path: root/src/display.rs

// Very readable, much clean wow.

use crate::consts::DISPLAY_UPDATE_SLEEP_TIME_MICROS;
use std::mem;
use std::time::SystemTime;

const COLORS: [u32; 4] = [0x00e0f8d0, 0x0088c070, 0x346856, 0x00081820];

const LINE_DOTS: u64 = 456;

mod lcdc_flags {
    pub const _BG_PRIORITY: u8 = 0b1;
    pub const OBJ_ENABLE: u8 = 0b10;
    pub const OBJ_SIZE: u8 = 0b100;
    pub const BG_TILEMAP_AREA: u8 = 0b1000;
    pub const BG_TILEDATA_AREA: u8 = 0b10000;
    pub const WIN_ENABLE: u8 = 0b100000;
    pub const WIN_TILEMAP_AREA: u8 = 0b1000000;
    pub const LCD_ENABLE: u8 = 0b10000000;
}

pub enum DisplayInterrupt {
    Vblank,
    Stat,
    Both,
    None,
}

#[derive(Debug)]
pub struct Display {
    framebuffer: Box<[u32; 160 * 144]>,
    bg_buffer: Box<[u8; 160 * 144]>,

    tiledata: Box<[u8; 0x3000]>,
    bg_map_attr: Box<[u8; 0x400]>,
    tilemaps: Box<[u8; 0x800]>,
    oam: Box<[u8; 0xa0]>,

    pub cram: Box<[u8; 0x80]>,
    pub bg_palette: u8,
    pub obj_palettes: [u8; 2],
    pub viewport_y: u8,
    pub viewport_x: u8,
    pub lcdc: u8,
    pub ly: u8,
    pub lyc: u8,
    pub lcd_interrupt_mode: u8,
    pub vram_bank: u8,

    pub cgb_mode: bool,

    pub window_x: u8,
    pub window_y: u8,
    pub window_internal_line_counter: u8,

    last_dt: SystemTime,

    pub stat: u64,

    pub redraw_request: Option<Box<[u32; 160 * 144]>>,
}

impl Display {
    pub fn new() -> Self {
        Self {
            framebuffer: Box::new([0; 160 * 144]),
            bg_buffer: Box::new([0; 160 * 144]),
            tiledata: Box::new([0; 0x3000]),
            bg_map_attr: Box::new([0; 0x400]),
            cram: Box::new([0; 0x80]),
            tilemaps: Box::new([0; 0x800]),
            oam: Box::new([0; 0xa0]),
            bg_palette: 0,
            vram_bank: 0,
            obj_palettes: [0; 2],
            viewport_y: 0,
            viewport_x: 0,
            lcdc: 0,
            ly: 0,
            window_x: 0,
            window_y: 0,
            window_internal_line_counter: 0,
            last_dt: SystemTime::now(),
            stat: 0,
            lyc: 0,
            cgb_mode: false,
            lcd_interrupt_mode: 0xff,
            redraw_request: None,
        }
    }

    pub fn cls(&mut self) {
        self.framebuffer = Box::new([COLORS[0]; 160 * 144]);
    }

    pub fn color_palette(&self, color_byte: u8, palette: u8, cgb_mode: bool) -> u32 {
        if cgb_mode {
            let color_pointer = palette * 8 + color_byte * 2;
            let color16b: u16 = (self.cram[color_pointer as usize] as u16)
                | ((self.cram[color_pointer as usize + 1] as u16) << 8);

            let red = ((0b11111 & color16b) << 3) as u32;
            let green = (((color16b >> 5) & 0b11111) << 3) as u32;
            let blue = (((color16b >> 10) & 0b11111) << 3) as u32;

