games/NXDoom: support RGB565 framebuffers and locate WADs via Kconfig dir

blit_screen() assumed a 32-bit ARGB framebuffer unconditionally - a
real limitation for any RGB565 board (this target's framebuffer is
FB_FMT_RGB16_565), not specific to any one board. Branch on
pinfo.bpp: 16bpp uses RGBTO16(), 32bpp keeps the existing ARGBTO32()
path, and anything else fails loudly via i_error() instead of reading/
writing past the intended pixel bounds silently. Also center the
scaled viewport within the framebuffer (new xoffset/yoffset fields)
rather than pinning it to the top-left corner, since the buffer is
typically larger than SCREENWIDTH/HEIGHT * scale.

buld_iwad_dir_list() never searched CONFIG_GAMES_NXDOOM_PREFDIR - that
Kconfig option is documented as the directory where DOOM WAD files are
stored, but was previously only used for the config/save file
location, forcing every launch to rely on the current directory or
DOOMWADDIR/DOOMWADPATH being set by hand. Add it to the IWAD search
path.

Build this as a standalone loadable module (MODULE = m) unconditionally
rather than tracking CONFIG_GAMES_NXDOOM directly, so it can be
installed/launched via nxpkg/nxstore rather than only ever being a
firmware built-in.

Signed-off-by: aviralgarg05 <gargaviral99@gmail.com>

Author: aviralgarg05

games/NXDoom/Makefile

@@ -2,7 +2,7 @@ include $(APPDIR)/Make.defs
 
 # Program options
 
-MODULE    = $(CONFIG_GAMES_NXDOOM)
+MODULE    = m
 PRIORITY  = $(CONFIG_GAMES_NXDOOM_PRIORITY)
 STACKSIZE = $(CONFIG_GAMES_NXDOOM_STACKSIZE)
 PROGNAME  = nxdoom

games/NXDoom/src/d_iwad.c

@@ -271,6 +271,18 @@ static void buld_iwad_dir_list(void)
 
   add_iwad_dir(m_dir_name(myargv[0]));
 
+  /* Add the board's configured DOOM data directory.  Kconfig documents
+   * CONFIG_GAMES_NXDOOM_PREFDIR as "Directory where DOOM WAD files are
+   * stored", but until now it was only used for the config/save file
+   * location -- nothing actually searched it for IWADs, forcing every
+   * launch to rely on the current directory or DOOMWADDIR/DOOMWADPATH
+   * being set by hand first.
+   */
+
+#ifdef CONFIG_GAMES_NXDOOM_PREFDIR
+  add_iwad_dir(CONFIG_GAMES_NXDOOM_PREFDIR);
+#endif
+
   /* Add DOOMWADDIR if it is in the environment */
 
   env = getenv("DOOMWADDIR");

games/NXDoom/src/i_video.c

@@ -92,6 +92,13 @@ struct graphics_state_s
 
   uint8_t scale;
 
+  /* Pixel offset to center the scaled game viewport within the frame
+   * buffer when the buffer is larger than SCREENWIDTH/HEIGHT * scale.
+   */
+
+  int xoffset;
+  int yoffset;
+
   bool inited; /* Track initialization */
 };
 
@@ -262,27 +269,61 @@ static void blit_screen(void)
   uint8_t p_idx;
   void *fbptr;
 
-  /* TODO: It would be best to do this more efficiently/with less memory.
-   * It also would be good if we could handle the palette translation here
-   * such that DOOM can be played on frame buffers with differing bit depths
-   * and pixel formats.
-   */
+  /* TODO: It would be best to do this more efficiently/with less memory. */
 
-  fbptr = g_graphics_state.fbmem;
-  for (unsigned y = 0; y < SCREENHEIGHT * g_graphics_state.scale; y++)
+  fbptr = g_graphics_state.fbmem +
+          g_graphics_state.yoffset * g_graphics_state.pinfo.stride +
+          g_graphics_state.xoffset *
+              (g_graphics_state.pinfo.bpp == 16 ? 2 : 4);
+
+  if (g_graphics_state.pinfo.bpp == 16)
     {
-      for (unsigned x = 0; x < SCREENWIDTH * g_graphics_state.scale; x++)
+      for (unsigned y = 0; y < SCREENHEIGHT * g_graphics_state.scale; y++)
         {
-          p_idx = g_graphics_state
-                      .scrnbuf[(y / g_graphics_state.scale) * SCREENWIDTH +
-                               (x / g_graphics_state.scale)];
-
-          ((uint32_t *)(fbptr))[x] =
-              ARGBTO32(g_palette[p_idx].a, g_palette[p_idx].r,
-                       g_palette[p_idx].g, g_palette[p_idx].b);
+          for (unsigned x = 0; x < SCREENWIDTH * g_graphics_state.scale; x++)
+            {
+              p_idx = g_graphics_state
+                          .scrnbuf[(y / g_graphics_state.scale) *
+                                       SCREENWIDTH +
+                                   (x / g_graphics_state.scale)];
+
+              ((uint16_t *)(fbptr))[x] =
+                  RGBTO16(g_palette[p_idx].r, g_palette[p_idx].g,
+                          g_palette[p_idx].b);
+            }
+
+          fbptr += g_graphics_state.pinfo.stride;
+        }
+    }
+  else if (g_graphics_state.pinfo.bpp == 32)
+    {
+      for (unsigned y = 0; y < SCREENHEIGHT * g_graphics_state.scale; y++)
+        {
+          for (unsigned x = 0; x < SCREENWIDTH * g_graphics_state.scale; x++)
+            {
+              p_idx = g_graphics_state
+                          .scrnbuf[(y / g_graphics_state.scale) *
+                                       SCREENWIDTH +
+                                   (x / g_graphics_state.scale)];
+
+              ((uint32_t *)(fbptr))[x] =
+                  ARGBTO32(g_palette[p_idx].a, g_palette[p_idx].r,
+                           g_palette[p_idx].g, g_palette[p_idx].b);
+            }
+
+          fbptr += g_graphics_state.pinfo.stride;
         }
+    }
+  else
+    {
+      /* Neither 16bpp nor 32bpp: the xoffset/stride math above assumed
+       * one of those two pixel sizes, so continuing would read/write
+       * past the intended pixel bounds on the very first frame.  Fail
+       * loudly instead of silently corrupting framebuffer memory.
+       */
 
-      fbptr += g_graphics_state.pinfo.stride;
+      i_error("Unsupported framebuffer depth: %u bpp",
+              g_graphics_state.pinfo.bpp);
     }
 }
 
@@ -724,6 +765,18 @@ void i_init_graphics(void)
   yscale = g_graphics_state.vinfo.yres / SCREENHEIGHT;
   g_graphics_state.scale = xscale > yscale ? yscale : xscale;
 
+  /* Center the scaled viewport within the frame buffer rather than
+   * pinning it to the top-left corner, since the buffer is typically
+   * larger than SCREENWIDTH/HEIGHT * scale.
+   */
+
+  g_graphics_state.xoffset =
+      (g_graphics_state.vinfo.xres -
+       SCREENWIDTH * g_graphics_state.scale) / 2;
+  g_graphics_state.yoffset =
+      (g_graphics_state.vinfo.yres -
+       SCREENHEIGHT * g_graphics_state.scale) / 2;
+
   /* Get frame buffer plane info */
 
   if (ioctl(g_graphics_state.fd, FBIOGET_PLANEINFO,