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<A HREF="toc.html">Contents</A>
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<HR NOSHADE>
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<H3><A NAME="10_18_1">10.18.1 Enabling anti-aliased lines</A></H3>
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<P> Anti-aliased lines are enabled by calling the method <A href="../ref/Image.html#_IMAGE_SETANTIALIASING">
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SetAntiAliasing()</A> in the <A href="../ref/Image.html#_C_IMAGE">
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Image class</A> in the script where you want to use anti-aliasing.</P>
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<P> The anti-aliasing for lines works by "smoothing" out the edges on
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the line by using a progressive scale of colors interpolated between
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the background color and the line color.</P>
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<P><DIV class="note"><B>Note:</B> The algorithm used for anti-aliasing
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of lines is quite simple. It would be possible to achieve even better
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result by doing some real 2D signal processing. However, doing real
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time 2D signal processing on a HTTP server would be foolish so the
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design is deliberately kept simple. To achieve best visual result
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always use a dark line color on a light background.</DIV></P>
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<P> An example will show that this, quite simple algorithm, gives a
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reasonable good result. The figures below shows a radar plot with and
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without anti-aliasing.</P>
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<P><DIV class="example">
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<BR> <A href="exframes/frame_radarex8.html" target="blank"><IMG border="0"
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HEIGHT="200" src="img/radarex8.png" WIDTH="300"></A>
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<BR><B>Figure 170:</B> Spiderplot without anti-aliasing <A href="exframes/frame_radarex8.html"
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target="blank">[src]</A>
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<P></P>
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</DIV></P>
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<P></P>
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<P><DIV class="example">
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<BR> <A href="exframes/frame_radarex8.1.html" target="blank"><IMG border="0"
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HEIGHT="200" src="img/radarex8.1.png" WIDTH="300"></A>
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<BR><B>Figure 171:</B> Spiderplot with anti-aliasing <A href="exframes/frame_radarex8.1.html"
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target="blank">[src]</A>
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<P></P>
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</DIV></P>
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<P></P>
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<P> One thing you need to keep in mind when deciding to use
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anti-aliasing is that it could have potentially a dramatic effect on
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the time it takes to generate the image. Line drawing with
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anti-aliasing turned on is roughly 8 times slower than the normal line
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drawing so treat this feature wisely.</P>
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<P> Furthermore there are a couple of "gotchas" you should be aware of
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when using anti-aliasing.</P>
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<OL>
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<LI> Anti-aliased lines uses up more of the available color-palette. The
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exact number of colors used is dependent on the line-angle, a near
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horizontal or near vertical line uses more colors (number of lines with
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different angles uses more colors). Hence it might not be possible to
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use anti-aliasing with color-gradient fill since the number of
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available colors in the palette might not be enough. A normal palette
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can keep around 256 colors. This means that you are advised to use a
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true-color image when using anti-aliasing.</LI>
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<LI> Anti-aliasing does not work very well together with background
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images since it assumes a the same solid color on each side of the
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line. Doing a more advanced anti-aliasing algorithm would simple take
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to much processing power.</LI>
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<LI>Anti-aliased lines will ignore the line width specified. They will
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always have a width of roughly 1.</LI>
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</OL>
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<P></P>
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