Slide 1: POVRAY Tutorial
204481 Foundation of Computer graphics Pradondet Nilagupta
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Slide 2: What is POV-Ray?
POVRAY = Persistence of Vision RayTracer POV-Ray is a high-quality, freely available ray-tracing software packag e that is available for PC, Macintosh a nd UNIX platforms. POV-Ray is no toy. POV-Ray is what is known as a "rendering engine".
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Slide 3: Written POV-Ray language
Describing scenes to POV-Ray is fairly simple Give POV-Ray a file containing a description of every object in the sce ne. POV-Ray takes this file and gener ates a picture, which you can then vie w.
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Slide 4: Object description of POVRAY
What type of object you want (one of POV-Ray's simple objects or one you've created yourself. Various attributes of the object (its color, how it reflects light, etc).
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Slide 5: What is ray-tracing?
Ray-tracing is a method of creating visual art in which a description of an object or scene is mathematically con verted into a picture. ray-tracing is the process of mathematically generating near-phot orealistic images from a given descrip tion of a scene via geometrical modeli ng of light rays.
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Slide 6: POV-Ray's Coordinate System
The coordinate system that POV-Ray uses, then, is called a three-dimensio nal (or 3D) Cartesian coordinate syste m. The axis we have drawn is not fixed in POV-Ray -- the way the axis looks (in terms of which axes are which) re ally depends on where you place your camera in POV-Ray.
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Slide 7: Vectors in POV-Ray
The term vector refers to any group of numbers describing a certain thing -- there are color vectors and normal vectors. vectors are surrounded by angle brackets (that's < and >). For example, to specify the origin in terms that POV-Ray understands, we would say <0,0,0>
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Slide 8: How to describe color: RGB and RGBF Vectors
In describing a color, each element of the vector corresponds to the amount of a prima ry color -- red, green and blue. Such a vector is called a RGB vector (for red green blue ve ctor). In a RGB vector, the numbers should be between 0.0 and 1.0. For example, the color black, is described by the color vector <0,0,0>. And color white, is specified by the color vector <1,1,1>.
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Slide 9: Normal Vectors
normal vectors are used to specify an orientation, not a distance.
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Slide 10: Normal Vector (cont.)
POV-Ray is kind enough to automatically define three normal vectors for you x (corresponding to <1,0,0>), the normal vector for a plane lying along the y and z axe s y (corresponding to <0, 1, 0>), the normal vector for a plane lying along the x and z axe s, z (corresponding to <0, 0, 1>), the normal vector for a plane lying along the x and y ax es.
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Slide 11: POV-Ray Source Code
There are three things you need to know about POV-Ray source code
POV-Ray source code is case sensitive POV-Ray ignores whitespace Ordering is unimportant
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Slide 12: Source Code (cont.)
camera { location <0, 2.25, -35> direction <0, 0, 10> up <0, 1, 0> right <1, 0, 0> look_at <0, 0, 90> } camera { location <0, 2.25, -35> direction <0, 0, 10> up <0, 1, 0> rig ht <1, 0, 0> look_at <0, 0, 90>}
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Slide 13: Comments in POV-Ray Source Code
Comments can be enclosed in /* and */, or, for single-line comments, can be prefixed with a //. Example // this is a single-line comment /* this is another comment. it can be as long as you want it to be */
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Slide 14: Including files
Including files is a feature of many languages that makes re-using code e asier Adding the string #include "filename" to the beginning of your file. Example #include "colors.inc"
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Slide 15: Creating simple objects
The building blocks of all POV-Ray objects and scenes are called primitiv es. Primitives are objects that POV-Ra y already knows about, and all you ha ve to do is describe a few attributes. POV-Ray primitives are usually simple geometric shapes such as spheres, cu bes, and cones.
