Geometrically Aware Drawing (GAD) 
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FX Draw implements Geometrically Aware Drawing (GAD) – but what does it mean?
Traditionally, drawing packages had a grid of points that the mouse jumped to while drawing. That allowed you to align figures that were based on lines but made it very difficult to do anything with curves or points of intersection. FX Draw rectifies this problem. While FX Draw still has a grid, it also knows a lot about geometry.
For example.
Drawing this diagram in most drawing packages is a difficult proposition. Not only do you need to draw a line that is tangential to a circle, but you also need to draw on the correct point of the first circle so that the line is tangential to both!
Drawing the diagram with FX Draw is almost trivial:
First, draw the two circles.
Second, place the cursor NEAR a point on one circle that would be the end of a line that is tangential to both.
When you are somewhere close, FX Draw will graphically show you what it has found. It will also add a message to the status bar at the bottom of the screen to tell you what it has found.
"Tangent to both circles"
If you start to draw the line now, it will automatically begin at the appropriate point. Finally, move to the other circle, look for the same message and the line is drawn.
We have drawn in the other three possible tangent lines. All are found automatically by FX Draw.
That is the crux of GAD. FX Draw automatically jumps to points which are of geometrical interest. It is "aware" of a wide variety of geometrical points and relationships.
The GridUnderneath all drawings there is a grid. In the absence of any other significant points FX Draw will automatically jump to the nearest grid point (unless the grid is disabled.)
All FiguresFX Draw will automatically jump to a point on a figure in preference to a grid point. This makes it easy to draw something that starts or finishes ON a circle for example. Points of geometrical interest are more "attractive" than points on a figure.
LinesFX Draw considers the end points, mid point, third points and quarter points to be important points on a line. FX Draw will also preferentially draw perpendiculars and parallels to existing lines. It will also preferentially make lines the same length or which bisect existing angles.
CirclesThe centre point and points on the circumference are attractive points to FX Draw. FX Draw will also draw lines that pass through the centre of the circle and are tangential to the circle. FX Draw can also determine tangents to two circles as shown previously.
ArcsThe end points and centre of arcs as well as the arc's centre of curvature are tracked as geometrically important points.
Points of IntersectionPoints of intersection between figures are attractive to FX Draw. FX Draw can find points of intersection for most figures including lines, circles, arcs, ellipses and Bezier curves.
Most figures have geometrically important points. We have not listed all of them here. Most importantly, the points are found automatically for you and the system tells you exactly what it is finding at all times.
