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A04_air_track_carCollisions.html
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A04_air_track_carCollisions.html
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<title>A04_air_track_carCollisions</title>
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<h2></h2>
<div class="highlight"><pre><span></span><span class="c1"># Filename: A04_air_track_carCollisions.py</span>
<span class="c1"># Written by: James D. Miller</span>
<span class="c1"># Python</span>
<span class="kn">import</span> <span class="nn">sys</span><span class="o">,</span> <span class="nn">os</span>
<span class="kn">import</span> <span class="nn">pygame</span>
<span class="kn">import</span> <span class="nn">datetime</span>
<span class="c1"># PyGame Constants</span>
<span class="kn">from</span> <span class="nn">pygame.locals</span> <span class="kn">import</span> <span class="o">*</span>
<span class="kn">from</span> <span class="nn">pygame.color</span> <span class="kn">import</span> <span class="n">THECOLORS</span>
<span class="c1">#=====================================================================</span>
<span class="c1"># Classes</span>
<span class="c1">#=====================================================================</span>
<span class="k">class</span> <span class="nc">GameWindow</span><span class="p">:</span>
<span class="k">def</span> <span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">screen_tuple_px</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">width_px</span> <span class="o">=</span> <span class="n">screen_tuple_px</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span>
<span class="bp">self</span><span class="o">.</span><span class="n">height_px</span> <span class="o">=</span> <span class="n">screen_tuple_px</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span>
<span class="c1"># Create a reference to display's surface object. This object is a pygame "surface".</span>
<span class="c1"># Screen dimensions in pixels (tuple)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">surface</span> <span class="o">=</span> <span class="n">pygame</span><span class="o">.</span><span class="n">display</span><span class="o">.</span><span class="n">set_mode</span><span class="p">(</span><span class="n">screen_tuple_px</span><span class="p">)</span>
<span class="c1"># Define the physics-world boundaries of the window.</span>
<span class="bp">self</span><span class="o">.</span><span class="n">left_m</span> <span class="o">=</span> <span class="mf">0.0</span>
<span class="bp">self</span><span class="o">.</span><span class="n">right_m</span> <span class="o">=</span> <span class="n">env</span><span class="o">.</span><span class="n">m_from_px</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">width_px</span><span class="p">)</span>
<span class="c1"># Paint screen black.</span>
<span class="bp">self</span><span class="o">.</span><span class="n">erase_and_update</span><span class="p">()</span>
<span class="k">def</span> <span class="nf">update_caption</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">title</span><span class="p">):</span>
<span class="n">pygame</span><span class="o">.</span><span class="n">display</span><span class="o">.</span><span class="n">set_caption</span><span class="p">(</span><span class="n">title</span><span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">caption</span> <span class="o">=</span> <span class="n">title</span>
<span class="k">def</span> <span class="nf">erase_and_update</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="c1"># Useful for shifting between the various demos.</span>
<span class="bp">self</span><span class="o">.</span><span class="n">surface</span><span class="o">.</span><span class="n">fill</span><span class="p">(</span><span class="n">THECOLORS</span><span class="p">[</span><span class="s2">"black"</span><span class="p">])</span>
<span class="n">pygame</span><span class="o">.</span><span class="n">display</span><span class="o">.</span><span class="n">flip</span><span class="p">()</span>
<span class="k">class</span> <span class="nc">Detroit</span><span class="p">:</span>
<span class="k">def</span> <span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">color</span><span class="o">=</span><span class="n">THECOLORS</span><span class="p">[</span><span class="s2">"white"</span><span class="p">],</span> <span class="n">left_px</span><span class="o">=</span><span class="mi">10</span><span class="p">,</span> <span class="n">width_px</span><span class="o">=</span><span class="mi">26</span><span class="p">,</span> <span class="n">height_px</span><span class="o">=</span><span class="mi">98</span><span class="p">,</span> <span class="n">v_mps</span><span class="o">=</span><span class="mi">1</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">color</span> <span class="o">=</span> <span class="n">color</span>
<span class="bp">self</span><span class="o">.</span><span class="n">height_px</span> <span class="o">=</span> <span class="n">height_px</span>
<span class="bp">self</span><span class="o">.</span><span class="n">top_px</span> <span class="o">=</span> <span class="n">game_window</span><span class="o">.</span><span class="n">height_px</span> <span class="o">-</span> <span class="bp">self</span><span class="o">.</span><span class="n">height_px</span>
<span class="bp">self</span><span class="o">.</span><span class="n">width_px</span> <span class="o">=</span> <span class="n">width_px</span>
<span class="bp">self</span><span class="o">.</span><span class="n">width_m</span> <span class="o">=</span> <span class="n">env</span><span class="o">.</span><span class="n">m_from_px</span><span class="p">(</span> <span class="n">width_px</span><span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">halfwidth_m</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">width_m</span><span class="o">/</span><span class="mf">2.0</span>
