2.1.2.2 General Output Options

2.1.2.2.1 Height and Width of Output

These switches set the height and width of the image in pixels. This specifies the image size for file output. The preview display, if on, will generally attempt to pick a video mode to accommodate this size but the display settings do not in any way affect the resulting file output.

2.1.2.2.2 Partial Output Options

When doing test rendering it is often convenient to define a small, rectangular sub-section of the whole screen so you can quickly check out one area of the image. The Start_Row, End_Row, Start_Column and End_Column options allow you to define the subset area to be rendered. The default values are the full size of the image from (1,1) which is the upper left to (w,h) on the lower right where w and h are the Width=n and Height=n values you have set.

Note: if the number specified is greater than 1 then it is interpreted as an absolute row or column number in pixels. If it is a decimal value between 0.0 and 1.0 then it is interpreted as a percent of the total width or height of the image.

For example: Start_Row=0.75 and Start_Column=0.75 starts on a row 75% down from the top at a column 75% from the left. Thus it renders only the lower-right 25% of the image regardless of the specified width and height.

The +SR, +ER, +SC and +EC switches work in the same way as the corresponding INI-style settings for both absolute settings or percentages. Early versions of POV-Ray allowed only start and end rows to be specified with +Sn and +En so they are still supported in addition to +SR and +ER.

When rendering a subset of *columns* (+sc/+ec) POV-Ray generates a full width image and fills the not rendered columns with black pixels. This should not be a problem for any image reading program no matter what file format is used.

when rendering a subset of *rows* (+sr/+er) POV-Ray writes the full height into the image file header and only writed those lines into the image that are rendered. This can cause problems with image reading programs that are not checking the file while reading and just read over the end.

if POV-Ray wrote the actual height of the partial image into the image header there would be no way to continue the trace in a later run.

2.1.2.2.3 Interrupting Options

On some operating systems once you start a rendering you must let it finish. The Test_Abort=on option or +X switch causes POV-Ray to test the keyboard for keypress. If you have pressed a key, it will generate a controlled user abort. Files will be flushed and closed but only data through the last full row of pixels is saved. POV-Ray exits with an error code 2 (normally POV-Ray returns 0 for a successful run or 1 for a fatal error).

When this option is on, the keyboard is polled on every line while parsing the scene file and on every pixel while rendering. Because polling the keyboard can slow down a rendering, the Test_Abort_Count=n option or +Xn switch causes the test to be performed only every n pixels rendered or scene lines parsed.

2.1.2.2.4 Resuming Options

If you abort a render while it is in progress or if you used the End_Row option to end the render prematurely, you can use Continue_Trace=on or +C option to continue the render later at the point where you left off. This option reads in the previously generated output file, displays the partial image rendered so far, then proceeds with the ray-tracing. This option cannot be used if file output is disabled with Output_to_file=off or -F.

The Continue_Trace option may not work if the Start_Row option has been set to anything but the top of the file, depending on the output format being used. Also POV-Ray cannot continue the file once it has been opened and saved again by any program

POV-Ray tries to figure out where to resume an interrupted trace by reading any previously generated data in the specified output file. All file formats contain the image size, so this will override any image size settings specified. Some file formats (namely TGA and PNG) also store information about where the file started (i. e. +SCn and +SRn options), alpha output +UA, and bit-depth +FNn, which will override these settings. It is up to the user to make sure that all other options are set the same as the original render.

The Create_Ini option or +GI switch provides an easy way to create an INI file with all of the rendering options, so you can re-run files with the same options, or ensure you have all the same options when resuming. This option creates an INI file with every option set at the value used for that rendering. This includes default values which you have not specified. For example if you run POV-Ray with...

 POVRAY +Isimple.pov MYOPTS +GIrerun.ini MOREOPTS

POV-Ray will create a file called rerun.ini with all of the options used to generate this scene. The file is not written until all options have been processed. This means that in the above example, the file will include options from both myopts.ini and moreopts.ini despite the fact that the +GI switch is specified between them. You may now re-run the scene with...

 POVRAY RERUN

or resume an interrupted trace with

 POVRAY RERUN +C

If you add other switches with the rerun.ini reference, they will be included in future re-runs because the file is re-written every time you use it.

The Create_Ini option is also useful for documenting how a scene was rendered. If you render waycool.pov with Create_Ini=on then it will create a file waycool.ini that you could distribute along with your scene file so other users can exactly re-create your image.