Gameboy Development Forum

Hi toxa,

yes, I nearly finished the game. Had some problems with platforms moving left and right. There is still a small bug with those platforms but I think its not worth to fix it.

seems that you are using HBlank interrupt to scroll background to 0, 0 for HUD and disable/enable sprites. i don't see your code, but probably new sdcc produces faster code and you switch sprites or update scroll a bit earlier. when there are sprites on the scanline the hblank periods are different:


please, show your HBlank ISR.

maybe it is much easier to use window for HUD: you switch it on at VBlank together with sprites off, then you switch sprites on and window off at scanline N. very short routine.

i also suggest to use the new style for LCD ISR's:

void scanline_isr_C() __critical __interrupt
{
  // your ISR payload here
}

and a tiny asm source for the vector:

    .area    _LCDVEC_HEADER (ABS)
    .org    0x48        ; LCD
.int_LCD:
    JP    _scanline_isr_C

if you don't use add/remove_LCD, then standard handler is not linked and there is an ability to write dedicated handlers without built-in handler chains iteration which is too long for HBlank.

compiling that is easy with LCC, just do

LCC -o my.gb file1.c file2.asm file3.c

Last edited by toxa (2020-10-26 08:36:09)

0xc1 is 0b11000001 while stat has only 7 meaningful bits and bit0 is readonly. so bit 7 and bit 0 are set for nothing here.

that is too much code for HBlank. 20 cycles of mode2 is only 5 PUSH commands.

1. you have HUD in the game only. so you just disable HBlank interrupt in menu (no need to manipulate handler, just set the mask). you don't need to check game states in the ISR itself.
2. use shadow background scroll registers, copy them in th isr.
3. VBL is long, you can never disable it and check your states there.

isr becomes very straightforward:

void lcd_isr() __critical __interrupt {
   SCX_REG = shadowSCX, SCY_REG = shadowSCY;
   SHOW_SPRITES;
}

you can modify shadowSCY to make shaking in VBlank ISR, if you wish.

Last edited by toxa (2020-10-27 06:34:05)

your game is almost perfect! i'm very impressed! the only flaw i managed to find is reading of uninitialized variable in

#define SET_BANK(N)        SWITCH_ROM_MBC1(N); old_bank = bank; bank = N

old_bank is initialized by garbage value from bank on the first use. the same with input. i noticed that because i changed the crt behaviour in the latest update of gbdk-2020, older versions filled all wram with zeros on start. i think new behaviour is better because it forces good habit of initializing values before using. fix:

//input
UBYTE input = 0;
UBYTE old_input;

//bank
UBYTE bank = 1;
UBYTE old_bank;

ps: you don't need bank variable at all, because there is already built-in bank tracking variable _current_bank. you only need old_bank here.

i just passed 1/2 of the game picking all the weapons, but was unable to catch that glitch.

probably it's "Inaccessable VRAM" issue. try enable them in BGB settings. i just enabled and see exeptions raised. maybe i should slow down set_*_data functions a bit.

i fixed some issues, please try it with RC1: https://github.com/chrismaltby/gb-studi … 0-v401.zip

Tried out the new version a couple days ago.

I like the new levels, the difficulty level feels good. In particular I'm a fan of the new second boss and the secret passages.

Thanks again for sharing it!

Hi bbbbbr, thanks for your feedback.

Hi toxa, a color version is not planned at the moment. I am working on a 4th level which can still fit into the 64kB ROM. Is the wait handler also necessry with your new RC1?

0x7f, i know how to explain. look:

without "while( STAT_REG & 3 );" you have this picture:



or this (if glitsh is always visible):



or even this (if glitch is always visible and candles AND inventory gets corrupted):



first cross is "scroll_bkg(scroll_pos,shake);" the second cross is exit from the ISR.

if you do "while( STAT_REG & 3 );" just before "scroll_bkg(scroll_pos,shake);" the picture becomes this:



glitch goes away, but you get inventory corruption because set_*_data() timing is spoiled by interrupt. and if you use both "while( STAT_REG & 3 );" and "add_LCD(wait_int_handler);" scrolling and exit points are both in safe areas:



the red-green area is "green" when there are no sprites in that scanline, and "red" when there are. that's why you see glitches when you have sprites overlapping the HUD.

Last edited by toxa (2020-10-30 06:36:34)

0x7f, why don't you use BANKED calls? your code is designed for that, you access banked data from code located in the same bank, say *_music. just declare those functions as BANKED and you don't have to care about saving/restoring the banks. another thing - you don't have to track bank number in code: if you decide to move music from bank3 into bank4, you don't have to search all the places where you do SET_BANK(3) before *_music and change it to SET_BANK(4). i also suggest "#pragma bank N" directive rather than a commandline  switches.

Last edited by toxa (2020-11-05 09:15:59)

I have a new version now ready. There a one additional level and also a new weapon.

https://user0x7f.itch.io/black-castle

Last edited by 0x7f (2020-11-29 11:59:39)

Pretty cool game!

Could have an option to switch weapons by using Select button.