<span class="bp">self</span><span class="o">.</span><span class="n">height_m</span> <span class="o">=</span> <span class="n">env</span><span class="o">.</span><span class="n">m_from_px</span><span class="p">(</span> <span class="n">height_px</span><span class="p">)</span>
<span class="c1"># Initialize the position and velocity of the car. These are affected by the</span>
<span class="c1"># physics calcs in the Track.</span>
<span class="bp">self</span><span class="o">.</span><span class="n">center_m</span> <span class="o">=</span> <span class="n">env</span><span class="o">.</span><span class="n">m_from_px</span><span class="p">(</span><span class="n">left_px</span><span class="p">)</span> <span class="o">+</span> <span class="bp">self</span><span class="o">.</span><span class="n">halfwidth_m</span>
<span class="bp">self</span><span class="o">.</span><span class="n">v_mps</span> <span class="o">=</span> <span class="n">v_mps</span>
<span class="bp">self</span><span class="o">.</span><span class="n">density_kgpm2</span> <span class="o">=</span> <span class="mf">600.0</span>
<span class="bp">self</span><span class="o">.</span><span class="n">m_kg</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">height_m</span> <span class="o">*</span> <span class="bp">self</span><span class="o">.</span><span class="n">width_m</span> <span class="o">*</span> <span class="bp">self</span><span class="o">.</span><span class="n">density_kgpm2</span>
<span class="c1"># Increment the car count. This class variable is shared amoung all instances of the</span>
<span class="c1"># car class.</span>
<span class="n">air_track</span><span class="o">.</span><span class="n">carCount</span> <span class="o">+=</span> <span class="mi">1</span>
<span class="c1"># Name this car based on this air_track attribute.</span>
<span class="bp">self</span><span class="o">.</span><span class="n">name</span> <span class="o">=</span> <span class="n">air_track</span><span class="o">.</span><span class="n">carCount</span>
<span class="nb">print</span> <span class="s2">"New car name ="</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">name</span>
<span class="c1"># Create a rectangle object based on these dimensions</span>
<span class="c1"># Left: distance from the left edge of the screen in px.</span>
<span class="c1"># Top: distance from the top edge of the screen in px.</span>
<span class="bp">self</span><span class="o">.</span><span class="n">rect</span> <span class="o">=</span> <span class="n">pygame</span><span class="o">.</span><span class="n">Rect</span><span class="p">(</span><span class="n">left_px</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">top_px</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">width_px</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">height_px</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">draw_car</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="c1"># Update the pixel position of the car's rectangle object to match the value</span>
<span class="c1"># controlled by the physics calculations.</span>
<span class="bp">self</span><span class="o">.</span><span class="n">rect</span><span class="o">.</span><span class="n">centerx</span> <span class="o">=</span> <span class="n">env</span><span class="o">.</span><span class="n">px_from_m</span><span class="p">(</span> <span class="bp">self</span><span class="o">.</span><span class="n">center_m</span><span class="p">)</span>
<span class="c1"># Draw the main rectangle.</span>
<span class="n">pygame</span><span class="o">.</span><span class="n">draw</span><span class="o">.</span><span class="n">rect</span><span class="p">(</span><span class="n">game_window</span><span class="o">.</span><span class="n">surface</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">color</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">rect</span><span class="p">)</span>
<span class="k">class</span> <span class="nc">AirTrack</span><span class="p">:</span>
<span class="k">def</span> <span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="c1"># Initialize the list of cars.</span>
<span class="bp">self</span><span class="o">.</span><span class="n">cars</span> <span class="o">=</span> <span class="p">[]</span>
<span class="bp">self</span><span class="o">.</span><span class="n">carCount</span> <span class="o">=</span> <span class="mi">0</span>
<span class="c1"># Coefficients of restitution.</span>
<span class="bp">self</span><span class="o">.</span><span class="n">coef_rest_base</span> <span class="o">=</span> <span class="mf">0.90</span> <span class="c1"># Useful for reseting things.</span>
<span class="bp">self</span><span class="o">.</span><span class="n">coef_rest_car</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">coef_rest_base</span>
<span class="bp">self</span><span class="o">.</span><span class="n">coef_rest_wall</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">coef_rest_base</span>
<span class="c1"># Component of gravity along the length of the track.</span>
<span class="bp">self</span><span class="o">.</span><span class="n">gbase_mps2</span> <span class="o">=</span> <span class="mf">9.8</span><span class="o">/</span><span class="mf">20.0</span> <span class="c1"># one 20th of g.</span>
<span class="bp">self</span><span class="o">.</span><span class="n">g_mps2</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">gbase_mps2</span>
<span class="bp">self</span><span class="o">.</span><span class="n">color_transfer</span> <span class="o">=</span> <span class="kc">False</span>
<span class="bp">self</span><span class="o">.</span><span class="n">collision_count</span> <span class="o">=</span> <span class="mi">0</span>
<span class="bp">self</span><span class="o">.</span><span class="n">fix_wall_stickiness</span> <span class="o">=</span> <span class="kc">True</span> <span class="c1"># False True</span>
<span class="bp">self</span><span class="o">.</span><span class="n">fix_car_stickiness</span> <span class="o">=</span> <span class="kc">True</span> <span class="c1"># False True</span>
