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************************************************************************** ************************************************************************** OBJECT EXPLODER INCLUDE FILE FOR PERSISTENCE OF VISION 3.x ************************************************************************** ************************************************************************** Created by Chris Colefax, March 1997 1.0 INSTALLATION 2.0 QUICK START 3.0 OPTIONS 3.1 A NOTE ON UNITS 3.2 OBJECT OPTIONS 3.2.1 explode_object 3.2.2 object_centre 3.2.3 object_size 3.2.4 object_corner1 3.2.5 object_corner2 3.2.6 object_hollow 3.3 PARTICLE OPTIONS 3.3.1 particle_res 3.3.2 particle_object 3.3.3 particle_texture 3.4 EXPLOSION OPTIONS 3.4.1 exp_location 3.4.2 exp_strength 3.4.3 exp_falloff 3.4.4 exp_gravity 3.4.5 exp_sky 3.4.6 exp_spin 3.5 GROUND PLANE OPTIONS 3.5.1 ground_plane 3.5.2 ground_dist 3.5.3 ground_reflection 3.5.4 max_bounces 3.6 TURBULENCE OPTIONS 3.6.1 exp_turb 3.6.2 scale_turb 3.6.3 rotate_turb 3.6.4 vel_turb 3.6.5 dir_turb 3.6.6 spin_turb 3.6.7 exp_seed 4.0 GENERATING THE EXPLOSION 5.0 CONTACTING THE AUTHOR ************************************************************************** 1.0 INSTALLATION ************************************************************************** Copy the Object Exploder include file (Explode.inc) to one of the directories (folders) in your POVRay library path. Normally this is the INCLUDE sub-directory of the directory where you installed POVRay, so if you installed POVRay in C:\POVRAY you should copy the Explode.inc file to C:\POVRAY\INCLUDE. On a Windows 95 system, this is probably something like: C:\Program Files\POV-Ray for Windows\Include On UNIX and similar systems, where filenames are case-sensitive, you may have to rename the include file so that it starts with a capital and the rest of its letters are lowercase. If you want to render the sample files you should also check that the naming of Map.gif is as shown. This will enable you to render the sample files without modification. 2.0 QUICK START ************************************************************************** The Object Exploder include file will take any existing POVRay object, from a simple sphere to a complex CSG object, and explode it into a mass of animated particles. There are many options you can use to affect the way the explosion occurs; to use any of these you simply add the following line to your POVRay scene file: #declare [variable-name] = [value] substituting the desired variable name and value where appropriate. After you have declared all the options you want to use, you add the following line to your POVRay scene file: #include "Explode.inc" The Object Exploder include file will then automatically create the animated explosion for you. Although only one option is required to create an explosion (explode_object) you will want to use the options listed below to ensure you get the sort of explosion that you want. 3.0 OPTIONS ************************************************************************** 3.1 A NOTE ON UNITS ******************** When using the Object Exploder options you will discover a number of variables that must be specified as a certain number of units. Just as in POVRay the units you wish to use are entirely up to you, eg. you may specify the object size in microns or miles, and the explosion clock in milliseconds or days. The important thing is that you keep the units that you use in a particular scene file consistent for that entire file, eg. if you are measuring distances in metres and time in seconds then speeds should be expressed as metres per second. This will ensure that you get the results you expect, and will save you a lot of trouble. 3.2 OBJECT OPTIONS ******************* The first step when using the Object Exploder include file is to specify a number of parameters that identify the object you wish to explode, as well as it's position in the POVRay universe. 3.2.1 explode_object ********************* This parameter indicates the object you want to explode, and can be either a predefined object or a completely new object definition, including textures and transformations, eg: #declare explode_object = object {MyObject scale 3} #declare explode_object = sphere {<0, 5, 0>, 3 pigment {Red}} Any POVRay object can be used, including CSG objects and triangle meshes. After you have specified the explode_object you must declare a number of variables that indicate the size and position of the object. Four vectors can be used for this, but only two are needed, and only the first two found will be used. For the best results you should try to make these measurements as accurate as possible. 3.2.2 object_centre ******************** This specifies the exact centre of the explode_object, and is best used when exploding spherical or cylindrical objects. Note: object_center can also be used to specify this variable. 3.2.3 object_size ****************** This specifies the X, Y, and Z dimensions of the explode_object, eg. if the explode_object was a sphere with a radius of 1 then the size would be <2, 2, 2>. 3.2.4 object_corner1 ********************* This specifies the lower-left hand corner of the object, and is best used when exploding box-like objects. 3.2.5 object_corner2 ********************* This vector specifies the upper-right hand corner of the object. 3.2.6 object_hollow ******************** This is a true / false value that indicates whether the explode_object is to be considered as a surface model only, or as a solid object. If object_hollow = true (default) then the object is considered to be hollow inside, and particles are created from the surface of the object. If object_hollow = false then the object is considered to be solid, and when it is exploded particles will be created inside the object as well as on the surface. Note that this may not work with all objects (eg. triangles, polygons) as they do not have clearly defined insides and outsides. 3.3 PARTICLE OPTIONS ********************* After you have specified all the desired object variables you can specify a number of options which will adjust the shape, size, and number of particles created when the object is exploded. 