nese/src/ppu.c

#include <string.h>

#include "ppu.h"

//#define DEBUG "PPU"
#include "log.h"


static const uint8_t mirror_schemes[][4] = {
    [nes_Mirror_Horizontal] = {0, 0, 1, 1},
    [nes_Mirror_Vertical]   = {0, 1, 0, 1},
    [nes_Mirror_Only_0]     = {0, 0, 0, 0},
    [nes_Mirror_Only_1]     = {1, 1, 1, 1},
    [nes_Mirror_Four]       = {0, 1, 2, 3},
};


void nes_ppu_set_mirroring(nes_PPU_Memory* mem,
                           nes_Nametable_Mirroring mirror) {
    for (int i = 0; i < 4; ++i) {
        mem->bank[nes_PPU_Nametable_Bank_Index + i] =
                vram_page(mem, (int)mirror_schemes[mirror][i]);
    }
}

void nes_ppu_find_hit_line(nes_PPU* ppu, nes_PPU_Memory* mem) {
    int sprite_bank = !!(mem->ctrl & ppu_Control_Sprite_Bank);
    oam_sprite sprite = *(oam_sprite*)mem->oam;
    int sprite_height = (mem->ctrl & ppu_Control_Sprite_Size) ?
                        16 : 8;
    int stride = 1;
    int y_off = 0;
    if (sprite.attr & oam_Attr_Flip_Y) {
        stride = -1;
        y_off = sprite_height - 1;
        sprite_bank = (sprite.index & 1);
        sprite.index &= 0xFEU;
    }

    sprite_bank = (sprite_bank << 2) | (sprite.index >> 6);

    const int data_off = ((sprite.index & 0x3FU) << 4) +
                         ((y_off & 8) << 1) + (y_off & 7);
    uint8_t* data = mem->bank[sprite_bank] + data_off;

    ppu->hit_line = -1;

    if (sprite.y + 1 <= nes_ppu_render_h && sprite.y > 0) {
        for (int line = 0; line < sprite_height; ++line) {
            if (data[0] | data[8]) {
                ppu->hit_line = sprite.y + 1 + line + nes_ppu_visible_line;
                break;
            }
            data += stride;
        }
    }
}


void nes_ppu_render_line(nes_PPU* ppu, nes_PPU_Memory* mem) {
    uint8_t* scanline_ptr = ppu->screen_data +
                   (    nes_ppu_render_w *
                        (ppu->scanline - nes_ppu_visible_line));
    uint8_t* ptr = scanline_ptr;

    if (!(mem->mask & ppu_Mask_Back)) {
        memset(ptr, 0xFFU, nes_ppu_render_w);
/*
        // Emulate the happy part of the backdrop override quirk
        int pal_idx = ((mem->addr & 0x3F00U) == 0x3F00U) ?
                      (mem->addr & 0x1FU) : 0;
        // Don't use the rendering palette (masked transparency)
        memset(ptr, mem->pal_bank[0x300 + pal_idx],
               nes_ppu_render_w);
*/
    } else {
        int back_bank = nes_PPU_Nametable_Bank_Index +
                   ((mem->addr >> 10) & 3);

        int y_coarse = (mem->addr >> 5) & 0x1F;
        int y_fine = mem->addr >> 12;
        int x_coarse = mem->addr & 0x1FU;

        const int bank_off = !!(mem->ctrl & ppu_Control_Back_Bank) << 2;

        const uint8_t* nametable = mem->bank[back_bank] + (y_coarse * 32) + x_coarse;
        const uint8_t* attrs = mem->bank[back_bank] + 0x3C0U + ((y_coarse >> 2) << 3);

        // Partial left column
        ptr += 8 - mem->x;

        // Omit if left column is masked
        if (mem->mask & ppu_Mask_Left_Back) {
            const uint8_t* pal = mem->palette +
                    (((attrs[x_coarse >> 2] >>
                        (   (x_coarse & 2) +
                            ((y_coarse & 2) << 1))) & 3) << 2);
            const int ch = *nametable;
            const int bank = (ch >> 6) + bank_off;
            const int addr_off = ((ch & 0x3F) << 4) + y_fine;
            const uint8_t* data = mem->bank[bank] + addr_off;
            const uint8_t pl0 = data[0];
            const uint8_t pl1 = data[8];
            const int pat0 = (pl0 & 0x55) | ((pl1 << 1) & 0xAA);
            const int pat1 = ((pl0 >> 1) & 0x55) | (pl1 & 0xAA);
            switch (mem->x) {
                case 0: ptr[-8] = pal[(pat1 >> 6) & 3];
                case 1: ptr[-7] = pal[(pat0 >> 6) & 3];
                case 2: ptr[-6] = pal[(pat1 >> 4) & 3];
                case 3: ptr[-5] = pal[(pat0 >> 4) & 3];
                case 4: ptr[-4] = pal[(pat1 >> 2) & 3];
                case 5: ptr[-3] = pal[(pat0 >> 2) & 3];
                case 6: ptr[-2] = pal[(pat1 >> 0) & 3];
                case 7: ptr[-1] = pal[(pat0 >> 0) & 3];
            }
        }

