Computer graphics -- 2007-2008 -- info.uvt.ro/Laboratory 7
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[edit] World box
The world box is nothing else than a simple cube that contains all the scene's objects and the camera. Thus the following constraints must be met:
- the world box must be inside the view volume; (or at least the sides that are visible;)
- the objects outside the world box should not be draws, as they will not be visible;
- the camera should not be allowed to exit the bounding box;
- it is advisable that the camera does not approaches the world box;
Usually for this box each of the sides has a particular texture -- like some stars when simulating a solar system.
Observation: when drawing the world box we should note that it must be drawn, so that the face polygon is on the inside. (Thus be careful to the vertex ordering.)
[edit] Particle engine
The best example of a particle engine is the emission of a comet.
For each particle we have the following properties:
- physical variables:
- position vector -- (positionX, positionY, positionZ);
- speed vector -- (speedX, speedY, speedY);
- acceleration vector -- (accelerationX, accelerationY, accelerationZ);
- display variables:
- color, material, texture, etc.;
- fading and fading factor -- how visible is the particle;
- life -- that should be decremented, and when it reaches 0 the particle should be destroyed or reused;
The physical laws are quite easy:
- at each step we update the speed by using the acceleration;
- at each step we update the position by using the speed;
- the time is considered constant -- usually 1;
- usually the particles go in the opposite direction of their source; thus we could initialize their speed with the speed of the source, but negative;
- usually the particles are emitted to form a cone, and are computed randomly;
Observation:
- usually the number of particles is constant;
- when a particle dies, a new one is created; usually we do this by reusing and reinitializing a particle;
- the bigger the time variable is, the smaller the number of frames is needed, but the movement is more fragmented;
[edit] Assignment
This is the seventh assignment, so please commit it to the folder assignment-07.
Implement the following simulation:
- we imagine a sphere that occupies half of the view volume; (this sphere should not be drawn;)
- on the surface of this sphere a comet is moving randomly; (be careful to implement a 'smooth (not fragmented) movement;)
- from this comet particles are emitted in the reverse direction of the comet; (thus the comet and the particles are moving in opposing directions;)
- the particles are emitted in the form of a cone;
- the entire world is inside the world box;
Bonus points:
- the comet and the particles are implemented as billboards;
- it should be possible to move the camera -- like in the previous laboratories -- but the camera should not be allowed to exit the world box;
Observations:
- as a starting point you could place the comet in the center of the system, and let it be static;
