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    Constants: Construction parameters
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    Frame: core geometric parameters
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    The body object
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    The plan object
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                  <h1>Learning by Example</h1>
                
                <h2 id="a-language-to-describe-a-sketch">A language to describe a sketch</h2>
<p>Pysketcher initial version <a href="">HPL Pysketcher</a> enable sketch definition in python. HPL is showing the hierachical nature of sketches. This is implemented via the Composition function. One can further grasp this using the graphviz_dot function applied to discover the composition herarchy implemented as a graphviz image <a href="#friction-sketch-hierarchy">see The hierarchy of the "friction" sketch</a> at the end of this page.</p>
<p>Due to the hierarchical nature of sketches, it is quite straightforward to think about using yaml as the syntax for defining a sketch.</p>
<p>Benefits are the following:</p>
<ul>
<li>Leaner sketch writing as only data relevant to the context needs to be defined</li>
<li>A more straightforward reading for the same reason</li>
<li>A more robust sketch definition <ul>
<li>The same set of rules is applied to generate a sketch</li>
<li>No further python idiom is be intermingled as opposed to the case of python defined sketches</li>
<li>Don't make me wrong! Data defined versus program defined there is no winner, it's just a matter of context</li>
</ul>
</li>
</ul>
<h2 id="example">Example</h2>
<p>This example provides the yaml content to define the Dry Friction case</p>
<h3 id="the-final-sketch">The final sketch</h3>
<p><img alt="dryfriction sketch" src="../images/dryfriction.svg" /></p>
<p>An inclined plan (the A-B edge) supports a blue rectangle which is dragged down by gravity. The plan makes an angle <span><span class="MathJax_Preview">\theta</span><script type="math/tex">\theta</script></span> with the ground level. Sketch implementation notebook includes a controller enabling the <span><span class="MathJax_Preview">\theta</span><script type="math/tex">\theta</script></span> angle to change. The whole plan, including the body, can rotate arround point B.</p>
<h3 id="support-files">Support files</h3>
<p>The example we are developing now is based upon the "Dry Friction mockup" notebook</p>
<ul>
<li>the rendered html version of the notbook can be viewed <a href="../resources/DryFriction.html">here</a></li>
<li>the notebook can be download <a href="../resources/DryFriction.ipynb">here</a></li>
</ul>
<h3 id="the-yaml-definition">The yaml definition</h3>
<p>Sketcher language is defined as a yaml compliant file or string. The yaml file is a dictionnary of "objects". Objects can be regular python objects or sketcher objects.
A skertcher object is composed as follow:</p>
<ul>
<li><strong>a formula</strong>: it's a leaf object, like Rectangle, Circle, Line etc or a composition</li>
<li><strong>a style list</strong>: line or fill colors, line stroke... declared as a yaml hierarchy</li>
<li><strong>a transformation list</strong>: the defined object can be transformed using sketcher transformation: translation, rotation...</li>
</ul>
<p>As a general rule, a new object suppose all parameters to be defined before they are used to construct it.</p>
<p><strong>For example, you can create a circle if the center and the radius have been defined earlier in the file.</strong></p>
<p>The general layout of a sketcher file is as follow:</p>
<ul>
<li><strong>Libraries, Construction Variables, Frame</strong><ul>
<li>declaration of the libraries used by the objects further declared: at least pysketcher is mandatory</li>
<li>various global variable which encompass the "Construction" variables which define the object main physical dimensions, positions...</li>
<li>some "actions" corresponding to executable python sentences<ul>
<li>One mandatory action is the setting of the drawing frame (drawing_tool.set_coordinate_system): it must be declared before any other pysketcher object is used.</li>
<li>Other use case of action is the setting of global parameters like default line color: (drawing_tool.set_linecolor('black')) for example</li>
</ul>
</li>
<li>this is stored in the head string thereafter</li>
<li>The example uses the following objects<ul>
<li>libraries: setting the libraries used for this sketch</li>
<li>constants: all the sketch dimensionning data</li>
<li>frame: all the shapes or geometric objects which will be used by the other shapes</li>
</ul>
</li>
</ul>
</li>
<li><strong>Sketcher Objects</strong><ul>
<li>Usually starting with the declaration of Pysketcher leaf objects (Geometry object like Line, Circle, Rectangle...)</li>
<li>May be aggregated using the composition object</li>
<li>Composition can be made of composition object (recursive behaviour)</li>
<li>Grouping leafs and composition will be further used to apply transformation latter on (based on the "physics")</li>
<li>The example uese three group of shapes<ul>
<li>The body object</li>
<li>The plan object</li>
<li>The friction main object</li>
</ul>
</li>
<li>The plan includes the body</li>
<li>The friction includes the plan (that will be able to rotate as a group) and the ground (will stay fixed)</li>
</ul>
</li>
</ul>
<h4 id="libraries">Libraries</h4>
<pre><code class="python">libraries = &quot;&quot;&quot;\
name: head
shapes:
    libraries: [&quot;from math import tan, radians, sin, cos&quot;,&quot;from pysketcher import *&quot;]
&quot;&quot;&quot;
</code></pre>

