+ *\r
+ * since renderer always draws line in 8bit mode, there are 2 spare bits:\r
+ * b \ mode: s/h as sonic\r
+ * 00 normal - -\r
+ * 01 shadow - pal index\r
+ * 10 hilight+op spr spr pal index\r
+ * 11 shadow +op spr - pal index\r
+ *\r
+ * not handled properly:\r
+ * - hilight op on shadow tile\r
+ * - AS + s/h (s/h sprite flag interferes with and cleared by AS code)\r