The #set keyword modifies the most recently created version of a variable. So, if a variable has been created previously with either #declare or #local, its value can be changed with the #set directive.
Example 2.2. Using the #set directive
#declare MyCounter = 0: #set MyCounter = MyCounter + 1;
One advantage is that it makes it more visually clear where variables are 'created', and where they are only 'changed'.
Another advantage is that if you try to change a variable that doesn't yet exist, it produces an error. This could happen if you make a typing mistake, like this:
#declare MyCounter = 0; #while (MyCounter < 10) #declare MyCountr = MyCounter+1; #end
This would normally cause an infinite loop, and may take a while to track down, especially in complex scenes and with typos that "look right" at a glance. If #set was used, it would cause an error ("#set cannot assign to uninitialized identifier MyCountr.") at that line, pointing you directly at the problem.
POV-Ray™ 3.5 in its official release does not accept all built-in constants and variables to be used in functions. Following tokens are recognized additionally in VM since MegaPOV 1.0: clock_delta, clock_on, false, final_clock, final_frame, frame_number, initial_clock, initial_frame, image_height, image_width, no, off, on, true, version, yes . All mentioned tokens return the same values as in the whole SDL parser.
As other animation options, also Frame_Step has its own equivalent in SDL. You can use the frame_step key-word to get the value which was passed to Frame_Step (see Section 2.1.1, “Frame_Step”). Default value is 1.
With the keyword date, time and/or a date can be used in your images. This might be useful in a macro to place a time stamp in your images, along with your name. The keyword date works like other string functions, except that you have to supply a format string.
Example 2.3. date function usage
Suppose it's Saturday 1 January. The following script:
#declare TheString=date("%a %B")
will return the string: Sat January
The most flexible implementation was chosen (which is probably not the easiest ...) because not all countries write dates in the same way. Just think of the difference between the USA and most parts of Europe. These are the possible specifiers for the format string: Please note that these should be equal for all platforms but if you don't get the expected result, contact the person who compiled your version to find out if there are differences.
Table 2.1. The following time formatting strings are available:
a | Abbreviated weekday name. |
A | Full weekday name. |
b | Abbreviated month name. |
B | Full month name. |
c | The strftime() format equaling the format string of "%x %X". |
d | Day of the month as a decimal number. |
H | The hour (24-hour clock) as a decimal number from 00 to 23. |
I | The hour (12-hour clock) as a decimal number from 01 to 12 |
j | The day of the year as a decimal number from 001 to 366 |
m | The month as a decimal number from 01 to 12. |
M | The minute as a decimal number from 00 to 59. |
p | "AM" or "PM". |
S | The seconds as a decimal number from 00 to 59. |
U | The week number of the year as a decimal number from 00 to 52. Sunday is considered the first day of the week. |
w | The weekday as a decimal number from 0 to 6. Sunday is (0) zero. |
W | The week of the year as a decimal number from 00 to 51. Monday is the first day of the week. |
x | The date representation of the current locale. |
X | The time representation of the current locale. |
y | The last two digits of the year as a decimal number. |
Y | The century as a decimal number. |
z | The time zone name or nothing if it is unknown. |
% | The percent sign is displayed. |
Note: | |
---|---|
To use the '%' character in the result, use it twice: date("%%") |
Refer to date.pov for an example scene. Please note that you might have to write the result in a file if you want to abort the rendering and continue later on. Otherwise you could get a different result because time goes on :-)
The keyword start_chrono sets an internal variable and returns the current internal clock counter of your computer. The return value is not important. However, you must assign this return value from start_chrono otherwise you get an error. Use it like this:
#declare Stopwatch = start_chrono;
or use it like this:
#if (start_chrono)
but not:
start_chrono //parsing stops with a fatal error
The keyword current_chrono returns the time in full seconds (no fractions of seconds) between start_chrono and current_chrono. The start value is not changed. A second current_chrono will still return the seconds between start_chrono and the second current_chrono.
If you don't call start_chrono somewhere before you call current_chrono, you will get the seconds elapsed since the beginning of the current render (parsing).
Example 2.4. Using the timer function
//reset the chrono and return the internal clock counter #declare ParseStart = start_chrono; ... syntax to be parsed //read the seconds elapsed since chrono_start #declare ParseEnd = current_chrono; #debug concat("\nParsing took ",str((ParseEnd, 1, 0)," seconds\n")
Refer to chrono.pov for a demo scene.
Some animators want to use filenames of previous, already rendered frames to average them to mimic motion_blur in one turn. But the concatenation of filename with frame number is not a trivial thing and can be platform dependant. MegaPOV allows you to get n-th filename of current animation. For stills it always returns filename without numbers.
