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<pclass="Note"><strong>Note:</strong> In version 3.7 the <code>hf_gray_16</code> keyword in the <code>global_settings</code> block has been deprecated. If encountered, it has no effect on the output type and will additionally generate a warning message.</p>
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<p>However grayscale output can still be used to generate heightfields for use in other POV-Ray scenes, and now should be specified by using <code>Grayscale_Output=true</code> as an INI option, or <code>+Fxg</code> (for output type 'x') as a command-line option. For example, <code>+Fng</code> for PNG and <code>+Fpg</code> for PPM (effectively PGM) grayscale output. By default this option is off.</p>
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<p>With <code>Grayscale_Output=true</code>, the <strong>output file</strong> will be in the form of a grayscale image that can be used to generate heightfields, because the height at any point is dependent on the brightness of the pixel. The brightness of a pixel is calculated in the same way that color images are converted to grayscale images:<em><code> height = 0.3 * red + 0.59 * green + 0.11 * blue</code></em>.</p>
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<p>It should also be noted that setting the <code>Grayscale_Output=true</code> INI option will <strong>NOT</strong> cause the preview display, if used, to be grayscale rather than color. See the section <ahref="r3_5.html#r3_5_1_1_5">Height Field</a> for a description of how POV-Ray heightfields are stored for each file type.</p>
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<pclass="Note"><strong>Note:</strong> Grayscale output implies the maximum bit-depth the format supports is 16, it is not valid to specify bits per color channel with 'g' (e.g. <code>+Fng16</code> is not allowed, and nor for that matter is <code>+Fn16g</code>). If bits per channel is provided via an INI option, it is ignored.</p>
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<p>Currently PNG, and PPM are the only file formats that support grayscale output.</p>
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<p>A <fontclass="Change">Change</font> as of version 3.7 has deprecated the <code>hf_gray_16</code> keyword in the <code>global_settings</code> block. If encountered, it has no effect on the output type and will additionally generate a warning message. Grayscale output can still be used to generate heightfields for use in other POV-Ray scenes. See: <ahref="r3_2.html#r3_2_4_1">Output File Type</a> for details.</p>
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</div>
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<aname="r3_4_1_5"></a>
@@ -899,6 +889,7 @@ <h5>3.4.2.1.5 Up and Right Vectors</h5>
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visible. All viewing rays are perpendicular to the y-axis. For type 2 and 4,
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the cylinder lies along the <code>right</code> vector. Viewing rays for type
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4 are perpendicular to the <code>right</code> vector.</p>
<pclass="Note"><strong>Note:</strong> The <code>up</code>, <code>right</code>, and <code>direction</code> vectors should always remain perpendicular to each other or the image will be distorted. If this is not the case a warning message will be printed. The vista buffer will not work for non-perpendicular camera vectors.</p>
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</div>
@@ -907,7 +898,7 @@ <h5>3.4.2.1.5 Up and Right Vectors</h5>
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<h5>3.4.2.1.6 Aspect Ratio</h5>
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<p>Together the <code>right</code><em>(width)</em> and <code>up</code><em>(height)</em> vectors define the <em>aspect ratio</em> of the resulting image.</p>
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<p>A <fontclass="Change">Change</font> in version 3.8 redefines how the <code>right</code> vector default is derived. Previously a fixed value, it is now a calculated value that is based on the image width and height specified at render time. As usual, the image width and height can be specified from either the pull down menu available in <em>GUI</em> versions <em>ONLY</em> or the <code>+Wn</code> and <code>+Hn</code> command-line options available to <em>ALL</em> versions. This behavior is conditional upon the <em>last</em> effective <code>#version</code> directive before the camera definition. The default <code>up</code> vector remains as <code><0,1,0></code>.</p>
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<p>A <fontclass="Change">Change</font> in version 3.8 redefines how the <code>right</code> vector default is derived. The default setting is now <code>right <image_width/image_height,0,0></code> as opposed to the <code>right <1.33,0,0></code>value used in previous versions. Requires <code>#version 3.8;</code> or equivalent INI setting or command-line option. See also: <ahref="r3_3.html#r3_3_2_5">Version Directive</a>. As usual, the image width and height can be specified from either the pull down menu available in <em>GUI</em> versions <em>ONLY</em> or the <code>+Wn</code> and <code>+Hn</code> command-line options available to <em>ALL</em> versions. The default <code>up</code> vector remains as <code><0,1,0></code>.</p>
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<p>To retain legacy behavior see the example below:</p>
<p>The following parameters deal with configuring radiosity and how it interacts with other features. See also these additional command line <ahref="r3_2.html#r3_2_8_8">options</a> for more control.</p>
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<p>The following parameters deal with configuring radiosity and how it interacts with other features. See also these additional command line <ahref="r3_2.html#r3_2_8_9">options</a> for more control.</p>
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</div>
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<aname="r3_4_3_3_4_1"></a>
@@ -2459,7 +2450,7 @@ <h6>3.4.3.3.4.4 Normal and Radiosity</h6>
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<divclass="content-level-h6" contains="Save and Load Radiosity Data" id="r3_4_3_3_4_5">
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<h6>3.4.3.3.4.5 Save and Load Radiosity Data</h6>
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<p>In general, it is not a good idea to save and load radiosity data if scene objects are moving. Even after the data is loaded, more samples may be taken during the final rendering phase, particularly if you've specified <code>always_sample on</code>.</p>
