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| author | Graeme Geldenhuys <graeme@mastermaths.co.za> | 2012-03-19 11:58:09 +0200 |
|---|---|---|
| committer | Graeme Geldenhuys <graeme@mastermaths.co.za> | 2012-03-19 11:58:09 +0200 |
| commit | 90ae43f347fe4075f76a5f37d011d39bd4c10ddd (patch) | |
| tree | a04fa64e893f21a07ed19704121e626877f4aef6 /docs/aggpas/gradients_tutorial.html | |
| parent | 88f1fc9acda900eecfcfc884a60e4958145e3fc0 (diff) | |
| download | fpGUI-90ae43f347fe4075f76a5f37d011d39bd4c10ddd.tar.xz | |
adds AGG docs in general.
These docs give you lots of background information on the working
of the AGG (Anti-Grain Geometry) library and how it works.
Using the knowledge you learn from this, you will be able to extend
the TAgg2D canvas for your own needs and applications.
Diffstat (limited to 'docs/aggpas/gradients_tutorial.html')
| -rw-r--r-- | docs/aggpas/gradients_tutorial.html | 539 |
1 files changed, 539 insertions, 0 deletions
diff --git a/docs/aggpas/gradients_tutorial.html b/docs/aggpas/gradients_tutorial.html new file mode 100644 index 00000000..b9302451 --- /dev/null +++ b/docs/aggpas/gradients_tutorial.html @@ -0,0 +1,539 @@ +<html><head><title>Anti-Grain Geometry - Working with Gradients</title> +<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> +<link rel="stylesheet" type="text/css" +href="gradients_tutorial_files/agg.css"> +</head><body><a name="PAGE_GRADIENTS_TUTORIAL"><b></b></a> + + +<table style="margin: 0px;" height="1px" width="640px" border="0" +cellpadding="0" cellspacing="0"> +<tbody><tr> +<td bgcolor="#583927"></td> +</tr> +</tbody></table> +<table style="margin: 0px;" width="640px" border="0" cellpadding="0" +cellspacing="0"> +<tbody><tr> +<td> +<table style="margin: 0px;" width="170px" border="0" cellpadding="0" +cellspacing="0"> +<tbody><tr><td><a href="http://www.antigrain.com/index.html" +class="mpmenu">Home/</a></td></tr> +<tr><td><a href="http://www.antigrain.com/tips/index.html" +class="mpmenu">Tips & Tricks/</a></td></tr> +<tr><td><a href="" class="mpmenu"></a></td></tr> +<tr><td><a href="" class="mpmenu"></a></td></tr> +<tr><td><a href="" class="mpmenu"></a></td></tr> +<tr><td><a href="" class="mpmenu"></a></td></tr> +</tbody></table> +</td> +<td width="1px" bgcolor="#583927"></td> +<td style="text-align: right;" valign="top" width="450px"> +<table style="margin: 0px;" border="0" cellpadding="0" cellspacing="0"> +<tbody><tr> +<td><img src="gradients_tutorial_files/agg_logo.gif" border="0"></td> +</tr> +<tr> +<td> +<table style="margin: 0px;" border="0" cellpadding="0" cellspacing="0"> +<tbody><tr height="15px"> +<td> <a class="topmenu" +href="http://www.antigrain.com/news/index.html">News</a> </td> +<td width="1px" bgcolor="#8e521d"></td> +<td> <a class="topmenu" +href="http://www.antigrain.com/doc/index.html">Docs</a> </td> +<td width="1px" bgcolor="#8e521d"></td> +<td> <a class="topmenu" +href="http://www.antigrain.com/download/index.html">Download</a> </td> +<td width="1px" bgcolor="#8e521d"></td> +<td> <a class="topmenu" +href="http://www.antigrain.com/maillist/index.html">Mailing List</a> </td> +<td width="1px" bgcolor="#8e521d"></td> +<td> <a class="topmenu" +href="http://www.antigrain.com/cvs/index.html">CVS</a> </td> +</tr> +</tbody></table> +</td> +</tr> +</tbody></table> +</td> +</tr> +</tbody></table> +<table style="margin: 0px;" height="1px" width="640px" bgcolor="#583927" + border="0" cellpadding="0" cellspacing="0"><tbody><tr><td></td></tr></tbody></table> + + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p> +</p></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td><h1>Working with Gradients<span +class="subtitle"><br>A Simple Step-by-Step Tutorial</span></h1></td></tr></tbody></table> + + + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>This + article will explain to you how to set up gradients and render them. +We will use a simple command-line example that produces the result in +the +<code>agg_test.ppm</code> file. You can use, for example +<a href="http://www.irfanview.com/"><img +src="gradients_tutorial_files/link.gif" border="0">IrfanView +(www.irfanview.com)</a> to see the +results.</p></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>You +will need to tell the compiler the <b>AGG</b> include directory and add +three source files to the project or to the command line: +<code>agg_rasterizer_scanline_aa.cpp</code>, +<code><a +href="http://www.antigrain.com/__code/src/agg_trans_affine.cpp.html">agg_trans_affine.cpp</a></code>, + and <code><a +href="http://www.antigrain.com/__code/src/agg_sqrt_tables.cpp.html">agg_sqrt_tables.cpp</a></code>. + You +can find the source file here: <a +href="http://www.antigrain.com/tips/gradients_tutorial/gradients.cpp"><img + src="gradients_tutorial_files/download.gif" border="0"> (gradients.cpp)</a>.</p></td></tr></tbody></table> + +<table width="640px" border="0" cellpadding="0" cellspacing="0"><tbody><tr><td><pre><span class="kw2">#include</span> <span class="op"><</span>stdio<span class="op">.</span>h<span class="op">></span> +<span class="kw2">#include</span> <span class="op"><</span>string<span class="op">.</span>h<span class="op">></span> +<span class="kw2">#include</span> <span class="str">"<a href="http://www.antigrain.com/__code/include/agg_pixfmt_rgb.h.html">agg_pixfmt_rgb.h</a>"</span> +<span class="kw2">#include</span> <span class="str">"<a href="http://www.antigrain.com/__code/include/agg_renderer_base.h.html">agg_renderer_base.h</a>"</span> +<span class="kw2">#include</span> <span class="str">"<a href="http://www.antigrain.com/__code/include/agg_renderer_scanline.h.html">agg_renderer_scanline.h</a>"</span> +<span class="kw2">#include</span> <span class="str">"<a href="http://www.antigrain.com/__code/include/agg_scanline_u.h.html">agg_scanline_u.h</a>"</span> +<span class="kw2">#include</span> <span class="str">"<a href="http://www.antigrain.com/__code/include/agg_rasterizer_scanline_aa.h.html">agg_rasterizer_scanline_aa.h</a>"</span> +<span class="kw2">#include</span> <span class="str">"<a href="http://www.antigrain.com/__code/include/agg_ellipse.h.html">agg_ellipse.h</a>"</span> +<span class="kw2">#include</span> <span class="str">"<a href="http://www.antigrain.com/__code/include/agg_span_gradient.h.html">agg_span_gradient.h</a>"</span> +<span class="kw2">#include</span> <span class="str">"<a href="http://www.antigrain.com/__code/include/agg_span_interpolator_linear.h.html">agg_span_interpolator_linear.h</a>"</span> + +<span class="kw1">enum</span> +<span class="op">{</span> + frame_width <span class="op">=</span> <span class="num">320</span><span class="op">,</span> + frame_height <span class="op">=</span> <span class="num">200</span> +<span class="op">}</span><span class="op">;</span> + +<span class="rem">// Writing the buffer to a .PPM file, assuming it has </span> +<span class="rem">// RGB-structure, one byte per color component</span> +<span class="rem">//--------------------------------------------------</span> +<span class="kw1">bool</span> write_ppm<span class="op">(</span><span class="kw1">const</span> <span class="kw1">unsigned</span> <span class="kw1">char</span><span class="op">*</span> buf<span class="op">,</span> + <span class="kw1">unsigned</span> width<span class="op">,</span> + <span class="kw1">unsigned</span> height<span class="op">,</span> + <span class="kw1">const</span> <span class="kw1">char</span><span class="op">*</span> file_name<span class="op">)</span> +<span class="op">{</span> + FILE<span class="op">*</span> fd <span class="op">=</span> fopen<span class="op">(</span>file_name<span class="op">,</span> <span class="str">"wb"</span><span class="op">)</span><span class="op">;</span> + <span class="kw1">if</span><span class="op">(</span>fd<span class="op">)</span> + <span class="op">{</span> + fprintf<span class="op">(</span>fd<span class="op">,</span> <span class="str">"P6 %d %d 255 "</span><span class="op">,</span> width<span class="op">,</span> height<span class="op">)</span><span class="op">;</span> + fwrite<span class="op">(</span>buf<span class="op">,</span> <span class="num">1</span><span class="op">,</span> width <span class="op">*</span> height <span class="op">*</span> <span class="num">3</span><span class="op">,</span> fd<span class="op">)</span><span class="op">;</span> + fclose<span class="op">(</span>fd<span class="op">)</span><span class="op">;</span> + <span class="kw1">return</span> <span class="kw1">true</span><span class="op">;</span> + <span class="op">}</span> + <span class="kw1">return</span> <span class="kw1">false</span><span class="op">;</span> +<span class="op">}</span> + + + +<span class="rem">// A simple function to form the gradient color array </span> +<span class="rem">// consisting of 3 colors, "begin", "middle", "end"</span> +<span class="rem">//---------------------------------------------------</span> +<span class="kw1">template</span><span class="op"><</span><span class="kw1">class</span> Array<span class="op">></span> +<span class="kw1">void</span> fill_color_array<span class="op">(</span>Array<span class="op">&</span> array<span class="op">,</span> + agg::<a href="http://www.antigrain.com/__code/include/agg_color_rgba.h.html#rgba8">rgba8</a> begin<span class="op">,</span> + agg::<a href="http://www.antigrain.com/__code/include/agg_color_rgba.h.html#rgba8">rgba8</a> middle<span class="op">,</span> + agg::<a href="http://www.antigrain.com/__code/include/agg_color_rgba.h.html#rgba8">rgba8</a> end<span class="op">)</span> +<span class="op">{</span> + <span class="kw1">unsigned</span> i<span class="op">;</span> + <span class="kw1">unsigned</span> half_size <span class="op">=</span> array<span class="op">.</span>size<span class="op">(</span><span class="op">)</span> <span class="op">/</span> <span class="num">2</span><span class="op">;</span> + <span class="kw1">for</span><span class="op">(</span>i <span class="op">=</span> <span class="num">0</span><span class="op">;</span> i <span class="op"><</span> half_size<span class="op">;</span> <span class="op">++</span>i<span class="op">)</span> + <span class="op">{</span> + array<span class="op">[</span>i<span class="op">]</span> <span class="op">=</span> begin<span class="op">.</span>gradient<span class="op">(</span>middle<span class="op">,</span> i <span class="op">/</span> <span class="kw1">double</span><span class="op">(</span>half_size<span class="op">)</span><span class="op">)</span><span class="op">;</span> + <span class="op">}</span> + <span class="kw1">for</span><span class="op">(</span><span class="op">;</span> i <span class="op"><</span> array<span class="op">.</span>size<span class="op">(</span><span class="op">)</span><span class="op">;</span> <span class="op">++</span>i<span class="op">)</span> + <span class="op">{</span> + array<span class="op">[</span>i<span class="op">]</span> <span class="op">=</span> middle<span class="op">.</span>gradient<span class="op">(</span>end<span class="op">,</span> <span class="op">(</span>i <span class="op">-</span> half_size<span class="op">)</span> <span class="op">/</span> <span class="kw1">double</span><span class="op">(</span>half_size<span class="op">)</span><span class="op">)</span><span class="op">;</span> + <span class="op">}</span> +<span class="op">}</span> + + + + +<span class="kw1">int</span> <span class="kw1">main</span><span class="op">(</span><span class="op">)</span> +<span class="op">{</span> + <span class="kw1">unsigned</span> <span class="kw1">char</span><span class="op">*</span> buffer <span class="op">=</span> <span class="kw1">new</span> <span class="kw1">unsigned</span> <span class="kw1">char</span><span class="op">[</span>frame_width <span class="op">*</span> frame_height <span class="op">*</span> <span class="num">3</span><span class="op">]</span><span class="op">;</span> + + agg::<a href="http://www.antigrain.com/doc/basic_renderers/basic_renderers.agdoc.html#rendering_buffer">rendering_buffer</a> rbuf<span class="op">(</span>buffer<span class="op">,</span> + frame_width<span class="op">,</span> + frame_height<span class="op">,</span> + <span class="op">-</span>frame_width <span class="op">*</span> <span class="num">3</span><span class="op">)</span><span class="op">;</span> + + <span class="rem">// Pixel format and basic renderers.</span> + <span class="rem">//-----------------</span> + <span class="kw1">typedef</span> agg::<a href="http://www.antigrain.com/__code/include/agg_pixfmt_rgb.h.html#pixfmt_rgb24">pixfmt_rgb24</a> pixfmt_type<span class="op">;</span> + <span class="kw1">typedef</span> agg::<a href="http://www.antigrain.com/doc/basic_renderers/basic_renderers.agdoc.html#renderer_base">renderer_base</a><span class="op"><</span>pixfmt_type<span class="op">></span> renderer_base_type<span class="op">;</span> + + + <span class="rem">// The gradient color array</span> + <span class="kw1">typedef</span> agg::<a href="http://www.antigrain.com/__code/include/agg_array.h.html#pod_auto_array">pod_auto_array</a><span class="op"><</span>agg::<a href="http://www.antigrain.com/__code/include/agg_color_rgba.h.html#rgba8">rgba8</a><span class="op">,</span> <span class="num">256</span><span class="op">></span> color_array_type<span class="op">;</span> + + + <span class="rem">// Gradient shape function (linear, radial, custom, etc)</span> + <span class="rem">//-----------------</span> + <span class="kw1">typedef</span> agg::<a href="http://www.antigrain.com/__code/include/agg_span_gradient.h.html#gradient_x">gradient_x</a> gradient_func_type<span class="op">;</span> + + + <span class="rem">// Span interpolator. This object is used in all span generators </span> + <span class="rem">// that operate with transformations during iterating of the spans,</span> + <span class="rem">// for example, image transformers use the interpolator too.</span> + <span class="rem">//-----------------</span> + <span class="kw1">typedef</span> agg::<a href="http://www.antigrain.com/__code/include/agg_span_interpolator_linear.h.html#span_interpolator_linear">span_interpolator_linear</a><span class="op"><</span><span class="op">></span> interpolator_type<span class="op">;</span> + + + <span class="rem">// Span allocator is an object that allocates memory for </span> + <span class="rem">// the array of colors that will be used to render the </span> + <span class="rem">// color spans. One object can be shared between different </span> + <span class="rem">// span generators.</span> + <span class="rem">//-----------------</span> + <span class="kw1">typedef</span> agg::<a href="http://www.antigrain.com/__code/include/agg_span_allocator.h.html#span_allocator">span_allocator</a><span class="op"><</span>agg::<a href="http://www.antigrain.com/__code/include/agg_color_rgba.h.html#rgba8">rgba8</a><span class="op">></span> span_allocator_type<span class="op">;</span> + + + <span class="rem">// Finally, the gradient span generator working with the agg::<a href="http://www.antigrain.com/__code/include/agg_color_rgba.h.html#rgba8">rgba8</a> </span> + <span class="rem">// color type. </span> + <span class="rem">// The 4-th argument is the color function that should have </span> + <span class="rem">// the [] operator returning the color in range of [0...255].</span> + <span class="rem">// In our case it will be a simple look-up table of 256 colors.</span> + <span class="rem">//-----------------</span> + <span class="kw1">typedef</span> agg::<a href="http://www.antigrain.com/__code/include/agg_span_gradient.h.html#span_gradient">span_gradient</a><span class="op"><</span>agg::<a href="http://www.antigrain.com/__code/include/agg_color_rgba.h.html#rgba8">rgba8</a><span class="op">,</span> + interpolator_type<span class="op">,</span> + gradient_func_type<span class="op">,</span> + color_array_type<span class="op">,</span> + span_allocator_type<span class="op">></span> span_gradient_type<span class="op">;</span> + + + <span class="rem">// The gradient scanline renderer type</span> + <span class="rem">//-----------------</span> + <span class="kw1">typedef</span> agg::<a href="http://www.antigrain.com/__code/include/agg_renderer_scanline.h.html#renderer_scanline_aa">renderer_scanline_aa</a><span class="op"><</span>renderer_base_type<span class="op">,</span> + span_gradient_type<span class="op">></span> renderer_gradient_type<span class="op">;</span> + + + <span class="rem">// Common declarations (pixel format and basic renderer).</span> + <span class="rem">//----------------</span> + pixfmt_type pixf<span class="op">(</span>rbuf<span class="op">)</span><span class="op">;</span> + renderer_base_type rbase<span class="op">(</span>pixf<span class="op">)</span><span class="op">;</span> + + + <span class="rem">// The gradient objects declarations</span> + <span class="rem">//----------------</span> + gradient_func_type gradient_func<span class="op">;</span> <span class="rem">// The gradient function</span> + agg::<a href="http://www.antigrain.com/__code/include/agg_trans_affine.h.html#trans_affine">trans_affine</a> gradient_mtx<span class="op">;</span> <span class="rem">// Affine transformer</span> + interpolator_type span_interpolator<span class="op">(</span>gradient_mtx<span class="op">)</span><span class="op">;</span> <span class="rem">// Span interpolator</span> + span_allocator_type <a href="http://www.antigrain.com/__code/include/agg_span_allocator.h.html#span_allocator">span_allocator</a><span class="op">;</span> <span class="rem">// Span Allocator</span> + color_array_type color_array<span class="op">;</span> <span class="rem">// Gradient colors</span> + + + <span class="rem">// Declare the gradient span itself. </span> + <span class="rem">// The last two arguments are so called "d1" and "d2" </span> + <span class="rem">// defining two distances in pixels, where the gradient starts</span> + <span class="rem">// and where it ends. The actual meaning of "d1" and "d2" depands</span> + <span class="rem">// on the gradient function.</span> + <span class="rem">//----------------</span> + span_gradient_type <a href="http://www.antigrain.com/__code/include/agg_span_gradient.h.html#span_gradient">span_gradient</a><span class="op">(</span><a href="http://www.antigrain.com/__code/include/agg_span_allocator.h.html#span_allocator">span_allocator</a><span class="op">,</span> + span_interpolator<span class="op">,</span> + gradient_func<span class="op">,</span> + color_array<span class="op">,</span> + <span class="num">0</span><span class="op">,</span> <span class="num">100</span><span class="op">)</span><span class="op">;</span> + + <span class="rem">// The gradient renderer</span> + <span class="rem">//----------------</span> + renderer_gradient_type ren_gradient<span class="op">(</span>rbase<span class="op">,</span> <a href="http://www.antigrain.com/__code/include/agg_span_gradient.h.html#span_gradient">span_gradient</a><span class="op">)</span><span class="op">;</span> + + + <span class="rem">// The rasterizing/scanline stuff</span> + <span class="rem">//----------------</span> + agg::<a href="http://www.antigrain.com/__code/include/agg_rasterizer_scanline_aa.h.html#rasterizer_scanline_aa">rasterizer_scanline_aa</a><span class="op"><</span><span class="op">></span> ras<span class="op">;</span> + agg::<a href="http://www.antigrain.com/__code/include/agg_scanline_u.h.html#scanline_u8">scanline_u8</a> sl<span class="op">;</span> + + + <span class="rem">// Finally we can draw a circle.</span> + <span class="rem">//----------------</span> + rbase<span class="op">.</span>clear<span class="op">(</span>agg::<a href="http://www.antigrain.com/__code/include/agg_color_rgba.h.html#rgba8">rgba8</a><span class="op">(</span><span class="num">255</span><span class="op">,</span> <span class="num">255</span><span class="op">,</span> <span class="num">255</span><span class="op">)</span><span class="op">)</span><span class="op">;</span> + + fill_color_array<span class="op">(</span>color_array<span class="op">,</span> + agg::<a href="http://www.antigrain.com/__code/include/agg_color_rgba.h.html#rgba8">rgba8</a><span class="op">(</span><span class="num">0</span><span class="op">,</span><span class="num">50</span><span class="op">,</span><span class="num">50</span><span class="op">)</span><span class="op">,</span> + agg::<a href="http://www.antigrain.com/__code/include/agg_color_rgba.h.html#rgba8">rgba8</a><span class="op">(</span><span class="num">240</span><span class="op">,</span> <span class="num">255</span><span class="op">,</span> <span class="num">100</span><span class="op">)</span><span class="op">,</span> + agg::<a href="http://www.antigrain.com/__code/include/agg_color_rgba.h.html#rgba8">rgba8</a><span class="op">(</span><span class="num">80</span><span class="op">,</span> <span class="num">0</span><span class="op">,</span> <span class="num">0</span><span class="op">)</span><span class="op">)</span><span class="op">;</span> + + agg::<a href="http://www.antigrain.com/__code/include/agg_ellipse.h.html#ellipse">ellipse</a> ell<span class="op">(</span><span class="num">50</span><span class="op">,</span> <span class="num">50</span><span class="op">,</span> <span class="num">50</span><span class="op">,</span> <span class="num">50</span><span class="op">,</span> <span class="num">100</span><span class="op">)</span><span class="op">;</span> + ras<span class="op">.</span>add_path<span class="op">(</span>ell<span class="op">)</span><span class="op">;</span> + + agg::<a href="http://www.antigrain.com/__code/include/agg_renderer_scanline.h.html#render_scanlines">render_scanlines</a><span class="op">(</span>ras<span class="op">,</span> sl<span class="op">,</span> ren_gradient<span class="op">)</span><span class="op">;</span> + + write_ppm<span class="op">(</span>buffer<span class="op">,</span> frame_width<span class="op">,</span> frame_height<span class="op">,</span> <span class="str">"agg_test.ppm"</span><span class="op">)</span><span class="op">;</span> + + <span class="kw1">delete</span> <span class="op">[</span><span class="op">]</span> buffer<span class="op">;</span> + <span class="kw1">return</span> <span class="num">0</span><span class="op">;</span> +<span class="op">}</span> +</pre></td></tr></tbody></table><font style="margin-left: 1em;"><i></i></font> + + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>It +looks rather complex, especially the necessity to declare a lot +of types and objects. But the “complexity” gives you freedom, for +example, you can define your own gradient functions or even arbitrary +distortions.</p></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>The +example renders a circle with linear gradient from (0,0) to (100,0). +In <b>AGG</b> you can define an arbitrary color function, in our case +it's a +simple look-up table generated from three colors, <code>start</code>, <code>middle</code>, + and +<code>end</code>.</p></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>Here + is the result (the axes and text were added in <a +href="http://www.xara.com/"><img src="gradients_tutorial_files/link.gif" + border="0"><b><nobr>Xara X</nobr></b></a>):</p></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td><center><img +src="gradients_tutorial_files/gradients1.png" title="" border="0"><br><i></i></center></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>It +also can seem like an overkill for this simple task, but later +you will see that it's not so. +<br><br><br></p></td></tr></tbody></table> + +<table style="margin: 0px;" height="1px" width="640px" bgcolor="#583927" + border="0" cellpadding="0" cellspacing="0"><tbody><tr><td></td></tr></tbody></table> +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>The +next step is one little modification. Modify the following:</p></td></tr></tbody></table> + +<table width="640px" border="0" cellpadding="0" cellspacing="0"><tbody><tr><td><pre> <span class="rem">// Declare the gradient span itself. </span> + <span class="rem">// The last two arguments are so called "d1" and "d2" </span> + <span class="rem">// defining two distances in pixels, where the gradient starts</span> + <span class="rem">// and where it ends. The actual meaning of "d1" and "d2" depands</span> + <span class="rem">// on the gradient function.</span> + <span class="rem">//----------------</span> + span_gradient_type <a href="http://www.antigrain.com/__code/include/agg_span_gradient.h.html#span_gradient">span_gradient</a><span class="op">(</span><a href="http://www.antigrain.com/__code/include/agg_span_allocator.h.html#span_allocator">span_allocator</a><span class="op">,</span> + span_interpolator<span class="op">,</span> + gradient_func<span class="op">,</span> + color_array<span class="op">,</span> + <span class="num">50</span><span class="op">,</span> <span class="num">100</span><span class="op">)</span><span class="op">;</span> +</pre></td></tr></tbody></table><font style="margin-left: 1em;"><i></i></font> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>The +result:</p></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td><center><img +src="gradients_tutorial_files/gradients2.png" title="" border="0"><br><i></i></center></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>It +should explain those freaky <code>d1</code> and <code>d2</code> +arguments. In fact, they +determine the geometrical <code>start</code> and <code>end</code> of the + gradient and their meaning +depends on the gradient function. +<br><br><br> +</p></td></tr></tbody></table><table style="margin: 0px;" height="1px" +width="640px" bgcolor="#583927" border="0" cellpadding="0" +cellspacing="0"><tbody><tr><td></td></tr></tbody></table> +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>Now +change the gradient function:</p></td></tr></tbody></table> + +<table width="640px" border="0" cellpadding="0" cellspacing="0"><tbody><tr><td><pre> <span