diff --git a/sww/include/sww/color.h b/sww/include/sww/color.h
index 097b452..22abb2e 100644
--- a/sww/include/sww/color.h
+++ b/sww/include/sww/color.h
@@ -53,7 +53,7 @@ enum {
   kViolet = Color_RGB(140, 0, 255), // Violet
 
   kBlack = Color_RGB(0, 0, 0),       // Black
-  kWhite = Color_RGB(255, 255, 255), // Black
+  kWhite = Color_RGB(255, 255, 255), // White
 };
 
 /* r = c1 * (1 - c2.alpha) + c2 * c2.alpha */
diff --git a/sww/source/perf_monitor.c b/sww/source/perf_monitor.c
index eeb9427..608f668 100644
--- a/sww/source/perf_monitor.c
+++ b/sww/source/perf_monitor.c
@@ -9,9 +9,9 @@ swwPerfMonitor *swwPerfMonitor_CreateWithCount(uint32_t value_count) {
   swwPerfMonitor *o = (swwPerfMonitor *)malloc(sizeof(swwPerfMonitor) +
                                                sizeof(float) * value_count);
   o->cursor = 0;
-  o->count = 0;
+  o->count = 1;
   o->capacity = value_count;
-  o->average_value = 0.f;
+  o->sum = 0.000001f;
   memset(o->values, 0, sizeof(float) * value_count);
 
   return o;
@@ -21,16 +21,18 @@ void swwPerfMonitor_Destroy(swwPerfMonitor *o) { free(o); }
 
 void swwPerfMonitor_Update(swwPerfMonitor *o, float frame_time) {
   float prev = 0.f;
-  if (o->count <= o->capacity) {
-    o->count++;
-  } else {
-    prev = o->values[o->cursor];
+  if (o->count == o->capacity) {
+    prev = o->values[(o->cursor + 1) % o->capacity];
   }
 
   o->cursor = (o->cursor + 1) % o->capacity;
   o->values[o->cursor] = frame_time;
 
-  o->average_value += (frame_time - prev) / o->count;
+  o->sum += frame_time - prev;
+
+  if (o->count < o->capacity) {
+    o->count++;
+  }
 }
 
 void swwPerfMonitor_Render(swwPerfMonitor *o, swwRenderer *renderer, Point2i c,
@@ -62,5 +64,4 @@ void swwPerfMonitor_Render(swwPerfMonitor *o, swwRenderer *renderer, Point2i c,
                            (Point2i){minx + w, MAX(maxy - pv, miny)}, kFgColor);
     }
   }
-  // printf("idx: %d, w: %d\n", idx, minx + w);
 }
diff --git a/sww/source/perf_monitor.h b/sww/source/perf_monitor.h
index 07343db..0fd12ec 100644
--- a/sww/source/perf_monitor.h
+++ b/sww/source/perf_monitor.h
@@ -12,7 +12,7 @@ typedef struct {
   uint32_t cursor;
   uint32_t capacity;
   uint32_t count;
-  float average_value;
+  float sum;
   float values[0];
 } swwPerfMonitor;
 
@@ -21,7 +21,7 @@ void swwPerfMonitor_Destroy(swwPerfMonitor *o);
 void swwPerfMonitor_Update(swwPerfMonitor *o, float frame_time);
 
 #define swwPerfMonitor_Create() swwPerfMonitor_CreateWithCount(30)
-#define swwPerfMonitor_GetAverage(o) (o)->average_value
+#define swwPerfMonitor_GetAverage(o) ((o)->sum / (o)->count)
 
 /* Draw the PerfMonitor as a layer on the canvas */
 void swwPerfMonitor_Render(swwPerfMonitor *o, swwRenderer *renderer,
diff --git a/sww/source/renderer/software_renderer.c b/sww/source/renderer/software_renderer.c
index 61d98ac..992b982 100644
--- a/sww/source/renderer/software_renderer.c
+++ b/sww/source/renderer/software_renderer.c
@@ -151,6 +151,7 @@ void DrawVLineClip(swwRenderer *o_, int32_t x, int32_t by, int32_t ey,
   uint8_t *p;
 
   uint32_t idx = 4 * (width * y + x);
+  uint32_t offset = 4 * width;
   if (Color_HasAlpha(color)) { // do alpha-blend
     uint32_t c;
     for (; y <= ey; y++) {
@@ -160,7 +161,7 @@ void DrawVLineClip(swwRenderer *o_, int32_t x, int32_t by, int32_t ey,
       p[1] = (uint8_t)(c >> 8) & 0xff;
       p[2] = (uint8_t)(c >> 16) & 0xff;
       p[3] = (uint8_t)(c >> 24) & 0xff;
-      idx += width;
+      idx += offset;
     }
   } else {
     for (; y <= ey; y++) {
@@ -169,7 +170,7 @@ void DrawVLineClip(swwRenderer *o_, int32_t x, int32_t by, int32_t ey,
       p[1] = (uint8_t)(color >> 8) & 0xff;
       p[2] = (uint8_t)(color >> 16) & 0xff;
       p[3] = (uint8_t)(color >> 24) & 0xff;
-      idx += width;
+      idx += offset;
     }
   }
 }
diff --git a/sww/test/shapes.c b/sww/test/shapes.c
index 460c88c..9df8881 100644
--- a/sww/test/shapes.c
+++ b/sww/test/shapes.c
@@ -98,7 +98,7 @@ int main() {
   while (!swwApp_ShouldExit()) {
     if (ud.need_render) {
       swwRenderer_ClearBlack(ud.renderer);
-      i = (i + 1) % 7;
+      i = (i + 1) % 8;
       switch (i) {
       case 0: {
         swwRenderer_DrawEllipse(ud.renderer, (Point2i){cw, ch}, 100, 200,
@@ -124,7 +124,13 @@ int main() {
                                   (Sizei){200, 36}, kOrange + Color_Alpha(0x80),
                                   1);
       } break;
-      case 6:
+      case 6: {
+        swwRenderer_DrawLine(ud.renderer, (Point2i){120, 20},
+                             (Point2i){120, 200}, kViolet);
+        swwRenderer_DrawLine(ud.renderer, (Point2i){20, 120},
+                             (Point2i){200, 120}, kOrange);
+      } break;
+      case 7:
       default: {
         swwRenderer_DrawArc(ud.renderer, (Point2i){cw, ch}, 150, 30.f, 90.f,
                             Color_RGB(0x00, 0x00, 0xff), 0);