Implement crosshair target lock-on (#814)

* Implement crosshair target lock-on

* Calculate lock-on offset in `R_ProjectSprite()`

* Introduce `HU_UpdateCrosshairLock()`

* A couple of changes

* More changes

* Update lock offset just once per tic

src/hu_stuff.c

@@ -226,6 +226,7 @@ static void HU_InitCrosshair(void);
 int hud_crosshair;
 boolean hud_crosshair_health;
 boolean hud_crosshair_target;
+boolean hud_crosshair_lockon; // [Alaux] Crosshair locks on target
 int hud_crosshair_color;
 int hud_crosshair_target_color;
 
@@ -1010,14 +1011,16 @@ static void HU_InitCrosshair(void)
 
     crosshair.w = SHORT(crosshair.patch->width)/2;
     crosshair.h = SHORT(crosshair.patch->height)/2;
-    crosshair.x = ORIGWIDTH/2;
   }
   else
     crosshair.patch = NULL;
 }
 
+mobj_t *crosshair_target; // [Alaux] Lock crosshair on target
+
 static void HU_UpdateCrosshair(void)
 {
+  crosshair.x = ORIGWIDTH/2;
   crosshair.y = (screenblocks <= 10) ? (ORIGHEIGHT-ST_HEIGHT)/2 : ORIGHEIGHT/2;
 
   if (hud_crosshair_health)
@@ -1036,12 +1039,14 @@ static void HU_UpdateCrosshair(void)
   else
     crosshair.cr = colrngs[hud_crosshair_color];
 
-  if (STRICTMODE(hud_crosshair_target))
+  if (STRICTMODE(hud_crosshair_target || hud_crosshair_lockon))
   {
     angle_t an = plr->mo->angle;
     ammotype_t ammo = weaponinfo[plr->readyweapon].ammo;
     fixed_t range = (ammo == am_noammo) ? MELEERANGE : 16*64*FRACUNIT;
     boolean intercepts_overflow_enabled = overflow[emu_intercepts].enabled;
+    
+    crosshair_target = linetarget = NULL;
 
     overflow[emu_intercepts].enabled = false;
     P_AimLineAttack(plr->mo, an, range, 0);
@@ -1053,14 +1058,23 @@ static void HU_UpdateCrosshair(void)
         P_AimLineAttack(plr->mo, an -= 2<<26, range, 0);
     }
     overflow[emu_intercepts].enabled = intercepts_overflow_enabled;
+    
+    crosshair_target = linetarget;
 
-    if (linetarget && !(linetarget->flags & MF_SHADOW))
+    if (hud_crosshair_target && crosshair_target
+        && !(crosshair_target->flags & MF_SHADOW))
     {
       crosshair.cr = colrngs[hud_crosshair_target_color];
     }
   }
 }
 
+void HU_UpdateCrosshairLock(int x, int y)
+{
+  crosshair.x += x;
+  crosshair.y += y;
+}
+
 static void HU_DrawCrosshair(void)
 {
   if (plr->playerstate != PST_LIVE ||

src/hu_stuff.h

@@ -96,6 +96,12 @@ extern int crispy_hud;
 extern int hud_crosshair;
 extern boolean hud_crosshair_health;
 extern boolean hud_crosshair_target;
+
+// [Alaux] Lock crosshair on target
+extern boolean hud_crosshair_lockon;
+extern mobj_t *crosshair_target;
+void HU_UpdateCrosshairLock(int x, int y);
+
 extern int hud_crosshair_color;
 extern int hud_crosshair_target_color;
 

src/m_menu.c

@@ -3300,6 +3300,7 @@ enum {
   stat2_xhair,
   stat2_xhairhealth,
   stat2_xhairtarget,
+  stat2_xhairlockon,
   stat2_xhaircolor,
   stat2_xhairtcolor,
 };
@@ -3308,6 +3309,7 @@ static void M_UpdateCrosshairItems (void)
 {
     DISABLE_ITEM(!hud_crosshair, stat_settings2[stat2_xhairhealth]);
     DISABLE_ITEM(!STRICTMODE(hud_crosshair), stat_settings2[stat2_xhairtarget]);
+    DISABLE_ITEM(!STRICTMODE(hud_crosshair), stat_settings2[stat2_xhairlockon]);
     DISABLE_ITEM(!hud_crosshair, stat_settings2[stat2_xhaircolor]);
     DISABLE_ITEM(!STRICTMODE(hud_crosshair && hud_crosshair_target),
         stat_settings2[stat2_xhairtcolor]);
@@ -3343,6 +3345,7 @@ setup_menu_t stat_settings2[] =
   {"ENABLE CROSSHAIR",      S_CHOICE,m_null,M_X,M_Y+stat2_xhair*M_SPC,       {"hud_crosshair"}, 0, M_UpdateCrosshairItems, crosshair_str},
   {"COLOR BY PLAYER HEALTH",S_YESNO, m_null,M_X,M_Y+stat2_xhairhealth*M_SPC, {"hud_crosshair_health"}},
   {"HIGHLIGHT ON TARGET",   S_YESNO, m_null,M_X,M_Y+stat2_xhairtarget*M_SPC, {"hud_crosshair_target"}, 0, M_UpdateCrosshairItems},
+  {"LOCK ON TARGET",        S_YESNO, m_null,M_X,M_Y+stat2_xhairlockon*M_SPC, {"hud_crosshair_lockon"}},
   {"DEFAULT COLOR",         S_CRITEM,m_null,M_X,M_Y+stat2_xhaircolor*M_SPC,  {"hud_crosshair_color"}, 0, NULL, hudcolor_str},
   {"HIGHLIGHT COLOR",       S_CRITEM,m_null,M_X,M_Y+stat2_xhairtcolor*M_SPC, {"hud_crosshair_target_color"}, 0, NULL, hudcolor_str},
 

src/m_misc.c

@@ -2044,6 +2044,13 @@ default_t defaults[] = {
     "1 to change crosshair color on target"
   },
 
+  {
+    "hud_crosshair_lockon",
+    (config_t *) &hud_crosshair_lockon, NULL,
+    {0}, {0,1}, number, ss_stat, wad_no,
+    "1 to lock crosshair on target"
+  },
+
   {
     "hud_crosshair_color",
     (config_t *) &hud_crosshair_color, NULL,

src/r_things.c

@@ -38,6 +38,7 @@
 #include "r_things.h"
 #include "r_bmaps.h" // [crispy] R_BrightmapForTexName()
 #include "m_swap.h"
+#include "hu_stuff.h" // [Alaux] Lock crosshair on target
 
 #define MINZ        (FRACUNIT*4)
 #define BASEYCENTER 100
@@ -548,6 +549,19 @@ void R_ProjectSprite (mobj_t* thing)
       flip = !flip;
     }
 
+  // [Alaux] Lock crosshair on target
+  if (STRICTMODE(hud_crosshair_lockon) && thing == crosshair_target)
+  {
+    HU_UpdateCrosshairLock
+    (
+      FixedMul(tx, xscale >> hires) >> FRACBITS,
+      (FixedMul(viewz - (interpz + crosshair_target->height/2), xscale >> hires) >> FRACBITS)
+      + (viewplayer->lookdir / MLOOKUNIT + viewplayer->recoilpitch)
+    );
+
+    crosshair_target = NULL; // Don't update it again until next tic
+  }
+
   // calculate edges of the shape
   // [crispy] fix sprite offsets for mirrored sprites
   tx -= flip ? spritewidth[lump] - spriteoffset[lump] : spriteoffset[lump];