diff --git a/bin/back b/bin/back
index 0927327..7189976 100755
Binary files a/bin/back and b/bin/back differ
diff --git a/obj/base.o b/obj/base.o
index b7571fb..1320741 100644
Binary files a/obj/base.o and b/obj/base.o differ
diff --git a/obj/display.o b/obj/display.o
index 6be9d23..14caf49 100644
Binary files a/obj/display.o and b/obj/display.o differ
diff --git a/src/base.c b/src/base.c
index 8d7d303..3877ed3 100644
--- a/src/base.c
+++ b/src/base.c
@@ -299,6 +299,7 @@ double distance_pt_cube_3d(double x0, double y0, double z0, cube cb) {
 
 // ---------------- //
 
+// intersects = !((a.max < b.min) || (b.max < a.min))
 double distance_seg_seg_1d(double s0, double e0, double s1, double e1) {
     double theta_s0 = -(((e1 - s1) * (s1 - s0)) / ((e1 - s1) * (e1 - s1)));
     double theta_e0 = -(((e1 - s1) * (s1 - e0)) / ((e1 - s1) * (e1 - s1)));
@@ -316,6 +317,14 @@ double distance_seg_seg_1d(double s0, double e0, double s1, double e1) {
     }
 }
 
+bool intersects_seg_seg_1d(double s0, double e0, double s1, double e1) {
+    int amin = mind(s0, e0);
+    int amax = maxd(s0, e0);
+    int bmin = mind(s1, e1);
+    int bmax = maxd(s1, e1);
+    return !((amax < bmin) || (bmax < amin));
+}
+
 double distance_seg_seg_2d(
     double s0x, double s0y,
     double e0x, double e0y,
@@ -329,6 +338,23 @@ double distance_seg_seg_2d(
     );
 }
 
+bool intersects_seg_seg_2d(
+    double x1, double y1,
+    double x2, double y2,
+    double x3, double y3,
+    double x4, double y4
+) {
+    double t = 
+        ((x1 - x3)*(y3 - y4) - (y1 - y3)*(x3 - x4))/
+        ((x1 - x2)*(y3 - y4) - (y1 - y2)*(x3 - x4));
+
+    double u = -(
+        ((x1 - x2)*(y1 - y3) - (y1 - y2)*(x1 - x3))/
+        ((x1 - x2)*(y3 - y4) - (y1 - y2)*(x3 - x4)));
+
+    return ((0.0 <= t && t <= 1.0) && (0.0 <= u && u <= 1.0));
+}
+
 double distance_seg_seg_3d(
     double s0x, double s0y, double s0z,
     double e0x, double e0y, double e0z,
@@ -345,8 +371,11 @@ double distance_seg_seg_3d(
 
 double distance_poly_poly_2d(pt_2d* t1, int len_1, pt_2d* t2, int len_2) {
     double res = 10000.0 ;
+    if(len_1 == 0 || len_2 == 0) {
+        return 727.27 ; // arbitrary
+    }
     for(int k1 = 0; k1 < len_1; k1++) {
-        for(int k2 = 0; k2 < len_1; k2++) {
+        for(int k2 = 0; k2 < len_2; k2++) {
             res = mind(res, distance_seg_seg_2d(
                 t1[k1].x, t1[k1].y, t1[(k1+1)%len_1].x, t1[(k1+1)%len_1].y,
                 t2[k2].x, t2[k2].y, t2[(k2+1)%len_2].x, t2[(k2+1)%len_2].y
@@ -356,6 +385,23 @@ double distance_poly_poly_2d(pt_2d* t1, int len_1, pt_2d* t2, int len_2) {
     return res;
 }
 
+bool intersects_poly_poly_2d(pt_2d* t1, int len_1, pt_2d* t2, int len_2) {
+    if(len_1 == 0 || len_2 == 0) {
+        return false ; // arbitrary
+    }
+    for(int k1 = 0; k1 < len_1; k1++) {
+        for(int k2 = 0; k2 < len_2; k2++) {
+            if(intersects_seg_seg_2d(
+                t1[k1].x, t1[k1].y, t1[(k1+1)%len_1].x, t1[(k1+1)%len_1].y,
+                t2[k2].x, t2[k2].y, t2[(k2+1)%len_2].x, t2[(k2+1)%len_2].y
+            )) {
+                return true;
+            }
+        }
+    }
+    return false;
+}
+
 // ------------------------------------------------------------------------------------------------ //
 
 void remove_entity(entity** arr, int* memlen, int* len, int index) {
diff --git a/src/base.h b/src/base.h
index 10a4703..5fd65f6 100644
--- a/src/base.h
+++ b/src/base.h
@@ -59,6 +59,15 @@ double distance_seg_seg_3d(
 );
 double distance_poly_poly_2d(pt_2d* t1, int len_1, pt_2d* t2, int len_2);
 