<span class="k">def</span> <span class="nf">update_SpeedandPosition</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">car</span><span class="p">,</span> <span class="n">dt_s</span><span class="p">):</span>
<span class="c1"># Add up all the forces on the car.</span>
<span class="n">car_forces_N</span> <span class="o">=</span> <span class="p">(</span><span class="n">car</span><span class="o">.</span><span class="n">m_kg</span> <span class="o">*</span> <span class="bp">self</span><span class="o">.</span><span class="n">g_mps2</span><span class="p">)</span> <span class="o">+</span> <span class="mf">0.0</span> <span class="o">+</span> <span class="mf">0.0</span>
<span class="c1"># Calculate the acceleration based on the forces and Newton's law.</span>
<span class="n">car_acc_mps2</span> <span class="o">=</span> <span class="n">car_forces_N</span> <span class="o">/</span> <span class="n">car</span><span class="o">.</span><span class="n">m_kg</span>
<span class="c1"># Calculate the velocity at the end of this time step.</span>
<span class="n">v_end_mps</span> <span class="o">=</span> <span class="n">car</span><span class="o">.</span><span class="n">v_mps</span> <span class="o">+</span> <span class="p">(</span><span class="n">car_acc_mps2</span> <span class="o">*</span> <span class="n">dt_s</span><span class="p">)</span>
<span class="c1"># Calculate the average velocity during this timestep.</span>
<span class="n">v_avg_mps</span> <span class="o">=</span> <span class="p">(</span><span class="n">car</span><span class="o">.</span><span class="n">v_mps</span> <span class="o">+</span> <span class="n">v_end_mps</span><span class="p">)</span><span class="o">/</span><span class="mf">2.0</span>
<span class="c1"># Use the average velocity to calculate the new position of the car.</span>
<span class="c1"># Physics note: v_avg*t is equivalent to (v*t + (1/2)*acc*t^2)</span>
<span class="n">car</span><span class="o">.</span><span class="n">center_m</span> <span class="o">=</span> <span class="n">car</span><span class="o">.</span><span class="n">center_m</span> <span class="o">+</span> <span class="p">(</span><span class="n">v_avg_mps</span> <span class="o">*</span> <span class="n">dt_s</span><span class="p">)</span>
<span class="c1"># Assign the final velocity to the car.</span>
<span class="n">car</span><span class="o">.</span><span class="n">v_mps</span> <span class="o">=</span> <span class="n">v_end_mps</span>
<span class="k">def</span> <span class="nf">check_for_collisions</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="c1"># Collisions with walls.</span>
<span class="c1"># Enumerate so can efficiently check car-car collisions below.</span>
<span class="k">for</span> <span class="n">i</span><span class="p">,</span> <span class="n">car</span> <span class="ow">in</span> <span class="nb">enumerate</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">cars</span><span class="p">):</span>
<span class="c1"># Collisions with Left and Right wall.</span>
<span class="c1"># If left-edge of the car is less than... OR If right-edge of car is greater than...</span>
<span class="k">if</span> <span class="p">((</span><span class="n">car</span><span class="o">.</span><span class="n">center_m</span> <span class="o">-</span> <span class="n">car</span><span class="o">.</span><span class="n">width_m</span><span class="o">/</span><span class="mf">2.0</span><span class="p">)</span> <span class="o"><</span> <span class="n">game_window</span><span class="o">.</span><span class="n">left_m</span><span class="p">)</span> <span class="ow">or</span> <span class="p">((</span><span class="n">car</span><span class="o">.</span><span class="n">center_m</span> <span class="o">+</span> <span class="n">car</span><span class="o">.</span><span class="n">width_m</span><span class="o">/</span><span class="mf">2.0</span><span class="p">)</span> <span class="o">></span> <span class="n">game_window</span><span class="o">.</span><span class="n">right_m</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">collision_count</span> <span class="o">+=</span> <span class="mi">1</span>
<span class="k">if</span> <span class="bp">self</span><span class="o">.</span><span class="n">fix_wall_stickiness</span><span class="p">:</span>
<span class="bp">self</span><span class="o">.</span><span class="n">correct_wall_penetrations</span><span class="p">(</span><span class="n">car</span><span class="p">)</span>
<span class="n">car</span><span class="o">.</span><span class="n">v_mps</span> <span class="o">=</span> <span class="o">-</span><span class="n">car</span><span class="o">.</span><span class="n">v_mps</span> <span class="o">*</span> <span class="bp">self</span><span class="o">.</span><span class="n">coef_rest_wall</span>
<span class="c1"># This makes use of the "enumerate"d for loop above. </span>
<span class="c1"># In doing so, it avoids checking the self-self case and avoids checking pairs twice</span>
<span class="c1"># like (2 with 3) and (3 with 2).</span>
<span class="c1"># Example checks: (1 with 2,3,4,5), (2 with 3,4,5), (3 with 4,5), (4 with 5) etc...</span>
<span class="k">for</span> <span class="n">ocar</span> <span class="ow">in</span> <span class="bp">self</span><span class="o">.</span><span class="n">cars</span><span class="p">[</span><span class="n">i</span><span class="o">+</span><span class="mi">1</span><span class="p">:]:</span>
<span class="c1"># Check for overlap with other rectangle.</span>
<span class="k">if</span> <span class="p">(</span><span class="nb">abs</span><span class="p">(</span><span class="n">car</span><span class="o">.</span><span class="n">center_m</span> <span class="o">-</span> <span class="n">ocar</span><span class="o">.</span><span class="n">center_m</span><span class="p">)</span> <span class="o"><</span> <span class="p">(</span><span class="n">car</span><span class="o">.</span><span class="n">halfwidth_m</span> <span class="o">+</span> <span class="n">ocar</span><span class="o">.</span><span class="n">halfwidth_m</span><span class="p">)):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">collision_count</span> <span class="o">+=</span> <span class="mi">1</span>