<h4 id="constants-construction-parameters">Constants: Construction parameters</h4>
<pre><code class="python">constants = &quot;&quot;&quot;\
name: constants
shapes:
    fontsize: 18         # size of the characters
    g: 9.81              # constant gravity
    theta: 30.0          # inclined plane angle
    L: 10.0              # sketch sizing parameter
    a: 1.0               #
    xmin: 0.0            # sketech min Abscissa
    ymin: -3.0           # sketech min Ordinate     
    rl: 2.0              # rectangle width
    rL: 1.0              # rectangle length
&quot;&quot;&quot;
</code></pre>

<h4 id="frame-core-geometric-parameters">Frame: core geometric parameters</h4>
<pre><code class="python">frame = &quot;&quot;&quot;\
name: frame
shapes:
    setframe:            # sketch setup
        action: &quot;drawing_tool.set_coordinate_system(xmin=xmin-L/5, xmax=xmin+1.5*L,ymin=ymin, ymax=ymin+1.5*L,instruction_file='tmp_mpl_friction.py')&quot;
    setblackline:        # default frame values and actions
        action: &quot;drawing_tool.set_linecolor('black')&quot;
    B: point(a+L,0)                      # wall right end
    A: point(a,tan(radians(theta))*L)    # wall left end
    normal_vec: point(sin(radians(theta)),cos(radians(theta)))     # Vector normal to wall
    tangent_vec: point(cos(radians(theta)),-sin(radians(theta)))   # Vector tangent to wall
    help_line: Line(A,B)                 # wall line
    x: a + 3*L/10.                       # contact point Abscissa
    y: help_line(x=x)                    # contact point Ordinate
    contact: point(x, y)                 # contact point: middle of the rectangle bottom edge
    c: contact + rL/2*normal_vec
&quot;&quot;&quot;
</code></pre>

<h4 id="the-body-object">The body object</h4>
<pre><code class="python">body = &quot;&quot;&quot;\
name: body
shapes:
    rectangle: 
        formula: Rectangle(contact, rl, rL)
        style:
            linecolor: blue
            filled_curves: blue
        transform: [&quot;rotate(-theta, contact)&quot;,
                    &quot;translate(-rl/2*tangent_vec)&quot;]
    N: 
        formula: Force(contact - rl*normal_vec, contact, r'$N$', text_pos='start')
        style:
            linecolor: black
    wheel: 
        formula: &quot;Composition({'outer': rectangle})&quot;   
        style:
            shadow: 1
    mc:
        formula: Text(r'$c$', c)
    body: 
        formula: &quot;Composition({'wheel': wheel, 'N': N, 'mc': mc})&quot;
        style:
            linecolor: black
&quot;&quot;&quot;
</code></pre>

<h4 id="the-plan-object">The plan object</h4>
<pre><code class="python">plan = &quot;&quot;&quot;\
name: plan
shapes:
    mB:
        formula: Text(r'$B$',B)
    mA:
        formula: Text(r'$A$', A)
    wall: 
        formula: Wall(x=[A[0], B[0]], y=[A[1], B[1]], thickness=-0.25,transparent=False)
        style:
            linecolor: black    
    x_const: 
        formula: Line(contact, contact + point(0,4))
        style:
            linestyle: dotted
        transform: rotate(-theta, contact)
    x_axis: 
        formula: &quot;Axis(start=contact+ 2*rl*normal_vec, length=2*rl,label='$x$', rotation_angle=-theta)&quot;
    plan: 
        formula: &quot;Composition({'body': body, 'inclined wall': wall, 'x start': x_const, 'x axis': x_axis, 'mA': mA, 'mB': mB})&quot;
&quot;&quot;&quot;
</code></pre>

<h4 id="the-friction-sketch">The friction sketch</h4>
<pre><code class="python">friction = &quot;&quot;&quot;\
name: friction
shapes:
    mg: 
        formula: Gravity(c, rl, text='$Mg$')
        style:
            linecolor: black
    angle: 
        formula: &quot;Arc_wText(r'$&lt;bslash&gt;theta$', center=B, radius=3, start_angle=180-theta, arc_angle=theta, fontsize=fontsize)&quot;
        style:
            linecolor: black
            linewidth: 1
    ground: 
         formula: Line((B[0]-L/10., 0), (B[0]-L/2.,0))
         stlye:
             linecolor: black
             linestyle: dashed
             linewidth: 1
    friction: 
            formula: &quot;Composition({'plan': plan, 'ground': ground, 'mg': mg, 'angle': angle})&quot;
&quot;&quot;&quot;
</code></pre>

<h3 id="using-the-parser">Using the parser</h3>
<p>To parse the above example, the following code do the job.</p>
<ol>
<li>libraries, constants and frame must be used first as all the other bits needs one or more variable they defines.</li>
<li>After, any other sketch can be parsed, the order just need to respect precedence (if one object uses another it must be parsed after)</li>
<li>this setting allows naturally a modular definition of sketch objects</li>
</ol>
<p>The parser checks for syntax precedence and warns of any detected error.</p>
<pre><code class="python">myfig = {}
if sketchParse(libraries,myfig):
    if sketchParse(constants,myfig):
        if sketchParse(frame,myfig):
            if sketchParse(body,myfig):
                if sketchParse(plan,myfig):
                    if sketchParse(friction,myfig):
                        print(&quot;success&quot;)
</code></pre>

<h3 id="friction-sketch-hierarchy">"friction" sketch hierarchy</h3>
<p><img alt="" src="../images/dotdryfriction.svg" /></p>
                
              
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