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<span id="Vector-Paths"></span><div class="header">
<p>
Next: <a href="Particles.html" accesskey="n" rel="next">Particles</a>, Previous: <a href="Fonts.html" accesskey="p" rel="prev">Fonts</a>, Up: <a href="Graphics.html" accesskey="u" rel="up">Graphics</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index.html" title="Index" rel="index">Index</a>]</p>
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<hr />
<span id="Vector-Paths-1"></span><h4 class="subsection">5.3.5 Vector Paths</h4>
<p>The <code>(chickadee graphics path)</code> module can be used to draw lines,
curves, circles, rectangles, and more in a scalable, resolution
independent manner. It is <em>not</em> an SVG compliant renderer, nor
does it intend to be. However, those familiar with SVG and/or the
HTML5 Canvas API should find lots of similarities.
</p>
<p><em>This API is considered to be experimental and may change
substantially in future releases of Chickadee. There are many missing
features.</em>
</p>
<p>The first step to rendering vector graphics is to create a
<em>path</em>: A series of commands that can be thought of as moving a
pen around a piece of paper. A path can be either open or closed. A
closed path draws a straight line from the last point in the path to
the first.
</p>
<dl>
<dt id="index-path">Procedure: <strong>path</strong> <em>. commands</em></dt>
<dd><p>Return a new path that follows <var>commands</var>.
</p>
<div class="lisp">
<pre class="lisp"><span class="syntax-open">(</span><span class="syntax-symbol">path</span> <span class="syntax-open">(</span><span class="syntax-symbol">move-to</span> <span class="syntax-open">(</span><span class="syntax-symbol">vec2</span> <span class="syntax-symbol">50.0</span> <span class="syntax-symbol">50.0</span><span class="syntax-close">)</span><span class="syntax-close">)</span>
<span class="syntax-open">(</span><span class="syntax-symbol">line-to</span> <span class="syntax-open">(</span><span class="syntax-symbol">vec2</span> <span class="syntax-symbol">500.0</span> <span class="syntax-symbol">50.0</span><span class="syntax-close">)</span><span class="syntax-close">)</span>
<span class="syntax-open">(</span><span class="syntax-symbol">line-to</span> <span class="syntax-open">(</span><span class="syntax-symbol">vec2</span> <span class="syntax-symbol">400.0</span> <span class="syntax-symbol">200.0</span><span class="syntax-close">)</span><span class="syntax-close">)</span>
<span class="syntax-open">(</span><span class="syntax-symbol">bezier-to</span> <span class="syntax-open">(</span><span class="syntax-symbol">vec2</span> <span class="syntax-symbol">500.0</span> <span class="syntax-symbol">250.0</span><span class="syntax-close">)</span> <span class="syntax-open">(</span><span class="syntax-symbol">vec2</span> <span class="syntax-symbol">380.0</span> <span class="syntax-symbol">300.0</span><span class="syntax-close">)</span> <span class="syntax-open">(</span><span class="syntax-symbol">vec2</span> <span class="syntax-symbol">400.0</span> <span class="syntax-symbol">400.0</span><span class="syntax-close">)</span><span class="syntax-close">)</span>
<span class="syntax-open">(</span><span class="syntax-symbol">line-to</span> <span class="syntax-open">(</span><span class="syntax-symbol">vec2</span> <span class="syntax-symbol">300.0</span> <span class="syntax-symbol">400.0</span><span class="syntax-close">)</span><span class="syntax-close">)</span>
<span class="syntax-open">(</span><span class="syntax-symbol">close-path</span><span class="syntax-close">)</span><span class="syntax-close">)</span>
</pre></div>
</dd></dl>
<p>Available drawing commands:
</p>
<dl>
<dt id="index-move_002dto">Procedure: <strong>move-to</strong> <em>point</em></dt>
<dd><p>Pick up the pen and move it to <var>point</var>.
</p></dd></dl>
<dl>
<dt id="index-line_002dto">Procedure: <strong>line-to</strong> <em>point</em></dt>
<dd><p>Draw a line from the current pen position to <var>point</var>.
</p></dd></dl>
<dl>
<dt id="index-bezier_002dto">Procedure: <strong>bezier-to</strong> <em>control1 control2 point</em></dt>
<dd><p>Draw a cubic bezier curve from the current pen position to
<var>point</var>. The shape of the curve is determined by the two control
points: <var>control1</var> and <var>control2</var>.
</p></dd></dl>
<dl>
<dt id="index-close_002dpath">Procedure: <strong>close-path</strong></dt>
<dd><p>Draw a straight line back to the first point drawn in the path.