<span class="k">if</span> <span class="bp">self</span><span class="o">.</span><span class="n">color_transfer</span> <span class="o">==</span> <span class="kc">True</span><span class="p">:</span>
<span class="p">(</span><span class="n">car</span><span class="o">.</span><span class="n">color</span><span class="p">,</span> <span class="n">ocar</span><span class="o">.</span><span class="n">color</span><span class="p">)</span> <span class="o">=</span> <span class="p">(</span><span class="n">ocar</span><span class="o">.</span><span class="n">color</span><span class="p">,</span> <span class="n">car</span><span class="o">.</span><span class="n">color</span><span class="p">)</span>
<span class="c1"># Prevent sticking to other cars.</span>
<span class="k">if</span> <span class="bp">self</span><span class="o">.</span><span class="n">fix_car_stickiness</span><span class="p">:</span>
<span class="bp">self</span><span class="o">.</span><span class="n">correct_car_penetrations</span><span class="p">(</span><span class="n">car</span><span class="p">,</span> <span class="n">ocar</span><span class="p">)</span>
<span class="c1"># Calculate the new post-collision velocities.</span>
<span class="p">(</span><span class="n">car</span><span class="o">.</span><span class="n">v_mps</span><span class="p">,</span> <span class="n">ocar</span><span class="o">.</span><span class="n">v_mps</span><span class="p">)</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">car_and_ocar_vel_AFTER_collision</span><span class="p">(</span> <span class="n">car</span><span class="p">,</span> <span class="n">ocar</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">car_and_ocar_vel_AFTER_collision</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">car</span><span class="p">,</span> <span class="n">ocar</span><span class="p">,</span> <span class="n">CR</span><span class="o">=</span><span class="kc">None</span><span class="p">):</span>
<span class="c1"># If no override CR is provided, use the car's value.</span>
<span class="k">if</span> <span class="p">(</span><span class="n">CR</span> <span class="o">==</span> <span class="kc">None</span><span class="p">):</span>
<span class="n">CR</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">coef_rest_car</span>
<span class="c1"># Calculate the AFTER velocities.</span>
<span class="n">car_vel_AFTER_mps</span> <span class="o">=</span> <span class="p">(</span> <span class="p">(</span><span class="n">CR</span> <span class="o">*</span> <span class="n">ocar</span><span class="o">.</span><span class="n">m_kg</span> <span class="o">*</span> <span class="p">(</span><span class="n">ocar</span><span class="o">.</span><span class="n">v_mps</span> <span class="o">-</span> <span class="n">car</span><span class="o">.</span><span class="n">v_mps</span><span class="p">)</span> <span class="o">+</span> <span class="n">car</span><span class="o">.</span><span class="n">m_kg</span><span class="o">*</span><span class="n">car</span><span class="o">.</span><span class="n">v_mps</span> <span class="o">+</span> <span class="n">ocar</span><span class="o">.</span><span class="n">m_kg</span><span class="o">*</span><span class="n">ocar</span><span class="o">.</span><span class="n">v_mps</span><span class="p">)</span><span class="o">/</span>
<span class="p">(</span><span class="n">car</span><span class="o">.</span><span class="n">m_kg</span> <span class="o">+</span> <span class="n">ocar</span><span class="o">.</span><span class="n">m_kg</span><span class="p">)</span> <span class="p">)</span>
<span class="n">ocar_vel_AFTER_mps</span> <span class="o">=</span> <span class="p">(</span> <span class="p">(</span><span class="n">CR</span> <span class="o">*</span> <span class="n">car</span><span class="o">.</span><span class="n">m_kg</span> <span class="o">*</span> <span class="p">(</span><span class="n">car</span><span class="o">.</span><span class="n">v_mps</span> <span class="o">-</span> <span class="n">ocar</span><span class="o">.</span><span class="n">v_mps</span><span class="p">)</span> <span class="o">+</span> <span class="n">car</span><span class="o">.</span><span class="n">m_kg</span><span class="o">*</span><span class="n">car</span><span class="o">.</span><span class="n">v_mps</span> <span class="o">+</span> <span class="n">ocar</span><span class="o">.</span><span class="n">m_kg</span><span class="o">*</span><span class="n">ocar</span><span class="o">.</span><span class="n">v_mps</span><span class="p">)</span><span class="o">/</span>
<span class="p">(</span><span class="n">car</span><span class="o">.</span><span class="n">m_kg</span> <span class="o">+</span> <span class="n">ocar</span><span class="o">.</span><span class="n">m_kg</span><span class="p">)</span> <span class="p">)</span>
<span class="k">return</span> <span class="p">(</span><span class="n">car_vel_AFTER_mps</span><span class="p">,</span> <span class="n">ocar_vel_AFTER_mps</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">correct_wall_penetrations</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">car</span><span class="p">):</span>
<span class="n">penetration_left_x_m</span> <span class="o">=</span> <span class="n">game_window</span><span class="o">.</span><span class="n">left_m</span> <span class="o">-</span> <span class="p">(</span><span class="n">car</span><span class="o">.</span><span class="n">center_m</span> <span class="o">-</span> <span class="n">car</span><span class="o">.</span><span class="n">halfwidth_m</span><span class="p">)</span>
<span class="k">if</span> <span class="n">penetration_left_x_m</span> <span class="o">></span> <span class="mi">0</span><span class="p">:</span>
<span class="n">car</span><span class="o">.</span><span class="n">center_m</span> <span class="o">+=</span> <span class="mi">2</span> <span class="o">*</span> <span class="n">penetration_left_x_m</span>
