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11.3.2  Parameters for changing features

Graphical features are changed by giving appropriate values to certain parameters. Several values can be given at once with an expression of the form feature=value1+value2+…. Some values can be set using optional arguments to graphic commands, which will set the feature locally; namely, it will only apply to that particular graphic object. Some values can be specified at the beginning of a line, which will set the feature globally; it will apply to all the graphic objects created on that line. For some features, both options are available.

Parameters for local features

Commands which create graphic objects, such as triangle, can have optional arguments to change a features of the object. For example, the argument color = red will make an object red.
Input:

triangle(0,1,1+i,color=red)

Output:

The features and their possible values are:

display or color
These two parameter names have the same effect. They control the following features.
Color
The following values will change the color:
  • An integer from 0 to 381.
    Integers from 0 to 255 correspond to the color palette, integers from 256 to 381 will be the spectrum of colors.
    The program
      rainbow() := {
        local j, C;
        C := [];
        for (j := 256; j < 382; j++) {
          C := append(C,square(j,j+1,color=j+filled));
          }
       }
    
    will show the colors;
    Input:
    rainbow();
    Output:
    The number of a color is its x-coordinate. To see just one color, say the color corresponding to n for 256 ≤ n ≤ 381, enter
    Input:
    rainbow()[n-256]
  • The names black, white, red, blue, green, magenta cyan or yellow.
Fill
The filled value creates a solid object.
Input:
triangle(0,1,1+i,display=filled)
Output:
Point markers
By default, points are drawn with a small cross. The following (self-explanatory) values change the marker.
rhombus_point
square_point
cross_point
star_point
plus_point
point_point
triangle_point
invisible_point
Point width
The values point_width_1,…,point_width_8 change the thickness of the lines in the point markers.
Line style
The following (self-explanatory) values change the style of lines.
solid_line
dash_line
dashdot_line
dashdotdot_line
cap_flat_line
cap_round_line
cap_square_line
Line widths
The values line_width_1,…,line_width_8 change the thickness of the lines.
thickness
This controls line thickness, it can be an integer from 1 to 7.
nstep
This sets the number of sampling points for three-dimensional objects.
tstep
This sets the step size of the parameter when drawing a one parameter parametric plot.
ustep
This sets the step size of the first parameter when drawing a two-parameter parametric plot.
vstep
This sets the step size of the second parameter when drawing a two-parameter parametric plot.
xstep
This sets the step size of the x variable.
ystep
This sets the step size of the y variable.
zstep
This sets the step size of the z variable.
frames
This sets the number of graphs computed when an animated graph is created with the animate or animate3d command.
legend
This adds a legend to a graphic object and should be a string. It is probably most useful when that object is a point or a polygon. If the object is a polygon, the legend will be placed in the middle of the last side. Other parameters for the graphic object will specify the color or position of the legend.
gl_texture
This sets an image file to be put on the graphic object; it should be the name of the file.

Parameters for global features

Parameters set at the beginning of a line change features on the entire graphic screen. It only takes effect when the line ends with a graphic command. For example, starting the line with title=title string will give the graphic screen a title.
Input:

title = "Some triangles"; triangle(0,1,1+i); triangle(2,3,3+i);

Output:

The parameters for features and their possible values are:

axes
This determines whether axes are shown or hidden; a value of 0 or false hides the axes, a value of 1 or true shows the axes.
labels
This sets labels for the axes; it should be a list of two strings ["x axis label","y axis label"].
label
This puts a labels on the graphic screen in the following ways.
title
This sets the title for the graphic window, it should be a string.
gl_texture
This sets the wallpaper of the graphic window to be an image file, it should be the name of the file.
gl_x_axis_name,gl_x_axis_name,gl_x_axis_name
These set the names of the axes.
gl_x_axis_unit,gl_x_axis_unit,gl_x_axis_unit
These set the units of the axes.
gl_x_axis_color,gl_x_axis_color,gl_x_axis_color
These set the colors of the axes labels; they take the same color options as the local parameter color.
gl_ortho
This ensures that the graph is orthonormal when it is set to 1.
gl_x,gl_y,gl_z
These define the framing of the graph; they should be intervals min..max. (They are not compatible with interactive graphs.)
gl_xtick,gl_ytick,gl_ztick
These determine the spacing of the ticks on the axes.
gl_shownames
This shows or hides object names, it can be true or false.
gl_rotation
This sets the axis of rotation for three-dimensional scene animations; it should be a direction vector [x,y,z].
gl_quaternion
This sets the quaternion for viewing three-dimensional scenes; it should be a fourtuple [x,y,z,t]. (This is not compatible with interactive graphs.)

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