Added documentation about viewport and yield data size

docs/Documentation/Porting your Romhack.md

@@ -37,6 +37,13 @@ similar for other games):
 
 Both OoT and SM64:
 
+- In any place where your game creates a viewport (whether statically or
+  dynamically) (search for `Vp` case-sensitive, `SPViewport`, and `G_MAXZ`),
+  change the maximum Z value from `G_MAXZ` to `G_NEW_MAXZ` and negate the
+  Y scale. For more information, see the comment next to `G_MAXZ` in the GBI.
+  Note that your romhack codebase may have the constant hardcoded, usually as
+  `511` which is supposed to be `(G_MAXZ/2)`, instead of actually writing
+  `G_MAXZ`; you need to change these too, there are several of these in SM64.
 - Remove uses of internal GBI features which have been removed in F3DEX3 (see
   @ref compatibility for full list). In OoT, the only changes needed are:
     - In `src/code/ucode_disas.c`, remove the switch statement cases for

gbi.h

@@ -16,10 +16,20 @@
 #ifndef F3DEX3_H
 #define F3DEX3_H
 
+/* Don't remove this line which defines F3DEX3 as F3DEX2. Other headers in your
+romhack codebase will likely assume that if the microcode is not F3DEX2, it is
+F3DEX1 or older, thus breaking F3DEX3 compatibility even more. */
 #define F3DEX_GBI_2  1
 #define F3DEX_GBI_PL 1
 #define F3DEX_GBI_3  1
 
+/* This is only included to check correctness of OS_YIELD_DATA_SIZE. If you are
+sure this is correct in your project, you can remove this include. */
+#include "ultra64/sptask.h"
+#if OS_YIELD_DATA_SIZE != 0xC00
+#error "F3DEX3 requires OS_YIELD_DATA_SIZE == 0xC00"
+#endif
+
 #ifdef REQUIRE_SEMICOLONS_AFTER_GBI_COMMANDS
 /* OoT style, semicolons required after using macros, cleaner code. If modding
 SM64, will have to fix a few places the codebase omits the semicolons. */