits, when filling full size.
+     */
+    if (dst->format->BitsPerPixel < 8) {
+        if (count == 1) {
+            const SDL_Rect *r = &rects[0];
+            if (r->x == 0 && r->y == 0 && r->w == dst->w && r->w == dst->h) {
+                if (dst->format->BitsPerPixel == 4) {
+                    Uint8 b = (((Uint8) color << 4) | (Uint8) color);
+                    SDL_memset(dst->pixels, b, dst->h * dst->pitch);
+                    return 1;
+                }
+            }
+        }
+        return SDL_SetError("SDL_FillRects(): Unsupported surface format");
+    }
+
 #if SDL_ARM_NEON_BLITTERS
     if (SDL_HasNEON() && dst->format->BytesPerPixel != 3 && fill_function == NULL) {
         switch (dst->format->BytesPerPixel) {