nes_ppu_test.c

static void render_scanline_bg_simple(struct NES_Core* nes, uint8_t line)
{
    const uint8_t row = (line >> 3) & 31;
    const uint8_t fine_line = line & 7;

    const uint16_t pattern_table_addr = ppu_get_bg_pattern_table_addr(nes);

    uint16_t nametable_addr = ppu_get_nametable_addr(nes) + (row * 32);

    for (uint8_t col = 0; col < 32; ++col)
    {
        const uint8_t tile_num = nes_ppu_read(nes, nametable_addr++);

        const uint8_t bit_plane0 = nes->cart.chr_rom[pattern_table_addr + fine_line + (tile_num * 16) + 0];
        const uint8_t bit_plane1 = nes->cart.chr_rom[pattern_table_addr + fine_line + (tile_num * 16) + 8];

        const uint8_t full = bit_plane0 | bit_plane1;

        for (uint8_t x = 0; x < 8; ++x)
        {
            const uint8_t bit = 1 << (7 - x);

            const uint32_t colour = (full & bit) ? 0xAAAAAAAA : 0;

            ppu_write_pixel(nes, colour, (col * 8) + x, line);
        }
    }
}