From 2a34f955ca83973388bca5859c11e490efaf4d21 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?L=C3=A9a=20Saviot?= <lea.saviot@numworks.com>
Date: Mon, 11 Mar 2019 15:25:24 +0100
Subject: [PATCH] [python/turtle] Fix some turtle jumps

There was a drawing glitch for instance when doing goto(100,100).
It was due to the tutle mileage being overflowed.
---
 python/port/mod/turtle/turtle.cpp | 25 +++++++++----------------
 python/port/mod/turtle/turtle.h   | 16 +++++++++++++++-
 2 files changed, 24 insertions(+), 17 deletions(-)

diff --git a/python/port/mod/turtle/turtle.cpp b/python/port/mod/turtle/turtle.cpp
index 20e9c15cd..0b7dcad89 100644
--- a/python/port/mod/turtle/turtle.cpp
+++ b/python/port/mod/turtle/turtle.cpp
@@ -335,24 +335,11 @@ bool Turtle::draw(bool force) {
     m_drawn = true;
   }
 
-  /* We sleep every time the turtle walks a mileageLimit amount, to allow user
-   * interruptions. The length of each sleep is determined by the speed of the
-   * turtle.
-   * With emscripten, sleep gives control to the web browser, which decides when
-   * to return from sleep: this makes the turtle significantly slower on the web
-   * emulator than on the calculator. We thus decided to sleep less often on the
-   * emscripten platform. */
-#if __EMSCRIPTEN__
-  constexpr KDCoordinate mileageLimit = 10000;
-#else
-  constexpr KDCoordinate mileageLimit = 1000;
-#endif
-
-  if (m_mileage > mileageLimit) {
+  if (m_mileage > k_mileageLimit) {
     if (micropython_port_interruptible_msleep(1 + (m_speed == 0 ? 0 : 3 * (k_maxSpeed - m_speed)))) {
       return true;
     }
-    m_mileage -= mileageLimit;
+    m_mileage -= k_mileageLimit;
   }
   return false;
 }
@@ -360,6 +347,7 @@ bool Turtle::draw(bool force) {
 bool Turtle::dot(mp_float_t x, mp_float_t y) {
   MicroPython::ExecutionEnvironment::currentExecutionEnvironment()->displaySandbox();
 
+  // Draw the dot if the pen is down
   if (m_penDown && hasDotBuffers()) {
     KDContext * ctx = KDIonContext::sharedContext();
     KDRect rect(
@@ -369,7 +357,12 @@ bool Turtle::dot(mp_float_t x, mp_float_t y) {
     ctx->blendRectWithMask(rect, m_color, m_dotMask, m_dotWorkingPixelBuffer);
   }
 
-  m_mileage += sqrt((x - m_x) * (x - m_x) + (y - m_y) * (y - m_y)) * 1000;
+  /* Increase the turtle's mileage. We need to make sure the mileage is not
+   * overflowed, otherwise we might skip some msleeps in draw. */
+  uint16_t additionalMileage = sqrt((x - m_x) * (x - m_x) + (y - m_y) * (y - m_y)) * 1000;
+  m_mileage = ((m_mileage > k_mileageLimit)
+      && ((m_mileage + additionalMileage) < k_mileageLimit)) ?
+    k_mileageLimit + 1 : m_mileage + additionalMileage;
 
   m_x = x;
   m_y = y;
diff --git a/python/port/mod/turtle/turtle.h b/python/port/mod/turtle/turtle.h
index 2b9d83b9c..87aa58e8f 100644
--- a/python/port/mod/turtle/turtle.h
+++ b/python/port/mod/turtle/turtle.h
@@ -154,7 +154,21 @@ private:
 
   uint8_t m_speed; // Speed is between 0 and 10
   KDCoordinate m_penSize;
-  KDCoordinate m_mileage;
+
+  /* We sleep every time the turtle walks a mileageLimit amount, to allow user
+   * interruptions. The length of each sleep is determined by the speed of the
+   * turtle.
+   * With emscripten, sleep gives control to the web browser, which decides when
+   * to return from sleep: this makes the turtle significantly slower on the web
+   * emulator than on the calculator. We thus decided to sleep less often on the
+   * emscripten platform. */
+#if __EMSCRIPTEN__
+  static constexpr uint16_t k_mileageLimit = 10000;
+#else
+  static constexpr uint16_t k_mileageLimit = 1000;
+#endif
+
+  uint16_t m_mileage;
   bool m_drawn;
 
 };