+bool intersects_seg_seg_1d(double s0, double e0, double s1, double e1);
+bool intersects_seg_seg_2d(
+    double x1, double y1,
+    double x2, double y2,
+    double x3, double y3,
+    double x4, double y4
+);
+bool intersects_poly_poly_2d(pt_2d* t1, int len_1, pt_2d* t2, int len_2);
+
 void remove_entity(entity** arr, int* memlen, int* len, int index);
 void add_entity(entity** arr, int* memlen, int* len, entity ent);
 
diff --git a/src/display.c b/src/display.c
index a7d6d99..803b11a 100644
--- a/src/display.c
+++ b/src/display.c
@@ -507,13 +507,14 @@ SDL_Vertex construct_vertex(double px, double py, int r, int g, int b) {
     return vtx ;
 }
 
-    double px0; double py0; double pz0;
-    double px1; double py1; double pz1;
-    double px2; double py2; double pz2;
-        double fpx0; double fpy0; double fpz0;
-        double fpx1; double fpy1; double fpz1;
-        double mpx0; double mpy0; double mpz0;
-        double mpx1; double mpy1; double mpz1;
+double px0; double py0; double pz0;
+double px1; double py1; double pz1;
+double px2; double py2; double pz2;
+double fpx0; double fpy0; double fpz0;
+double fpx1; double fpy1; double fpz1;
+double mpx0; double mpy0; double mpz0;
+double mpx1; double mpy1; double mpz1;
+
 void renderTriangle(
     SDL_Renderer* renderer,
     double x0, double y0, double z0,
@@ -784,34 +785,50 @@ int fillPolygon(int sf, cube_0 c, int trig, pt_2d* ret) {
                 ret
             );
         }
-    }/* else if(sf == 2 || sf == 3) { // y
-        renderTriangleRotated(renderer, 
-            c.x, c.y + c.h*(sf==2), c.z, 
-            c.x + c.w, c.y + c.h*(sf==2), c.z, 
-            c.x + c.w, c.y + c.h*(sf==2), c.z + c.d, 
-            c.red, c.green, c.blue, c
-        );
-        renderTriangleRotated(renderer, 
-            c.x, c.y + c.h*(sf==2), c.z, 
-            c.x, c.y + c.h*(sf==2), c.z + c.d, 
-            c.x + c.w, c.y + c.h*(sf==2), c.z + c.d, 
-            c.red, c.green, c.blue, c
-        );
+    } else if(sf == 2 || sf == 3) { // y
+        if(trig == 0) {
+            return returnTriangle(
+                c.x, c.y + c.h*(sf==2), c.z, 
+                c.x + c.w, c.y + c.h*(sf==2), c.z, 
+                c.x + c.w, c.y + c.h*(sf==2), c.z + c.d, 
+                ret
+            );
+        } else {
+            return returnTriangle(
+                c.x, c.y + c.h*(sf==2), c.z, 
+                c.x, c.y + c.h*(sf==2), c.z + c.d, 
+                c.x + c.w, c.y + c.h*(sf==2), c.z + c.d, 
+                ret
+            );
+        }
     } else {                        // z
-        renderTriangleRotated(renderer, 
-            c.x, c.y, c.z + c.d*(sf==4), 
-            c.x + c.w, c.y, c.z + c.d*(sf==4), 
-            c.x + c.w, c.y + c.h, c.z + c.d*(sf==4), 
-            c.red, c.green, c.blue, c
-        );
-        renderTriangleRotated(renderer, 
-            c.x, c.y, c.z + c.d*(sf==4), 
-            c.x, c.y + c.h, c.z + c.d*(sf==4), 
-            c.x + c.w, c.y + c.h, c.z + c.d*(sf==4), 
-            c.red, c.green, c.blue, c
-        );
-    }*/
-   return 0;
+        if(trig == 0) {
+            return returnTriangle(
+                c.x, c.y, c.z + c.d*(sf==4), 
+                c.x + c.w, c.y, c.z + c.d*(sf==4), 
+                c.x + c.w, c.y + c.h, c.z + c.d*(sf==4), 
+                ret
+            );
+        } else {
+            return returnTriangle(
+                c.x, c.y, c.z + c.d*(sf==4), 
+                c.x, c.y + c.h, c.z + c.d*(sf==4), 
+                c.x + c.w, c.y + c.h, c.z + c.d*(sf==4), 
+                ret
+            );
+        }
+    }
+}
+
+bool isCollidingSfOfCube(int sf1, cube_0 c1, int sf2, cube_0 c2) {
+    for(int n = 0; n < 4; n++) {
+        int len1 = fillPolygon(sf1, c1, n%2, tri1);
+        int len2 = fillPolygon(sf2, c2, n/2, tri2);
+        if(intersects_poly_poly_2d(tri1, len1, tri2, len2)) {
+            return true;
+        }
+    }
+    return false ;
 }
 
