nese/src/ppu.h

#ifndef NESE_PPU_H_
#define NESE_PPU_H_

#include <stdint.h>


#define nes_ppu_render_w    (256U)
#define nes_ppu_render_h    (240U)

#define nes_ppu_scanline_dots   (341U)
#define nes_ppu_prerender_line  (0U)
#define nes_ppu_visible_line    (1U)
#define nes_ppu_postrender_line (241U)
#define nes_ppu_vblank_line     (242U)
#define nes_ppu_frame_end_line  (262U)

typedef struct {
    uint8_t y;
    uint8_t index;
    uint8_t attr;
    uint8_t x;
} oam_sprite;

typedef enum {
    oam_Attr_Pal_Mask   = 0b00000011,
    oam_Attr_Background = 0b00100000,
    oam_Attr_Flip_X     = 0b01000000,
    oam_Attr_Flip_Y     = 0b10000000,
} oam_Attribute;


typedef enum {
    ppu_reg_ctrl = 0,
    ppu_reg_mask,
    ppu_reg_status,
    ppu_reg_oam_addr,
    ppu_reg_oam_data,
    ppu_reg_scroll,
    ppu_reg_addr,
    ppu_reg_data,
} ppu_reg_offset;

typedef enum {
    ppu_Control_Nametable_Mask  = 0b00000011,
    ppu_Control_Scroll_Page_X   = 0b00000001,
    ppu_Control_Scroll_Page_Y   = 0b00000010,
    ppu_Control_VRAM_Inc        = 0b00000100,
    ppu_Control_Sprite_Bank     = 0b00001000,
    ppu_Control_Back_Bank       = 0b00010000,
    ppu_Control_Sprite_Size     = 0b00100000,
    ppu_Control_Master          = 0b01000000,
    ppu_Control_VBlank          = 0b10000000,
} nes_ppu_Control;

typedef enum {
    ppu_Mask_Greyscale      = 0b00000001,
    ppu_Mask_Left_Back      = 0b00000010,
    ppu_Mask_Left_Sprite    = 0b00000100,
    ppu_Mask_Back           = 0b00001000,
    ppu_Mask_Sprite         = 0b00010000,
    ppu_Mask_More_Red       = 0b00100000,
    ppu_Mask_More_Green     = 0b01000000,
    ppu_Mask_More_Blue      = 0b10000000,
} nes_ppu_Mask;

typedef enum {
    ppu_Status_Open_Bus_Mask    = 0b00011111,
    ppu_Status_Overflow         = 0b00100000,
    ppu_Status_Hit              = 0b01000000,
    ppu_Status_VBlank           = 0b10000000,
} nes_ppu_Status;


#define NES_CHR_ROM_PAGE_SIZE   (0x0400U)
#define NES_VRAM_PAGE_SIZE      (0x0400U)

#define NES_PPU_CHR_SIZE    (0x2000U)
#define NES_PPU_VRAM_SIZE   (0x1000U)
#define NES_PPU_RAM_SIZE    (0x4000U)
#define NES_PPU_OAM_SIZE    (64U * 4U)
#define NES_PPU_PAL_START   (0x3F00U)

typedef struct {
    // Registers &c.
    uint8_t ctrl;
    uint8_t mask;
    uint8_t status;
    uint8_t oam_addr;
    uint16_t addr; // aka "v"
    uint8_t data;
    uint8_t x; // Fine X scroll
    uint16_t t; // temp VRAM addr
    uint8_t latch; // aka "w" - TODO: Could this be a flag?
    uint8_t addr_inc; // Auto-increment (1 or 32)

    // Memory banks
    uint8_t* chr;
    int n_chr_banks;
    uint8_t* chr_ram; // TODO: Could this be a flag?
    uint8_t* bank[16];
    uint8_t vram[NES_PPU_VRAM_SIZE];
    uint8_t pal_bank[NES_CHR_ROM_PAGE_SIZE]; // Mirrored in banks 12-15, also pal
    uint8_t oam[NES_PPU_OAM_SIZE];
} nes_PPU_Memory;


static inline uint8_t* chr_page(nes_PPU_Memory* mem,
                                int page) {
    return &mem->chr[page * NES_CHR_ROM_PAGE_SIZE];
}

static inline uint8_t* vram_page(nes_PPU_Memory* mem,
                                 int page) {
    return &mem->vram[page * NES_VRAM_PAGE_SIZE];
}

#define nes_PPU_Nametable_Bank_Index    (8U)

typedef enum {
    nes_Mirror_Horizontal = 0,
    nes_Mirror_Vertical,
    nes_Mirror_Only_0,
    nes_Mirror_Only_1,
    nes_Mirror_Four,
} nes_Nametable_Mirroring;

void nes_ppu_set_mirroring(nes_PPU_Memory* mem,
                           nes_Nametable_Mirroring mirror);

typedef struct {
    int scanline;
    int hit_line;
    uint8_t line_data[nes_ppu_render_w];
} nes_PPU;

void nes_ppu_find_hit_line(nes_PPU*, nes_PPU_Memory*);

void nes_ppu_render_line(nes_PPU*, nes_PPU_Memory*);


#endif // NESE_PPU_H_