Road Scrolling demo(SGDK)

#include <genesis.h>

#include "State_vscroll.h"
#include "../res/gfx.h"
#include "Globals.h"


typedef struct
{
    s8 color;
    s16 position;

} Segment;


// road segments
#define SEG_COUNT 64
Segment s[SEG_COUNT];


static int m_Size = 16;

// lookup table to index into the road
static int m_Index[112];

// v-scroll offset
static int m_Lines[112];


static int m_Position = 0;
static int m_Offset = 0;
static int m_CurrentSegment = 0;



void State_VScroll_Start()
{
    fix32 size = FIX32(1.0f);
    fix32 amount = FIX32(0.055f);

    int i = 111;
    int place = -1;
    do
    {
        m_Index[i] = place + fix32ToInt(size);
        place++;

        if (place > 20)
        {
            size = fix32Add(size, fix32Mul(size, amount));
        }
        KLog_S2("i ", i, " index ", m_Index[i]);
        i--;
    } while (i >= 0);



    int co = 16;
    int pos = 0;
    for(i=0;i<SEG_COUNT;i++)
    {
        s[i].color = co;
        s[i].position = pos;

        co = co == 16? -112 : 16;

        pos += m_Size;
    }


    SYS_disableInts();

    // Set palette to black
    VDP_setPaletteColors(0, (u16*)palette_black, 63);

    int ind = TILE_USERINDEX;

    VDP_drawImageEx(PLAN_B, &gfx_outtest, TILE_ATTR_FULL(PAL0, FALSE, FALSE, FALSE, ind), 0, 0, FALSE, DMA);

    VDP_setPalette(PAL0, gfx_outtest.palette->data);


    internalHIntCB = &State_HScroll_HInt;
    VDP_setHInterrupt(TRUE);
    VDP_setHIntCounter(0);

    SYS_enableInts();
}


fix16 inc = FIX16(0.33);

void State_VScroll_Update()
{

    if (Pad1.Down == PAD_HELD)
    {
        m_Position++;
        m_Offset++;
    }



    if (m_Offset == m_Size)
    {
        m_CurrentSegment++;
        if (m_CurrentSegment >= SEG_COUNT)
        {
            m_CurrentSegment = 0;
            m_Position = 0;
        }
    }
    int indexSegment = m_CurrentSegment;
    for (int i = 0; i < 112; ++i)
    {
        // % SEG_COUNT
        int index = ((m_Index[i] + m_Position) >> 3) & 0x3F;
        m_Lines[i] = s[index].color;
    }

    KLog_S1("fps ", getFPS());
}

void State_VScroll_End()
{

}


void State_VScroll_VInt()
{
    VDP_setVerticalScroll(PLAN_B, 256);
}


void State_HScroll_HInt()
{
    if (GET_VCOUNTER > 111 && GET_VCOUNTER < 224)
    {
        VDP_setVerticalScroll(PLAN_B, m_Lines[GET_VCOUNTER - 112]);
    }
}

SimpleState VScroll_State =
{
    State_VScroll_Start,
    State_VScroll_Update,
    State_VScroll_End,
    State_VScroll_VInt
};