Using Inkscape for web animation

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1 Introduction

This short tutorial will provide some tips on editing SVG pictures in Inkscape in order to add some SVG-SMIL animation and interactivity with other tools. Inkscape doesn't allow SVG code editing, but it is useful to learn some Inskscape tricks in order to prepare the SVG for creating animations made from complex clipart that you could find on http://openclipart.org.

Examples in this page were tested on Jan 2014 with Firefox and Chrome.

Prerequisites:

See also:

  • SVG (Short overview)
  • SVG links (links to various SVG resources)

Below we will use the following examples:

Dragon head silhouette
Original: dragon-head-silhouette-by-kuba (openclipart.org)
Revised version: dragon-head-silhouette.svg
Animated version: dragon-head-silhouette-anim.svg
Manga girl
Original: girl with silver hair by Ying-Chun Liu PaulLiu
Cleaned version: paulliu_girl_with_silver_hair-mod.svg
Animated version: paulliu_girl_with_silver_hair-mod2.svg

2 Optimizing and translating to plain SVG

Since Inkscape is primairly a drawing tool and not a web drawing tool, it includes extensions that add functionality to the editor (e.g. layers) and power to "plain" SVG. According to the XML standard this is perfectly legal if a namespace mechanism is used. Web browsers do not understand the "inkscape" and "sodipodi" elements and simply ignore these.

In addition, drawings may use weird coordinates, include unused definitions, the drawing canvas may be too big, etc. As a consequence you should optimize the drawing, even if in theory this is not strictly necessary. Cleaning and optimizing is particularly important if you plan to import SVG drawings to HTML5 via the object or the img element.

Anyhow, in order to insure that pictures show as intended, you should try both optimizing and translating to plain SVG. This may not always work, but most of the time it does. Ok, so if possible, do the following (as also explained in the Using SVG with HTML5 tutorial:

Optimizing
  1. Fit the document size to the picture size: Menu File->Document Properties. In the Custom size panel, open Resize page to content, then click Resize page to drawing or selection.
  2. Remove unused DEF's: File->Vacuum Defs.
  3. Optimize SVG: File -> Save as... -> Optimized SVG.
    • Tick "Enable viewboxing in the save dialog. This operation will do two things, Insert correct viewBox, and set width and height attributes to 100% (this is very useful if you plan to import drawings with the HTML object or img tags, i.e. you can easily define the SVG image size).
    • You may untick "Simple colors"
Translate to plain SVG
  1. Remove non-standard SVG/Inkscape XML: File -> Save as... -> plain SVG
Since this operation will remove layers and other Inkscape specific information, keep a copy of the old file if necessary
As of Jan 2014, this operation may seem to fail, e.g. the whole picture can become black for a reason we can't figure out. Save the file (maybe under a different name), then re-open it again. The blackness may just be a display error. Do not panic !
Same file (left after saving), right (after re-opening)

3 Identifying and naming SVG elements

In order to write animation code, it is probably best to give special meaninful ID's to the objects that you would like to manipulate. E.g. avoid working with path3404 etc. and call it leg_left for example.

Procedure:

(1) Open the Inskscape XML Tree Editor
Menu: Edit -> XML Editor or (Shift-CTRL-X)
(2) Use the selection tool to identify objects in the drawing
Hit F1 (or the top button in the toolbar to the left)
Select the element, either in the drawing pane or by clicking on elements in the XML Editor.
You may have to ungroup an element in the drawing pane in order to make it clickable. We rather suggest to start from the parent projet in the drawing pane, then explore its children in the XML editor pane. However, some folks have strange ideas on grouping ... try the best.
Selecting an SVG element (either in the drawing tool or the XML editor)
(3) Click on id in the XML editor
In the bottom panel, change its name, then click Set
Changing a property value
Again, use meaningful id names !