class="rem">// Gradient shape function (linear, radial, custom, etc)</span> + <span class="rem">//-----------------</span> + <span class="kw1">typedef</span> agg::<a href="http://www.antigrain.com/__code/include/agg_span_gradient.h.html#gradient_circle">gradient_circle</a> gradient_func_type<span class="op">;</span> +</pre></td></tr></tbody></table><font style="margin-left: 1em;"><i></i></font> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>Set <code>d1</code> + back to 0:</p></td></tr></tbody></table> + +<table width="640px" border="0" cellpadding="0" cellspacing="0"><tbody><tr><td><pre> <span class="rem">// Declare the gradient span itself. </span> + <span class="rem">// The last two arguments are so called "d1" and "d2" </span> + <span class="rem">// defining two distances in pixels, where the gradient starts</span> + <span class="rem">// and where it ends. The actual meaning of "d1" and "d2" depands</span> + <span class="rem">// on the gradient function.</span> + <span class="rem">//----------------</span> + span_gradient_type <a href="http://www.antigrain.com/__code/include/agg_span_gradient.h.html#span_gradient">span_gradient</a><span class="op">(</span><a href="http://www.antigrain.com/__code/include/agg_span_allocator.h.html#span_allocator">span_allocator</a><span class="op">,</span> + span_interpolator<span class="op">,</span> + gradient_func<span class="op">,</span> + color_array<span class="op">,</span> + <span class="num">0</span><span class="op">,</span> <span class="num">100</span><span class="op">)</span><span class="op">;</span> +</pre></td></tr></tbody></table><font style="margin-left: 1em;"><i></i></font> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>And +modify the circle:</p></td></tr></tbody></table> + +<table width="640px" border="0" cellpadding="0" cellspacing="0"><tbody><tr><td><pre> agg::<a href="http://www.antigrain.com/__code/include/agg_ellipse.h.html#ellipse">ellipse</a> ell<span class="op">(</span><span class="num">0</span><span class="op">,</span> <span class="num">0</span><span class="op">,</span> <span class="num">120</span><span class="op">,</span> <span class="num">120</span><span class="op">,</span> <span class="num">100</span><span class="op">)</span><span class="op">;</span> +</pre></td></tr></tbody></table><font style="margin-left: 1em;"><i></i></font> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>The +result:</p></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td><center><img +src="gradients_tutorial_files/gradients3.png" title="" border="0"><br><i></i></center></td></tr></tbody></table> +<table width="640px"><tbody><tr><td style="text-align: justify;"><p><br><br><br> +</p></td></tr></tbody></table><table style="margin: 0px;" height="1px" +width="640px" bgcolor="#583927" border="0" cellpadding="0" +cellspacing="0"><tbody><tr><td></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>Modify + <code>d1</code> again: +</p></td></tr></tbody></table><table width="640px" border="0" +cellpadding="0" cellspacing="0"><tbody><tr><td><pre> <span class="rem">// Declare the gradient span itself. </span> + <span class="rem">// The last two arguments are so called "d1" and "d2" </span> + <span class="rem">// defining two distances in pixels, where the gradient starts</span> + <span class="rem">// and where it ends. The actual meaning of "d1" and "d2" depands</span> + <span class="rem">// on the gradient function.</span> + <span class="rem">//----------------</span> + span_gradient_type <a href="http://www.antigrain.com/__code/include/agg_span_gradient.h.html#span_gradient">span_gradient</a><span class="op">(</span><a href="http://www.antigrain.com/__code/include/agg_span_allocator.h.html#span_allocator">span_allocator</a><span class="op">,</span> + span_interpolator<span class="op">,</span> + gradient_func<span class="op">,</span> + color_array<span class="op">,</span> + <span class="num">50</span><span class="op">,</span> <span class="num">100</span><span class="op">)</span><span class="op">;</span> +</pre></td></tr></tbody></table><font style="margin-left: 1em;"><i></i></font> + +<table width="640px"><tbody><tr><td><center><img +src="gradients_tutorial_files/gradients4.png" title="" border="0"><br><i></i></center></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>So +that, in case of a radial gradient, <code>d1</code> and <code>d2</code> +define the starting +and ending radii. +<br><br><br> +</p></td></tr></tbody></table><table style="margin: 0px;" height="1px" +width="640px" bgcolor="#583927" border="0" cellpadding="0" +cellspacing="0"><tbody><tr><td></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>By +default the origin point for the gradients is (0,0). How to draw a +gradient +in some other place? The answer is to use affine transformations. +Strictly +speaking, the transformations are fully defined by the span +interpolator. In our case +we use <a +href="http://www.antigrain.com/__code/include/agg_span_interpolator_linear.h.html#span_interpolator_linear">span_interpolator_linear</a> + with an affine matrix. The linear interpolator +allows you to speed up the calculations vastly, because we calculate the + floating +point coordinates only in the begin and end of the horizontal spans and +then +use a fast, integer, Bresenham-like interpolation with <b>Subpixel +Accuracy</b>.