Beginnings of some docs for SolveSpace.

[git-p4: depot-paths = "//depot/solvespace/": change = 1800]

doc/rep.txt

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+
+The user enters requests. A request might be a line segment, or a plane,
+or to step and repeat a group of entities, or anything else. Each
+request has a groupid associated with it; a group will contain one or
+more requests. The request will generate entities, and possibly equations.
+
+Special requests would include an include, which gives us a concept of
+hierarchy. An include pulls in all the entities from another SolveSpace
+part, and fixes them up to a rotation and translation; so that introduces
+six free variables. This means that the part is rigidly constrained,
+but that it still must be placed, and that entities within the included
+part are available to constrain against.
+
+An entity is some geometric thing in the sketch. This might be a
+line segment, or a datum point, or something else. Some requests
+correspond to a single entity, in a straightforward way. Other requests
+generate multiple entities, in some relationship (that is constrained
+automatically, through the generated equations) to other parts of the
+sketch. Each entity has a groupid, which is inherited from the request
+that generated it.
+
+One important entity is a pwl. That's a piecewise linear segment. Its
+endpoints are fixed, so it generates no parameters.
+
+The entity is described in terms of paramgroups. A paramgroup corresponds
+to one or more solver parameters, grouped in such a way as to have
+geometric meaning. For example, a point would correspond to three params,
+x, y, and z.
+
+The paramgroups break down in to params. These are the unknowns in the
+solver equations.
+
+The user enters constraints. Each constraint has groupid. The constraints
+generate equations too.
+
+
+
+
+The items that generate unknowns are:
+
+    POINT:
+
+        three unknowns, (x, y, z)
+
+
+Entities are:
+
+    DATUM POINT:
+
+        one point
+
+    DATUM PLANE:
+
+        one point; the plane is through that point, and normal to the
+        vector from that point to the origin
+
+    LINE SEGMENT:
+
+        two endpoints

doc/tutorial.txt

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+
+In mechanical drawing, it's common to use a parallel projection of a
+3d model into a 2d drawing. A parallel projection is also known as an
+axonometric projection; orthographic, isometric, dimetric, and trimetric
+projections are examples of such a projection. In a parallel projection,
+any two lines that are parallel in real life must also appear parallel
+on the drawing.
+
+This differs from a perspective projection. In a perspective projection,
+objects that are closer to the "camera" appear larger than objects
+that are farther away. This means that some lines that are parallel in
+real life will not be parallel on the drawing; they will converge at a
+vanishing point. This may cause confusion.
+
+By default, NTsolver displays a parallel projection of the model. To
+display a perspective projection, choose #LINK(configuration) in the text
+window, and set the perspective factor to something other than zero.
+The distance from the "camera" to the model is equal to one thousand
+pixels divided by the perspective factor.
+
+
+
+The user interface consists of two windows: a large graphics window that
+displays the model being drawn, and a smaller text window, that displays
+information about the model.
+
+After starting a new file, the model is empty except for the three
+coordinate planes. The graphics window's view is aligned so that the XY
+plane is parallel to the plane of your monitor.
+
+NTsolver requires a mouse with a scrollwheel or center button. To pan
+the view to the left or right, center-drag the mouse. To rotate the view
+around the horizontal or vertical axes of the screen, shift-center-drag
+the mouse. To rotate the view around the axis perpendicular to the screen,
+control-center-drag the mouse.
+
+After moving the view, it's possible to orient the view back on to the
+active workplane. Choose #MENU(Sketch -> Draw in Workplane), or press
+#KEY(W). This produces an orthographic projection of the model. When
+drawing lines and curves in a workplane, it's convenient to work with
+the view oriented on to that workplane.
+
+To zoom in, rotate the mouse wheel, or choose #MENU(View -> Zoom In /
+Out). This will not have any visible effect until a model has been
+drawn, though, since the coordinate planes are automatically scaled to
+fit on-screen.
+
+The text window works like a web browser; any underlined text is a link,
+which may be activated by clicking on it. At the top of the text window,
+two rows of links will show and hide different features of the sketch
+(workplanes, normals, points, constraints, shaded, faces, mesh, hidden
+lines).
+
+Below that, the text window displays a list of groups. A group is a set of
+entities, like lines, circles, or planes. In a new file, two groups exist:
+the references, and a drawing group. The references are the coordinate
+planes (XY, YZ, and ZX); they provide the initial geometric entities to
+constrain against. The drawing group is active; if you draw a line, or
+a rectangle, or some other new geometry, then that geometry will appear
+in the active drawing group.
+
+
+
+
+To start, we