        // TODO: Mapper ppu_bus

        ++x_coarse;
        ++nametable;

        void __attribute__((always_inline)) inline render_bg(void) {
            const uint8_t* pal = mem->palette +
                (((attrs[x_coarse >> 2] >>
                    (   (x_coarse & 2) +
                        ((y_coarse & 2) << 1))) & 3) << 2);
            const int ch = *nametable;
            const int bank = (ch >> 6) + bank_off;
            const int addr_off = ((ch & 0x3F) << 4) + y_fine;
            const uint8_t* data = mem->bank[bank] + addr_off;
            const uint8_t pl0 = data[0];
            const uint8_t pl1 = data[8];
            const int pat0 = (pl0 & 0x55) | ((pl1 << 1) & 0xAA);
            const int pat1 = ((pl0 >> 1) & 0x55) | (pl1 & 0xAA);

            ptr[0] = pal[(pat1 >> 6) & 3];
            ptr[1] = pal[(pat0 >> 6) & 3];
            ptr[2] = pal[(pat1 >> 4) & 3];
            ptr[3] = pal[(pat0 >> 4) & 3];
            ptr[4] = pal[(pat1 >> 2) & 3];
            ptr[5] = pal[(pat0 >> 2) & 3];
            ptr[6] = pal[(pat1 >> 0) & 3];
            ptr[7] = pal[(pat0 >> 0) & 3];
            ptr += 8;
        }

        // Left Nametable
        for (; x_coarse < 32; ++x_coarse) {
            render_bg();
            // TODO: Mapper ppu_bus
            ++nametable;
        }

        // Right Nametable
        back_bank ^= 0b01;
        nametable = mem->bank[back_bank] + (y_coarse * 32);
        attrs = mem->bank[back_bank] + 0x3C0U + ((y_coarse >> 2) << 3);

        for (x_coarse = 0; x_coarse < (mem->addr & 0x1FU); ++x_coarse) {
            render_bg();
            // TODO: Mapper ppu_bus
            ++nametable;
        }

        // Partial right column
        {
            const uint8_t* pal = mem->palette +
                    (((attrs[x_coarse >> 2] >>
                        (   (x_coarse & 2) +
                            ((y_coarse & 2) << 1))) & 3) << 2);
            const int ch = *nametable;
            const int bank = (ch >> 6) + bank_off;
            const int addr_off = ((ch & 0x3F) << 4) + y_fine;
            const uint8_t* data = mem->bank[bank] + addr_off;
            const uint8_t pl0 = data[0];
            const uint8_t pl1 = data[8];
            const int pat0 = (pl0 & 0x55) | ((pl1 << 1) & 0xAA);
            const int pat1 = ((pl0 >> 1) & 0x55) | (pl1 & 0xAA);
            switch (mem->x) {
                case 8: ptr[7] = pal[(pat0 >> 0) & 3];
                case 7: ptr[6] = pal[(pat1 >> 0) & 3];
                case 6: ptr[5] = pal[(pat0 >> 2) & 3];
                case 5: ptr[4] = pal[(pat1 >> 2) & 3];
                case 4: ptr[3] = pal[(pat0 >> 4) & 3];
                case 3: ptr[2] = pal[(pat1 >> 4) & 3];
                case 2: ptr[1] = pal[(pat0 >> 6) & 3];
                case 1: ptr[0] = pal[(pat1 >> 6) & 3];
            }
        }
    }

    // TODO: Mapper ppu_bus

    if (!(mem->mask & ppu_Mask_Left_Back)) {
        memset(scanline_ptr, 0xFFU, 8);
    }

