Terminal Graphics in VisiData
VisiData can display low-resolution terminal graphics with a reasonable amount of user interactivity.
Sheet: the drawable context base class (part of core vdtui.py)
Plotter: pixel-addressable display of entire terminal with (x,y) integer pixel coordinates
Canvas: zoomable/scrollable virtual canvas with (x,y) coordinates in arbitrary units
InvertedCanvas: a Canvas with inverted y-axis
Graph: an InvertedCanvas with axis labels, a legend, and gridlines
- The async
Graph.reload()iterates over the given
sourceSheet) and calls
Canvas.polyline()to indicate what to render.
Canvas.refresh()triggers an async
Canvas.render(), which iterates over the polylines and labels and calls the
Plotter.draw(), which determines the characters and colors to represent the pixels.
Plotter is a
Sheet with a pixel-addressable drawing surface that covers the entire terminal (minus the status line). Pixels and labels are plotted at exact locations in the terminal window, and must be recalculated after any zoomlevel change or terminal resizing.
Plotter.draw(scr) is called multiple times per second to update the screen, and chooses a curses attribute for each pixel. By default, the most common attr is chosen for each pixel, but if
options.disp_pixel_random is set, an attr will be randomly chosen from the naturally weighted set of attrs (this may cause blocks of pixels to flicker between their possible attrs). If an attr is in the
Canvas.hiddenAttrs set, then it is not considered for display at all (and its rows will be ignored during selection).
All Plotter coordinates must be integer numbers of pixels. [For performance reasons, they are presumed to already be integers, to save unnecessary calls to
round().] Methods which plot multiple pixels on the canvas should be careful to gauge the display correctly; simply calling
round() on each calculated float coordinate will work but can cause display artifacts.
For Plotter methods,
y must be integers, where
0 <= x < plotwidth, and
0 <= y < plotheight.
(0,0) is in the upper-left corner of the terminal window.
Pixels can be plotted directly onto a Plotter with these methods:
Plotter.plotpixel(x, y, attr, row=None)
Plotter.plotline(x1, y1, x2, y2, attr, row=None)
Plotter.plotlabel(x, y, text, attr)
attr is a curses attribute, and
row is the object associated with the pixel.
plot* methods append the
These properties and methods are also available:
Plotter.plotwidthis the width of the terminal, in pixels.
Plotter.plotheightis the height of the terminal, in pixels.
Plotter.rowsWithin(bbox)generates the rows plotted within the given region.
Plotter.hideAttr(attr, hide=True)adds attr to
hide, and removes it otherwise.
Plotter.refresh()is called whenever the screen size changes, and should also be invoked whenever new content is added.
rowsWithin takes a
Box object (described below). The
Box class is otherwise unused by the Plotter.
Canvas is a
Plotter with a virtual surface on which lines and labels can be rendered in arbitrary units.
The onscreen portion (the area within the visible bounds) is scaled and rendered onto the
Plotter, with the minimum coordinates in the upper-left [same orientation as
Canvas user interface supports zoom, scroll, cursor definition, and selection of the underlying rows. The
source attribute should be the Sheet which owns the plotted
A call to
Canvas.refresh() will trigger
Canvas.render(), which is decorated with
@asyncthread as it may take a perceptible amount of time for larger datasets. Any active
render threads are cancelled first.
Point helper classes
While the Plotter API requires literal integer values for
Canvas methods generally take float values contained in either
Point is simply a container for an
(x,y) coordinate (passed to the constructor). The individual components are stored as
.y, and the computed
.xy property will return
(x,y) as a simple tuple.
Point can also stringify itself reasonably.
Box is effectively a rectangle stretching over some area of the canvas. The constructor takes
(x,y,w,h), but a
Box can also be constructed using the
BoundingBox(x1,y1,x2,y2) helper. [Note that in the BoundingBox case, the order of the individual points is not guaranteed; the individual coordinates may be swapped for convenience.]
Box has these members and properties:
ymin: the minimum coordinates of the area.
ymax: the maximum coordinates of the area.
ycenter: the central coordinates of the area.
h: the width and height of the area.
contains(x, y): returns True if
(x,y)is inside the bounding box.
Canvas.polyline(vertexes, attr, row=None)adds a multi-segment line from the list of (x,y)
vertexes. One vertex draws a point; two vertexes draws a single line. Note that the vertexes are not Point objects (unlike parameters for other methods).
Canvas.label(xy, text, attr, row=None)adds
xy(Point in canvas units).
Canvas.fixPoint(xyplotter, xycanvas)sets the position of the
xycanvas(Point in Canvas units) is plotted at
xyplotter(Point in Plotter units).
Canvas.zoomTo(bbox)sets the visible bounds so the given canvas coordinates will fill the entire Plotter area.
aspectRatiowill still be obeyed.
attrfor the given
key, assigning a new color from
keyhas not been seen before. These keys are plotted as legends on the upper right corner of the canvas. The last color is given out for all remaining keys and is labeled "other".
Canvas.resetBounds()needs to be called after some or all points have been rendered, but before anything can be plotted. It initializes the width and height of the canvas, visible area, and/or cursor.
Canvas.reset()clears the canvas in preparation for
Canvas.canvasBoxreflects the bounds of the entire canvas.
Canvas.visibleBoxdefines the onscreen canvas area.
Canvas.cursorBoxdefines the cursor region in canvas coordinates.
Canvas.zoomlevelis a settable property, which sets the
zoomlevelof 1.0 makes the entire canvas visible. Does not change the position of the
Canvas.aspectRatio, if set, maintains a proportional width and height of the
aspectRatioof 1.0 should be square.
Canvas.canvasCharHeightis the width and height of one terminal character, in canvas units.
These properties reserve an area of the Plotter that is outside the visibleBox: -
During a mouse event, these properties indicate the mouse position for the current mouse event:
Canvas.canvasMouse: a Point in canvas coordinates
Plotter.plotterMouse: a Point in plotter (pixel) coordinates
Sheet.mouseY: individual values in curses (character) coordinates
InvertedCanvas is a
Canvas with a few internal methods overridden, such that the Y axis is inverted. For an
InvertedCanvas, the minimum coordinates are in the lower-left.
InvertedCanvas has not much else of interest. It should be completely interchangeable with
Graph is an
InvertedCanvas with axis labels and/or gridlines.
Graph.__init__(name, sheet, rows, xcols, ycols)constructor
rowsis a list of the rows to iterate over (from the given
xcolsis a list of key columns forming the x-axis and color keys.
ycolsis a list of numeric columns to be plotted on the y-axs.