Parametric Shape Stimulus

Description

A user-defined, two-dimensional shape stimulus.

The shape is defined by a list of vertices. By default, the outline of the shape is computed via a cubic B-spline approximation, for which the vertices serve as control points, resulting in a smooth edge. However, if spline_resolution is set to zero, the provided vertices are used as-is and connected with straight line segments, producing a polygon. Once the shape’s outline has been established, the interior is filled with the specified color.

Note: The outline of the shape is determined when the stimulus is loaded. To change the value of vertices or spline_resolution while the experiment is running, you must unload the stimulus, change the desired parameter, then reload the stimulus.

Vertex Coordinates

The coordinate grid on which the shape’s vertices lie is a square with center given by vertex_coord_center_x and vertex_coord_center_y and edge length given by vertex_coord_range. If any of these parameters is omitted, its value is inferred from the other parameters (if present) and the bounding box of the shape, i.e. the smallest rectangle that encloses the entire shape. Note that if spline_resolution is non-zero, the bounding box is determined from the spline approximation of the shape edge, not the raw vertices.

Note: Since the coordinate grid is always square, setting x_size and y_size to different values will stretch the shape along the larger dimension.

Signature

stimulus/parametric_shape

Required Parameters

vertices

Example:

[[-2, -2], [0, 2], [0, 0], [2, -2], [0, -1], [-2, -2]]

Set of points that define the shape, in arbitrary coordinates (see above). Must be a list of two or more sub-lists, with each sub-list containing two numbers.

Optional Parameters

spline_resolution

Default:

50

Number of points in the cubic B-spline approximation computed from vertices. Higher values will produce a smoother edge.

Must be greater than or equal to zero. If zero, no spline approximation is computed, and the provided vertices are connected with straight line segments.

vertex_coord_center_x

x coordinate of the center of the vertex coordinate grid (see above for details)

vertex_coord_center_y

y coordinate of the center of the vertex coordinate grid (see above for details)

vertex_coord_range

Edge length of the vertex coordinate grid (see above for details)

margin_pixels

Default:

0

Number of pixels at the edge of the stimulus rectangle (i.e. the region specified by x_size, y_size x_position, y_position, and rotation) that are not drawn on. Must be a floating-point number greater than or equal to zero.

If parts of the shape at the edge of the vertex coordinate grid appear rough or truncated, increasing the number of margin pixels may eliminate the issue.

use_antialiasing

Default:

YES

If YES, anti-aliasing will be used to smooth the rendered edges of the shape

max_size_x

Maximum horizontal size (degrees).

If omitted, the maximum horizontal size is set to the value of x_size when the stimulus is loaded.

max_size_y

Maximum vertical size (degrees).

If omitted, the maximum vertical size is set to the value of y_size when the stimulus is loaded.

color

Default:

1.0,1.0,1.0

The color of the stimulus, expressed as a comma-separated list of red, green, and blue components. Each component may be described by any valid expression, but the expression must result in a value between 0 and 1 (inclusive).

alpha_multiplier

Default:

1.0

By default, the alpha multiplier controls the transparency of the stimulus. 1.0 is fully opaque, while 0.0 is fully tranparent.

Changes to the parameters source_blend_factor and dest_blend_factor can alter how (or if) the alpha multiplier is used.

source_blend_factor

Options:
zero
one
source_color
one_minus_source_color
dest_color
one_minus_dest_color
source_alpha
one_minus_source_alpha
dest_alpha
one_minus_dest_alpha
Default:

source_alpha

Source blending factor.

The parameters source_blend_factor, dest_blend_factor, source_alpha_blend_factor, and dest_alpha_blend_factor provide detailed control over how the color components and alpha multiplier of each fragment of the stimulus (the “source”) are combined with the color and alpha values already present in the framebuffer (the “destination”), which in turn result from blending the stimulus display background with any stimuli drawn beneath the source stimulus. These parameters correspond directly to the four arguments of the OpenGL function glBlendFuncSeparate. Please refer to that function’s reference page for explanations of the different blend factor options.

Note: Irrespective of the blend factors used, the blend equation is always GL_FUNC_ADD.

dest_blend_factor

Default:

one_minus_source_alpha

Destination blending factor. Accepts the same values as source_blend_factor.

source_alpha_blend_factor

Source alpha blending factor. Accepts the same values as source_blend_factor.

If omitted, the value of source_blend_factor is used.

dest_alpha_blend_factor

Destination alpha blending factor. Accepts the same values as source_blend_factor.

If omitted, the value of dest_blend_factor is used.

x_size

Example:

5.0

Horizontal size (degrees).

If omitted, the value of y_size is used. It is an error to omit both x_size and y_size (unless fullscreen is YES).

y_size

Example:

5.0

Vertical size (degrees).

If omitted, the value of x_size is used. It is an error to omit both x_size and y_size (unless fullscreen is YES).

x_position

Default:

0.0

Horizontal center position (degrees)

y_position

Default:

0.0

Vertical center position (degrees)

rotation

Default:

0.0

Rotation (degrees)

fullscreen

Default:

NO

If YES, the stimulus is sized to fill the display. In this mode, x_size, y_size, x_position, y_position, and rotation are ignored.

deferred

Options:
no
yes
explicit
Default:

no

Controls when the stimulus is loaded. If no, the stimulus is loaded at experiment load time. If yes, the stimulus is loaded the first time it is queued. If explicit, the stimulus must be loaded explictly with Load Stimulus.

display

Name of the display on which the stimulus will be presented. If omitted, the default display (if available) will be used.

Placement

Allowed at top level:

Yes

Allowed parent:

Folder, Frame List Stimulus, Layer Stimulus, List Replicator, Movie Stimulus, Range Replicator, Stimulus Group