diff --git a/src/ppu.rs b/src/ppu.rs index 0d2d520..1b2260c 100644 --- a/src/ppu.rs +++ b/src/ppu.rs @@ -98,24 +98,27 @@ impl Ppu { fn draw_scanline(&mut self) { let mut scanline: [u8; GB_WIDTH * 4] = [0; GB_WIDTH * 4]; - let scroll_y = self.pos.scroll_y; - let scroll_x = self.pos.scroll_x; - // let window_y = self.pos.window_y; - // let window_x = self.pos.window_x - 7; - let tile_map_addr = match self.lcd_control.bg_tile_map_addr() { TileMapAddress::X9800 => 0x9800, TileMapAddress::X9C00 => 0x9C00, }; - let y_pos: u16 = scroll_y as u16 + self.pos.line_y as u16; - let tile_row: u16 = (y_pos as u16 / 8) * 32; + let y_pos = self.pos.line_y as u16 + self.pos.scroll_y as u16; - for (i, chunk) in scanline.chunks_mut(4).enumerate() { - let x_pos = i as u8 + scroll_x; + // There are always 20 rows of tiles in the LCD Viewport + // 160 / 20 = 8, so we can figure out the row of a tile with the following + let tile_row: u16 = y_pos as u16 / 8; + + for (line_x, chunk) in scanline.chunks_mut(4).enumerate() { + let x_pos = line_x as u16 + self.pos.scroll_x as u16; + + // There are always 18 columns of tiles in the LCD Viewport + // 144 / 18 = 8, so we can figure out the column of a tile with the following let tile_column = x_pos / 8; - let tile_addr = tile_map_addr + tile_row as u16 + tile_column as u16; + // A tile is 8 x 8, and any given pixel in a tile comes from two bytes + // so the size of a tile is (8 + 8) * 2 which is 32 + let tile_addr = tile_map_addr + (tile_row * 32) as u16 + tile_column as u16; let tile_number = self.read_byte(tile_addr); let tile_data_addr = match self.lcd_control.tile_data_addr() { @@ -128,13 +131,11 @@ impl Ppu { let higher = self.read_byte(tile_data_addr + line as u16); let lower = self.read_byte(tile_data_addr + line as u16 + 1); - let pixels = Pixels::from_bytes(higher, lower); - // println!("Hi: {:#010b} | Lo: {:#010b}", higher, lower); - let bit = x_pos % 8; + let bit = x_pos as usize % 8; let palette = self.monochrome.bg_palette; - let shade = palette.colour(pixels.colour_id(bit)); + let shade = palette.colour(pixels.pixel(7 - bit)); // Flip Horizontally chunk.copy_from_slice(&shade.into_rgba()); } @@ -530,7 +531,7 @@ impl Pixels { Self([higher, lower]) } - pub fn colour_id(&self, bit: u8) -> u8 { + pub fn pixel(&self, bit: usize) -> u8 { let higher = &self.0[0] >> bit; let lower = &self.0[1] >> bit;