<span class="n">penetration_right_x_m</span> <span class="o">=</span> <span class="p">(</span><span class="n">car</span><span class="o">.</span><span class="n">center_m</span> <span class="o">+</span> <span class="n">car</span><span class="o">.</span><span class="n">halfwidth_m</span><span class="p">)</span> <span class="o">-</span> <span class="n">game_window</span><span class="o">.</span><span class="n">right_m</span>
<span class="k">if</span> <span class="n">penetration_right_x_m</span> <span class="o">></span> <span class="mi">0</span><span class="p">:</span>
<span class="n">car</span><span class="o">.</span><span class="n">center_m</span> <span class="o">-=</span> <span class="mi">2</span> <span class="o">*</span> <span class="n">penetration_right_x_m</span>
<span class="k">def</span> <span class="nf">correct_car_penetrations</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">car</span><span class="p">,</span> <span class="n">ocar</span><span class="p">):</span>
<span class="n">relative_spd_mps</span> <span class="o">=</span> <span class="nb">abs</span><span class="p">(</span><span class="n">car</span><span class="o">.</span><span class="n">v_mps</span> <span class="o">-</span> <span class="n">ocar</span><span class="o">.</span><span class="n">v_mps</span><span class="p">)</span>
<span class="n">penetration_m</span> <span class="o">=</span> <span class="p">(</span><span class="n">car</span><span class="o">.</span><span class="n">halfwidth_m</span> <span class="o">+</span> <span class="n">ocar</span><span class="o">.</span><span class="n">halfwidth_m</span><span class="p">)</span> <span class="o">-</span> <span class="nb">abs</span><span class="p">(</span><span class="n">car</span><span class="o">.</span><span class="n">center_m</span> <span class="o">-</span> <span class="n">ocar</span><span class="o">.</span><span class="n">center_m</span><span class="p">)</span>
<span class="n">penetration_time_s</span> <span class="o">=</span> <span class="n">penetration_m</span> <span class="o">/</span> <span class="n">relative_spd_mps</span>
<span class="c1"># First, back up the two cars, to their collision point, along their incoming trajectory paths.</span>
<span class="c1"># Use BEFORE collision velocities here!</span>
<span class="n">car</span><span class="o">.</span><span class="n">center_m</span> <span class="o">-=</span> <span class="n">car</span><span class="o">.</span><span class="n">v_mps</span> <span class="o">*</span> <span class="n">penetration_time_s</span>
<span class="n">ocar</span><span class="o">.</span><span class="n">center_m</span> <span class="o">-=</span> <span class="n">ocar</span><span class="o">.</span><span class="n">v_mps</span> <span class="o">*</span> <span class="n">penetration_time_s</span>
<span class="c1"># Calculate the velocities along the normal AFTER the collision. Use a CR (coefficient of restitution)</span>
<span class="c1"># of 1 here to better avoid stickiness.</span>
<span class="p">(</span><span class="n">car_vel_AFTER_mps</span><span class="p">,</span> <span class="n">ocar_vel_AFTER_mps</span><span class="p">)</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">car_and_ocar_vel_AFTER_collision</span><span class="p">(</span> <span class="n">car</span><span class="p">,</span> <span class="n">ocar</span><span class="p">,</span> <span class="n">CR</span><span class="o">=</span><span class="mf">1.0</span><span class="p">)</span>
<span class="c1"># Finally, travel another penetration time worth of distance using these AFTER-collision velocities.</span>
<span class="c1"># This will put the cars where they should have been at the time of collision detection.</span>
<span class="n">car</span><span class="o">.</span><span class="n">center_m</span> <span class="o">+=</span> <span class="n">car_vel_AFTER_mps</span> <span class="o">*</span> <span class="n">penetration_time_s</span>
<span class="n">ocar</span><span class="o">.</span><span class="n">center_m</span> <span class="o">+=</span> <span class="n">ocar_vel_AFTER_mps</span> <span class="o">*</span> <span class="n">penetration_time_s</span>
<span class="k">def</span> <span class="nf">make_some_cars</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">nmode</span><span class="p">):</span>
<span class="c1"># Update the caption at the top of the Pygame window frame.</span>
<span class="n">game_window</span><span class="o">.</span><span class="n">update_caption</span><span class="p">(</span><span class="s2">"Air Track (basic): Demo #"</span> <span class="o">+</span> <span class="nb">str</span><span class="p">(</span><span class="n">nmode</span><span class="p">))</span>
<span class="k">if</span> <span class="p">(</span><span class="n">nmode</span> <span class="o">==</span> <span class="mi">1</span><span class="p">):</span>
<span class="n">air_track</span><span class="o">.</span><span class="n">g_mps2</span> <span class="o">=</span> <span class="mi">0</span>
<span class="n">air_track</span><span class="o">.</span><span class="n">carCount</span> <span class="o">=</span> <span class="mi">0</span>
<span class="bp">self</span><span class="o">.</span><span class="n">cars</span><span class="o">.</span><span class="n">append</span><span class="p">(</span> <span class="n">Detroit</span><span class="p">(</span><span class="n">color</span><span class="o">=</span><span class="n">THECOLORS</span><span class="p">[</span><span class="s2">"red"</span> <span class="p">],</span> <span class="n">left_px</span> <span class="o">=</span> <span class="mi">240</span><span class="p">,</span> <span class="n">width_px</span><span class="o">=</span><span class="mi">26</span><span class="p">,</span> <span class="n">v_mps</span><span class="o">=</span> <span class="mf">0.2</span><span class="p">))</span>
