Players sliding in the same direction will no longer attack each other

We check to see what the difference in velocities is, if it's small then
no attack is made. Otherwise, only the player going faster will attack.

src/game/interaction.c

@@ -47,6 +47,9 @@
 #define INT_ATTACK_NOT_WEAK_FROM_ABOVE                                                \
     (INT_GROUND_POUND_OR_TWIRL | INT_PUNCH | INT_KICK | INT_TRIP | INT_HIT_FROM_BELOW)
 
+#define INT_ATTACK_SLIDE                                                              \
+    (INT_SLIDE_KICK | INT_FAST_ATTACK_OR_SHELL)
+
 u8 sDelayInvincTimer;
 s16 sInvulnerable;
 u32 interact_coin(struct MarioState *, u32, struct Object *);
@@ -1189,6 +1192,21 @@ u8 determine_player_damage_value(u32 interaction) {
     return 1;
 }
 
+u8 player_is_sliding(struct MarioState* m) {
+    if (m->action & (ACT_FLAG_BUTT_OR_STOMACH_SLIDE | ACT_FLAG_DIVING)) {
+        return TRUE;
+    }
+
+    switch (m->action) {
+        case ACT_CROUCH_SLIDE:
+        case ACT_SLIDE_KICK_SLIDE:
+        case ACT_BUTT_SLIDE_AIR:
+        case ACT_HOLD_BUTT_SLIDE_AIR:
+            return TRUE;
+    }
+    return FALSE;
+}
+
 u32 interact_player(struct MarioState* m, UNUSED u32 interactType, struct Object* o) {
     if (gServerSettings.playerInteractions == PLAYER_INTERACTIONS_NONE) { return FALSE; }
 
@@ -1212,9 +1230,27 @@ u32 interact_player(struct MarioState* m, UNUSED u32 interactType, struct Object
     u8 isInCutscene = ((m->action & ACT_GROUP_MASK) == ACT_GROUP_CUTSCENE) || ((m2->action & ACT_GROUP_MASK) == ACT_GROUP_CUTSCENE);
     u8 isInvulnerable = (m2->action & ACT_FLAG_INVULNERABLE) || m2->invincTimer != 0 || m2->hurtCounter != 0 || isInCutscene;
     if ((interaction & INT_ANY_ATTACK) && !(interaction & INT_HIT_FROM_ABOVE) && !isInvulnerable) {
+
+        // determine if slide attack should be ignored
+        if ((interaction & INT_ATTACK_SLIDE) && player_is_sliding(m2)) {
+            // determine the difference in velocities
+            Vec3f velDiff;
+            vec3f_dif(velDiff, m->vel, m2->vel);
+
+            if (vec3f_length(velDiff) < 40) {
+                // the difference vectors are not different enough, do not attack
+                return FALSE;
+            }
+            if (vec3f_length(m2->vel) > vec3f_length(m->vel)) {
+                // the one being attacked is going faster, do not attack
+                return FALSE;
+            }
+        }
+
         if (m->action == ACT_GROUND_POUND) {
             m2->squishTimer = max(m2->squishTimer, 20);
         }
+
         if (m2->playerIndex == 0) {
             m2->interactObj = m->marioObj;
             if (interaction & INT_KICK) {