add flag to ignore line-of-sight hits for transparent background surfaces

src/game/bg.c

@@ -4590,6 +4590,10 @@ bool bgTestHitInRoom(struct coord *frompos, struct coord *topos, s32 roomnum, st
 	numbatches = g_Rooms[roomnum].numvtxbatches;
 
 	for (i = 0; i < numbatches; batch++, i++) {
+#ifndef PLATFORM_N64
+		if (hitthing->ignore_xlu && batch->type == VTXBATCHTYPE_XLU)
+			continue;
+#endif
 		j = bg0f1612e4(&batch->bbmin, &batch->bbmax, &from, &dist, &sp94, &hitthing->pos);
 
 		if (j == 0) {

src/game/prop.c

@@ -983,7 +983,7 @@ struct prop *shotCalculateHits(s32 handnum, bool isshooting, struct coord *gunpo
 bool shotTestLos(struct coord *gunpos2d, struct coord *gundir2d, struct coord *gunpos3d, struct coord *gundir3d, struct coord *endpos3d)
 {
 	struct prop **propptr;
-	struct hitthing sp664;
+	struct hitthing hitthing;
 	struct coord delta;
 	struct shotdata shotdata;
 	s32 i;
@@ -993,6 +993,9 @@ bool shotTestLos(struct coord *gunpos2d, struct coord *gundir2d, struct coord *g
 	RoomNum *roomsptr;
 	struct prop *prop;
 
+	// ignore transparent surfaces
+	hitthing.ignore_xlu = 1;
+
 	shotdata.gunpos3d.x = gunpos3d->x;
 	shotdata.gunpos3d.y = gunpos3d->y;
 	shotdata.gunpos3d.z = gunpos3d->z;
@@ -1040,11 +1043,11 @@ bool shotTestLos(struct coord *gunpos2d, struct coord *gundir2d, struct coord *g
 
 	// Check for BG hits first
 	for (i = 0; rooms[i] != -1; i++) {
-		if (bgTestHitInRoom(&shotdata.gunpos3d, endpos3d, rooms[i], &sp664)) {
+		if (bgTestHitInRoom(&shotdata.gunpos3d, endpos3d, rooms[i], &hitthing)) {
 			// check if it's far enough away from the end point
-			if (fabsf(sp664.pos.x - endpos3d->x) >= 0.1f ||
-					fabsf(sp664.pos.y - endpos3d->y) >= 0.1f ||
-					fabsf(sp664.pos.z - endpos3d->z) >= 0.1f) {
+			if (fabsf(hitthing.pos.x - endpos3d->x) >= 0.1f ||
+					fabsf(hitthing.pos.y - endpos3d->y) >= 0.1f ||
+					fabsf(hitthing.pos.z - endpos3d->z) >= 0.1f) {
 				return false;
 			}
 		}

src/include/types.h

@@ -5750,6 +5750,9 @@ struct hitthing {
 	s16 unk28;
 	s16 texturenum;
 	s16 unk2c;
+#ifndef PLATFORM_N64
+	s16 ignore_xlu;
+#endif
 };
 
 struct hit {