</p></dd></dl>
<dl>
<dt id="index-arc">Procedure: <strong>arc</strong> <em>center rx ry angle-start angle-end</em></dt>
<dd><p>Draw an elliptical arc spanning the angle range [<var>angle-start</var>,
<var>angle-end</var>], centered at <var>center</var> with radii <var>rx</var> and
<var>ry</var> (set both to the same value for a circular arc.)
</p></dd></dl>
<dl>
<dt id="index-arc_002dto">Procedure: <strong>arc-to</strong> <em>c1 c2 radius</em></dt>
<dd><p>Draw a circular arc with radius <var>radius</var> that is tangential to the
line segment formed by the current pen position and <var>c1</var>, as well
as the line segment formed by <var>c1</var> and <var>c2</var>. The result is a
smooth corner.
</p></dd></dl>
<p>Included are some helpful procedures for generating common types of
paths:
</p>
<dl>
<dt id="index-line">Procedure: <strong>line</strong> <em>start end</em></dt>
<dd><p>Return a path that draws a straight line from <var>start</var> to <var>end</var>.
</p></dd></dl>
<dl>
<dt id="index-polyline">Procedure: <strong>polyline</strong> <em>. points</em></dt>
<dd><p>Return a path that draws a series of lines connecting <var>points</var>.
</p></dd></dl>
<dl>
<dt id="index-bezier_002dpath-1">Procedure: <strong>bezier-path</strong> <em>p1 c1 c2 p2 . points</em></dt>
<dd><p>Return a path that draws a series of bezier points starting at
<var>p1</var>, moving to <var>p2</var> using control points <var>c1</var> and
<var>c2</var>, and proceeding to draw additional bezier curves as defined
by <var>points</var>. Each additional curve requires 3 additional
arguments: two control points and and an ending point.
</p></dd></dl>
<dl>
<dt id="index-rectangle">Procedure: <strong>rectangle</strong> <em>bottom-left width height</em></dt>
<dd><p>Return a path that draws a rectangle whose bottom-left corner is at
<var>bottom-left</var> and whose size is defined by <var>width</var> and
<var>height</var>.
</p></dd></dl>
<dl>
<dt id="index-square">Procedure: <strong>square</strong> <em>bottom-left size</em></dt>
<dd><p>Return a path draws a square whose bottom-left corner is at
<var>bottom-left</var> and whose size is defined by <var>size</var>.
</p></dd></dl>
<dl>
<dt id="index-rounded_002drectangle">Procedure: <strong>rounded-rectangle</strong> <em>bottom-left width height [#:radius 4.0] [#:radius-bottom-left] [#:radius-bottom-right] [#:radius-top-left] [#:radius-top-right]</em></dt>
<dd>
<p>Return a path that draws a rectangle with rounded corners whose
bottom-left corner is at <var>bottom-left</var> and whose size is defined
by <var>width</var> and <var>height</var>. The argument <var>radius</var> is used to
define the corner radius for all corners. To use a different radius
value for a corner, use <var>radius-bottom-left</var>,
<var>radius-bottom-right</var>, <var>radius-top-left</var>, and/or
<var>radius-top-right</var>.
</p></dd></dl>
<dl>
<dt id="index-regular_002dpolygon">Procedure: <strong>regular-polygon</strong> <em>center num-sides radius</em></dt>
<dd><p>Return a path that draws a regular polygon with <var>num-sides</var> sides
centered on the point <var>center</var> with each vertex <var>radius</var> units
away from the center.
</p></dd></dl>
<dl>
<dt id="index-ellipse">Procedure: <strong>ellipse</strong> <em>center rx ry</em></dt>
<dd><p>Return a path that draws an ellipsed centered on the point
<var>center</var> with radii <var>rx</var> and <var>ry</var>.
</p></dd></dl>
<dl>
<dt id="index-circle">Procedure: <strong>circle</strong> <em>center r</em></dt>
<dd><p>Return a path that draws a circle centered on the point <var>center</var>
with radius <var>r</var>.
</p></dd></dl>
<p>With one or more paths created, a <em>painter</em> is needed to give the
path its style and placement in the final picture. Painters can be
combined together to form arbitrarily complex pictures.
</p>
<dl>
<dt id="index-stroke">Procedure: <strong>stroke</strong> <em>. paths</em></dt>
<dd><p>Apply a stroked drawing style to <var>paths</var>.
</p></dd></dl>
<dl>
<dt id="index-fill">Procedure: <strong>fill</strong> <em>. paths</em></dt>
<dd><p>Apply a filled drawing style to <var>paths</var>.
</p></dd></dl>
<dl>
<dt id="index-fill_002dand_002dstroke">Procedure: <strong>fill-and-stroke</strong> <em>. paths</em></dt>
<dd><p>Apply a filled and stroked drawing style to <var>paths</var>.
