39.17.6 SVG Images

SVG (Scalable Vector Graphics) is an XML format for specifying images. If your Emacs build has SVG support, you can create and manipulate these images with the following functions from the svg.el library.

function svg-create width height \&rest args

Create a new, empty SVG image with the specified dimensions. args is an argument plist with you can specify following:

:stroke-width

The default width (in pixels) of any lines created.

:stroke

The default stroke color on any lines created.

This function returns an SVG object, a Lisp data structure that specifies an SVG image, and all the following functions work on that structure. The argument svg in the following functions specifies such an SVG object.

function svg-gradient svg id type stops

Create a gradient in svg with identifier id. type specifies the gradient type, and can be either linear or radial. stops is a list of percentage/color pairs.

The following will create a linear gradient that goes from red at the start, to green 25% of the way, to blue at the end:

(svg-gradient svg "gradient1" 'linear
              '((0 . "red") (25 . "green") (100 . "blue")))

The gradient created (and inserted into the SVG object) can later be used by all functions that create shapes.

All the following functions take an optional list of keyword parameters that alter the various attributes from their default values. Valid attributes include:

:stroke-width

The width (in pixels) of lines drawn, and outlines around solid shapes.

:stroke-color

The color of lines drawn, and outlines around solid shapes.

:fill-color

The color used for solid shapes.

:id

The identified of the shape.

:gradient

If given, this should be the identifier of a previously defined gradient object.

:clip-path

Identifier of a clip path.

function svg-rectangle svg x y width height \&rest args

Add to svg a rectangle whose upper left corner is at position x/y and whose size is width/height.

(svg-rectangle svg 100 100 500 500 :gradient "gradient1")

function svg-circle svg x y radius \&rest args

Add to svg a circle whose center is at x/y and whose radius is radius.

function svg-ellipse svg x y x-radius y-radius \&rest args

Add to svg an ellipse whose center is at x/y, and whose horizontal radius is x-radius and the vertical radius is y-radius.

function svg-line svg x1 y1 x2 y2 \&rest args

Add to svg a line that starts at x1/y1 and extends to x2/y2.

function svg-polyline svg points \&rest args

Add to svg a multiple-segment line (a.k.a. “polyline") that goes through points, which is a list of X/Y position pairs.

(svg-polyline svg '((200 . 100) (500 . 450) (80 . 100))
              :stroke-color "green")

function svg-polygon svg points \&rest args

Add a polygon to svg where points is a list of X/Y pairs that describe the outer circumference of the polygon.

(svg-polygon svg '((100 . 100) (200 . 150) (150 . 90))
             :stroke-color "blue" :fill-color "red")

function svg-path svg commands \&rest args

Add the outline of a shape to svg according to commands, see SVG Path Commands.

Coordinates by default are absolute. To use coordinates relative to the last position, or – initially – to the origin, set the attribute :relative to t. This attribute can be specified for the function or for individual commands. If specified for the function, then all commands use relative coordinates by default. To make an individual command use absolute coordinates, set :relative to nil.

(svg-path svg
      '((moveto ((100 . 100)))
        (lineto ((200 . 0) (0 . 200) (-200 . 0)))
        (lineto ((100 . 100)) :relative nil))
      :stroke-color "blue"
      :fill-color "lightblue"
      :relative t)

function svg-text svg text \&rest args

Add the specified text to svg.

(svg-text
 svg "This is a text"
 :font-size "40"
 :font-weight "bold"
 :stroke "black"
 :fill "white"
 :font-family "impact"
 :letter-spacing "4pt"
 :x 300
 :y 400
 :stroke-width 1)

function svg-embed svg image image-type datap \&rest args

Add an embedded (raster) image to svg. If datap is nil, image should be a file name; otherwise it should be a string containing the image data as raw bytes. image-type should be a MIME image type, for instance "image/jpeg".

(svg-embed svg "~/rms.jpg" "image/jpeg" nil
           :width "100px" :height "100px"
           :x "50px" :y "75px")

function svg-clip-path svg \&rest args

Add a clipping path to svg. If applied to a shape via the :clip-path property, parts of that shape which lie outside of the clipping path are not drawn.

(let ((clip-path (svg-clip-path svg :id "foo")))
  (svg-circle clip-path 200 200 175))
(svg-rectangle svg 50 50 300 300
               :fill-color "red"
               :clip-path "url(#foo)")

function svg-node svg tag \&rest args

Add the custom node tag to svg.

(svg-node svg
          'rect
          :width 300 :height 200 :x 50 :y 100 :fill-color "green")

function svg-remove svg id

Remove the element with identifier id from the svg.

function svg-image svg

Finally, the svg-image takes an SVG object as its argument and returns an image object suitable for use in functions like insert-image.

Here’s a complete example that creates and inserts an image with a circle:

(let ((svg (svg-create 400 400 :stroke-width 10)))
  (svg-gradient svg "gradient1" 'linear '((0 . "red") (100 . "blue")))
  (svg-circle svg 200 200 100 :gradient "gradient1"
                  :stroke-color "green")
  (insert-image (svg-image svg)))

SVG Path Commands

SVG paths allow creation of complex images by combining lines, curves, arcs, and other basic shapes. The functions described below allow invoking SVG path commands from a Lisp program.

command moveto points

Move the pen to the first point in points. Additional points are connected with lines. points is a list of X/Y coordinate pairs. Subsequent moveto commands represent the start of a new subpath.

(svg-path svg '((moveto ((200 . 100) (100 . 200) (0 . 100))))
          :fill "white" :stroke "black")

command closepath

End the current subpath by connecting it back to its initial point. A line is drawn along the connection.

