Replace resolution-related hard-coded numbers with constants

Source/doom.cpp

@@ -2,7 +2,7 @@
 
 int doom_quest_time;
 int doom_stars_drawn;
-void *pDoomCel;
+BYTE *pDoomCel;
 BOOL doomflag;
 int DoomQuestState;
 
@@ -91,5 +91,5 @@ void doom_draw()
 		}
 	}
 
-	CelDecodeOnly(SCREEN_X, PANEL_Y - 1, (BYTE *)pDoomCel, 1, 640);
+	CelDecodeOnly(SCREEN_X, PANEL_Y - 1, pDoomCel, 1, SCREEN_WIDTH);
 }

Source/doom.h

@@ -2,11 +2,11 @@
 #ifndef __DOOM_H__
 #define __DOOM_H__
 
-extern int doom_quest_time;  // weak
-extern int doom_stars_drawn; // weak
-extern void *pDoomCel;
-extern int doomflag;       // weak
-extern int DoomQuestState; // idb
+extern int doom_quest_time;
+extern int doom_stars_drawn;
+extern BYTE *pDoomCel;
+extern int doomflag;
+extern int DoomQuestState;
 
 /*
 void doom_reset_state();

Source/scrollrt.cpp

@@ -2214,7 +2214,7 @@ void scrollrt_draw_game_screen(BOOL draw_cursor)
 
 	if (drawpanflag == 255) {
 		drawpanflag = 0;
-		hgt = 480;
+		hgt = SCREEN_HEIGHT;
 	} else {
 		hgt = 0;
 	}
@@ -2632,7 +2632,7 @@ void DrawAndBlit()
 	}
 	if (talkflag) {
 		DrawTalkPan();
-		hgt = 480;
+		hgt = SCREEN_HEIGHT;
 	}
 	scrollrt_draw_cursor_item();
 	unlock_buf(0);