<span class="bp">self</span><span class="o">.</span><span class="n">cars</span><span class="o">.</span><span class="n">append</span><span class="p">(</span> <span class="n">Detroit</span><span class="p">(</span><span class="n">color</span><span class="o">=</span><span class="n">THECOLORS</span><span class="p">[</span><span class="s2">"blue"</span><span class="p">],</span> <span class="n">left_px</span> <span class="o">=</span> <span class="mi">340</span><span class="p">,</span> <span class="n">width_px</span><span class="o">=</span><span class="mi">26</span><span class="p">,</span> <span class="n">v_mps</span><span class="o">=</span> <span class="o">-</span><span class="mf">0.2</span><span class="p">))</span>
<span class="k">elif</span> <span class="p">(</span><span class="n">nmode</span> <span class="o">==</span> <span class="mi">2</span><span class="p">):</span>
<span class="n">air_track</span><span class="o">.</span><span class="n">g_mps2</span> <span class="o">=</span> <span class="n">air_track</span><span class="o">.</span><span class="n">gbase_mps2</span>
<span class="n">air_track</span><span class="o">.</span><span class="n">carCount</span> <span class="o">=</span> <span class="mi">0</span>
<span class="bp">self</span><span class="o">.</span><span class="n">cars</span><span class="o">.</span><span class="n">append</span><span class="p">(</span> <span class="n">Detroit</span><span class="p">(</span><span class="n">color</span><span class="o">=</span><span class="n">THECOLORS</span><span class="p">[</span><span class="s2">"yellow"</span> <span class="p">],</span> <span class="n">left_px</span> <span class="o">=</span> <span class="mi">240</span><span class="p">,</span> <span class="n">width_px</span><span class="o">=</span><span class="mi">26</span><span class="p">,</span> <span class="n">v_mps</span><span class="o">=</span> <span class="o">-</span><span class="mf">0.1</span><span class="p">))</span>
<span class="bp">self</span><span class="o">.</span><span class="n">cars</span><span class="o">.</span><span class="n">append</span><span class="p">(</span> <span class="n">Detroit</span><span class="p">(</span><span class="n">color</span><span class="o">=</span><span class="n">THECOLORS</span><span class="p">[</span><span class="s2">"green"</span><span class="p">],</span> <span class="n">left_px</span> <span class="o">=</span> <span class="mi">440</span><span class="p">,</span> <span class="n">width_px</span><span class="o">=</span><span class="mi">50</span><span class="p">,</span> <span class="n">v_mps</span><span class="o">=</span> <span class="o">-</span><span class="mf">0.2</span><span class="p">))</span>
<span class="k">elif</span> <span class="p">(</span><span class="n">nmode</span> <span class="o">==</span> <span class="mi">3</span><span class="p">):</span>
<span class="n">air_track</span><span class="o">.</span><span class="n">carCount</span> <span class="o">=</span> <span class="mi">0</span>
<span class="n">air_track</span><span class="o">.</span><span class="n">g_mps2</span> <span class="o">=</span> <span class="mi">0</span>
<span class="bp">self</span><span class="o">.</span><span class="n">cars</span><span class="o">.</span><span class="n">append</span><span class="p">(</span> <span class="n">Detroit</span><span class="p">(</span><span class="n">color</span><span class="o">=</span><span class="n">THECOLORS</span><span class="p">[</span><span class="s2">"yellow"</span> <span class="p">],</span> <span class="n">left_px</span> <span class="o">=</span> <span class="mi">240</span><span class="p">,</span> <span class="n">width_px</span><span class="o">=</span><span class="mi">26</span><span class="p">,</span> <span class="n">v_mps</span><span class="o">=</span> <span class="o">-</span><span class="mf">0.1</span><span class="p">))</span>
<span class="bp">self</span><span class="o">.</span><span class="n">cars</span><span class="o">.</span><span class="n">append</span><span class="p">(</span> <span class="n">Detroit</span><span class="p">(</span><span class="n">color</span><span class="o">=</span><span class="n">THECOLORS</span><span class="p">[</span><span class="s2">"green"</span><span class="p">],</span> <span class="n">left_px</span> <span class="o">=</span> <span class="mi">440</span><span class="p">,</span> <span class="n">width_px</span><span class="o">=</span><span class="mi">50</span><span class="p">,</span> <span class="n">v_mps</span><span class="o">=</span> <span class="o">-</span><span class="mf">0.2</span><span class="p">))</span>
<span class="k">class</span> <span class="nc">Environment</span><span class="p">:</span>
<span class="k">def</span> <span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">length_px</span><span class="p">,</span> <span class="n">length_m</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">px_to_m</span> <span class="o">=</span> <span class="n">length_m</span><span class="o">/</span><span class="nb">float</span><span class="p">(</span><span class="n">length_px</span><span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">m_to_px</span> <span class="o">=</span> <span class="p">(</span><span class="nb">float</span><span class="p">(</span><span class="n">length_px</span><span class="p">)</span><span class="o">/</span><span class="n">length_m</span><span class="p">)</span>
<span class="c1"># Convert from meters to pixels</span>
<span class="k">def</span> <span class="nf">px_from_m</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">dx_m</span><span class="p">):</span>
<span class="k">return</span> <span class="nb">int</span><span class="p">(</span><span class="nb">round</span><span class="p">(</span><span class="n">dx_m</span> <span class="o">*</span> <span class="bp">self</span><span class="o">.</span><span class="n">m_to_px</span><span class="p">))</span>
<span class="c1"># Convert from pixels to meters</span>
<span class="k">def</span> <span class="nf">m_from_px</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">dx_px</span><span class="p">):</span>
