Using Intervals to move the Panda

Intervals and Sequences

Intervals

Intervals are tasks that change a property from one value to another over a specified period of time. Starting an interval effectively starts a background process that modifies the property over the specified period of time.

Sequences

Sequences, sometimes called MetaIntervals, are a type of interval that contains other intervals. Playing a sequence will cause each contained interval to execute in sequence, one after the other.

The Program

Update the Code

The next step is to cause the panda to actually move back and forth. Update the code to the following:

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#include "pandaFramework.h"
#include "pandaSystem.h"

#include "genericAsyncTask.h"
#include "asyncTaskManager.h"

#include "cIntervalManager.h"
#include "cLerpNodePathInterval.h"
#include "cMetaInterval.h"

// Global stuff
PT(AsyncTaskManager) taskMgr = AsyncTaskManager::get_global_ptr();
PT(ClockObject) globalClock = ClockObject::get_global_clock();
NodePath camera;

// Task to move the camera
AsyncTask::DoneStatus SpinCameraTask(GenericAsyncTask *task, void *data) {
  double time = globalClock->get_real_time();
  double angledegrees = time * 6.0;
  double angleradians = angledegrees * (3.14 / 180.0);
  camera.set_pos(20 * sin(angleradians), -20.0 * cos(angleradians), 3);
  camera.set_hpr(angledegrees, 0, 0);

  return AsyncTask::DS_cont;
}

int main(int argc, char *argv[]) {
  // Open a new window framework and set the title
  PandaFramework framework;
  framework.open_framework(argc, argv);
  framework.set_window_title("My Panda3D Window");

  // Open the window
  WindowFramework *window = framework.open_window();
  camera = window->get_camera_group(); // Get the camera and store it

  // Load the environment model
  NodePath scene = window->load_model(framework.get_models(),
    "models/environment");
  scene.reparent_to(window->get_render());
  scene.set_scale(0.25, 0.25, 0.25);
  scene.set_pos(-8, 42, 0);

  // Load our panda
  NodePath pandaActor = window->load_model(framework.get_models(),
    "models/panda-model");
  pandaActor.set_scale(0.005);
  pandaActor.reparent_to(window->get_render());

  // Load the walk animation
  window->load_model(pandaActor, "models/panda-walk4");
  window->loop_animations(0);

  // Create the lerp intervals needed to walk back and forth
  PT(CLerpNodePathInterval) pandaPosInterval1, pandaPosInterval2,
    pandaHprInterval1, pandaHprInterval2;
  pandaPosInterval1 = new CLerpNodePathInterval("pandaPosInterval1",
    13.0, CLerpInterval::BT_no_blend,
    true, false, pandaActor, NodePath());
  pandaPosInterval1->set_start_pos(LPoint3(0, 10, 0));
  pandaPosInterval1->set_end_pos(LPoint3(0, -10, 0));

  pandaPosInterval2 = new CLerpNodePathInterval("pandaPosInterval2",
    13.0, CLerpInterval::BT_no_blend,
    true, false, pandaActor, NodePath());
  pandaPosInterval2->set_start_pos(LPoint3(0, -10, 0));
  pandaPosInterval2->set_end_pos(LPoint3(0, 10, 0));

  pandaHprInterval1 = new CLerpNodePathInterval("pandaHprInterval1", 3.0,
    CLerpInterval::BT_no_blend,
    true, false, pandaActor, NodePath());
  pandaHprInterval1->set_start_hpr(LPoint3(0, 0, 0));
  pandaHprInterval1->set_end_hpr(LPoint3(180, 0, 0));

  pandaHprInterval2 = new CLerpNodePathInterval("pandaHprInterval2", 3.0,
    CLerpInterval::BT_no_blend,
    true, false, pandaActor, NodePath());
  pandaHprInterval2->set_start_hpr(LPoint3(180, 0, 0));
  pandaHprInterval2->set_end_hpr(LPoint3(0, 0, 0));

  // Create and play the sequence that coordinates the intervals
  PT(CMetaInterval) pandaPace;
  pandaPace = new CMetaInterval("pandaPace");
  pandaPace->add_c_interval(pandaPosInterval1, 0,
    CMetaInterval::RS_previous_end);
  pandaPace->add_c_interval(pandaHprInterval1, 0,
    CMetaInterval::RS_previous_end);
  pandaPace->add_c_interval(pandaPosInterval2, 0,
    CMetaInterval::RS_previous_end);
  pandaPace->add_c_interval(pandaHprInterval2, 0,
    CMetaInterval::RS_previous_end);
  pandaPace->loop();

  // Add our task.
  taskMgr->add(new GenericAsyncTask("Spins the camera",
    &SpinCameraTask, nullptr));

  // This is a simpler way to do stuff every frame,
  // if you're too lazy to create a task.
  Thread *current_thread = Thread::get_current_thread();
  while (framework.do_frame(current_thread)) {
    // Step the interval manager
    CIntervalManager::get_global_ptr()->step();
  }

  framework.close_framework();
  return 0;
}

When the pandaPosInterval1 interval is started, it will gradually adjust the position of the panda from (0, 10, 0) to (0, -10, 0) over a period of 13 seconds. Similarly, when the pandaHprInterval1 interval is started, the heading of the panda will rotate 180 degrees over a period of 3 seconds.

The pandaPace sequence above causes the panda to move in a straight line, turn, move in the opposite straight line, and finally turn again. The code pandaPace.loop() causes the Sequence to be started in looping mode.

Run the Program

The result of all this is to cause the panda to pace back and forth from one tree to the other.