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Slide 16: Describing primitives
Object_Name { Object_Parameters Some_Simple_Attribute Some_Other_Simple_Attribute Some_ Complex_Attribute { Some_Attribute Some_Other_Attribute }
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Slide 17: Example
sphere { <0, 0, 0>, 5 pigment { color rgb <1, 0, 0> } }
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Slide 18: The Camera
This example defines a camera located at <2,5,-10> and pointing at the origin.
camera { location <2,5,-10> look_at <0,0,0> }
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Slide 19: Light sources
There are a few different types of light sources in POV-Ray. We will concentrate here on the most simple (and useful): the point light source. A point light source can be thought of a s an infinitely small object that emits l ight. <0,10,-10> color rgb <1,1,1> }
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light_source {
Slide 20: First POVRAY
// Persistence of Vision RayTracer version 2 Scene description file // File: Lesson_1.pov // Description: Chrome Sphere on checkers // Date: January 5, 2000 // Author: Pradondet Nilagupta // #include "shapes.inc" #include "colors.inc" #include "textures.inc"
camera { location <0, 2.25, -35> direction <0, 0, 10> up <0, 1, 0> right <1, 0, 0> look_at <0, 0, 90> } //Key Light light_source {<50, 100, -80> color White} //Back Light light_source {<100, 50, 80> color Blue} Jump to first page
Slide 21: First POVRAY
First we'll place our plane into the picture. At the end of your source file, type:
object { plane {y, 0} pigment {color rgb <1, 1, 1>} }
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Slide 22: First POVRAY
Now let's add the sphere. Type:
object { sphere {<0, 1.5, 1> 1.5} pigment {color rgb <1, 1, 1>} }
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Slide 23: Camera Again
The camera defines what you exactly you see when you render an image. camera { location <loc> sky <sky vector> up <up vector> right <right vector> direction <direction vector> look_at <target> /* translations, rotations, and scales */ }
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Slide 24: Camera Again
When declaring a camera, components that appear should do so in this order. This is bec ause some later components modify previou s ones, and putting them in the wrong order may result in your camera not doing exactly what you expect. Location is pretty self evident; it tells POVRay where in space to locate the camera. It t akes an <x, y, z> vector of the location.
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Slide 25: Camera Again
Sky is used to tell the camera which way is up. Modifying this value can be used to roll t he camera around its central axis. Up, right, and direction are used to modify the field of view and aspect ratio of the imag e. Direction and look_at are used to point the camera at a specific point in the scene. Direction is more typically used with up and r ight to define field of view then to position th e camera, though.
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Slide 26: Location
The location keyword tells POV-Ray where to position the camera. This parameter must always be specified. It takes an <x, y, z> vector which tells the location of the camera.
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Slide 27: Up Vector
The up vector is used to define the height of the viewing pyramid The default value of the up vector is "up <0, 1, 0>". This, together with the value "right <4/3, 0, 0>" (also default) defines the aspect ratio of the rendered imag e to be (4/3) / (1) = 4/3.
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Slide 28: Right Vector
The right vector controls the width of the view. The angular width of the viewing pyramid can be found with the followi ng equation. width = 2 * atan(|right| / |direction|)
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Slide 29: Direction
The direction vector is primarily used in conjunction with up and right to define the field of view. Increasing the magnitude of the direction vector "stretches" the viewing pyramid and creates a telephoto sort of effect. Decreasing the magnitude of the direction vector "compresses" the viewing pyramid an d gives the effect of a wide-angle camera.
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Slide 30: Direction
direction <0, 0, 0.5>
direction <0, 0, 1>
direction <0, 0, 2>
direction <0, 0, 4>
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Slide 31: Look At
The look_at parameter controls the orientation of the camera. It is by far the easiest way to get the camera to point at the thing you want it to point at. One thing to keep in mind when using look_at is that the location and look_at points should never be s et so that the camera is looking direct ly down (parallel to the y-axis).
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Slide 32: Sky
The vector tells the camera which way is up. This is not to be confused with the up vector which defines the aspect ratio. The default sky vector is <0, 1, 0>. By modifiying this value, you can roll the camera around its central axis. The sky vector, if specified, must appear before the look_at point is specified.
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Slide 33: Sky
The first image below is rendered with "sky <2, 1, 0>", and the second with "sky <0, -1, 0>".
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Slide 34: Common Object Types
plane, sphere, torus, box, cylinder, cone, lathe, prism (extruded shape), blob, and text.
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Slide 35: The Plane
The plane consists of only two values; which of the 3 major axis it cr osses, and it's position on that axis. T he plane will be perpendicular to the axis declared
object { plane {y, -1.5} //{axis, location} pigment {color rgb <.5,.5,.5>} }
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Slide 36: Sphere
The sphere also consists of only two values; the location, and the radius. The location defines the center of the sphere.
object { sphere {<0, .5, 0> 1} //{<location> radius} pigment {color rgb <1,1,1>} //scale <2,1,1> //scale to make an elipse }
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Slide 37: Torus
The torus definition consists of two radius statements. The first, or major radius extends from the center of the t orus to the mid-line of the rim. The sec ond, or minor radius defines the radiu s of the cross section of the rim.
object { torus {1.75, .5} //{outer radius, rad. of cross section} pigment {color rgb <1,1,1>} translate <0,.5,0> //must use translate to move } //its location.
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Slide 38: Box
POV defines boxes as two points. The points form opposite corners of the box such as lower back right and upp er front left.
object { box {<-1, -1, -1> // first corner position < 1, 1, 1>} // second corner position pigment {color rgb <1,1,1>} }
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Slide 39: Cylinder
object { cylinder {<0,-1,0>, <0,1,0>, 1 //{<1st point>, <2nd point>, radius //open //uncomment to make it a tube } pigment {color rgb <1,1,1>} }
A cylinder consists of 4 values. The first three, first point, second point, and radius are mandatory. Th e fourth, open, is optional.
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Slide 40: Cone
A cone is very similar to a cylinder; the difference being that you can define the radi us of both ends. The first point defines one e nd of the cone. The first radius defines the r adius of the cone at this point. The second p oint and its radius define the center of the ot her end of the cone
object{ cone {<0,-1,0>, 1.0, //{<1st point>, 1st radius <0,1,0>, 0.0 //{<2nd point>, 2nd radius //open //uncomment to make it open ended } pigment {color rgb <1,1,1>} }
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Slide 41: Color and Texture
object { sphere {<0, 1.5, 1> 1.5} pigment {color rgb <1, 1, 1>} } object { sphere {<0, 1.5, 1> 1.5} texture {PinkAlabaster} }
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Slide 42: Pigment
object { plane {y, 0} pigment {checker color rgb <0,0,1> color rgb <0,1,0>} scale 2 }
The pigment is defined as checker, and is given two colors. You could also use textures instead of colors to make, say, a black marbl e and white marble tile floor. The statement scale 2 scales the size of the squares.
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Slide 43: Finish
the term "finish" refers to the quality of the surface (shiny, dull, reflective, etc.). There are some pre-defined finishes in th e colors.inc file. object { sphere {<0, 1.5, 1> 1.5} pigment {color rgb <1, 1, 1>} finish { ambient .2 } }
ambient has to do witht he amount of light on the "shaddow" side of the object. Is it completel y dark (black) or sligh tly lit? .2 is pretty dar k, but not black.
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Slide 44: Diffuse and Specular
diffuse refers to the way the light changes from sark to light. A high number means the light changes from light to shaddow very gra dually; conversely, a low number (like 0.1) w ould have a very abrupt change from light to shaddow. specular is the small round highlight on the surface. A small number will create a tiny "dot" of "pure" light; a large number will cre ate a larger highlight.
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Slide 45: Diffuse and Specular
object { sphere {<0, 1.5, 1> 1.5} pigment {color rgb <1, 1, 1>} finish { ambient .2 diffuse .5 } } object { sphere {<0, 1.5, 1> 1.5} pigment {color rgb <1, 1, 1>} finish { ambient .2 diffuse .5 } specular .25 }
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Slide 46: Reflection
object { sphere {<0, 1.5, 1> 1.5} pigment {color rgb <1, 1, 1>} finish { ambient .2 diffuse .5 } specular .25 reflection 1 }
reflection is just that: reflection. 1 means the objects is 100% reflective (liek a mirror); 0 means there is no re flection.
