From 6f3f391d8af9d8cab09091da9d26e04c7aeaea96 Mon Sep 17 00:00:00 2001
From: En Yi <en.yi@tutanota.com>
Date: Mon, 22 Apr 2024 22:42:32 +0800
Subject: [PATCH] Rework the offset collision checking

Change the function to check for collision at the specified point.
This is much straightforward to use.
The offset point to check must be computed before passing into the
function.
---
 engine/collisions.c   | 13 ++++++-------
 engine/collisions.h   |  2 +-
 scenes/game_systems.c | 23 +++++++++++++----------
 3 files changed, 20 insertions(+), 18 deletions(-)

diff --git a/engine/collisions.c b/engine/collisions.c
index 75d12e6..8f00151 100644
--- a/engine/collisions.c
+++ b/engine/collisions.c
@@ -155,18 +155,17 @@ uint8_t check_collision_line(const CollideEntity_t* ent, TileGrid_t* grid, bool
 }
 
 // TODO: This should be a point collision check, not an  AABB check
-uint8_t check_collision_offset(Entity_t* p_ent, Vector2 pos, Vector2 bbox_sz, TileGrid_t* grid, Vector2 offset)
+uint8_t check_collision_at(Entity_t* p_ent, Vector2 pos, Vector2 bbox_sz, TileGrid_t* grid)
 {
-    Vector2 new_pos = Vector2Add(pos, offset);
     CollideEntity_t ent = {
         .p_ent = p_ent,
-        .bbox = (Rectangle){new_pos.x, new_pos.y, bbox_sz.x, bbox_sz.y},
+        .bbox = (Rectangle){pos.x, pos.y, bbox_sz.x, bbox_sz.y},
         .prev_bbox = (Rectangle){pos.x, pos.y, bbox_sz.x, bbox_sz.y},
         .area = (TileArea_t){
-            .tile_x1 = (new_pos.x) / grid->tile_size,
-            .tile_y1 = (new_pos.y) / grid->tile_size,
-            .tile_x2 = (new_pos.x + bbox_sz.x - 1) / grid->tile_size,
-            .tile_y2 = (new_pos.y + bbox_sz.y - 1) / grid->tile_size
+            .tile_x1 = (pos.x) / grid->tile_size,
+            .tile_y1 = (pos.y) / grid->tile_size,
+            .tile_x2 = (pos.x + bbox_sz.x - 1) / grid->tile_size,
+            .tile_y2 = (pos.y + bbox_sz.y - 1) / grid->tile_size
         }
     };
     
diff --git a/engine/collisions.h b/engine/collisions.h
index f8629f8..189c7a0 100644
--- a/engine/collisions.h
+++ b/engine/collisions.h
@@ -59,7 +59,7 @@ typedef struct CollideEntity {
 void remove_entity_from_tilemap(EntityManager_t *p_manager, TileGrid_t* tilemap, Entity_t* p_ent);
 uint8_t check_collision(const CollideEntity_t* ent, TileGrid_t* grid, bool check_oneway);
 uint8_t check_collision_line(const CollideEntity_t* ent, TileGrid_t* grid, bool check_oneway);
-uint8_t check_collision_offset(Entity_t* p_ent, Vector2 pos, Vector2 bbox_sz, TileGrid_t* grid, Vector2 offset);
+uint8_t check_collision_at(Entity_t* p_ent, Vector2 pos, Vector2 bbox_sz, TileGrid_t* grid);
 bool check_on_ground(Entity_t* p_ent, Vector2 prev_pos, Vector2 bbox_sz, TileGrid_t* grid);
 uint8_t check_bbox_edges(TileGrid_t* tilemap, Entity_t* p_ent, Vector2 bbox, bool ignore_fragile);
 #endif // __COLLISION_FUNCS_H
diff --git a/scenes/game_systems.c b/scenes/game_systems.c
index 7dca325..6ff436a 100644
--- a/scenes/game_systems.c
+++ b/scenes/game_systems.c
@@ -134,7 +134,7 @@ static bool check_collision_and_move(
         Vector2 point_to_test = {0};
         point_to_test.x = ent->position.x;
         point_to_test.y = other_pos->y - p_bbox->size.y + 1;
-        if (!check_collision_offset(ent, point_to_test, p_bbox->size, tilemap, (Vector2){0}))
+        if (!check_collision_at(ent, point_to_test, p_bbox->size, tilemap))
         {
             ent->position = point_to_test;
             goto collision_end;
@@ -142,7 +142,7 @@ static bool check_collision_and_move(
 
         point_to_test.x = other_pos->x - p_bbox->size.x + 1;
         point_to_test.y = ent->position.y;
-        if (!check_collision_offset(ent, point_to_test, p_bbox->size, tilemap, (Vector2){0}))
+        if (!check_collision_at(ent, point_to_test, p_bbox->size, tilemap))
         {
             ent->position = point_to_test;
             goto collision_end;
@@ -150,7 +150,7 @@ static bool check_collision_and_move(
 
         point_to_test.x = other_pos->x + other_bbox.x - 1;
         point_to_test.y = ent->position.y;
-        if (!check_collision_offset(ent, point_to_test, p_bbox->size, tilemap, (Vector2){0}))
+        if (!check_collision_at(ent, point_to_test, p_bbox->size, tilemap))
         {
             ent->position = point_to_test;
             goto collision_end;
@@ -158,7 +158,7 @@ static bool check_collision_and_move(
 
         point_to_test.x = ent->position.x;
         point_to_test.y = other_pos->y + other_bbox.y - 1;
-        if (!check_collision_offset(ent, point_to_test, p_bbox->size, tilemap, (Vector2){0}))
+        if (!check_collision_at(ent, point_to_test, p_bbox->size, tilemap))
         {
             ent->position = point_to_test;
             goto collision_end;
@@ -465,9 +465,12 @@ void player_movement_input_system(Scene_t* scene)
             }
         }
 
-        uint8_t collide_type = check_collision_offset(
-                p_player, p_player->position, p_bbox->size,
-                &tilemap, (Vector2){0, p_bbox->size.y - PLAYER_HEIGHT}
+        Vector2 point_to_check = Vector2Add(
+            p_player->position,
+            (Vector2){0, p_bbox->size.y - PLAYER_HEIGHT}
+        );
+        uint8_t collide_type = check_collision_at(
+                p_player, point_to_check, p_bbox->size, &tilemap
         );
         if (collide_type == 1)
         {
@@ -561,10 +564,10 @@ void player_bbox_update_system(Scene_t* scene)
             }
         }
 
+        Vector2 point_to_check = Vector2Add(p_player->position, offset);
         if (
-            check_collision_offset(
-                p_player, p_player->position, new_bbox,
-                &tilemap, offset 
+            check_collision_at(
+                p_player, point_to_check, new_bbox, &tilemap
             ) != 1
         )
         {