nesemu/ppu/ppu.c

//
// Created by william on 12/30/23.
//

#include <stddef.h>
#include "../include/ppu.h"

void ppu_init(PPU *ppu, byte *registers_ram, byte *oam_dma_register) {
    ppu->registers = registers_ram;
    ppu->registers[PPU_REGISTER_CTRL] = 0x00;
    ppu->registers[PPU_REGISTER_MASK] = 0x00;
    ppu->registers[PPU_REGISTER_STATUS] = 0x00;
    ppu->registers[PPU_REGISTER_OAM_ADDR] = 0x00;
    ppu->registers[PPU_REGISTER_OAM_DATA] = 0x00;
    ppu->registers[PPU_REGISTER_SCROLL] = 0x00;
    ppu->registers[PPU_REGISTER_ADDR] = 0x00;
    ppu->registers[PPU_REGISTER_DATA] = 0x00;
    ppu->oam_dma_register = oam_dma_register;
    ppu->odd_frame = false;
}

long frame = 0;
int x, y = 0;

void ppu_cycle(PPU *ppu) {
    int frame_width = 341;
    int frame_height = 262;
    bool rendering_enabled = ppu_read_flag(ppu, PPU_REGISTER_MASK, PPU_MASK_SHOW_BG | PPU_MASK_SHOW_SP);
    if (rendering_enabled && ppu->odd_frame) {
        // With rendering enabled, the odd frames are shorter
        // TODO: and doing the last cycle of the last dummy nametable fetch there instead
        frame_width = 339;
        frame_height = 261;
    }

    x++;
    if (x >= frame_width) {
        x = 0;
        y++;
    }

    if (y >= frame_height) {
        y = 0;
        frame++;
        ppu->odd_frame = !ppu->odd_frame;
    }
}

bool ppu_read_flag(PPU *ppu, size_t reg, byte mask) {
    return ppu->registers[reg] & mask;
}

//byte ppu_read_register(PPU *ppu, size_t reg, byte mask) {
//    return ppu->registers[reg] & mask;
//}

void ppu_read_register(PPU *ppu, byte reg) {
    if (reg == PPU_REGISTER_STATUS) {
        ppu->w = false;
    }
}

void ppu_write_register(PPU *ppu, byte reg) {
    if (reg == PPU_REGISTER_SCROLL || reg == PPU_REGISTER_ADDR) {
        ppu->w = !ppu->w;
    }

    if (reg == PPU_REGISTER_OAM_DATA) {
        ppu->registers[PPU_REGISTER_OAM_ADDR]++;
    }
}