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Slide 47: Transparency
object { sphere {<0, 1.5, 1> 1.5} pigment {color rgbf <1,1,1,.75>} finish { ambient .1 diffuse .5 specular .5 } }
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Slide 48: Finish Reference
finish { ambient ambient lighting brilliance brilliance crand crand amount diffuse diffuse lighting ior index of refraction metallic phong phong highlighting phong_size phong size reflection reflected light refraction refract toggle roughness roughness specular specular highlighting }
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Slide 49: Finish
The sum of the values of ambient, diffuse, and reflection should be about 1.0. Much hig her, and your colors will saturate and look fla t. Much lower, and your colors will appear da rk. Objects with reflection and refraction (actually, any object with a nonzero filter) wi ll increase your rendering time. Reflection re quires an extra ray to be traced to determine the reflected color, while with transparent ob jects, an extra ray must be traced to determi ne the color that is being filtered.
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Slide 50: Finish
You usually don't need both phong and specular highlights. The argument to refraction should be 1 or 0 only.
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Slide 51: Ambient
Them ambient finish controls how much of the color of a surface comes from ambient li ghting. Its parameter is a float value in the range 0.0 to 1.0 (typically). The default value is 0.1 Low values mean that objects which are not directly lit will retain some of their color. Higher values can make an object appear to glow
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Slide 52: Brilliance
Brilliance modifies the behavior of diffuse lighting. Brilliance takes a float parameter which modifies how diffuse light bounces off an obj ect. The default value is 1.0. The flatter this angle is, the less the surface is illuminated. Higher brilliance values make t he light illuminate less at flat angles The first image was rendered with the default, the second with brillance 5, and the third with brilliance 0.2.
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Slide 53: Crand
Crand can be used to simulate very rough surfaces like concrete and sand which have grainy surfaces. Crand takes a float parameter from 0.0 to 1.0. The default is 0.0 You should not use crand in animations. the first image is again the default, while the second has crand 0.1 thrown in
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Slide 54: Diffuse
Diffuse light is basically light that comes from a light source and diffuse s in all directions. The value can range from 0.0 (no light from light sources) to 1.0 (very well lit). The default value is 0.6. The first is the default, the second has diffuse 0.3, and the third has diff use 0.9.
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Slide 55: Ior
This value controls the index of refraction for transparent objects whi ch refract.
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Slide 56: Metallic
The metallic keyword is a modifier for the phong and specular highlights. Metallic takes no parameter; either it's there or it's not. The first was rendered with phong highlighting without metallic, and the second is with metallic
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Slide 57: Phong
The phong keyword creates a highlight on an object that is the color of the light source. Phong takes a float parameter which expresses how bright the highlight should be . The size of the highlight can be controlled with the phong_size parameter. First image: no highlights, second image: phong 0.9
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Slide 58: Phong Size
The phong_size parameter is a modifier for the phong finish. It takes a float parameter (greater than zero) which defines how large the phong highlight will be. Typical values ra nge from 1 (pretty dull) to 250 (very shiny). The default is 40. The images were rendered with "phong_size 40" (default), "phong_size 4", and "phong_size 180", respectively.
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Slide 59: Reflection
The reflection finish gives an object a mirrored or partially mirrored surface. This object will then reflect other objects in the scene. A value of 0 turns off reflection for the object, a value of 1 gives the object a perfectly mirrored surface (al most). The first scene has no reflection, the second has reflection 0.3.
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Slide 60: Refraction
Refraction only has meaning on objects that have at least a little bit of transparency. Refraction is the bending of light rays as the y pass into a more dense or less dense medi um You can change the ior of a refracting object with the "ior" keyword. Some examples of indices of refraction are "ior 1.000292" (air) "ior 1.33" (water), and "ior 1.5" (glass). The first image has no refraction, the second has "ior 1.5", and the third has "ior 2.0".