4 Path surgery

4.1 Simplifying drawings

According to the tutorial advanced, the main use of the Simplify command (Ctrl+L) is reducing the number of nodes on a path while almost preserving its shape. “The amount of simplification (called the threshold) depends on the size of the selection. Therefore, if you select a path along with some larger object, it will be simplified more aggressively than if you select that path alone. Moreover, the Simplify command is accelerated. This means that if you press Ctrl+L several times in quick succession (so that the calls are within 0.5 sec from each other), the threshold is increased on each call. (If you do another Simplify after a pause, the threshold is back to its default value.) By making use of the acceleration, it is easy to apply the exact amount of simplification you need for each case.” (retrieved Jan 2014).

4.2 Cutting a path in two parts

Sometimes, e.g. in the dragon head silhouette drawing, the whole SVG picture is just a single path. If you plan to animate some detail, you will have to cut it off.

Procedure:

(1) Get the path edit tool
Hit F2 or select second tool in the left tool palette

(2) Select the path you plan to edit

You now will see control points that you can use to change the shape (but that's not our purpose here)
Zoom in, e.g.++ by hitting the + button on the keyboard or by using the View menu. Try View->Zoom->Drawing or View->Zoom-Selection
Inkscape path editor
(3) Cut
Hold down SHIFT key and select two (not linked) points that will define the cut
Click Break path at selected nodes in the upper toolbar
Menu Path->Break Apart will break the path into two paths
Select path control points and cut

Some extra tips:

The breaking may fail, i.e. change the path itself. Undo if this happens.
If an object is not path (e.g. a rectangle), you can convert it to a path object: (Menu: Path -> Object to Path). But there is no way back !
Use the XML Editor to select an element if necessary (i.e. if you can't select the one you need)

Alternative:

Redraw the object you plan to animate
Remove the points from the path that include the part that you wanted to cut off
Maybe combine the two strategies ....

Example showing cut Dragon tongue (don't try this with a live one)

4.3 Kill part of path

  • Hit F2
  • Select a control point and hit the DELETE key
  • Kill other points, until the subpath / subshape you want to remove is gone ....
  • Then use the curve controls (little circles that stick out from the control points) to smoothen if necessary.

5 Constructive solid geometry

Constructive solid geometry is a popular 2D/3D modelin technique that allows to create interesting shapes from other shapes. See the Subtractive geometry in Adobe Flash CS6 where we show how to create a Moon symbol by subtracting a circle from a circle. A similar functionaly exist in Stich Era, Stich Era, an embroidery software. OpenScad is a 3D CAD tool where people design models by coding.

Read:

Tips:

  • In order to achieve what you want you often will have to destroy objects. In other words, you may first have to create copies. Either move these away temporarily or just pile 2 objects on top of each other: CTRL-C, deselect, then CTRL-SHIFT-V

Example to create an eye from a dragon head outline

  • Draw a yellow rectangle over the eye
  • Move it backwards: Menu: Object -> Lower (or PageDown key) and position. You now should see a yellow eye
  • Copy / Paste in place the dragon head. In the XML Editor, you now should see a new path
  • Select both dragon head and a rectangle
  • Menu: Path -> Difference or CTRL-
  • You know should have an eye.

6 Adding animation in Inkscape

You cannot ! Therefore, we suggest to export the drawing to simple SVG and to use a text editor.

If you added objects to animated and if you did change the id's names as suggested above, programming will now be much easier. Make sure to add xmlns:xlink="http://www.w3.org/1999/xlink" declaration in the SVG root if you use any sort of links !!

6.1 Dragon example

The animation code we added at the end of the file (using linking) is:

    <animate xlink:href="#eye"
	     dur="12s" begin="1s"
	     to="#000000" from="#CC9933"
	     repeatCount="indefinite"   
	     calcMode="linear" attributeName="fill"/>

    <animate id="nose_anim1"
	     xlink:href="#nose"
	     dur="2s" begin="0s; nose_anim2.end"
	     from="yellow" to="red"
	     attributeType="CSS"
	     calcMode="linear" attributeName="fill"/>

    <animate id="nose_anim2"
	     xlink:href="#nose"
	     dur="2s" begin="nose_anim1.end"
	     to="yellow" from="red"
	     calcMode="linear" attributeName="fill"/>

