diff --git a/demos/tetris/grboard.h b/demos/tetris/grboard.h
index b4d39bf..f83de4e 100644
--- a/demos/tetris/grboard.h
+++ b/demos/tetris/grboard.h
@@ -206,13 +206,13 @@ void gr_erasepiece_unmarked(sprite *p) {
 
    px += STARTBOARD_X;
    py += STARTBOARD_Y;
-   
+      
    for(byte t=0; t<4; t++) {
-      int x = px + data->offset_x;
-      int y = py + data->offset_y;
+      int x = px; byte x1 = data->offset_x; x+= (int) x1; 
+      int y = py; byte y1 = data->offset_y; y+= (int) y1;
 
-      int cx = zx + data->offset_x;      
-      int cy = zy + data->offset_y;
+      int cx = p->x; cx += (int) x1;      
+      int cy = p->y; cy += (int) y1;
 
       data++;
 
diff --git a/demos/tetris/tetris.c b/demos/tetris/tetris.c
index 7bc86a6..5fa1206 100644
--- a/demos/tetris/tetris.c
+++ b/demos/tetris/tetris.c
@@ -152,13 +152,13 @@ void handle_player_input() {
          if(collides(&new_pos)) {
             break;
          }         
-         gr_erasepiece(&player);
-         gr_drawpiece(&new_pos);
+         // gr_erasepiece(&player);
+         // gr_drawpiece(&new_pos);
 
          // flicker-free version      
-         // ck_markpiece(&new_pos);           
-         // gr_erasepiece_unmarked(&player);  
-         // gr_drawpiece(&new_pos);           
+         ck_markpiece(&new_pos);           
+         gr_erasepiece_unmarked(&player);  
+         gr_drawpiece(&new_pos);           
 
          ck_drawpiece(&new_pos);
          sprite_copy(&player,&new_pos);
@@ -168,13 +168,13 @@ void handle_player_input() {
    }
 
    if(allowed == 1) {
-      gr_erasepiece(&player);
-      gr_drawpiece(&new_pos);
+      // gr_erasepiece(&player);
+      // gr_drawpiece(&new_pos);
 
       // flicker-free version      
-      // ck_markpiece(&new_pos);           
-      // gr_erasepiece_unmarked(&player);  
-      // gr_drawpiece(&new_pos);           
+      ck_markpiece(&new_pos);           
+      gr_erasepiece_unmarked(&player);  
+      gr_drawpiece(&new_pos);           
 
       sprite_copy(&player, &new_pos);
    }
@@ -207,13 +207,13 @@ void gameLoop() {
          }
          else {
             // automatic drop does not collide, simply draw it
-            gr_erasepiece(&player);   // erase and draw are as close as possible
-            gr_drawpiece(&new_pos);
+            // gr_erasepiece(&player);   // erase and draw are as close as possible
+            // gr_drawpiece(&new_pos);
 
             // flicker-free version      
-            // ck_markpiece(&new_pos);           
-            // gr_erasepiece_unmarked(&player);  
-            // gr_drawpiece(&new_pos);           
+            ck_markpiece(&new_pos);           
+            gr_erasepiece_unmarked(&player);  
+            gr_drawpiece(&new_pos);           
 
             sprite_copy(&player, &new_pos);   
             ck_drawpiece(&player);