diff --git a/src/rendering/clouds/clo_walking.c b/src/rendering/clouds/clo_walking.c
index 6c74c7f..5dd6672 100644
--- a/src/rendering/clouds/clo_walking.c
+++ b/src/rendering/clouds/clo_walking.c
@@ -23,6 +23,24 @@ typedef struct
     int max_segments;
 } CloudWalkingNextAction;
 
+/*
+ * Private structure for the walker.
+ */
+struct CloudsWalker
+{
+    Vector3 start;
+    Vector3 end;
+    Vector3 diff;
+
+    double cursor;
+    double max_length;
+    double step_size;
+
+    CloudWalkerStepInfo last_segment;
+
+    CloudWalkingNextAction next_action;
+};
+
 
 int cloudsOptimizeWalkingBounds(CloudsLayerDefinition* layer, Vector3* start, Vector3* end)
 {
@@ -78,32 +96,91 @@ int cloudsOptimizeWalkingBounds(CloudsLayerDefinition* layer, Vector3* start, Ve
 
 CloudsWalker* cloudsCreateWalker(Renderer* renderer, CloudsLayerDefinition* layer, Vector3 start, Vector3 end)
 {
+    CloudsWalker* result;
+
+    result = (CloudsWalker*)malloc(sizeof (CloudsWalker));
+
+    result->start = start;
+    result->end = end;
+    result->diff = v3Sub(end, start);
+    result->max_length = v3Norm(result->diff);
+    result->cursor = 0.0;
+    result->step_size = 1.0;
+
+    result->last_segment.renderer = renderer;
+    result->last_segment.layer = layer;
+    result->last_segment.walked_distance = 0.0;
+    result->last_segment.end = start;
+
+    result->next_action.order = CLOUD_WALKING_CONTINUE;
+
+    return result;
 }
 
 void cloudsDeleteWalker(CloudsWalker* walker)
 {
+    free(walker);
 }
 
-void cloudsWalkerPerformStep(CloudsWalker* walker)
+void cloudsSetStepSize(CloudsWalker* walker, double step)
 {
+    /* TODO Negative step => automatic */
+    walker->step_size = step;
+}
+
+int cloudsWalkerPerformStep(CloudsWalker* walker)
+{
+    if (walker->next_action.order == CLOUD_WALKING_STOP || walker->cursor >= walker->max_length)
+    {
+        walker->next_action.order = CLOUD_WALKING_STOP;
+        return 0;
+    }
+    else if (walker->next_action.order == CLOUD_WALKING_CONTINUE)
+    {
+        /* TODO Limit to end */
+        walker->last_segment.start = walker->last_segment.end;
+        walker->last_segment.walked_distance = walker->cursor;
+
+        walker->cursor += walker->step_size;
+
+        walker->last_segment.end = v3Add(walker->start, v3Scale(walker->diff, walker->cursor / walker->max_length));
+        walker->last_segment.length = walker->step_size;
+
+        return 1;
+    }
+    else
+    {
+        /* TODO */
+        return 0;
+    }
 }
 
 void cloudsWalkerOrderStop(CloudsWalker* walker)
 {
+    walker->next_action.order = CLOUD_WALKING_STOP;
 }
 
 void cloudsWalkerOrderRefine(CloudsWalker* walker, double precision)
 {
+    walker->next_action.order = CLOUD_WALKING_REFINE;
+    walker->next_action.precision = precision;
 }
 
 void cloudsWalkerOrderSubdivide(CloudsWalker* walker, double max_segments)
 {
+    walker->next_action.order = CLOUD_WALKING_SUBDIVIDE;
+    walker->next_action.max_segments = max_segments;
 }
 
 CloudWalkerStepInfo* cloudsWalkerGetLastSegment(CloudsWalker* walker)
 {
+    return &walker->last_segment;
 }
 
 void cloudsStartWalking(CloudsWalker* walker, FuncCloudsWalkingCallback callback, void* data)
 {
+    while (cloudsWalkerPerformStep(walker))
+    {
+        callback(walker);
+    }
 }
diff --git a/src/rendering/clouds/clo_walking.h b/src/rendering/clouds/clo_walking.h
index 28a77b7..49366da 100644
--- a/src/rendering/clouds/clo_walking.h
+++ b/src/rendering/clouds/clo_walking.h
@@ -26,9 +26,9 @@ typedef struct
     Vector3 end;
     double length;
 
-    int refined;
+    /*int refined;
     int subdivision_level;
-    double precision_asked;
+    double precision_asked;*/
 
     void* data;
 } CloudWalkerStepInfo;
@@ -65,12 +65,21 @@ CloudsWalker* cloudsCreateWalker(Renderer* renderer, CloudsLayerDefinition* laye
  */
 void cloudsDeleteWalker(CloudsWalker* walker);
 
+/**
+ * Define the segment size for next steps.
+ *
+ * @param walker The walker to configure
+ * @param step The step length, negative for automatic
+ */
+void cloudsSetStepSize(CloudsWalker* walker, double step);
+
 /**
  * Perform a single step.
  *
  * @param walker The walker to use
+ * @return 1 to continue the loop, 0 to stop
  */
-void cloudsWalkerPerformStep(CloudsWalker* walker);
+int cloudsWalkerPerformStep(CloudsWalker* walker);
 
 /**
  * Order the walker to stop.
diff --git a/src/testing/test_clouds.c b/src/testing/test_clouds.c
index 68c6c05..add42e7 100644
--- a/src/testing/test_clouds.c
+++ b/src/testing/test_clouds.c
@@ -202,6 +202,7 @@ static double _getLayerDensitySinX(Renderer* renderer, CloudsLayerDefinition* la
 
 START_TEST(test_clouds_walking)
 {
+    /* Init */
     CloudsLayerDefinition* layer;
     layer = cloudsGetLayerType().callback_create();
     layer->lower_altitude = -1.0;
@@ -214,7 +215,35 @@ START_TEST(test_clouds_walking)
     renderer->render_quality = 8;
     renderer->clouds->getLayerDensity = _getLayerDensitySinX;
 
-    // TODO
+    CloudsWalker* walker = cloudsCreateWalker(renderer, layer, v3(-0.4, 0.0, 0.0), v3(10.0, 0.0, 0.0));
+    CloudWalkerStepInfo* segment;
+    int result;
+
+    /* First step */
+    cloudsSetStepSize(walker, 0.3);
+    result = cloudsWalkerPerformStep(walker);
+    segment = cloudsWalkerGetLastSegment(walker);
+    ck_assert_int_eq(result, 1);
+    ck_assert_double_eq(segment->walked_distance, 0.0);
+    ck_assert_vector_values(segment->start, -0.4, 0.0, 0.0);
+    ck_assert_vector_values(segment->end, -0.1, 0.0, 0.0);
+    ck_assert_double_eq(segment->length, 0.3);
+
+    /* Second step */
+    result = cloudsWalkerPerformStep(walker);
+    segment = cloudsWalkerGetLastSegment(walker);
+    ck_assert_int_eq(result, 1);
+    ck_assert_double_eq(segment->walked_distance, 0.3);
+    ck_assert_vector_values(segment->start, -0.1, 0.0, 0.0);
+    ck_assert_vector_values(segment->end, 0.2, 0.0, 0.0);
+    ck_assert_double_eq(segment->length, 0.3);
+
+    /* Order to refine second step around the entry point */
+    cloudsWalkerOrderRefine(walker, 0.01);
+    /* TODO */
+
+    /* Clean up */
+    cloudsDeleteWalker(walker);
 
     cloudsGetLayerType().callback_delete(layer);
     rendererDelete(renderer);