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<pclass="Note"><strong>Note:</strong> The method to load and save radiosity data has been changed to a command line option. See section <ahref="r3_2.html#r3_2_8_8_2">radiosity load and save</a> for more details.</p>
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<pclass="Note"><strong>Note:</strong> The method to load and save radiosity data has been changed to a command line option. See section <ahref="r3_2.html#r3_2_8_9_2">radiosity load and save</a> for more details.</p>
<p>You should note that the number of spline segments, i. e. curves between two points, depends on the spline type used. For linear splines you get n-1 segments connecting the points P[i], i=1,...,n. A quadratic spline gives you n-2 segments because the last point is only used for determining the slope, as explained above (thus you will need at least three points to define a
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quadratic spline). The same holds for cubic splines where you get n-3 segments with the first and last point used only for slope calculations (thus needing at least four points). The bezier spline requires 4 points per segment, creating n/4 segments.</p>
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<p>If you want to get a closed quadratic and cubic spline with smooth transitions at the end points you have to make sure that in the cubic case P[n-1] = P[2] (to get a closed curve), P[n] = P[3] and P[n-2] = P[1] (to smooth the transition). In the quadratic case P[n-1] = P[1] (to close the curve) and P[n] = P[2].</p>
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<p>The surface normal determination for lathes depends upon the order in which the splines points are specified. The following code will render with the color Red on the outside and the color Blue on the inside.</p>
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<p>The surface normal determination for lathes depends upon the order in which the splines points are specified. For <code>interior_texture</code> to work as expected, the outline of the underlying 2D shape must be specified in counter-clockwise order, except for holes which must be specified in clockwise order, and they must not self-intersect.</p>
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<p>The following code will render with the color Red on the outside and the color Blue on the inside.</p>
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<pre>
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#declare Lathe_InitialOrder = lathe {
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bezier_spline
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<p>The <code>bezier_spline</code> is an alternate kind of cubic spline. Points 1 and 4 specify the end points of a segment and points 2 and 3 are control points which specify the slope at the endpoints. Points 2 and 3 do not actually lie on the spline. They adjust the slope of the spline. If you draw an imaginary line between point 1 and 2, it represents the slope at point 1. It is a line tangent to the curve at point 1. The greater the distance between 1 and 2, the flatter the curve. With a short tangent the spline can bend more. The same holds true for control point 3 and endpoint 4. If you want the spline to be smooth between segments, point 3 and 4 on one segment and point 1 and 2 on the next segment must form a straight line and point 4 of one segment must be the same as point one on the next segment.</p>
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<p>By default linear sweeping is used to create the prism, that is, the prism's walls are perpendicular to the x-z plane. The size of the curve does not change during the sweep. You can also use <code>conic_sweep</code> that leads to a prism with cone-like walls by scaling the curve down during the sweep.</p>
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<p>Like cylinders the prism is normally closed. You can remove the caps on the prism by using the <code>open</code> keyword. If you do, you should not use it in CSG operations, because the result may not be as expected.</p>
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<p>The surface normal determination for prism sides depends upon the order in which the splines points are specified. Prism ends have normals which face outward at one end and inward at the other end. The following code will render sides with the color Red on the outside and the color Blue on the inside.</p>
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<p>The surface normal determination for prism sides depends upon the order in which the splines points are specified. Prism ends have normals which face outward at one end and inward at the other end. For <code>interior_texture</code> to work as expected, the outline of the underlying 2D shape must be specified in counter-clockwise order, except for holes which must be specified in clockwise order, and they must not self-intersect.</p>
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<p>The following code will render sides with the color Red on the outside and the color Blue on the inside.</p>
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<pre>
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#declare Prism_InitialOrder = prism {
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linear_spline
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}
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</pre>
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<p>The actual normal determination is more complicated for complex splines. If the surface normal is important to the visual result, it is best to check how the prism is being rendered by testing with substantially different inside and outside textures.</p>
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<p>There is presently a inconsistency with the bezier spline mode of the prism in that the point order with respect to side surface normals is reversed from all other prism spline types. The behavior of the bezier spline prism will likely be aligned with the other spline types in a later release. Further end behavior may be made consistent for all spline types.</p>
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<p>If additional accuracy is required you can add the <code><ahref="r3_5.html#r3_5_1_5_11">sturm</a></code> object modifier.</p>
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<p>For an explanation of the spline concept read the description for the <ahref="r3_5.html#r3_5_1_1_8">Lathe</a> object.</p>
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<p>See also the tutorials on <ahref="t2_3.html#t2_3_1_1">Lathe</a> and <ahref="t2_3.html#t2_3_1_3">Prism</a> objects.</p></div>
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