#declare File_Name=output_filename(Frame_Number)
Example 2.5. Averaging frames with output_filename function
You can force every 10th frame to be averaged content of previous nine frames, this way:
#if(mod(frame_number,10)=9) #declare Averaged_Frames=pigment{ average #local Counter=1; #while(Counter<10) [1 image_map{output_filename(frame_number-Counter)}] #set Counter=Counter+1; #end } // placing of pigment in output area #else // conventional scene #end
You probably already know that the image_width and image_height keywords return the sizes of a rendered image. But there are cases when you would like to change the content of a scene depending on the sizes of the images used for maps. For this purpose the image_width and image_height keywords are extended with an optional parameter which is the identifier of an item using an image.
#declare Identifier=image_width [ (ITEM_WITH_IMAGE) ]; #declare Identifier=image_height [ (ITEM_WITH_IMAGE) ]; ITEM_WITH_IMAGE: PIGMENT_ID | NORMAL_ID | TEXTURE_ID
The usage of the dimension_size is extended since MegaPOV 1.1 with a measurement of floats, vectors and colors. If you want to write a universal script which works differently depending on the number of components in an identifier, you can use the dimension_size to get 1,2,3,4 or 5 as number of the components in the given identifier.
#declare Identifier=dimension_size ( FLOAT | VECTOR | COLOR );
MegaPOV 1.1 allows the verification of the type (and in some cases subtypes) of identifiers. It is possible thanks to the is function which tests the internal type of an identifier.
#declare Identifier=is ( IDENTIFIER , TYPE | SUBTYPE ); TYPE: array | camera | color | color_map | density | density_map | finish | float | fog | function | interior | light_source | material | media | normal | normal_map | object | pigment | pigment_map | rainbow | sky_sphere | slope_map | spline | string | texture | texture_map | transform | vector SUBTYPE: SPLINE_TYPE | OBJECT_TYPE | CAMERA_TYPE SPLINE_TYPE: akima_spline | basic_x_spline | cubic_spline | extended_x_spline | general_x_spline | linear_spline | natural_spline | quadratic_spline | sor_spline | tcb_spline OBJECT_TYPE: bicubic_patch | blob | box | cone | cubic | cylinder | disc | height_field | intersection | isosurface | julia_fractal | lathe | merge | mesh | parametric | plane | poly | polygon | prism | quadric | quartic | smooth_triangle | sor | sphere | sphere_sweep | superellipsoid | text | torus | triangle | union CAMERA_TYPE: cylinder | fisheye | omnimax | orthographic | panoramic | perspective | spherical | ultra_wide_angle | user_defined
An example using the is keyword can be found in the mp_types.inc include file (see Section 3.3, “The 'mp_types.inc' include file”).
MegaPOV delivers new pre-defined functions. These new internal functions can be accessed through the mp_functions.inc include file, so it should be included in your scene to make use of them.
f_triangle function has 10 parameters:
FLOAT f_triangle(
FLOAT V1x, FLOAT V1y, FLOAT V1z, FLOAT V2x, FLOAT V2y, FLOAT V2z, FLOAT V3x, FLOAT V3y, FLOAT V3z, FLOAT Thickness)
;
The parameters V1x, V1y, V1z describe the coordinates of the first vertex in the triangle.
The parameters V2x, V2y, V2z describe the coordinates of the second vertex in the triangle.
The parameters V3x, V3y, V3z describe the coordinates of the third vertex in the triangle.
The parameter Thickness describes how thick the triangle is.
Note | |
---|---|
In order to achieve the fastest calculation, try to pass the parameters so that the side V1-V2 represents the longest side and V1-V3 represents the shortest side. |
The polynomial solver is accessible from scripts via the float functions n_roots and nth_root with the following syntax:
INT n_roots(
FLOAT an, ..., FLOAT a0, BOOL sturm_flag, FLOAT epsilon)
;
FLOAT nth_root(
FLOAT nth, FLOAT an, ..., FLOAT a0, BOOL sturm_flag, FLOAT epsilon)
;
n_roots returns the number of roots derived from the polynomial given by the parameters a_{n}, ..., a_{0} and calculated under the conditions specified by the parameters sturm_flag and epsilon.
nth_root returns the value of the nth root of a given polynomial.
The sturm flag turns on a different algorithm of calculation. Its usage influences the number of returned roots. Epsilon (positive) value means that the roots below Epsilon value are ignored. Epsilon=0 means that none of the roots are ignored.
Important | |
---|---|
You don't have to call n_roots before nth_root, but if you do call nth_root with the wrong root number then it causes an error and breaks parsing. It is better to call n_roots first to verify the number of available roots. |
Example 2.6. Polynomial solver usage
Imagine that we have x^{3}+6*x^{2}-x-6 and that we are interested in its roots for further calculations. So if we declare:
#declare N=n_roots(1, 6, -1, -6, off, 0);
then N has value 3 because the mentioned equation has 3 roots. If we are interested in what roots it has, we can use the following calls:
#declare R0=nth_root(0, 1, 6, -1, -6, off, 0); #declare R1=nth_root(1, 1, 6, -1, -6, off, 0); #declare R2=nth_root(2, 1, 6, -1, -6, off, 0);
And it returns R0=-6, R1=1 and R2=-1. So finally we know that x^{3}+6*x^{2}-x-6=(x+6)*(x-1)*(x+1) .