</p></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>Add +the following code somewhere before calling <code>agg::<a +href="http://www.antigrain.com/__code/include/agg_renderer_scanline.h.html#render_scanlines">render_scanlines</a>(ras, + sl, ren_gradient);</code></p></td></tr></tbody></table> + +<table width="640px" border="0" cellpadding="0" cellspacing="0"><tbody><tr><td><pre> gradient_mtx <span class="op">*=</span> agg::<a href="http://www.antigrain.com/__code/include/agg_trans_affine.h.html#trans_affine_scaling">trans_affine_scaling</a><span class="op">(</span><span class="num">0</span><span class="op">.</span><span class="num">75</span><span class="op">,</span> <span class="num">1</span><span class="op">.</span><span class="num">2</span><span class="op">)</span><span class="op">;</span> + gradient_mtx <span class="op">*=</span> agg::<a href="http://www.antigrain.com/__code/include/agg_trans_affine.h.html#trans_affine_rotation">trans_affine_rotation</a><span class="op">(</span><span class="op">-</span>agg::<a href="http://www.antigrain.com/__code/include/agg_basics.h.html#pi">pi</a><span class="op">/</span><span class="num">3</span><span class="op">.</span><span class="num">0</span><span class="op">)</span><span class="op">;</span> + gradient_mtx <span class="op">*=</span> agg::<a href="http://www.antigrain.com/__code/include/agg_trans_affine.h.html#trans_affine_translation">trans_affine_translation</a><span class="op">(</span><span class="num">100</span><span class="op">.</span><span class="num">0</span><span class="op">,</span> <span class="num">100</span><span class="op">.</span><span class="num">0</span><span class="op">)</span><span class="op">;</span> + gradient_mtx<span class="op">.</span>invert<span class="op">(</span><span class="op">)</span><span class="op">;</span> +</pre></td></tr></tbody></table><font style="margin-left: 1em;"><i></i></font> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>And +modify the circle:</p></td></tr></tbody></table> + +<table width="640px" border="0" cellpadding="0" cellspacing="0"><tbody><tr><td><pre> agg::<a href="http://www.antigrain.com/__code/include/agg_ellipse.h.html#ellipse">ellipse</a> ell<span class="op">(</span><span class="num">100</span><span class="op">,</span> <span class="num">100</span><span class="op">,</span> <span class="num">120</span><span class="op">,</span> <span class="num">120</span><span class="op">,</span> <span class="num">100</span><span class="op">)</span><span class="op">;</span> +</pre></td></tr></tbody></table><font style="margin-left: 1em;"><i></i></font> + +<table width="640px"><tbody><tr><td><center><img +src="gradients_tutorial_files/gradients5.png" title="" border="0"><br><i></i></center></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>The +code of initializing of the affine matrix should be obvious except +for some strange <code>gradient_mtx.invert()</code>. It's necessary +because +the gradient generator uses <b>reverse</b> transformations instead of +<b>direct</b> ones. In other words it takes the destination point, +applies the transformations and obtains the coordinates in the gradient. +Note that the affine transformations allow you to turn a circular +gradient +into elliptical. +<br><br><br> +</p></td></tr></tbody></table><table style="margin: 0px;" height="1px" +width="640px" bgcolor="#583927" border="0" cellpadding="0" +cellspacing="0"><tbody><tr><td></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>Now +it should be obvious how to define a linear gradient from some +<code>Point1</code> to <code>Point2</code>. So, get back to the original + code and +add the following function:</p></td></tr></tbody></table> + +<table width="640px" border="0" cellpadding="0" cellspacing="0"><tbody><tr><td><pre><span class="rem">// Calculate the affine transformation matrix for the linear gradient </span> +<span class="rem">// from (x1, y1) to (x2, y2). gradient_d2 is the "base" to scale the</span> +<span class="rem">// gradient. Here d1 must be 0.0, and d2 must equal gradient_d2.</span> +<span class="rem">//---------------------------------------------------------------</span> +<span class="kw1">void</span> calc_linear_gradient_transform<span class="op">(</span><span class="kw1">double</span> x1<span class="op">,</span> <span class="kw1">double</span> y1<span class="op">,</span> <span class="kw1">double</span> x2<span class="op">,</span> <span class="kw1">double</span> y2<span class="op">,</span> + agg::<a href="http://www.antigrain.com/__code/include/agg_trans_affine.h.html#trans_affine">trans_affine</a><span class="op">&</span> mtx<span class="op">,</span> + <span class="kw1">double</span> gradient_d2 <span class="op">=</span> <span class="num">100</span><span class="op">.</span><span class="num">0</span><span class="op">)</span> +<span class="op">{</span> + <span class="kw1">double</span> dx <span class="op">=</span> x2 <span class="op">-</span> x1<span class="op">;</span> + <span class="kw1">double</span> dy <span class="op">=</span> y2 <span class="op">-</span> y1<span class="op">;</span> + mtx<span class="op">.