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@@ -1,8 +1,57 @@
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## A language to describe a sketch
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-Pysketcher initial version [HPL Pysketcher]() defines sketch in python.
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+Pysketcher initial version [HPL Pysketcher]() 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 [see The hierarchy of the "friction" main object](#the-hierarchy-of-the-friction-main-object) at the end of this page.
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+
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+Due to the hierarchical nature of sketches, it is quite straightforward to think about using yaml as the syntax for defining a sketch.
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+
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+The benefits are as follow:
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+
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+* A leaner presentation of the sketch as only the data making sense is going to be used
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+* A more straightforward reading of the composition hierachy
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+* A more robust sketch definition as only a set of rules will be applied to define a sketch and no further python idiom will be intermingled
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## Example
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+
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+This example provides the yaml content to define the Dry Friction case
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+
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+### The final sketch
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+
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+
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+An inclined plan (the A-B edge) supports a blue rectangle which is pulled donward by the gravity. The plan makes an angle $\theta$. The sketch design enable the $\theta$ angle to change. The whole plan including the body can rotate arround the point B.
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+
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+### The yaml definition
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+
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+Sketcher language is defined as a yaml compliant file or string. The yaml file is a dictionnary of
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+
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+* functionnal objects (leaf objects, like Rectangle, Circle, Line etc or composition)
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+* extended with object style (line or fill colors, line stroke...)
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+* to which transformation are applied (translation, rotation...)
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+
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+As a general rule, a new object suppose all parameters to be defined before they are used to construct it.
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+
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+**For example, you can create a circle if the center and the radius have been defined earlier in the file.**
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+
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+The general layout of a sketcher file is as follow:
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+
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+* **Libraries, Construction Variables, Frame**
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+ * declaration of the libraries used by the objects further declared: at least pysketcher is mandatory
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+ * various global variable which encompass the "Construction" variables which define the object main physical dimensions, positions...
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+ * some "actions" corresponding to executable python sentences
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+ * 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.
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+ * Other use case of action is the setting of global parameters like default line color: (drawing_tool.set_linecolor('black')) for example
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+* **Objects**
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+ * Usually starting with the declaration of leaf simple objects
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+ * then aggregated using the composition object
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+ * Composition can be made of composition object
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+ * grouping leafs and composition will be further used to apply transformation latter on (based on the "physics")
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+ * The example presents three group of objects
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+ * The body object
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+ * The plan object
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+ * The friction main object
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+ * The plan includes the body
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+ * The friction includes the plan (that will be able to rotate as a group) and the ground (will stay fixed)
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+
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+#### Libraries, Construction Variables, Frame
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```yaml
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libraries: ["from math import tan, radians, sin, cos",
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"from pysketcher import *"]
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@@ -28,6 +77,9 @@ x: a + 3*L/10.
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y: help_line(x=x)
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contact: point(x, y)
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c: contact + rL/2*normal_vec
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+```
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+#### The body object
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+```yaml
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rectangle:
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formula: Rectangle(contact, rl, rL)
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style:
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@@ -51,6 +103,9 @@ body:
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formula: "Composition({'wheel': wheel, 'N': N, 'mg': mg})"
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style:
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linecolor: black
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+```
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+#### The plan object
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+```yaml
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mB:
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formula: Text(r'$B$',B)
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mA:
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@@ -79,6 +134,14 @@ x_axis:
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formula: "Axis(start=contact+ 2*rl*normal_vec, length=2*rl,label='$x$', rotation_angle=-theta)"
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plan:
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formula: "Composition({'body': body, 'angle': angle, 'inclined wall': wall, 'x start': x_const, 'x axis': x_axis, 'mA': mA, 'mB': mB})"
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+```
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+#### The friction main object
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+```yaml
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+
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friction:
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formula: "Composition({'plan': plan, 'ground': ground})"
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-```
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+```
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+
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+### The hierarchy of the "friction" main object
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+
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+
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