It is recommended to read the previous articles to better understand this one:

• GameBoy Dev00
• GameBoy Dev01
• GameBoy Dev02
• GameBoy Dev03
• GameBoy Dev04
• GameBoy Dev05
• GameBoy Dev06

In the previous article, we learned how to manipulate the GameBoy’s color palette. This time, we will create a program that shows us all possible combinations. The transition is a bit fast, but we can change the value of the delay to make it slower or pause the emulator itself and look at the color combination of the palette to know which BGP_REG configuration we should assign.

The code is as follows:

#include <gb/gb.h>
#include <stdio.h>
#include "CyberPunkTiles.c"
#include "CyberPunkMap.c"

UINT8 i;

void technicolor_rainbow(){
    // Default palette: 11 10 01 00 -> E4
    // 2^8: 256
    for(i=0; i<255; i++){
        BGP_REG = i;
        delay(100);
    }
}

void main(){
    // grep TILESET_TILE_COUNT CyberPunkTiles.h
    set_bkg_data(0, 106, TILESET);

    // grep TILEMAP_ CyberPunkMap.h
    set_bkg_tiles(0, 0, 20, 18, TILEMAP);

    SHOW_BKG;
    DISPLAY_ON;

    while(1){
        BGP_REG = 0xE4;
        waitpad(J_START);
        technicolor_rainbow();
        delay(100);
    }
}

We compile it:

We load the ROM into the emulator and every time we press Start, we will see the effect: