diff --git a/apps/tools/twndel/data/bong.ogg b/apps/tools/twndel/data/bong.ogg
index 491187a..867e8cc 100644
--- a/apps/tools/twndel/data/bong.ogg
+++ b/apps/tools/twndel/data/bong.ogg
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:d21d0f0b782445db579d11e2506b24cd1ac9d664ee33aeaf807761aa7b6fd710
-size 4848
+oid sha256:d5a728e246088087dce9c01c8f9fd03775196d79c2811dacdd3fe1dac9ab9f2b
+size 7932
diff --git a/apps/tools/twndel/state.h b/apps/tools/twndel/state.h
index 1acf518..fbe224f 100644
--- a/apps/tools/twndel/state.h
+++ b/apps/tools/twndel/state.h
@@ -78,6 +78,10 @@ typedef struct State {
 
     Object *objects;
     uint8_t objects_sz;
+
+    /* which axes are blocked and which are not */
+    /* order: x, y, z */
+    bool axis_mask[3];
 } State;
 
 
diff --git a/apps/tools/twndel/tool.c b/apps/tools/twndel/tool.c
index 42b9914..e43c6a3 100644
--- a/apps/tools/twndel/tool.c
+++ b/apps/tools/twndel/tool.c
@@ -247,13 +247,53 @@ static void process_operation_move_point(Operation *op) {
     /* TODO: show thresholds */
 
     /* change along axes, delta is accumulated when threshold is met*/
-    int16_t zch = (int16_t)(floorf(vec3_dot(b, (Vec3){0,0,1}) * (float)POINTS_PER_METER));
-    op->data.move_point.delta_x += zch;
-    state.points[op->data.move_point.point].x += zch;
+    int16_t xch = (int16_t)(floorf(vec3_dot(b, (Vec3){0,0,1}) * (float)POINTS_PER_METER)) * !state.axis_mask[0];
+    xch -= xch % state.grid_snap_granularity;
+    state.points[op->data.move_point.point].x += xch;
+    op->data.move_point.delta_x += xch;
+
+    int16_t ych = (int16_t)(floorf(vec3_dot(b, (Vec3){0,-1,0}) * (float)POINTS_PER_METER)) * !state.axis_mask[1];
+    ych -= ych % state.grid_snap_granularity;
+    state.points[op->data.move_point.point].y += ych;
+    op->data.move_point.delta_y += ych;
+
+    int16_t zch = (int16_t)(floorf(vec3_dot(b, (Vec3){-1,0,0}) * (float)POINTS_PER_METER)) * !state.axis_mask[2];
+    zch -= zch % state.grid_snap_granularity;
+    state.points[op->data.move_point.point].z += zch;
+    op->data.move_point.delta_z += zch;
+
+    if (xch != 0 || ych != 0 || zch != 0)
+        audio_play("/data/bong.ogg", NULL, false, 0.12f, 0.0f);
+}
+
+
+static void reverse_operation_move_point(Operation *op) {
+    SDL_assert(op->kind == OPERATION_MOVE_POINT);
+    state.points[op->data.move_point.point].x -= op->data.move_point.delta_x;
+    state.points[op->data.move_point.point].y -= op->data.move_point.delta_y;
+    state.points[op->data.move_point.point].z -= op->data.move_point.delta_z;
+    audio_play("/data/drop.ogg", NULL, false, 0.4f, 0.0f);
 }
 
 
 static void process_operations(void) {
+    if (input_action_just_pressed("undo")) {
+        /* TODO: checks and defined limit */
+        Operation *op = &state.op_stack[state.op_stack_ptr % UNDO_STACK_SIZE];
+        state.op_stack_ptr--;
+
+        switch (op->kind) {
+        case OPERATION_MOVE_POINT: {
+            reverse_operation_move_point(op);
+
+            break;
+        }
+
+        default:
+            (void)0;
+        }
+    }
+
     if (!state.op_active) {
         uint16_t point_select; uint8_t obj_select;
         if (find_closest_point(&obj_select, &point_select)) {
@@ -280,6 +320,7 @@ static void process_operations(void) {
 
             break;
         }
+
         default:
             (void)0;
         }
@@ -294,13 +335,20 @@ void game_tick(void) {
         state.camera_position = (Vec3){2,1,2};
         state.camera_direction = vec3_norm(((Vec3){-2,-1,-2}));
         state.camera_zoom = 0.5f;
+        state.grid_snap_granularity = 16;
+        state.axis_mask[1] = 1; state.axis_mask[2] = 1;
         init = true;
     }
 
     input_action("toggle_display_mode", "Q");
     input_action("toggle_projection", "E");
 