    <animate id="tongue_anim1"
	     xlink:href="#tongue"
	     dur="12s" begin="1s"
	     values="#501616;black;#501616" 
	     repeatCount="indefinite"
	     calcMode="linear" attributeName="fill"/>

    <animateTransform id="tongue_anim1a"
	     xlink:href="#tongue"
	     dur="6s" begin="1s; tongue_anim2a.end"
	     to="0.99" from="1.0" 
	     attributeName="transform" type="scale"
	     />

    <animateTransform id="tongue_anim2a"
	     xlink:href="#tongue"
	     dur="6s" begin="tongue_anim1a.end"
	     from="0.99" to="1.0" 
	     attributeName="transform" type="scale"
	     />

Notice:

  • Rotations in the HTML file were made with CSS, i.e. we rotate the HTML object element.
  • Instead of chaining two animations (nose_anime1 and nose_anime2), rather use the values attribute (tongue_anim1). Less code, more elegant ...
  • The header of the SVG file (includes a viewBox and set width and height to 100% (good for inclusion in HTML5)
  • the chaining of the nose and tongue animation as explained in the SVG-SMIL animation tutorial
  • Doing transform animations can be very hairy with imported pictures, because drawings are often transformed in various ways and animating these has strange effects on the coordinate system. The same is true for motion animation. E.g. instead of redrawing a tongue, we just cut it off an existing path. Scaling will scale the whole coordinate system used to define the tongue, not just the tongue itself ...

6.2 Dealing with path objects

Animating the size of a path element or doing a motion animation with a path element can be very hairy, since this type of animation actually changes the coordinate system of the element. For example, when you grow a path using a animateTransform, the element may just move somewhere. If you understand math, you probably could figure out a good solution. I can't, therefore I suggest the following strategy:

  1. From your animated SVG file, copy / paste the path you plan to animate to a new SVG file
  2. Adjust the drawing Canvevas: Menu: File->Document Properties->Custom Size; Select Resize page to drawing or selection
  3. Save the new file as optimized SVG
  4. Insert an svg element into the animation file
  5. Copy/paste the code from the new SVG file between the svg element
  6. Adjust the the x and y position of the <svg>element</code>
  7. Remove the old path if not already done so.

The following example includes a modified eye that is animated, i.e. we substituted the original left eye by a new version.

Code excerpt:

  <desc>-------------------------------------------------------------------------</desc>
  <desc>Below is some substituted code for the eye. We use a embedded svg element</desc>

  <svg viewBox="0 0 28.5 33.2"
       width="28.5" height="33.2"
       x="369" y="143"
       >
    <defs id="defs6005">
      <linearGradient id="eyeGrad" y2="193.43" gradientUnits="userSpaceOnUse" y1="159.23"
              gradientTransform="matrix(0.95876002,-0.28420001,0.28420001,0.95876002,-353.16135,-55.73074)" x2="315.38" x1="314.7">
	<stop stop-color="#000000" offset="0"/>
	<stop stop-color="#b9b9b9" offset="1"/>
      </linearGradient>
      <linearGradient id="eyeGrad2" y2="193.43" gradientUnits="userSpaceOnUse" y1="159.23"
              gradientTransform="matrix(0.95876002,-0.28420001,0.28420001,0.95876002,-353.16135,-55.73074)" x2="315.38" x1="314.7">
	<stop stop-color="#000000" offset="0"/>
	<stop stop-color="#00ffff" offset="1"/>
      </linearGradient>

    </defs>
    <g id="eye_left" transform="translate(14.286238,-7.203961)">
      <path id="path4885" stroke-linejoin="round"
            d="m12.943,19.954a16.25,13.5,73.489,0,1,-25.887,7.6734,16.25,13.5,73.489,0,1,25.887,-7.6734z"
            stroke="#000000" stroke-linecap="square" stroke-width="1.09999478" fill="url(#eyeGrad2)"/>
    </g>
    <circle id="pupil_left" r="1" cx="15" cy="15" fill="#8b0000"/>
  </svg>
  
