## Maxima – 271 – draw – 18

Marco Bruno

Continuo da qui, copio dal Reference Manual, PDF scaricabile da qui, sono a p.838.

`transform`
Default value: `none`.

If `transform` is `none`, the space is not transformed and graphic objects are drawn as defined. When a space transformation is desired, a list must be assigned to option `transform`. In case of a 2D scene, the list takes the form `[f1(x,y), f2(x,y), x, y]`. In case of a 3D scene, the list is of the form `[f1(x,y,z), f2(x,y,z), f3(x,y,z), x, y, z]`.

The names of the variables defined in the lists may be different to those used in the definitions of the graphic objects.

``````(%i1) th : %pi / 4\$

(%i2) draw2d(
color = "#e245f0",
proportional_axes = 'xy,
line_width = 8,
triangle([3,2],[7,2],[5,5]),
border = false,
fill_color = yellow,
transform = [cos(th)*x - sin(th)*y,
sin(th)*x + cos(th)*y, x, y],
triangle([3,2],[7,2],[5,5]) )\$``````

Translation in 3D.

``````(%i3) draw3d(
color = "#a02c00",
explicit(20*exp(-x^2-y^2)-10,x,-3,3,y,-3,3),
transform = [x+10,y+10,z+10,x,y,z],
color = blue,
explicit(20*exp(-x^2-y^2)-10,x,-3,3,y,-3,3) )\$``````

`transparent`
Default value: `false`.

If `transparent` is `false`, interior regions of polygons are filled according to `fill_color`.

This option affects the following graphic objects in `gr2d`: `polygon`, `rectangle` and `ellipse`.

``````(%i4) draw2d(polygon([[3,2],[7,2],[5,5]]),
transparent = true,
color = blue,
polygon([[5,2],[9,2],[7,5]]) )\$``````

`unit_vectors`
Default value: `false`.

If `unit_vectors` is `true`, vectors are plotted with module `1`. This is useful for plotting vector fields. If `unit_vectors` is `false`, vectors are plotted with its original length. This option is relevant only for vector objects.

``````(%i5) draw2d(xrange = [-1,6],
yrange = [-1,6],
vector([0,0],[5,2]),
unit_vectors = true,
color = red,
vector([0,3],[5,2]))\$``````

`user_preamble`
Default value: `""` (empty string).

Expert Gnuplot users can make use of this option to fine tune Gnuplot’s behaviour by writing settings to be sent before the `plot` or `splot` command.

The value of this option must be a string or a list of strings (one per line).

Since this is a global graphics option, its position in the scene description does not
matter.

Tell Gnuplot to draw axes and grid on top of graphics objects:

``````(%i6) draw2d(
xaxis = true, xaxis_type=solid,
yaxis = true, yaxis_type=solid,
user_preamble = "set grid front",
region(x^2+y^2<1 ,x,-1.5,1.5,y,-1.5,1.5))\$``````

Tell gnuplot to draw all contour lines in black:

``````(%i7) draw3d(
contour=both,
surface_hide=true,enhanced3d=true,wired_surface=true,
contour_levels=10,
user_preamble="set for [i=1:8] linetype i dashtype i linecolor 0",
explicit(sin(x)*cos(y),x,1,10,y,1,10));
(%o7)                          [gr3d(explicit)]``````

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