### 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.

triangle(1+i/2,2+i,1/2+2 i,color=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)

triangle(1+i/2,2+i,1/2+2 i,display=filled)

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

rainbow():={ local j,C; C:=[]; for (j:=256;j<382;j++) { C:=append(C,square(j,j+1,color=j+filled)); } }

followed by

axes=false; rainbow();

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

title="Some triangles"; triangle(0+i/5,1+i/5,1+i); triangle(2+i/5,3+i/5,3+i);

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.)