</p></dd></dl>
<dl>
<dt id="index-with_002dstyle">Syntax: <strong>with-style</strong> <em>((style-name value) ...) painter</em></dt>
<dd><p>Apply all the given style settings to <var>painter</var>.
</p>
<p>Possible style attributes are:
</p>
<ul>
<li> <code>blend-mode</code>
</li><li> <code>fill-color</code>
</li><li> <code>stroke-color</code>
</li><li> <code>stroke-width</code>
</li><li> <code>stroke-feather</code>
</li><li> <code>stroke-cap</code>
</li></ul>
<div class="lisp">
<pre class="lisp"><span class="syntax-open">(</span><span class="syntax-symbol">with-style</span> <span class="syntax-open">(</span><span class="syntax-open">(</span><span class="syntax-symbol">stroke-color</span> <span class="syntax-symbol">green</span><span class="syntax-close">)</span>
<span class="syntax-open">(</span><span class="syntax-symbol">stroke-width</span> <span class="syntax-symbol">4.0</span><span class="syntax-close">)</span><span class="syntax-close">)</span>
<span class="syntax-open">(</span><span class="syntax-symbol">stroke</span> <span class="syntax-open">(</span><span class="syntax-symbol">circle</span> <span class="syntax-open">(</span><span class="syntax-symbol">vec2</span> <span class="syntax-symbol">100.0</span> <span class="syntax-symbol">100.0</span><span class="syntax-close">)</span> <span class="syntax-symbol">50.0</span><span class="syntax-close">)</span><span class="syntax-close">)</span><span class="syntax-close">)</span>
</pre></div>
</dd></dl>
<p>Fill colors may be either solid colors (see <a href="Colors.html">Colors</a>) or gradients.
For gradient fills, there are two styles: linear or radial.
</p>
<dl>
<dt id="index-linear_002dgradient">Procedure: <strong>linear-gradient</strong> <em>[#:origin (vec2 0 0)] [#:start-color white] [#:end-color black] [#:rotation 0] [#:offset 0] [#:length 100]</em></dt>
<dd>
<p>Return a new linear gradient that transitions from <var>start-color</var>
on the left to <var>end-color</var> on the right over <var>length</var> pixels.
<var>offset</var> may be used to push the gradient start point to the
right, creating a solid block of <var>start-color</var> on the right hand
side of the painter. The line’s direction may be changed by
specifying a <var>rotation</var> value. The starting point for the
gradient is determined by <var>origin</var> and defaults to the lower left
corner of the painter’s bounding box.
</p></dd></dl>
<dl>
<dt id="index-radial_002dgradient">Procedure: <strong>radial-gradient</strong> <em>[#:origin (vec2 0 0)] [#:start-color white] [#:end-color black] [#:radius 50.0] [#:radius-x] [#:radius-y] [#:rotation 0] [#:offset 0]</em></dt>
<dd>
<p>Return a new radial gradient that transitions from <var>start-color</var>
at the point <var>origin</var> to <var>end-color</var> at <var>radius</var> pixels
away. <var>offset</var> specifies the distance from the origin where
<var>start-color</var> begins to transition. The default is to immediately
start transitioning. The default shape of this type of gradient is a
circle, but it can also be made elliptical by specifying different
<var>radius-x</var> and <var>radius-y</var> values. When the gradient shape is
elliptical, <var>rotation</var> can be used to rotate it.
</p></dd></dl>
<dl>
<dt id="index-gradient_003f">Procedure: <strong>gradient?</strong> <em>obj</em></dt>
<dd><p>Return <code>#t</code> when <var>obj</var> is a gradient object.
</p></dd></dl>
<p>Painters can also be transformed and combined to form new painters.
</p>
<dl>
<dt id="index-transform">Procedure: <strong>transform</strong> <em>matrix painter</em></dt>
<dd><p>Apply <var>matrix</var>, a 3x3 transformation matrix (see <a href="Matrices.html">Matrices</a>), to
<var>painter</var>.
</p></dd></dl>
<dl>
<dt id="index-translate">Procedure: <strong>translate</strong> <em>v painter</em></dt>
<dd><p>Translate <var>painter</var> by the 2D vector <var>v</var>.
</p></dd></dl>
<dl>
<dt id="index-rotate">Procedure: <strong>rotate</strong> <em>angle painter</em></dt>
<dd><p>Rotate <var>painter</var> by <var>angle</var> radians.
</p></dd></dl>
<dl>
<dt id="index-scale">Procedure: <strong>scale</strong> <em>x painter</em></dt>
<dd><p>Scale <var>painter</var> by the scalar <var>x</var>.
</p></dd></dl>
<dl>
<dt id="index-horizontal_002dflip">Procedure: <strong>horizontal-flip</strong> <em>painter</em></dt>
<dd><p>Flip <var>painter</var> horizontally.
