26.3.2  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+…+valueN. 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.

The features and their possible values are:

• display or color — These two parameter names have the same effect. See Section 19.1.2 for information on supported values.
• thickness — This controls line thickness, it can be an integer from 1 to 7.
• nstep — The number of sampling points for 3D objects.
• tstep — The step size of the parameter when drawing a one parameter parametric plot.
• ustep — The step size of the first parameter when drawing a two-parameter parametric plot.
• vstep — The step size of the second parameter when drawing a two-parameter parametric plot.
• xstep — The step size of the x variable.
• ystep — The step size of the y variable.
• zstep — The step size of the z variable.
• frames — 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.

Examples (of the filled option)

To see the rainbow colors, you can enter and compile the program:

followed by

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: rainbow()[n-256].

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=titlestring will give the graphic screen a title.

Example

The parameters for global 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 labels on the graphic screen in the following ways.
  • To set the units on the axes, it can be a list of two or three strings, [“x units”,“y units”] or [“x units”,“y units”,“z units”].
  • To place a string at a particular point, it can be a list of two integers followed by a string. The integers determine the point, starting from (0,0) in the top left of the screen.
• 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_y_axis_name, gl_z_axis_name — These set the names of the axes.
• gl_x_axis_unit, gl_y_axis_unit, gl_z_axis_unit — These set the units of the axes.
• gl_x_axis_color, gl_y_axis_color, gl_z_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 ranges 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 3D scene animations; it should be a direction vector [x,y,z].
• gl_quaternion — This sets the quaternion for viewing 3D scenes; it should be a fourtuple [x,y,z,t]. (This is not compatible with interactive graphs.)