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Slide 61: Roughness
The roughness parameter controls the size of the highlight produced by the specular ke yword. Typical values range from 1.0 (sand paper) to 0.0005 (polished glass). The defaul t roughness is 0.05. High values give very a very soft, very large highlight. Small values give a very small, tigh t highlight. 0 is a very bad number for rough ness. All use "specular 0.9". The first uses the default roughness, the second uses "roughne ss 0.75", the third "roughness 0.001".
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Slide 62: Specular
The specular finish is similar to phong, but this one is more accurate as far as physical l aws are concerned. It produces a highlight o n the object where the reflection of the light source would be if the object were reflective The size of the highlight can be controlled (to some extent) with the roughness parame ter. Here's what specular (0.9) looks like.
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Slide 63: Normal Reference
Here's the general syntax for a bump map. normal { bump_map { type "filename" [bump_size size] [interpolate mode] [use_color] [use_index] [once] [map_type map mode] } }
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Slide 64: Normal
The normal component of a texture allows you to create effects on the surface of an obj ect Normals have three parts, the type, the modifiers, and then transformations. A normal can only have one type, and that is one of bumps, dents, ripples, waves, or wrinkles. They each take a depth parameter between 0.0 (Flat) and 1.0 (Violent).
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Slide 65: Normal
here's a standard ripples normal and another with "turbulence 0.7". Note the ripples have been translated to p ut their center on the top of the sphe re.
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Slide 66: Bumps
The bumps normal creates a random bumpy pattern on the object. The bumps normal takes a float parameter from 0.0 (Flat) to 1.0 (Mou ntainous) that describes the depth of the bumps.
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Slide 67: Dents
The surface appears to have dents (naturally enough) beaten into it. Dents takes a float parameter from 0. 0 (Brand New) to 1.0
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Slide 68: Ripples
The ripples normal creates evenly space, smooth ripples which originate from 10 random locations inside the b ox with corners <0, 0, 0>, <1, 1, 1>. All the waves have the same frequenc y, so the ripple effect is smooth at a s ignificant distance from the center.
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Slide 69: Waves
Waves are similar to ripples, except instead of creating smooth, even ripples, it creates more rough and tu mble waves. Theoretically these look more like deep ocean waves. The wa ves normal takes the standard 0.0 (B ecalmed) to 1.0 (Tsunami) parameter .
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Slide 70: Wrinkles
This normal specifier basically makes the object look like it had been wadd ed up and then stretched back out ag ain.
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Slide 71: Declarations (variables)
Variables are a way to store and recall frequently used items. In POV variables (declarations) can store a n umber, a word, an entire object, or e ven an ent ire scene. Example
#declare sizeOfSphere = 1.5 object { sphere {<0, 1.5, 1> sizeOfSphere} pigment {color rgb <1, 1, 1>} }
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Slide 72: Declarations
Example #declare MyPrettyWhite = rgb <1,1,1> object { sphere {<0, 1.5, 1> 1.5} pigment {MyPrettyWhite} }
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Slide 73: Declarations
#declare #declare #declare #declare XPosition = 0 ZPosition = 1 MyPrettyWhite = rgb <1,1,1> MyRadius = .5
object { sphere {< XPosition, .5, ZPosition > MyRadius} pigment {MyPrettyWhite} }
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Slide 74: Declarations
#declare WhiteBall = sphere { < XPosition, MyRadius, ZPosition > MyRadius pigment {MyPrettyWhite} } Now replace the code for each of the objects so that it looks like this: object {WhiteBall}
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Slide 75: Declarations
#declare MyPrettyWhite = rgb <1,1,1> #declare MyRadius = .5 #declare XPosition = 0 #declare ZPosition = 1 #include "shapes.inc" #declare WhiteBall = sphere { < XPosition, MyRadius, ZPosition > MyRadius pigment {MyPrettyWhite} } camera { location <0, 2.25, -35> direction <0, 0, 10> up <0, 1, 0> right <1.25, 0, 0> look_at <0, 0, 90> } //Key Light light_source {<50, 100, -80> color MyPrettyWhite} //Back Light light_source {<100, 50, 80> color rgb <0,0,1>} object { plane {y, 0} pigment {MyPrettyWhite} scale 2 } #declare BallCount = 1 #while (BallCount < 21) object {WhiteBall} #declare MyRadius = MyRadius + . 1 #declare XPosition = XPosition + .1 #declare ZPosition = ZPosition + 4 #declare WhiteBall = sphere { < XPosition, MyRadius, ZPosition > M yRadius pigment {MyPrettyWhite}} #declare BallCount = BallCount + 1 #end
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Slide 76: Declarations
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Slide 77: Transformations
Transformations, in ray-tracing terms, are attributes that change the position, size or orientation of objects (and of the various attributes of the o bjects). The most common types of transformations, and the ones that P OV-Ray supports, are translations, rot ations and scalings.