            (red << 16) | (green << 8) | blue
        } else {
            COLORS[((palette >> (color_byte << 1)) & 0b11) as usize]
        }
    }

    pub fn print_tile(&mut self, tile: u8, x: u8, y: u8, l: usize, bg_map_attr: u8) {
        let tile_pointer = if self.lcdc & lcdc_flags::BG_TILEDATA_AREA != 0 {
            ((tile as u16) << 4) as usize
        } else {
            ((tile as i8 as i32) * 16) as usize + 0x1000
        } + if bg_map_attr & 0b1000 != 0 { 0x1800 } else { 0 };

        for b in (0..8).rev() {
            let data = (((self.tiledata[tile_pointer + l * 2] as u8) >> b) & 1)
                | ((((self.tiledata[tile_pointer + l * 2 + 1] as u8) >> b) & 1) << 1);

            let pxx = (x as i32 + 7 - b as i32) as u8;
            let pxy = y as i32;

            if pxy < 144 && pxx < 160 {
                self.framebuffer[pxy as usize * 160 + pxx as usize] = self.color_palette(
                    data,
                    if self.cgb_mode {
                        bg_map_attr & 0b111
                    } else {
                        self.bg_palette
                    },
                    self.cgb_mode,
                );
                self.bg_buffer[pxy as usize * 160 + pxx as usize] = data;
            }
        }
    }
    pub fn print_all_tiles(&mut self) {
        for i in 0..=255 {
            for l in 0..8 {
                self.print_tile(i, (i % 20) * 8, (i / 20) * 8, l, 0);
            }
        }
    }

    pub fn w(&mut self, addr: u16, value: u8) {
        if self.vram_bank == 0 {
            if addr < 0x1800 {
                self.tiledata[addr as usize] = value;
            } else if addr >= 0x7e00 {
                self.oam[addr as usize - 0x7e00] = value;
            } else {
                self.tilemaps[addr as usize - 0x1800] = value;
            }
        } else {
            if addr < 0x1800 {
                self.tiledata[addr as usize + 0x1800] = value;
            } else if addr < 0x1c00 {
                self.bg_map_attr[addr as usize - 0x1800] = value;
            }
        }
    }

    pub fn r(&self, addr: u16) -> u8 {
        if self.vram_bank == 0 {
            if addr < 0x1800 {
                self.tiledata[addr as usize]
            } else if addr >= 0x7e00 {
                self.oam[addr as usize - 0x7e00]
            } else {
                self.tilemaps[addr as usize - 0x1800]
            }
        } else {
            if addr < 0x1800 {
                self.tiledata[addr as usize + 0x1800]
            } else if addr < 0x1c00 {
                self.bg_map_attr[addr as usize - 0x1800]
            } else {
                0
            }
        }
    }

    pub fn print_bg(&mut self) {
        let tilemap_pointer = if self.lcdc & lcdc_flags::BG_TILEMAP_AREA != 0 {
            0x400
        } else {
            0
        };

        let y_tile = (self.ly + self.viewport_y) as usize;

        for x in 0..32 {
            let tile = self.tilemaps[tilemap_pointer + (y_tile / 8) * 32 + x];
            let bg_map_attr = self.bg_map_attr[(y_tile / 8) * 32 + x];
            self.print_tile(
                tile,
                x as u8 * 8 - self.viewport_x,
                self.ly,
                (y_tile % 8) as usize,
                bg_map_attr,
            );
        }
    }

    pub fn print_win(&mut self) {
        if self.lcdc & lcdc_flags::WIN_ENABLE == 0 {
            return;
        }

        let tilemap_pointer = if self.lcdc & lcdc_flags::WIN_TILEMAP_AREA != 0 {
            0x400
        } else {
            0
        };

        if self.ly < self.window_y {
            return;
        }

        let tilemap_y_px = (self.ly - self.window_y) as usize;
        let y_tile = tilemap_y_px / 8;
        let tile_y_px = tilemap_y_px % 8;

        for lx in 0..32 {
            let tile_index = y_tile * 32 + lx;
            if tilemap_pointer + tile_index as usize >= 2048 {
                return;
            }

            let tile = self.tilemaps[(tilemap_pointer + tile_index) as usize];
            if (lx as u8 * 8) as u32 + (self.window_x - 7) as u32 > 255 {
                continue;
            }
            let tilemap_x_px = lx as u8 * 8 + self.window_x - 7;

            self.print_tile(tile, tilemap_x_px, self.ly, tile_y_px as usize, 0);
        }
        self.window_internal_line_counter += 1;
    }

    pub fn print_obj(&mut self) {
        if self.lcdc & lcdc_flags::OBJ_ENABLE == 0 {
            return;
        }