<span class="k">return</span> <span class="nb">float</span><span class="p">(</span><span class="n">dx_px</span><span class="p">)</span> <span class="o">*</span> <span class="bp">self</span><span class="o">.</span><span class="n">px_to_m</span>
<span class="k">def</span> <span class="nf">get_local_user_input</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="c1"># Get all the events since the last call to get().</span>
<span class="k">for</span> <span class="n">event</span> <span class="ow">in</span> <span class="n">pygame</span><span class="o">.</span><span class="n">event</span><span class="o">.</span><span class="n">get</span><span class="p">():</span>
<span class="k">if</span> <span class="p">(</span><span class="n">event</span><span class="o">.</span><span class="n">type</span> <span class="o">==</span> <span class="n">pygame</span><span class="o">.</span><span class="n">QUIT</span><span class="p">):</span>
<span class="k">return</span> <span class="s1">'quit'</span>
<span class="k">elif</span> <span class="p">(</span><span class="n">event</span><span class="o">.</span><span class="n">type</span> <span class="o">==</span> <span class="n">pygame</span><span class="o">.</span><span class="n">KEYDOWN</span><span class="p">):</span>
<span class="k">if</span> <span class="p">(</span><span class="n">event</span><span class="o">.</span><span class="n">key</span> <span class="o">==</span> <span class="n">K_ESCAPE</span><span class="p">):</span>
<span class="k">return</span> <span class="s1">'quit'</span>
<span class="k">elif</span> <span class="p">(</span><span class="n">event</span><span class="o">.</span><span class="n">key</span><span class="o">==</span><span class="n">K_1</span><span class="p">):</span>
<span class="k">return</span> <span class="mi">1</span>
<span class="k">elif</span> <span class="p">(</span><span class="n">event</span><span class="o">.</span><span class="n">key</span><span class="o">==</span><span class="n">K_2</span><span class="p">):</span>
<span class="k">return</span> <span class="mi">2</span>
<span class="k">elif</span> <span class="p">(</span><span class="n">event</span><span class="o">.</span><span class="n">key</span><span class="o">==</span><span class="n">K_3</span><span class="p">):</span>
<span class="k">return</span> <span class="mi">3</span>
<span class="k">elif</span> <span class="p">(</span><span class="n">event</span><span class="o">.</span><span class="n">key</span><span class="o">==</span><span class="n">K_s</span><span class="p">):</span>
<span class="n">air_track</span><span class="o">.</span><span class="n">fix_wall_stickiness</span> <span class="o">=</span> <span class="ow">not</span> <span class="n">air_track</span><span class="o">.</span><span class="n">fix_wall_stickiness</span>
<span class="n">air_track</span><span class="o">.</span><span class="n">fix_car_stickiness</span> <span class="o">=</span> <span class="ow">not</span> <span class="n">air_track</span><span class="o">.</span><span class="n">fix_car_stickiness</span>
<span class="k">elif</span> <span class="p">(</span><span class="n">event</span><span class="o">.</span><span class="n">key</span><span class="o">==</span><span class="n">K_c</span><span class="p">):</span>
<span class="n">air_track</span><span class="o">.</span><span class="n">color_transfer</span> <span class="o">=</span> <span class="ow">not</span> <span class="n">air_track</span><span class="o">.</span><span class="n">color_transfer</span>
<span class="k">else</span><span class="p">:</span>
<span class="k">return</span> <span class="s2">"Nothing set up for this key."</span>
<span class="k">elif</span> <span class="p">(</span><span class="n">event</span><span class="o">.</span><span class="n">type</span> <span class="o">==</span> <span class="n">pygame</span><span class="o">.</span><span class="n">KEYUP</span><span class="p">):</span>
<span class="k">pass</span>
<span class="k">elif</span> <span class="p">(</span><span class="n">event</span><span class="o">.</span><span class="n">type</span> <span class="o">==</span> <span class="n">pygame</span><span class="o">.</span><span class="n">MOUSEBUTTONDOWN</span><span class="p">):</span>
<span class="k">pass</span>
<span class="k">elif</span> <span class="p">(</span><span class="n">event</span><span class="o">.</span><span class="n">type</span> <span class="o">==</span> <span class="n">pygame</span><span class="o">.</span><span class="n">MOUSEBUTTONUP</span><span class="p">):</span>
<span class="k">pass</span>
<span class="c1">#============================================================</span>
<span class="c1"># Main procedural functions.</span>
<span class="c1">#============================================================</span>
<span class="k">def</span> <span class="nf">main</span><span class="p">():</span>
<span class="c1"># A few globals.</span>
<span class="k">global</span> <span class="n">env</span><span class="p">,</span> <span class="n">game_window</span><span class="p">,</span> <span class="n">air_track</span>
<span class="c1"># Initiate Pygame</span>
<span class="n">pygame</span><span class="o">.</span><span class="n">init</span><span class="p">()</span>
<span class="c1"># Tuple to define window dimensions</span>
<span class="n">window_size_px</span> <span class="o">=</span> <span class="n">window_width_px</span><span class="p">,</span> <span class="n">window_height_px</span> <span class="o">=</span> <span class="mi">950</span><span class="p">,</span> <span class="mi">120</span>
<span class="c1"># Instantiate an Environment object for converting back and forth from pixels and meters.</span>
<span class="c1"># The also creates the local client.</span>
<span class="n">env</span> <span class="o">=</span> <span class="n">Environment</span><span class="p">(</span><span class="n">window_width_px</span><span class="p">,</span> <span class="mf">1.5</span><span class="p">)</span>
<span class="c1"># Instantiate the window.</span>
<span class="n">game_window</span> <span class="o">=</span> <span class="n">GameWindow</span><span class="p">(</span><span class="n">window_size_px</span><span class="p">)</span>