3.3.1 particle_res ******************* This is the most important of the particle options, and specifies the number of particles to create. It should be specified as a vector, but may be specified as a float (eg. 3 = <3, 3, 3>). When the object is exploded it is broken up into a grid of particles, with the number of particles in each direction taken from the X, Y, and Z components of this vector, eg. #declare particle_res = <7, 3, 5> will create 7 particles in the X direction, 3 in the Y direction, and 5 in the Z direction, which gives 7 * 3 * 5 particles, or 105 particles in total. Each component of the vector can be 1 or larger. However, adjusting this variable can drastically alter the speed it takes to generate the explosion, so keep this in mind when trying larger numbers. 3.3.2 particle_object ********************** This specifies the shape of the individual particles created by the Object Exploder, and should generally be a unit sized object centred around the origin (the default is box {<-.5, -.5, -.5>, <.5, .5, .5>}). The particle_object can include texture information, but this will only be used if object_hollow = false. Note also that this will give all particles the same texture; if you want the particles to be textured based on their location inside the object you should use the particle_texture option. 3.3.3 particle_texture *********************** This specifies the texture of the inside of the object, and will only be used if object_hollow = false. Using this option allows you to texture particles differently according to their position within the object, eg. if you use a gradient that goes from white at the bottom of the object to red at the top, any particles from the bottom of the object will be white while any from the top will be red. The default particle_texture = texture {pigment {rgb <.5, .5, .5>}} 3.4 EXPLOSION OPTIONS ********************** The following parameters specify the actual characteristics of the explosion itself (ie. the force that breaks apart the object). 3.4.1 exp_location ******************* This specifies the vector location of the explosion, and determines the direction in which the particles will move after the explosion, eg. making this the same as the object_centre will explode the particles outwards in all directions, while placing this below the object will explode the particles upwards. By default this is at the origin. 3.4.2 exp_strength ******************* This specifies the force of the explosion. It is actually the velocity given to each particle at the start of the explosion. Larger numbers will make the objects explode more quickly, while smaller numbers will make the explosion seem smaller. Specifying 0 for this option will not actually move the particles, and is useful for giving the impression of an object that cracks without actually blowing up (it is best used with the exp_gravity option). Specifying negative numbers will cause the particles to move in the opposite direction, and can be used to create an imploding object, rather than an exploding object. 3.4.3 exp_falloff ****************** Normally all particles are given the same velocity (specified by exp_strength) at the start of the explosion, regardless of their distance from the explosion itself. You can use the exp_falloff option to make particles further from the explosion receive less of the explosion's force than particles that are near the explosion. The number specified actually indicates the distance at which the exp_strength drops to 25% of its original strength, eg. #declare exp_falloff = 10 means that a particle 10 units away from the exp_location will only receive 25% of the force specified by exp_strength. 3.4.4 exp_gravity ****************** This specifies the strength of the force of gravity, declared as a float (NOT a vector). Normally this is 0 (ie. no gravity), but specifying otherwise will cause particles to be pulled to the ground. 3.4.5 exp_sky ************** This specifies the direction vector that points in the up direction (normally this it y, ie. <0, 1, 0>). It works in a similar way to the sky keyword in the POVRay camera, and it useful when using a different coordinate system (eg. #declare exp_sky = z if the z-axis points upwards). This vector determines the direction of the gravity (opposite to the sky, of course) and is also used as the normal of the ground plane if one is specified (see section 3.5). 3.4.6 exp_spin *************** This option can be used to cause the exploded particles to spin as they move through space. It can be specified as a vector or float, and indicates the number of spins to make per each unit of time, eg. #declare exp_spin = <.5, 1, 0> will spin each particle 180 degrees about the x-axis and 360 degrees about the y-axis for every unit of time that passes. Usually it is easier to #declare this option as a float value that indicates the amount of spin you wish to give each particle, eg. #declare exp_spin = .3 3.5 GROUND PLANE OPTIONS ************************* The Object Exploder include file has the ability to add a ground plane to the scene. If a particle hits this plane it can automatically rebound off it or it can stop and come to rest on the plane. Note that the Object Exploder include file will not actually create a ground plane object for you, giving you the option to use any sort of object you like to represent the ground. 3.5.1 ground_plane ******************* This is a true / false value that indicates whether a ground plane is present or not. Normally this is false, but setting it to true will cause the Object Exploder to check each particle's movement against this plane to see if it rebounds or stops. Also, any particles underneath the plane will not be created. 3.5.2 ground_dist ****************** This specifies the distance of the ground from the origin, and is the same as the distance value as specified in the plane object. Note that the normal direction of the plane is always the same as exp_sky (the default if <0, 1, 0>; see section 3.4.5). Normally the ground_dist = 0. 3.5.3 ground_reflection ************************ This specifies the amount of energy a particle retains after hitting the ground plane. ground_reflection = 1 means that the particles retains all it's energy, and will bounce back to the same height each time it hits the ground. ground_reflection = 0 means that the particle retains none of it's energy after hitting the plane, and therefore it comes to a stop. Values in between 0 and 1 will cause the particle to bounce less high each time it hits the plane, eventually coming to a stop. Values larger than 1 will cause the particle to bounce higher each time it hits the plane. 