        // Making unreadable magic code is my brand
        for o in (0..40).rev() {
            let mut y = self.oam[o * 4] - 9;
            let x = self.oam[o * 4 + 1];
            let mut tile = self.oam[o * 4 + 2];
            let opts = self.oam[o * 4 + 3];
            let bg_priority_flag = opts & 0b10000000 != 0;
            let x_flip = opts & 0b100000 != 0;
            let y_flip = opts & 0b1000000 != 0;
            let palette = (opts >> 4) & 1;
            let tile_vram = if self.cgb_mode && opts & 0b1000 != 0 {
                0x1800
            } else {
                0
            };
            let cgb_palette = opts & 0b111;
            let obj_size = if self.lcdc & lcdc_flags::OBJ_SIZE != 0 {
                tile &= 0xfe;
                y += 8;
                16
            } else {
                8
            };

            let tile_pointer = ((tile as u16) << 4) as usize + tile_vram;

            if y < self.ly || y >= self.ly + obj_size {
                continue;
            }

            let l = if y_flip {
                y - self.ly
            } else {
                obj_size - 1 - (y - self.ly)
            };

            for b in 0..8 {
                let pxx = if x_flip {
                    x as i32 + b as i32 - 8 as u8 as i32
                } else {
                    x as i32 + 7 - b as i32 - 8 as u8 as i32
                };
                let pxy = self.ly as i32;

                let data = (((self.tiledata[tile_pointer + l as usize * 2] as u8) >> b) & 1)
                    | ((((self.tiledata[tile_pointer + l as usize * 2 + 1] as u8) >> b) & 1) << 1);

                if pxy < 144 && pxx < 160 && pxy >= 0 && pxx >= 0 {
                    if data != 0
                        && !((bg_priority_flag/* && self.lcdc & lcdc_flags::BG_PRIORITY != 0 */)
                            && self.bg_buffer[pxy as usize * 160 + pxx as usize] != 0)
                    {
                        self.framebuffer[pxy as usize * 160 + pxx as usize] = self.color_palette(
                            data,
                            if self.cgb_mode {
                                cgb_palette + 8
                            } else {
                                self.obj_palettes[palette as usize]
                            },
                            self.cgb_mode,
                        );
                    }
                }
            }
        }
    }

    pub fn update_display(&mut self, cycles: u64) -> DisplayInterrupt {
        let mut ret_interrupt = DisplayInterrupt::None;
        self.stat += cycles;
        if self.lcdc & lcdc_flags::LCD_ENABLE != 0 && self.stat >= LINE_DOTS {
            self.print_bg();
            self.print_win();
            self.print_obj();
            self.ly = (self.ly + 1) % 154;
            self.stat %= LINE_DOTS;
            if self.ly == 0x90 {
                ret_interrupt = DisplayInterrupt::Vblank;
                if self.lcd_interrupt_mode == 1 {
                    ret_interrupt = DisplayInterrupt::Both;
                }
                if SystemTime::now()
                    .duration_since(self.last_dt)
                    .unwrap()
                    .as_micros()
                    > DISPLAY_UPDATE_SLEEP_TIME_MICROS as u128
                {
                    self.redraw_request = Some(self.framebuffer.clone());
                    self.last_dt = SystemTime::now();
                }

                self.window_internal_line_counter = 0;
            }
            if self.ly < 0x90 && (self.lcd_interrupt_mode == 0 || self.lcd_interrupt_mode == 2) {
                ret_interrupt = DisplayInterrupt::Stat;
            }

            if self.lcd_interrupt_mode == 3 && self.ly == self.lyc + 1 {
                ret_interrupt = DisplayInterrupt::Stat;
            }
        }
        if self.lcdc & lcdc_flags::LCD_ENABLE == 0 {
            self.ly = 0;
        }

        return ret_interrupt;
    }

    pub fn get_redraw_request(&mut self) -> Option<Box<[u32; 160 * 144]>> {
        let mut result = None;

        mem::swap(&mut result, &mut self.redraw_request);

        result
    }
}