better, teleport-based collision resolution

src/comp/mechanical.c

@@ -68,22 +68,18 @@ void mechanical_move(entity_t *e, vec2 direction, fixed_t dt, map_t const *map)
     if(facing >= 0)
         p->facing = facing;
 
-    fixed_t new_x = p->x + fmul(m->vx, dt);
-    fixed_t new_y = p->y + fmul(m->vy, dt);
-    rect new_hitbox = rect_translate(p->hitbox, (vec2){ new_x, new_y });
+    vec2 new_pos = { p->x + fmul(m->vx, dt), p->y + fmul(m->vy, dt) };
+    new_pos = map_move(map, (vec2){ p->x, p->y }, new_pos, p->hitbox);
 
-    // TODO ECS: New collision/ejection system based on teleports
-    if(!map_collides(map, new_hitbox)) {
-        if(f && f->current_attack && f->attack_follows_movement) {
-            physical_t *attack = getcomp(f->current_attack, physical);
-            attack->x += (new_x - p->x);
-            attack->y += (new_y - p->y);
-        }
-
-        p->x = new_x;
-        p->y = new_y;
+    if(f && f->current_attack && f->attack_follows_movement) {
+        physical_t *attack = getcomp(f->current_attack, physical);
+        attack->x += (new_pos.x - p->x);
+        attack->y += (new_pos.y - p->y);
     }
 
+    p->x = new_pos.x;
+    p->y = new_pos.y;
+
     /* TODO: Without acceleration, the movement model is broken */
     m->vdx = fmul(m->vdx, fix(0.8));
     m->vdy = fmul(m->vdy, fix(0.8));

src/fixed.h

@@ -86,3 +86,8 @@ static inline fixed_t fease(fixed_t x)
         return fix(1) - 2 * fmul(x, x);
     }
 }
+
+static inline fixed_t fclamp(fixed_t x, fixed_t min, fixed_t max)
+{
+    return (x <= min) ? min : (x >= max) ? max : x;
+}

src/map.c

@@ -1,5 +1,6 @@
 #include "map.h"
 #include <stdlib.h>
+#include <gint/defs/util.h>
 
 rect tile_shape(tileset_t const *tileset, int id)
 {
@@ -22,6 +23,18 @@ map_cell_t *map_cell(map_t const *m, int x, int y)
     return &m->cells[y * m->width + x];
 }
 
+bool map_cell_walkable(map_t const *m, map_cell_t const *cell)
+{
+    if(!cell)
+        return false;
+    if(m->tileset->tiles[cell->base].solid)
+        return false;
+    if(cell->decor && m->tileset->tiles[cell->decor].solid)
+        return false;
+
+    return true;
+}
+
 bool map_collides(map_t const *m, rect hitbox)
 {
     int y_min = ffloor(hitbox.t);
@@ -52,3 +65,85 @@ bool map_collides(map_t const *m, rect hitbox)
 
     return false;
 }
+
+vec2 map_move(map_t const *m, vec2 old_pos, vec2 new_pos, rect hitbox)
+{
+    int x = ffloor(new_pos.x);
+    int y = ffloor(new_pos.y);
+
+    /* If there is no collision, accept immediately */
+    if(!map_collides(m, rect_translate(hitbox, new_pos)))
+        return new_pos;
+
+    /* Find the nearest walkable cell */
+    fixed_t best_d2 = fix(999);
+    fixed_t best_x = fix(-1), best_y = fix(-1);
+
+    for(int cy = y-1; cy <= y+1; cy++)
+    for(int cx = x-1; cx <= x+1; cx++) {
+        map_cell_t *cell = map_cell(m, cx, cy);
+        if(!map_cell_walkable(m, cell))
+            continue;
+
+        fixed_t closest_x = fclamp(new_pos.x, fix(cx), fix(cx+1)-1);
+        fixed_t closest_y = fclamp(new_pos.y, fix(cy), fix(cy+1)-1);
+
+        fixed_t d2 = dist2(new_pos, (vec2){ closest_x, closest_y });
+        if(d2 < best_d2) {
+            best_d2 = d2;
+            best_x = closest_x;
+            best_y = closest_y;
+        }
+    }
+
+    /* If there is no walkable cell, prevent movement */
+    if(best_x < 0 || best_y < 0)
+        return old_pos;
+
+    /* In that cell, clamp to the limits imposed by neighboring cells */
+    x = ffloor(best_x);
+    y = ffloor(best_y);
+    fixed_t nx = fdec(best_x);
+    fixed_t ny = fdec(best_y);
+
+    /* Limits at edges */
+    if(!map_cell_walkable(m, map_cell(m, x-1, y)))
+        nx = max(nx, -hitbox.l);
+    if(!map_cell_walkable(m, map_cell(m, x+1, y)))
+        nx = min(nx, fix(1) - hitbox.r);
+    if(!map_cell_walkable(m, map_cell(m, x, y-1)))
+        ny = max(ny, -hitbox.t);
+    if(!map_cell_walkable(m, map_cell(m, x, y+1)))
+        ny = min(ny, fix(1) - hitbox.b);
+
+    /* Limits at corners */
+    if(!map_cell_walkable(m, map_cell(m, x-1, y-1))
+            && nx < -hitbox.l && ny < -hitbox.t) {
+        nx = -hitbox.l;
+        ny = -hitbox.t;
+    }
+    if(!map_cell_walkable(m, map_cell(m, x+1, y-1))
+            && nx > fix(1) - hitbox.r && ny < -hitbox.t) {
+        nx = fix(1) - hitbox.r;
+        ny = -hitbox.t;
+    }
+    if(!map_cell_walkable(m, map_cell(m, x-1, y+1))
+            && nx < -hitbox.l && ny > fix(1) - hitbox.b) {
+        nx = -hitbox.l;
+        ny = fix(1) - hitbox.b;
+    }
+    if(!map_cell_walkable(m, map_cell(m, x+1, y+1))
+            && nx > fix(1) - hitbox.r && ny > fix(1) - hitbox.b) {
+        nx = fix(1) - hitbox.r;
+        ny = fix(1) - hitbox.b;
+    }
+
+    /* If the new position is valid, use it, otherwise refuse the movement. We
+       catch here some potential bugs, plus a whole lot of unhandled cases when
+       the hitbox is larger than a tile */
+    new_pos = (vec2){ fix(x) + nx, fix(y) + ny };
+    if(!map_collides(m, rect_translate(hitbox, new_pos)))
+        return new_pos;
+
+    return old_pos;
+}

src/map.h

@@ -96,5 +96,12 @@ typedef struct
 /* Get a pointer to the cell at (x,y) in map; NULL if out of bounds. */
 map_cell_t *map_cell(map_t const *m, int x, int y);
 
+/* Check whether a map cell is walkable, only accounting for full hitboxes. */
+bool map_cell_walkable(map_t const *m, map_cell_t const *cell);
+
 /* Check whether a hitbox collides with the map. */
 bool map_collides(map_t const *m, rect hitbox);
+
+/* Returns the new position of an object with a hitbox trying to move from
+   [old_pos] to [new_pos]. */
+vec2 map_move(map_t const *m, vec2 old_pos, vec2 new_pos, rect hitbox);