Move some buffer constants into buffer/Constants

src/common/buffer/Constants.ts

@@ -4,3 +4,27 @@
  */
 
 export const DEFAULT_COLOR = 256;
+export const DEFAULT_ATTR = (0 << 18) | (DEFAULT_COLOR << 9) | (256 << 0);
+
+export const CHAR_DATA_ATTR_INDEX = 0;
+export const CHAR_DATA_CHAR_INDEX = 1;
+export const CHAR_DATA_WIDTH_INDEX = 2;
+export const CHAR_DATA_CODE_INDEX = 3;
+
+/**
+ * Null cell - a real empty cell (containing nothing).
+ * Note that code should always be 0 for a null cell as
+ * several test condition of the buffer line rely on this.
+ */
+export const NULL_CELL_CHAR = '';
+export const NULL_CELL_WIDTH = 1;
+export const NULL_CELL_CODE = 0;
+
+/**
+ * Whitespace cell.
+ * This is meant as a replacement for empty cells when needed
+ * during rendering lines to preserve correct aligment.
+ */
+export const WHITESPACE_CELL_CHAR = ' ';
+export const WHITESPACE_CELL_WIDTH = 1;
+export const WHITESPACE_CELL_CODE = 32;