<span class="c1"># Instantiate an air track (this adds an empty car list to the track).</span>
<span class="n">air_track</span> <span class="o">=</span> <span class="n">AirTrack</span><span class="p">()</span>
<span class="c1"># Make some cars (run demo #1).</span>
<span class="n">air_track</span><span class="o">.</span><span class="n">make_some_cars</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="c1"># Instantiate clock to help control the framerate.</span>
<span class="n">myclock</span> <span class="o">=</span> <span class="n">pygame</span><span class="o">.</span><span class="n">time</span><span class="o">.</span><span class="n">Clock</span><span class="p">()</span>
<span class="c1"># Control the framerate.</span>
<span class="n">framerate_limit</span> <span class="o">=</span> <span class="mi">400</span>
<span class="n">time_s</span> <span class="o">=</span> <span class="mf">0.0</span>
<span class="n">user_done</span> <span class="o">=</span> <span class="kc">False</span>
<span class="k">while</span> <span class="ow">not</span> <span class="n">user_done</span><span class="p">:</span>
<span class="c1"># Erase everything.</span>
<span class="n">game_window</span><span class="o">.</span><span class="n">surface</span><span class="o">.</span><span class="n">fill</span><span class="p">(</span><span class="n">THECOLORS</span><span class="p">[</span><span class="s2">"black"</span><span class="p">])</span>
<span class="c1"># Get the delta t for one frame (this changes depending on system load).</span>
<span class="n">dt_s</span> <span class="o">=</span> <span class="nb">float</span><span class="p">(</span><span class="n">myclock</span><span class="o">.</span><span class="n">tick</span><span class="p">(</span><span class="n">framerate_limit</span><span class="p">)</span> <span class="o">*</span> <span class="mf">1e-3</span><span class="p">)</span>
<span class="c1"># Check for user initiated stop or demo change.</span>
<span class="n">resetmode</span> <span class="o">=</span> <span class="n">env</span><span class="o">.</span><span class="n">get_local_user_input</span><span class="p">()</span>
<span class="k">if</span> <span class="p">(</span><span class="n">resetmode</span> <span class="ow">in</span> <span class="p">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">9</span><span class="p">]):</span>
<span class="nb">print</span> <span class="s2">"reset mode ="</span><span class="p">,</span> <span class="n">resetmode</span>
<span class="c1"># This should remove all references to the cars and effectively deletes them.</span>
<span class="n">air_track</span><span class="o">.</span><span class="n">cars</span> <span class="o">=</span> <span class="p">[]</span>
<span class="c1"># Now just black everything out and update the screen.</span>
<span class="n">game_window</span><span class="o">.</span><span class="n">erase_and_update</span><span class="p">()</span>
<span class="c1"># Build new set of cars based on the reset mode.</span>
<span class="n">air_track</span><span class="o">.</span><span class="n">make_some_cars</span><span class="p">(</span> <span class="n">resetmode</span><span class="p">)</span>
<span class="k">elif</span> <span class="p">(</span><span class="n">resetmode</span> <span class="o">==</span> <span class="s1">'quit'</span><span class="p">):</span>
<span class="n">user_done</span> <span class="o">=</span> <span class="kc">True</span>
<span class="k">elif</span> <span class="p">(</span><span class="n">resetmode</span> <span class="o">!=</span> <span class="kc">None</span><span class="p">):</span>
<span class="nb">print</span> <span class="n">resetmode</span>
<span class="c1"># Update velocity and x position of each car based on the dt_s for this frame.</span>
<span class="k">for</span> <span class="n">car</span> <span class="ow">in</span> <span class="n">air_track</span><span class="o">.</span><span class="n">cars</span><span class="p">:</span>
<span class="n">air_track</span><span class="o">.</span><span class="n">update_SpeedandPosition</span><span class="p">(</span><span class="n">car</span><span class="p">,</span> <span class="n">dt_s</span><span class="p">)</span>
<span class="c1"># Check for collisions and apply collision physics to determine resulting</span>
<span class="c1"># velocities.</span>
<span class="n">air_track</span><span class="o">.</span><span class="n">check_for_collisions</span><span class="p">()</span>
<span class="nb">print</span> <span class="s2">"Collision count ="</span><span class="p">,</span> <span class="n">air_track</span><span class="o">.</span><span class="n">collision_count</span><span class="p">,</span> <span class="n">air_track</span><span class="o">.</span><span class="n">fix_wall_stickiness</span><span class="p">,</span> <span class="n">air_track</span><span class="o">.</span><span class="n">fix_car_stickiness</span>
<span class="c1"># Draw the car at the new position.</span>
<span class="k">for</span> <span class="n">car</span> <span class="ow">in</span> <span class="n">air_track</span><span class="o">.</span><span class="n">cars</span><span class="p">:</span>
<span class="n">car</span><span class="o">.</span><span class="n">draw_car</span><span class="p">()</span>
<span class="c1"># Update the total time since starting.</span>
<span class="n">time_s</span> <span class="o">+=</span> <span class="n">dt_s</span>
<span class="c1"># Make this update visible on the screen.</span>
<span class="n">pygame</span><span class="o">.</span><span class="n">display</span><span class="o">.</span><span class="n">flip</span><span class="p">()</span>
<span class="c1">#============================================================</span>
<span class="c1"># Run the main program. </span>
<span class="c1">#============================================================</span>
<span class="n">main</span><span class="p">()</span>
</pre></div>
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