 double is_overlapping(cube_0 c1, cube_0 c2) {
@@ -820,8 +837,11 @@ double is_overlapping(cube_0 c1, cube_0 c2) {
     int sfToDraw2 = surfaceDrawOrder2(camx, camy, camz, c2);
     for(int k1 = 0; k1 < sfToDraw1; k1 ++) {
         for(int k2 = 0; k2 < sfToDraw2; k2 ++) {
-            if(false/*isCollidingSfOfCube(drawOrder[k1], c1, drawOrder2[k2], c2)*/) {
-                return 1.0;
+            if(isCollidingSfOfCube(drawOrder[k1], c1, drawOrder2[k2], c2)) {
+                return (
+                    distance_pt_cube_0_3d(camx, camy, camz, c2) -
+                    distance_pt_cube_0_3d(camx, camy, camz, c1)
+                ); // cannot be 0
             }
         }
     }
@@ -974,11 +994,79 @@ void insertionSort_ent(entity* arr, int len) {
     }
 }
 
+void slide_cb(cube_0* arr, int left, int right) {
+    for(int k = right-1; k >= left && k >= 0; k--) {
+        swap_cb(arr, k, k+1);
+    }
+}
+
+void insertionDepthSort_cb(cube_0* arr, int len) {
+    // n³ //
+    for(int k0 = 0; k0 < len; k0++) {
+        int k = k0 ;
+        int j = k-1 ;
+        while(j >= 0) {
+            if(is_overlapping(arr[j], arr[k]) > 0.001) {
+                slide_cb(arr, j, k);
+                k = j;
+            }
+            j -= 1;
+        }
+    }
+}
+
 void drawCurrentRoom(SDL_Renderer* renderer) {
-    insertionSort_cb(current_room->map, current_room->map_size);
+    //insertionSort_cb(current_room->map, current_room->map_size);
+    insertionDepthSort_cb(current_room->map, current_room->map_size);
     insertionSort_tp(current_room->tps, current_room->tps_size);
     insertionSort_ent(current_room->ents, current_room->ent_len);
 
+    // debugPower 
+    for(int k1 = 0; k1 < current_room->map_size; k1++) {
+        for(int k2 = k1+1; k2 < current_room->map_size; k2++) {
+            current_room->map[k1].blue = 0 ;
+            current_room->map[k1].green = 0 ;
+            current_room->map[k1].red = 182 ;
+
+            current_room->map[k2].blue = 0 ;
+            current_room->map[k2].green = 0 ;
+            current_room->map[k2].red = 182 ;
+        }
+    }
+
+    for(int k1 = 0; k1 < current_room->map_size; k1++) {
+        for(int k2 = k1+1; k2 < current_room->map_size; k2++) {
+            if(is_overlapping(current_room->map[k1], current_room->map[k2]) > 0.001) {
+                current_room->map[k1].blue = 0 ;
+                current_room->map[k1].green = 182 ;
+                current_room->map[k1].red = 0 ;
+
+                current_room->map[k2].blue = 0 ;
+                current_room->map[k2].green = 182 ;
+                current_room->map[k2].red = 182 ;
+            } else if(is_overlapping(current_room->map[k1], current_room->map[k2]) < -0.001) {
+                current_room->map[k1].blue = 0 ;
+                current_room->map[k1].green = 182 ;
+                current_room->map[k1].red = 182 ;
+
+                current_room->map[k2].blue = 0 ;
+                current_room->map[k2].green = 182 ;
+                current_room->map[k2].red = 0 ;
+            } else {
+                if(current_room->map[k1].green != 182) {
+                    current_room->map[k1].blue = 0 ;
+                    current_room->map[k1].green = 0 ;
+                    current_room->map[k1].red = 182 ;
+                }
+                if(current_room->map[k2].green != 182) {
+                    current_room->map[k2].blue = 0 ;
+                    current_room->map[k2].green = 0 ;
+                    current_room->map[k2].red = 182 ;
+                }
+            }
+        }
+    }
+
     if(true || draw_type == 0) {
         for(int k = 0; k < current_room->map_size; k++) {
             drawFullCube(renderer, current_room->map[k]);