+    input_action("toggle_x_axis", "Z");
+    input_action("toggle_y_axis", "X");
+    input_action("toggle_z_axis", "C");
+
     input_action("select", "LCLICK");
+    input_action("undo", "F");
 
     if (input_action_just_pressed("toggle_display_mode")) {
         audio_play("/data/click.wav", NULL, false, 0.7f, 0.0f);
@@ -312,32 +360,46 @@ void game_tick(void) {
         state.camera_is_orthographic = !state.camera_is_orthographic;
     }
 
+    if (input_action_just_pressed("toggle_x_axis")) {
+        state.axis_mask[0] = 0; state.axis_mask[1] = 1; state.axis_mask[2] = 1;
+    }
+
+    if (input_action_just_pressed("toggle_y_axis")) {
+        state.axis_mask[0] = 1; state.axis_mask[1] = 0; state.axis_mask[2] = 1;
+    }
+
+    if (input_action_just_pressed("toggle_z_axis")) {
+        state.axis_mask[0] = 1; state.axis_mask[1] = 1; state.axis_mask[2] = 0;
+    }
+
     process_camera_movement();
     process_operations();
 
     /* axis helpers */
     /* idea: black out inactives when dragging points */
     /* idea: double selection of axes for diagonal edits */
-    draw_line_3d((Vec3){0}, (Vec3){0,0,256}, 1, (Color){255,0,0,125});
+    draw_line_3d((Vec3){0}, (Vec3){256,0,0}, 1, state.axis_mask[0] ? (Color){0,0,0,75} : (Color){255,0,0,125});
     draw_billboard("/data/x.png",
-                   (Vec3){0,0,2},
-                   (Vec2){0.1f, 0.1f},
-                   (Rect){0},
-                   (Color){255,0,0,255},
-                   false);
-    draw_line_3d((Vec3){0}, (Vec3){256,0,0}, 1, (Color){0,0,255,125});
-    draw_billboard("/data/y.png",
                    (Vec3){2,0,0},
                    (Vec2){0.1f, 0.1f},
                    (Rect){0},
-                   (Color){0,0,255,255},
+                   state.axis_mask[0] ? (Color){0,0,0,255} : (Color){255,0,0,255},
                    false);
-    draw_line_3d((Vec3){0}, (Vec3){0,256,0}, 1, (Color){75,125,25,125});
-    draw_billboard("/data/z.png",
+
+    draw_line_3d((Vec3){0}, (Vec3){0,256,0}, 1, state.axis_mask[1] ? (Color){0,0,0,75} : (Color){75,125,25,125});
+    draw_billboard("/data/y.png",
                    (Vec3){0,1.5f,0},
                    (Vec2){0.1f, 0.1f},
                    (Rect){0},
-                   (Color){75,125,25,255},
+                   state.axis_mask[1] ? (Color){0,0,0,255} : (Color){75,125,25,255},
+                   false);
+
+    draw_line_3d((Vec3){0}, (Vec3){0,0,256}, 1, state.axis_mask[2] ? (Color){0,0,0,75} : (Color){0,0,255,125});
+    draw_billboard("/data/z.png",
+                   (Vec3){0,0,2},
+                   (Vec2){0.1f, 0.1f},
+                   (Rect){0},
+                   state.axis_mask[2] ? (Color){0,0,0,255} : (Color){0,0,255,255},
                    false);
 
     for (uint8_t obj = 0; obj < state.objects_sz; ++obj)
diff --git a/include/twn_audio.h b/include/twn_audio.h
index f6304a0..37deabf 100644
--- a/include/twn_audio.h
+++ b/include/twn_audio.h
@@ -8,6 +8,7 @@
 /* plays audio file at specified channel or at scratch channel if NULL is passed, without ability to refer to it later */
 /* path path must contain valid file extension to infer which file format it is */
 /* supported formats: .ogg, .xm */
+/* mono or stereo only */
 TWN_API void audio_play(const char *audio,
                         const char *channel,    /* optional */
                         bool  repeat,           /* default: false */
diff --git a/src/twn_audio.c b/src/twn_audio.c
index 0bd3bfb..e4c599c 100644
--- a/src/twn_audio.c
+++ b/src/twn_audio.c
@@ -9,6 +9,9 @@
 #include <physfs.h>
 #include <physfsrwops.h>
 
+#define STB_VORBIS_MAX_CHANNELS 2
+#define STB_VORBIS_NO_STDIO
+#define STB_VORBIS_NO_INTEGER_CONVERSION
 #define STB_VORBIS_NO_PUSHDATA_API
 #define STB_VORBIS_HEADER_ONLY
 #include <stb_vorbis.c>