Splines in POV-Ray™ can be used to create objects through rotation, translation or by being a border of a surface. Usually it is hard to match those surfaces with calculations developed in SDL because they are mostly hard-coded within the source core code of POV-Ray™. The spline feature introduced in POV-Ray™ 3.5 makes such operations much easier but some spline types are still missing. sor_spline is introduced to access the surface of the sor object in SDL.
To use the data from the sor object in a sor_spline, the order of coordinates has to be changed. The old y coordinate is now the clock value in the spline. The advantage is that one sor_spline can hold data from five old sor-s. That's because every spline can operate up to five dimensions along the clock value.
Example 2.7. Conversion from the sor object definition to the sor_spline type in spline
spline{ sor_spline -1.000000,0.000000*x 0.000000,0.118143*x 0.540084,0.620253*x 0.827004,0.210970*x 0.962025,0.194093*x 1.000000,0.286920*x 1.033755,0.468354*x } sor{ 7 <0.000000, -1.000000> <0.118143, 0.000000> <0.620253, 0.540084> <0.210970, 0.827004> <0.194093, 0.962025> <0.286920, 1.000000> <0.468354, 1.033755> }
An akima_spline is a spline that goes smoothly (pleasingly for some) through all points. ACM Press abstracts original work of Hiroshi Akima:
This method is devised in such a way that the resultant curve will pass through the given points and will appear smooth and natural. It is based on a piecewise function composed of a set of polynomials, each of degree three, at most, and applicable to successive intervals of the given points. In this method, the slope of the curve is determined at each given point locally, and each polynomial representing a portion of the curve between a pair of given points is determined by the coordinates of and the slopes at the points. Comparison indicates that the curve obtained by this new method is closer to a manually drawn curve than those drawn by other mathematical methods. | ||
--The Guide to Computing Literature. |
Syntax is:
spline { akima_spline time_Val_1, <Vector_1> [,] time_Val_2, <Vector_2> [,] ... time_Val_n, <Vector_n> }
This spline is also known as Kochanek-Bartels spline.
Syntax is:
spline { tcb_spline [TCB_PARAMETERS] time_Val_1 [TCB_PARAMETERS], <Vector_1> [TCB_PARAMETERS][,] time_Val_2 [TCB_PARAMETERS], <Vector_2> [TCB_PARAMETERS][,] ... time_Val_n [TCB_PARAMETERS], <Vector_n> [TCB_PARAMETERS] } TCB_PARAMETERS: [tension FLOAT] [continuity FLOAT] [bias FLOAT]
The tension, continuity and bias are fully optional. Depending on the place where they appear, they control the spline in different ways:
What is controlled by these parameters?
Note | |
---|---|
A tcb_spline needs additional control points before and after the spline. This is required to control the first and last segment of the spline. |
A very nice property of x splines is that they can go through a control point as well as just approximate it.
Syntax is:
spline { basic_x_spline [freedom_degree FLOAT] time_Val_1, <Vector_1> [,] time_Val_2, <Vector_2> [,] ... time_Val_n, <Vector_n> }
Note | |
---|---|
A basic_x_spline needs additional control points before and after the spline. This is required to control the first and last segment of the spline. |
The extended_x_spline offers the possibility to mix smooth curves and sharp edges in an unrestricted way in one spline.
Syntax is:
spline { extended_x_spline [freedom_degree FLOAT] time_Val_1, <Vector_1> [freedom_degree FLOAT ][,] time_Val_2, <Vector_2> [freedom_degree FLOAT ][,] ... time_Val_n, <Vector_n> [freedom_degree FLOAT ] }
Since MegaPOV 1.0 it is possible to read values stored in a spline with a notation similar to an array. Previously once the spline was declared, it was only possible to evaluate it for a specified argument. Now two new usages are possible: you can get the number of entries and read the exact values placed in splines.
SPLINE_USAGE: SPLINE_EVALUATION | SPLINE_MEASUREMENT | SPLINE_ENTRY SPLINE_EVALUATION: #declare Spline_Value = MySpline(Val); #declare Spline_Value = MySpline(Val, SPLINE_TYPE); SPLINE_MEASUREMENT: #declare Number_Of_Entries = dimension_size( MySpline ); SPLINE_ENTRY: #declare Float_Time_Parameter = MySpline[ Counter ][ 0 ]; #declare Vector_Value_Of_Entry = MySpline[ Counter ][ 1 ];
This patch adds a new option to the transform syntax that modifies the transform to be suited for transforming normal vectors.
When a mesh is transformed by the transformation matrix M the normals need to be transformed with the transpose of the inverse of M. This is handled automatically by this patch.
Syntax is:
transform { ... normal on|off }
The default value is off so you get a standard transform.