gfx/d3d8, gfx/d3d9: surface dylib_load failure for d3d{8,9}.dll

Both drivers' *_initialize_symbols() return false silently when
LoadLibrary("d3d8.dll") / ("d3d9.dll") fails. The caller in turn
returns NULL silently from the video driver's init(), so the only
diagnostic the user gets is the generic

   [ERROR] [Video] Cannot open video driver. Exiting...

from video_driver_init_internal(), with no hint that the legacy
runtime is the problem. Even --verbose does not help, because there
is no log call between the driver being selected and init() returning
NULL.

This is increasingly common on modern Windows installs that ship only
d3d8thk.dll (the kernel thunk layer) and not the user-mode d3d8.dll
runtime; recently made more visible by the qb change that lets D3D8
build without d3d8.lib being available at link time, which means more
people end up running a d3d8-enabled binary on a system where the
runtime DLL is missing.

Falling back to d3d8thk.dll is not an option -- it does not export
Direct3DCreate8, it is only the GDI-side thunk syscalls. So just log
clearly and let the caller fail.

Log dylib_error() (already populated by dylib_load on Win32 via
set_dl_err) and a one-liner pointing the user at the legacy DX runtime
or at picking a different video driver. Also log if the DLL loads but
Direct3DCreate{8,9} cannot be resolved, since that path is silent too.

No behavioural change beyond the new log lines; the error return is
unchanged.

Author: LibretroAdmin

gfx/common/d3d9_common.c

@@ -72,8 +72,19 @@ bool d3d9_initialize_symbols(enum gfx_ctx_api api)
    if (!(g_d3d9_dll  = dylib_load("d3d9d.dll")))
 #endif
    if (!(g_d3d9_dll  = dylib_load("d3d9.dll")))
+   {
+      /* On a system where the D3D9 user-mode runtime is missing, the
+       * caller would otherwise see only the generic "Cannot open video
+       * driver" message. Surface the real cause here. */
+      RARCH_ERR("[D3D9] Failed to load d3d9.dll: %s\n",
+            dylib_error() ? dylib_error() : "(no error reported)");
+      RARCH_ERR("[D3D9] The DirectX 9 runtime is not present on this "
+            "system. Install it or pick a different video driver.\n");
       return false;
-   D3D9Create                 = (D3D9Create_t)dylib_proc(g_d3d9_dll, "Direct3DCreate9");
+   }
+   if (!(D3D9Create = (D3D9Create_t)dylib_proc(g_d3d9_dll, "Direct3DCreate9")))
+      RARCH_ERR("[D3D9] d3d9.dll does not export Direct3DCreate9: %s\n",
+            dylib_error() ? dylib_error() : "(no error reported)");
 #else
    D3D9Create                 = Direct3DCreate9;
 #endif

gfx/drivers/d3d8.c

@@ -215,8 +215,25 @@ static bool d3d8_initialize_symbols(enum gfx_ctx_api api)
       g_d3d8_dll            = dylib_load("d3d8.dll");
 
    if (!g_d3d8_dll)
+   {
+      /* On modern Windows the legacy D3D8 user-mode runtime is not
+       * installed by default (only d3d8thk.dll, the kernel thunk
+       * layer, ships with the OS). Tell the user explicitly --
+       * otherwise the only message they see is the generic
+       * "Cannot open video driver" from video_driver_init_internal. */
+      RARCH_ERR("[D3D8] Failed to load d3d8.dll: %s\n",
+            dylib_error() ? dylib_error() : "(no error reported)");
+      RARCH_ERR("[D3D8] The legacy DirectX 8 runtime is not present "
+            "on this system. Install it (e.g. via the legacy DirectX "
+            "End-User Runtimes from Microsoft) or pick a different "
+            "video driver.\n");
       return false;
-   D3DCreate                = (D3DCreate_t)dylib_proc(g_d3d8_dll, "Direct3DCreate8");
+   }
+   if (!(D3DCreate = (D3DCreate_t)dylib_proc(g_d3d8_dll, "Direct3DCreate8")))
+   {
+      RARCH_ERR("[D3D8] d3d8.dll does not export Direct3DCreate8: %s\n",
+            dylib_error() ? dylib_error() : "(no error reported)");
+   }
 #else
    D3DCreate                = Direct3DCreate8;
 #endif