    // TODO: Mapper VROM switch
/*
    if (mem->mask & ppu_Mask_Sprite) {
        // This time, we do need overflow protection
//        uint8_t sprite_data[nes_ppu_render_w + 8] = {0};

        const int sprite_height = (mem->ctrl & ppu_Control_Sprite_Size) ?
                                  16 : 8;
        const int scanline = ppu->scanline - nes_ppu_visible_line;

        int bank = !!(mem->ctrl & ppu_Control_Sprite_Bank) << 2;

        int n_sprites = 0;
        const oam_sprite* sprites = (oam_sprite*)mem->oam;
        const oam_sprite* sprite = sprites +
                                   NES_PPU_SPRITE_COUNT - 1;
        for ( ; sprite >= sprites && n_sprites < 8; --sprite) {
            int y = sprite->y + 1;
            if (y > scanline || y + sprite_height <= scanline) {
                continue;
            }

            int y_off = scanline - y;
            if (sprite->attr & oam_Attr_Flip_Y) y_off = sprite_height - y_off - 1;

            int ch = sprite->index;
            if (mem->ctrl & ppu_Control_Sprite_Size) {
                bank = (ch & 1) << 2;
                ch &= 0xFEU;
            }

            bank += (ch >> 6);
            const int addr_off = ((ch & 0x3fU) << 4) + ((y_off & 8) << 1) + (y_off & 7);
            const uint8_t* data = mem->bank[bank] + addr_off;
            const uint8_t pl0 = data[0];
            const uint8_t pl1 = data[8];
            const int pat0 = (pl0 & 0x55) | ((pl1 << 1) & 0xAA);
            const int pat1 = ((pl0 >> 1) & 0x55) | (pl1 & 0xAA);

            const uint8_t* pal = &mem->palette[0x10 + ((sprite->attr & oam_Attr_Pal_Mask) << 2)];
            uint8_t* dst = scanline_ptr + sprite->x;

            const int over_x = ((int)sprite->x + 8) - nes_ppu_render_w;

            // TODO: X Flip
            switch (over_x) {
            default:
            {   int pal_idx = (pat1 << 0) & 3;
                if (    (   !(sprite->attr & oam_Attr_Background) ||
                            dst[7] == 0xFFU)
                        && pal_idx) {
                    dst[7] = pal[pal_idx];
                }
            }
            case 1:
            {   int pal_idx = (pat0 << 0) & 3;
                if (    (   !(sprite->attr & oam_Attr_Background) ||
                            dst[6] == 0xFFU)
                        && pal_idx) {
                    dst[6] = pal[pal_idx];
                }
            }
            case 2:
            {   int pal_idx = (pat1 << 2) & 3;
                if (    (   !(sprite->attr & oam_Attr_Background) ||
                            dst[5] == 0xFFU)
                        && pal_idx) {
                    dst[5] = pal[pal_idx];
                }
            }
            case 3:
            {   int pal_idx = (pat0 << 2) & 3;
                if (    (   !(sprite->attr & oam_Attr_Background) ||
                            dst[4] == 0xFFU)
                        && pal_idx) {
                    dst[4] = pal[pal_idx];
                }
            }
            case 4:
            {   int pal_idx = (pat1 << 4) & 3;
                if (    (   !(sprite->attr & oam_Attr_Background) ||
                            dst[3] == 0xFFU)
                        && pal_idx) {
                    dst[3] = pal[pal_idx];
                }
            }
            case 5:
            {   int pal_idx = (pat0 << 4) & 3;
                if (    (   !(sprite->attr & oam_Attr_Background) ||
                            dst[2] == 0xFFU)
                        && pal_idx) {
                    dst[2] = pal[pal_idx];
                }
            }
            case 6:
            {   int pal_idx = (pat1 << 6) & 3;
                if (    (   !(sprite->attr & oam_Attr_Background) ||
                            dst[1] == 0xFFU)
                        && pal_idx) {
                    dst[1] = pal[pal_idx];
                }
            }
            case 7:
            {   int pal_idx = (pat0 << 6) & 3;
                if (    (   !(sprite->attr & oam_Attr_Background) ||
                            dst[0] == 0xFFU)
                        && pal_idx) {
                    dst[0] = pal[pal_idx];
                }
            }
            }

            ++n_sprites;
        }

        if (n_sprites >= 8) {
            mem->status |= ppu_Status_Overflow;
        } else {
            mem->status &= ~ppu_Status_Overflow;
        }
    }
*/

    // Increment internal registers
    if (mem->mask & (ppu_Mask_Sprite | ppu_Mask_Back)) {
        uint16_t mask = 0b10000011111;
        mem->addr = (mem->addr & ~mask) | (mem->t & mask);

        int y_scroll = (mem->addr >> 12) |
                       ((mem->addr >> 2) & 0xF8U);
        if (nes_ppu_render_h - 1 == y_scroll) {
            y_scroll = 0;
            mem->addr ^= 0x800;
        } else if (0xFFU == y_scroll) {
            y_scroll = 0;
        } else {
            ++y_scroll;
        }
        mem->addr = (mem->addr & ~0b111001111100000) |
                    ((y_scroll & 7) << 12) |
                    ((y_scroll & 0xF8U) << 2);
    }
}