</span>reset<span class="op">(</span><span class="op">)</span><span class="op">;</span> + mtx <span class="op">*=</span> agg::<a href="http://www.antigrain.com/__code/include/agg_trans_affine.h.html#trans_affine_scaling">trans_affine_scaling</a><span class="op">(</span>sqrt<span class="op">(</span>dx <span class="op">*</span> dx <span class="op">+</span> dy <span class="op">*</span> dy<span class="op">)</span> <span class="op">/</span> gradient_d2<span class="op">)</span><span class="op">;</span> + mtx <span class="op">*=</span> agg::<a href="http://www.antigrain.com/__code/include/agg_trans_affine.h.html#trans_affine_rotation">trans_affine_rotation</a><span class="op">(</span>atan2<span class="op">(</span>dy<span class="op">,</span> dx<span class="op">)</span><span class="op">)</span><span class="op">;</span> + mtx <span class="op">*=</span> agg::<a href="http://www.antigrain.com/__code/include/agg_trans_affine.h.html#trans_affine_translation">trans_affine_translation</a><span class="op">(</span>x1<span class="op">,</span> y1<span class="op">)</span><span class="op">;</span> + mtx<span class="op">.</span>invert<span class="op">(</span><span class="op">)</span><span class="op">;</span> +<span class="op">}</span> +</pre></td></tr></tbody></table><font style="margin-left: 1em;"><i></i></font> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>Then + modify the circle:</p></td></tr></tbody></table> + +<table width="640px" border="0" cellpadding="0" cellspacing="0"><tbody><tr><td><pre> agg::<a href="http://www.antigrain.com/__code/include/agg_ellipse.h.html#ellipse">ellipse</a> ell<span class="op">(</span><span class="num">100</span><span class="op">,</span> <span class="num">100</span><span class="op">,</span> <span class="num">80</span><span class="op">,</span> <span class="num">80</span><span class="op">,</span> <span class="num">100</span><span class="op">)</span><span class="op">;</span> +</pre></td></tr></tbody></table><font style="margin-left: 1em;"><i></i></font> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>And +add the transformations:</p></td></tr></tbody></table> + +<table width="640px" border="0" cellpadding="0" cellspacing="0"><tbody><tr><td><pre> calc_linear_gradient_transform<span class="op">(</span><span class="num">50</span><span class="op">,</span> <span class="num">50</span><span class="op">,</span> <span class="num">150</span><span class="op">,</span> <span class="num">150</span><span class="op">,</span> gradient_mtx<span class="op">)</span><span class="op">;</span> +</pre></td></tr></tbody></table><font style="margin-left: 1em;"><i></i></font> + +<table width="640px"><tbody><tr><td><center><img +src="gradients_tutorial_files/gradients6.png" title="" border="0"><br><i></i></center></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>Try +to play with different parameters, +transformations, and gradient functions: <a +href="http://www.antigrain.com/__code/include/agg_span_gradient.h.html#gradient_circle">gradient_circle</a>, + <a +href="http://www.antigrain.com/__code/include/agg_span_gradient.h.html#gradient_x">gradient_x</a>, + +<a +href="http://www.antigrain.com/__code/include/agg_span_gradient.h.html#gradient_y">gradient_y</a>, + <a +href="http://www.antigrain.com/__code/include/agg_span_gradient.h.html#gradient_diamond">gradient_diamond</a>, + <a +href="http://www.antigrain.com/__code/include/agg_span_gradient.h.html#gradient_xy">gradient_xy</a>, + <a +href="http://www.antigrain.com/__code/include/agg_span_gradient.h.html#gradient_sqrt_xy">gradient_sqrt_xy</a>, + <a +href="http://www.antigrain.com/__code/include/agg_span_gradient.h.html#gradient_conic">gradient_conic</a>. +Also look at the gradient functions and try to write your own. Actually, + +the set of the gradient functions in <b>AGG</b> is rather poor, it just +demonstrates +the possibilities. For example, repeating or reflecting gradients should +be implemented in gradient functions (or you can write adaptors that +will +use the existing functions). +</p></td></tr></tbody></table><table style="margin: 0px;" height="1px" +width="640px" bgcolor="#583927" border="0" cellpadding="0" +cellspacing="0"><tbody><tr><td></td></tr></tbody></table> +<table width="640px" border="0" cellpadding="0" cellspacing="0"> +<tbody><tr><td><center><span class="authors"> +Copyright <span class="larger">©</span> 2002-2006 +<a href="http://www.antigrain.com/mcseem/index.html"><b>Maxim Shemanarev</b></a> +</span></center></td></tr> +<tr><td><center><span class="authors"> +Web Design and Programming +<a href="http://www.antigrain.com/mcseem/index.html"><b>Maxim Shemanarev</b></a> +</span></center></td></tr> +</tbody></table> +<br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br> +<br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br> +<br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br> +<br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br> +</body></html>
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