probably made the ROOK, BISHOP and QUEEN moves work

src/chess.c

@@ -75,23 +75,59 @@ bool compare_pos(pos_t a, pos_t b) {
     return a.x == b.x && a.y == b.y;
 }
 
+pos_t pos_multiply_scalar(pos_t a, int b) {
+    return (pos_t){a.x*b, a.y*b};
+}
+
 /**
  * check the wanted pos_t against all valid move options
  * of the current piece
  */
 bool is_move_legal(move_t move) {
     valid_move_t valid_moves[PIECE_COUNT] = DEFAULT_VALID_MOVES;
-    for (int i = 0; i < PIECE_COUNT; i++) {
+    switch (move.piece) {
-        for (int j = 0; 
+        case NONE:
-            j < valid_moves[i].piece_move_count && 
+        case PAWN:
-            move.piece == valid_moves[i].piece; 
+        case KNIGHT:
-            j++
+        case KING:
-        ) {
+            for (int i = 0; i < PIECE_COUNT; i++) {
-            pos_t new_pos = {move.from.x+move.to.x, move.from.y+move.to.y};
+                for (int j = 0; 
-            if (compare_pos(new_pos, valid_moves[i].options[j]) == true) {
+                    j < valid_moves[i].piece_move_count && 
-                return true;
+                    move.piece == valid_moves[i].piece; 
+                    j++
+                ) {
+                    pos_t new_pos = {move.from.x+move.to.x, move.from.y+move.to.y};
+                    if (compare_pos(new_pos, valid_moves[i].options[j]) == true) {
+                        return true;
+                    }
+                }
             }
-        }
+            break;
+        case ROOK:
+        case BISHOP:
+        case QUEEN:
+            for (int i = 0; i < PIECE_COUNT; i++) {
+                for (int j = 0; 
+                    j < valid_moves[i].piece_move_count && 
+                    move.piece == valid_moves[i].piece; 
+                    j++
+                ) {
+                    /** NOTE: BOARD_HORIZONTAL assuming HORIZONTAL & VERTICAL are the same */
+                    for (int k = 0; k < BOARD_HORIZONTAL; k++) {
+                        pos_t new_pos = {
+                            move.from.x+move.to.x, 
+                            move.from.y+move.to.y
+                        };
+                        if (compare_pos(
+                            new_pos, 
+                            pos_multiply_scalar(valid_moves[i].options[j], k)
+                        ) == true) {
+                            return true;
+                        }
+                    }
+                }
+            }
+            break;            
     }
 
     return false;