add an extensions directory and first extension, sdl rwops stream integration

ostd/ext/sdl_rwops.hh

@@ -0,0 +1,49 @@
+/* SDL RWops integration.
+ *
+ * This file is part of OctaSTD. See COPYING.md for futher information.
+ */
+
+#ifndef OSTD_EXT_SDL_RWOPS_HH
+#define OSTD_EXT_SDL_RWOPS_HH
+
+#ifdef OSTD_EXT_SDL_USE_SDL1
+#include <SDL/SDL.h>
+#else
+#include <SDL2/SDL.h>
+#endif
+
+#include "ostd/types.hh"
+#include "ostd/stream.hh"
+
+namespace ostd {
+namespace sdl {
+
+inline SDL_RWops *stream_to_rwops(Stream &s) {
+    SDL_RWops *rwr = SDL_AllocRW();
+    if (!rwr) {
+        return nullptr;
+    }
+    rwr->hidden.unknown.data1 = &s;
+    rwr->seek = [](SDL_RWops *rw, Int64 pos, int whence) -> Int64 {
+        Stream *is = (Stream *)rw->hidden.unknown.data1;
+        if (!pos && whence == SEEK_CUR)
+            return (Int64)is->tell();
+        if (is->seek(((StreamOffset)pos, (StreamSeek)whence))
+            return (Int64)is->tell();
+        return -1;
+    }
+    rwr->read = [](SDL_RWops *rw, void *buf, Size size, Size nb) -> Size {
+        Stream *is = (Stream *)rw->hidden.unknown.data1;
+        return f->read_bytes(buf, size * nb) / size;
+    }
+    rwr->write = [](SDL_RWops *rw, const void *buf, Size size, Size nb) -> Size {
+        Stream *is = (Stream *)rw->hidden.unknown.data1;
+        return f->write_bytes(buf, size * nb) / size;
+    }
+    rw->close = [](SDL_RWops *) -> int { return 0; }
+}
+
+}
+}
+
+#endif