</p></dd></dl>
<dl>
<dt id="index-vertical_002dflip">Procedure: <strong>vertical-flip</strong> <em>painter</em></dt>
<dd><p>Flip <var>painter</var> vertically.
</p></dd></dl>
<dl>
<dt id="index-pad">Procedure: <strong>pad</strong> <em>pad-x pad-y painter</em></dt>
<dd><p>Add <var>pad-x</var> and <var>pad-y</var> amount of empty space around
<var>painter</var>.
</p></dd></dl>
<dl>
<dt id="index-superimpose">Procedure: <strong>superimpose</strong> <em>. painters</em></dt>
<dd><p>Stack <var>painters</var> on top of each other.
</p></dd></dl>
<p>The next batch of procedures is taken straight out of the picture
language described in
<a href="https://mitpress.mit.edu/sites/default/files/sicp/full-text/book/book-Z-H-15.html#%_sec_2.2.4">Structure and Interpretation of Computer Programs</a> section 2.2.4.
</p>
<dl>
<dt id="index-beside">Procedure: <strong>beside</strong> <em>. painters</em></dt>
<dd><p>Place <var>painters</var> next to each other in a row.
</p></dd></dl>
<dl>
<dt id="index-below">Procedure: <strong>below</strong> <em>. painters</em></dt>
<dd><p>Place <var>painters</var> next to each other in a column.
</p></dd></dl>
<dl>
<dt id="index-right_002dsplit">Procedure: <strong>right-split</strong> <em>painter n</em></dt>
<dd><p>Subdivide <var>painter</var> into 3 sections, recursively, like so:
</p>
<pre class="verbatim">*----------------*----------------*
| | |
| | right-split |
| | n - 1 |
| | |
| painter *----------------*
| | |
| | right-split |
| | n - 1 |
| | |
*----------------*----------------*
</pre>
</dd></dl>
<dl>
<dt id="index-up_002dsplit">Procedure: <strong>up-split</strong> <em>painter n</em></dt>
<dd><p>Subdivide <var>painter</var> into 3 sections, recursively, like so:
</p>
<pre class="verbatim">*----------------*----------------*
| | |
| up-split | up-split |
| n - 1 | n - 1 |
| | |
*----------------*----------------*
| |
| painter |
| |
| |
*----------------*----------------*
</pre>
</dd></dl>
<dl>
<dt id="index-corner_002dsplit">Procedure: <strong>corner-split</strong> <em>painter n</em></dt>
<dd><p>Subdivide <var>painter</var> into 4 sections, recursively, like so:
</p>
<pre class="verbatim">*----------------*----------------*
| | |
| up-split | corner-split |
| n - 1 | n - 1 |
| | |
*----------------*----------------*
| | |
| painter | right-split |
| | n - 1 |
| | |
*----------------*----------------*
</pre>
</dd></dl>
<p>As in real life, a painter cannot paint anything without a canvas.
Once a painter has been associated with a canvas, it can finally be
rendered to the screen.
</p>
<dl>
<dt id="index-make_002dcanvas">Procedure: <strong>make-canvas</strong> <em>painter [#:matrix]</em></dt>
<dd><p>Return a new canvas that will <var>painter</var> will draw on. Optionally,
a 3x3 <var>matrix</var> may be specified to apply an arbitrary
transformation to the resulting image.
</p></dd></dl>
<dl>
<dt id="index-make_002dempty_002dcanvas">Procedure: <strong>make-empty-canvas</strong> <em>[#:matrix]</em></dt>
<dd><p>Return a new canvas that no painter is using. Optionally, a 3x3
<var>matrix</var> may be specified to apply an arbitrary transformation to
the image, should a painter later be associated with this canvas.
</p></dd></dl>
<dl>
<dt id="index-canvas_003f">Procedure: <strong>canvas?</strong> <em>obj</em></dt>
<dd><p>Return <code>#t</code> is <var>obj</var> is a canvas.
</p></dd></dl>
<dl>
<dt id="index-set_002dcanvas_002dpainter_0021">Procedure: <strong>set-canvas-painter!</strong> <em>canvas painter</em></dt>
<dd><p>Associate <var>painter</var> with <var>canvas</var>.
</p></dd></dl>
<dl>
<dt id="index-set_002dcanvas_002dmatrix_0021">Procedure: <strong>set-canvas-matrix!</strong> <em>canvas matrix</em></dt>
<dd><p>Set the 3x3 transformation matrix of <var>canvas</var> to <var>matrix</var>.
</p></dd></dl>
<dl>
<dt id="index-draw_002dcanvas">Procedure: <strong>draw-canvas</strong> <em>canvas</em></dt>
<dd><p>Render <var>canvas</var> to the screen.
</p></dd></dl>
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