Research: The Pokemon Ruby/Sapphire Dissassembly/Decompilation Project

ProjectRevoTPP said:

Ok, time for a practical example.

Consider implementing instant text in Ruby/Sapphire. Emerald supports text speed 0, but R/S does not, so you cant just change speed to 0. If you only had the assembly, you would have to make quite the number of changes to support it. Specifically, InterpretText needs to be in a loop and conditionally break when it is the end of the string. This means you need to redirect a bunch of functions and handwrite the new assembly.

Now, lets look at what you need to do with a fully matching C file available.

Here is Ruby/Sapphire's normal InterpretText function in C:

Code:

static u8 InterpretText(struct Window *win)
{
    u8 c = win->text[win->textIndex++];

    switch (c)
    {
    case 0xFF:
        ClipRight(win);
        win->state = WIN_STATE_END;
        return 0;
    case 0xFD:
        win->state = WIN_STATE_PLACEHOLDER;
        return 2;
    case 0xFE:
        ClipRight(win);
        win->state = WIN_STATE_NEWLINE;
        return 2;
    case 0xFB:
        DrawInitialDownArrow(win);
        win->state = WIN_STATE_PARAGRAPH;
        return 2;
    case 0xFA:
        DrawInitialDownArrow(win);
        win->state = WIN_STATE_NEWLINE_WAIT;
        return 2;
    case 0xFC:
        return HandleExtCtrlCode(win);
    }

    sPrintGlyphFuncs[win->textMode](win, c);
    return 1;
}

Adding Instant text support is as simple as:

Code:

 static u8 InterpretText(struct Window *win)
 {
[COLOR="Red"]-    u8 c = win->text[win->textIndex++];[/COLOR]
[COLOR="SeaGreen"]+    u8 instantText = gSaveBlock2.speedchoiceConfig.instantText; // part of my speedchoice hack. ignore it for the example[/COLOR].
 
 
[COLOR="SeaGreen"]+    while(1)
+    {
+        u8 c = win->text[win->textIndex++];
+[/COLOR]
     switch (c)
     {
     case 0xFF:
         ClipRight(win);
         win->state = WIN_STATE_END;
         return 0;
     case 0xFD:
         win->state = WIN_STATE_PLACEHOLDER;
         return 2;
     case 0xFE:
         ClipRight(win);
         win->state = WIN_STATE_NEWLINE;
         return 2;
     case 0xFB:
         DrawInitialDownArrow(win);
         win->state = WIN_STATE_PARAGRAPH;
         return 2;
     case 0xFA:
         DrawInitialDownArrow(win);
         win->state = WIN_STATE_NEWLINE_WAIT;
         return 2;
     case 0xFC:
         return HandleExtCtrlCode(win);
[COLOR="Red"]-    }[/COLOR]
[COLOR="red"]-[/COLOR]
[COLOR="SeaGreen"]+        default:[/COLOR]
     sPrintGlyphFuncs[win->textMode](win, c);
[COLOR="SeaGreen"]+[/COLOR]
[COLOR="SeaGreen"]+        if(instantText == ON)[/COLOR]
[COLOR="SeaGreen"]+            break;[/COLOR]
[COLOR="SeaGreen"]+        else[/COLOR]
[COLOR="SeaGreen"]     return 1;[/COLOR]
[COLOR="SeaGreen"]+        }[/COLOR]
[COLOR="SeaGreen"]+    }[/COLOR]
 }

...and recompile the ROM to recalculate all the pointers.

Adding a new feature is as simple as that. There is virtually NO mangling with assembly anymore!

And that's whats really important about this project. When you have a decompiled C base that can recompile into a ROM with 0 issues (unlike C injection, which still requires you redirect stuff) this can rebuild without issues since it is the original ROM dissassembled.

Here's a video showing off the change, although its rather old:

https://youtu.be/5YG0uhWqvxI

The two side effects in the video (slight slowdown sometimes and player name printed incorrectly) were as a result of older code not working. The above C works and wouldnt have those issues.

You could also change part of scrcmd.c (waitbutton) to allow holdKeys rather than newKeys so you could also have a Hold to Mash feature with that instant text.

Click to expand...