stage3: restructure into a folder-based layout

It's an absolute mess, but should make integrating stage3_revamp easier…

src/stageinfo.c

@@ -12,10 +12,10 @@
 
 #include "stages/stage1/stage1.h"
 #include "stages/stage2/stage2.h"
+#include "stages/stage3/stage3.h"
 #include "stages/stage4/stage4.h"
 #include "stages/stage5/stage5.h"
 #include "stages/stage6/stage6.h"
-#include "stages/stage3.h"
 #include "stages/extra.h"
 
 #ifdef DEBUG

src/stages/meson.build

@@ -4,6 +4,7 @@ stages_src = []
 stages = [
     'stage1',
     'stage2',
+    'stage3',
     'stage4',
     'stage5',
     'stage6',
@@ -18,8 +19,6 @@ endforeach
 # them into the "stages" array
 
 stages_src += files(
-    'stage3.c',
-    'stage3_events.c',
     'extra.c',
 )
 

src/stages/stage3/background_anim.c

@@ -0,0 +1,32 @@
+/*
+ * This software is licensed under the terms of the MIT License.
+ * See COPYING for further information.
+ * ---
+ * Copyright (c) 2011-2019, Lukas Weber <[email protected]>.
+ * Copyright (c) 2012-2019, Andrei Alexeyev <[email protected]>.
+ */
+
+#include "taisei.h"
+
+#include "background_anim.h"
+#include "draw.h"
+
+#include "global.h"
+#include "stageutils.h"
+
+// TODO
+
+TASK(animate_bg, NO_ARGS) {
+	for(;;) {
+		YIELD;
+		stage3d_update(&stage_3d_context);
+	}
+}
+
+void stage3_bg_init_fullstage(void) {
+	INVOKE_TASK(animate_bg);
+}
+
+void stage3_bg_init_spellpractice(void) {
+	INVOKE_TASK(animate_bg);
+}