(svg-path svg '((moveto ((200 . 100) (100 . 200) (0 . 100)))
                (closepath)
                (moveto ((75 . 125) (100 . 150) (125 . 125)))
                (closepath))
          :fill "red" :stroke "black")

command lineto points

Draw a line from the current point to the first element in points, a list of X/Y position pairs. If more than one point is specified, draw a polyline.

(svg-path svg '((moveto ((200 . 100)))
                (lineto ((100 . 200) (0 . 100))))
          :fill "yellow" :stroke "red")

command horizontal-lineto x-coordinates

Draw a horizontal line from the current point to the first element in x-coordinates. Specifying multiple coordinates is possible, although usually this doesn’t make sense.

(svg-path svg '((moveto ((100 . 200)))
                (horizontal-lineto (300)))
          :stroke "green")

command vertical-lineto y-coordinates

Draw vertical lines.

(svg-path svg '((moveto ((200 . 100)))
                (vertical-lineto (300)))
          :stroke "green")

command curveto coordinate-sets

Using the first element in coordinate-sets, draw a cubic Bézier curve from the current point. If there are multiple coordinate sets, draw a polybezier. Each coordinate set is a list of the form (x1 y1 x2 y2 x y), where (x, y) is the curve’s end point. (x1, y1) and (x2, y2) are control points at the beginning and at the end, respectively.

(svg-path svg '((moveto ((100 . 100)))
                (curveto ((200 100 100 200 200 200)
                          (300 200 0 100 100 100))))
          :fill "transparent" :stroke "red")

command smooth-curveto coordinate-sets

Using the first element in coordinate-sets, draw a cubic Bézier curve from the current point. If there are multiple coordinate sets, draw a polybezier. Each coordinate set is a list of the form (x2 y2 x y), where (x, y) is the curve’s end point and (x2, y2) is the corresponding control point. The first control point is the reflection of the second control point of the previous command relative to the current point, if that command was curveto or smooth-curveto. Otherwise the first control point coincides with the current point.

(svg-path svg '((moveto ((100 . 100)))
                (curveto ((200 100 100 200 200 200)))
                (smooth-curveto ((0 100 100 100))))
          :fill "transparent" :stroke "blue")

command quadratic-bezier-curveto coordinate-sets

Using the first element in coordinate-sets, draw a quadratic Bézier curve from the current point. If there are multiple coordinate sets, draw a polybezier. Each coordinate set is a list of the form (x1 y1 x y), where (x, y) is the curve’s end point and (x1, y1) is the control point.

(svg-path svg '((moveto ((200 . 100)))
                (quadratic-bezier-curveto ((300 100 300 200)))
                (quadratic-bezier-curveto ((300 300 200 300)))
                (quadratic-bezier-curveto ((100 300 100 200)))
                (quadratic-bezier-curveto ((100 100 200 100))))
          :fill "transparent" :stroke "pink")

command smooth-quadratic-bezier-curveto coordinate-sets

Using the first element in coordinate-sets, draw a quadratic Bézier curve from the current point. If there are multiple coordinate sets, draw a polybezier. Each coordinate set is a list of the form (x y), where (x, y) is the curve’s end point. The control point is the reflection of the control point of the previous command relative to the current point, if that command was quadratic-bezier-curveto or smooth-quadratic-bezier-curveto. Otherwise the control point coincides with the current point.

(svg-path svg '((moveto ((200 . 100)))
                (quadratic-bezier-curveto ((300 100 300 200)))
                (smooth-quadratic-bezier-curveto ((200 300)))
                (smooth-quadratic-bezier-curveto ((100 200)))
                (smooth-quadratic-bezier-curveto ((200 100))))
          :fill "transparent" :stroke "lightblue")

command elliptical-arc coordinate-sets

Using the first element in coordinate-sets, draw an elliptical arc from the current point. If there are multiple coordinate sets, draw a sequence of elliptical arcs. Each coordinate set is a list of the form (rx ry x y), where (x, y) is the end point of the ellipse, and (rx, ry) are its radii. Attributes may be appended to the list:

:x-axis-rotation

The angle in degrees by which the x-axis of the ellipse is rotated relative to the x-axis of the current coordinate system.

:large-arc

If set to t, draw an arc sweep greater than or equal to 180 degrees. Otherwise, draw an arc sweep smaller than or equal to 180 degrees.

:sweep

If set to t, draw an arc in positive angle direction. Otherwise, draw it in negative angle direction.

(svg-path svg '((moveto ((200 . 250)))
                (elliptical-arc ((75 75 200 350))))
          :fill "transparent" :stroke "red")
(svg-path svg '((moveto ((200 . 250)))
                (elliptical-arc ((75 75 200 350 :large-arc t))))
          :fill "transparent" :stroke "green")
(svg-path svg '((moveto ((200 . 250)))
                (elliptical-arc ((75 75 200 350 :sweep t))))
          :fill "transparent" :stroke "blue")
(svg-path svg '((moveto ((200 . 250)))
                (elliptical-arc ((75 75 200 350 :large-arc t
                                     :sweep t))))
          :fill "transparent" :stroke "gray")
(svg-path svg '((moveto ((160 . 100)))
                (elliptical-arc ((40 100 80 0)))
                (elliptical-arc ((40 100 -40 -70
                                     :x-axis-rotation -120)))
                (elliptical-arc ((40 100 -40 70
                                     :x-axis-rotation -240))))
          :stroke "pink" :fill "lightblue"
          :relative t)