3.5.4 max_bounces ****************** This option specifies the maximum number of times a particle will rebound off a plane before coming to a stop (even if ground_reflection >= 1). This is necessary because of the way the rebounds are calculated: each time a particle is checked for rebounds all the particles rebounds prior to the current rebound need to be recalculated (this is a limitation in the way POVRay handles variables from frame to frame in an animation). This means that on a particle's second rebound the first rebound has to be calculated again, while on the third rebound the first and second rebounds have to recalculated. Because calculating each rebound requires solving a quadratic equation as well as a number of other calculations, this can add a considerable amount to the time needed to generate the explosion. For this reason, you can use the max_bounces option to limit the number of bounces a particle will make. By default this is set to 1 (ie. each particle will bounce once, and then stop). Setting it to 0 will stop particles bouncing at all, while increasing the number will allow particles to bounce more times before coming to a stop. 3.6 TURBULENCE OPTIONS *********************** By default the Object Exploder include file creates the explosion particles in a perfect grid (specified by the particle_res option), and each particle is the same size, and travels at the same speed. While this is fine for some explosions it is less than realistic. To remedy this you can add turbulence to the explosion, adding a little randomness to each particle's size and speed. 3.6.1 exp_turb *************** This option controls the overall amount of turbulence added to the explosion (normally this is 0). Good values range from 0 (no turbulence) to 1 (lots of turbulence), but any value can be used. Changing this value will add equal turbulence to all aspects of the explosion. If you wish to adjust the turbulence of individual areas of the explosion you can use the following parameters. (Note that all the individual turbulence options are multiplied by exp_turb to find the final turbulence, so you will have to make sure that exp_turb is not 0 before using the other turbulence options). 3.6.2 scale_turb ***************** This option controls the amount of turbulence added to the scaling of the particles. It is specified as a factor of the particle size, eg. scale_turb = .5 will give particles scaled up to 50% larger or smaller than normal. 3.6.3 rotate_turb ****************** This option controls the amount of turbulence added to the rotation of the particles. It is specified as a fraction of 360 degrees, eg. rotate_turb = .1 will give particles rotated up to 36 degrees away from normal. 3.6.4 vel_turb *************** This option controls the amount of turbulence added to the velocity of the particles. It is specified as a factor of the particle velocity, eg. #declare vel_turb = .3 will give particles with velocities up to 30% more or less than normal. 3.6.5 dir_turb *************** This option controls the amount of turbulence added to the direction of the particles movement. It is specified as a fraction of 360 degrees, eg. #declare dir_turb = .2 will give particles that move up to 20 degrees away from normal. 3.6.6 spin_turb **************** This option controls the amount of turbulence added to the spin of each particle, and only applies when you have specified a non-zero value for exp_spin (see section 3.4.6). It is measured as a factor of the total spin amount, eg. #declare spin_turb = .7 will give particles that spin up to 70% more or less than normal. 3.6.7 exp_seed *************** This option specifies that random number seed used when adding turbulence to the explosion. Normally this is 0, but any integer value can be used. 4.0 GENERATING THE EXPLOSION ************************************************************************** After you have declared all the desired variables you have to specify the explode_clock variable (and then include the "Explode.inc" file, of course). This variable indicates the current time value of the explosion, where 0 is just before the explosion starts. Normally the explode_clock is equal to POVRay's internal clock variable. This may not, however, be what you require for a particular animation. Because of this you are given the option to #declare explode_clock to be any value you want. You can use this to create still scenes from a particular way through the explosion, eg. #declare explode_clock = 1.47 will create a still scene of the explosion 1.47 units of time after it started. (Note that when explode_clock is less than or equal to 0 the explode_object is placed in the scene without being altered at all). Usually you will declare explode_clock to be some function of POVRay's internal clock variable. Sometimes this will be as simple as: #declare explode_clock = clock * 5 which will create an explode_clock that goes 5 times as fast as the internal clock. You could use 0.5 to make the explode_clock half as fast as the internal clock, or any number you wish. Sometimes, however, you might want a more complicated explode_clock, such as one that starts only at a particular time, or one that goes backwards, or one that starts fast and slows down. All of these can be easily accomplished using POVRay's various float functions, and the #if and #switch directives. For some examples of using explode_clock in this way take a look at the sample animations that came with the Object Exploder include file. 5.0 CONTACTING THE AUTHOR ************************************************************************** If you wish to contact me with bug reports, bug fixes, criticisms, comments, suggested improvements, questions, etc. you can reach me by email at: ccolefax@geocities.com or by regular mail at: Chris Colefax PO Box 110 Kuranda, Queensland Australia 4872 ************************************************************************** POV-Ray(tm) and Persistence of Vision(tm) are registered trademarks of the POV-Ray Team(tm)