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Slide 78: Translation
A translation is a transformation that moves an object relative to its current position. A translation of <-1,4,2> results in the cube being moved left one unit, up four, and back two.
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Slide 79: Rotation
A rotation is a transformation that changes the orientation of an object (the way that it's facing). A rotation of <0,0,45> rotates the cube 45 degrees around the z axis,
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Slide 80: Rotation
if we translated the cube first, and then rotated it
if we rotated the cube first, and then translated it
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Slide 81: Scaling
Scaling changes the size of the object with respect to its current size. If we scaled the object with the string scale <1,4,1>, we would get a result like this
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Slide 82: Example
torus { 3, 11 pigment { color Yellow } scale <1.5,1,1> rotate <-45,0,0> translate <0,2,0> } This code makes a yellow torus, slightly widened around the x axis, ro tated -45 degrees around the x axis a nd with its center at <0,2,0>.
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Slide 83: Constructive Solid Geometry
The five types of CSG are: Union Merge Intersection Difference Inverse
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Slide 84: Union
Union is a way of joining objects together. union{ object{greenBox} object{redTorus} rotate <20, -65, 0> }
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Slide 85: Merge
#declare greenBox = box{ <-2, 1, -2>, <2, -1, 2> pigment{color rgbf <0, 1, 0, .5>} } #declare redTorus = torus{ 1.25, // MAJOR radius (0,0,0 to midline of ring 0.5 // MINOR radius (radius of cross section of ring pigment{color rgbf <1, 0, 0, .5>} translate 1*y }
Render the image and you'll see that the torus now does not ex tend inside the box.
merge{ object{greenBox} object{redTorus} rotate <20, -65, 0> }
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Slide 86: Union and Merge
Union
Merge
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Slide 87: Intersection
Intersection renders only the areas where the objects in the CSG intersec t, or overlap.
intersection{ object{greenBox} object{redTorus} rotate <20, -65, 0> }
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Slide 88: Difference
POV will render the first object minus any following objects.
difference{ object{greenBox} object{redTorus} rotate <20, -65, 0> }
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Slide 89: Troubleshooting
CSG has one major flaw that you should be aware of. When surfaces of CSG objects are identical, strange arti facts can appear. difference{ object{greenBox} box{ <-1, 1, -1>, <1, -1, 1> pigment{color rgb <1, 0, 0>} } rotate <20, -65, 0> }
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Slide 90: Troubleshooting
That is because as rays from the light source(s) reach the two objects, sometimes t hey hit the red box first, and other times the y hit the green box first. The problem is eliminated by ensuring the objects in a CSG have "clearance" from each other. Stretching the y values of the red box beyond those of the green box alleviates the problem.
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Slide 91: Troubleshooting
difference{ object{greenBox} box{ <-1, 1.5, -1>, <1, -1.5, 1> pigment{color rgb <1, 0, 0>} } rotate <20, -65, 0> } Rendered without the difference to show the overlap or "clearance."
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Slide 92: END
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