  <!-- original eye removed
  <g
     id="eye_left">
    <path
       d="m 329.5,176.61218 a 13.5,16.25 0 1 1 -27,0 13.5,16.25 0 1 1 27,0 z"
       transform="matrix(0.95876,-0.2842,0.2842,0.95876,28.837,77.84)"
       id="path4885"
       style="fill:url(#linearGradient6649);stroke:#000000;stroke-width:1.10000002;stroke-linecap:square;stroke-linejoin:round" />
  </g>

  ......
  -->

  <animateTransform id="eye_anim5"
	     xlink:href="#eye_left"
	     dur="6s" begin="1s"
	     values = "1.0;0.9;1.0"
	     repeatCount="indefinite"
	     additive="sum"
	     attributeName="transform" type="scale"/>

  <animate id="eye_anim6"
	     xlink:href="#pupil_left"
	     dur="6s" begin="1s"
	     values = "1;2;1"
	     repeatCount="indefinite"
	     attributeName="r"/>

6.3 Moving an object along a path

6.3.1 Introduction

In order to move the object along a path you will need two objects. The object that you want to animate and the object that represents the path.

Example: http://tecfaetu.unige.ch/etu-maltt/tetris/karanis0/stic-2/ex11/drawingThree.svg

6.3.2 Procedure

  • Create an object by using the ellipse tool and name it "ellipseObj" (Edit-->xml editor-->id"ellipseObj"-->set) -- this is the moving object
  • Create an ellipse and call it "ellipsePath" (Edit-->xml editor-->id"ellipsePath"-->set) -- this is the path
  • If you want an anti-clock movement (select the object-->object-->Flip Vertical)
  • Save the file as plain svg
  • Open the file with an xml editor


You will see the following code:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!-- Created with Inkscape (http://www.inkscape.org/) -->

<svg
   xmlns:dc="http://purl.org/dc/elements/1.1/"
   xmlns:cc="http://creativecommons.org/ns#"
   xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
   xmlns:svg="http://www.w3.org/2000/svg"
   xmlns="http://www.w3.org/2000/svg"
   xmlns:xlink="http://www.w3.org/1999/xlink"
   version="1.1"
   width="744.09448"
   height="1052.3622"
   id="svg2">
  <metadata
     id="metadata3007">
    <rdf:RDF>
      <cc:Work
         rdf:about="">
        <dc:format>image/svg+xml</dc:format>
        <dc:type
           rdf:resource="http://purl.org/dc/dcmitype/StillImage" />
        <dc:title></dc:title>
      </cc:Work>
    </rdf:RDF>
  </metadata>
  <defs
     id="defs3005" />
  <g
     id="layer1">
<!--ellipseObj-->
    <path
       d="m 511.42859,652.36218 a 42.857145,17.142858 0 1 1 -85.71429,0 42.857145,17.142858 0 1 1 85.71429,0 z"
       transform="translate(0,-202)"
       id="ellipseObj"
       style="fill:#1d0075;fill-opacity:0.96808543;stroke:#000000;stroke-width:3.7420001;stroke-miterlimit:4;stroke-opacity:1;stroke-dasharray:none" />
<!--ellipsePath-->
    <path
       d="m 382.85714,235.21933 a 85.714287,34.285713 0 1 1 -171.42857,0 85.714287,34.285713 0 1 1 171.42857,0 z"
       transform="matrix(1.8089222,0,0,2.480639,-168.9369,-401.13206)"
       id="ellipsePath"
       style="fill:#1d0075;fill-opacity:0.02659577;stroke:#000000;stroke-width:3.7420001;stroke-miterlimit:4;stroke-opacity:1;stroke-dasharray:none" />
  </g>
</svg>
  • In order to avoid the errors it would be nice to clean up the code and add a few extra lines.

By repairing the code you will end up with something like this:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
	<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN"                             
  "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
<!-- Created with Inkscape (http://www.inkscape.org/) -->

<svg
   xmlns="http://www.w3.org/2000/svg"
   xmlns:xlink="http://www.w3.org/1999/xlink"
   version="1.1"
   width="744.09448"
   height="1052.3622"
   id="svg2">
  <g
     id="layer1">
    <path
       d="m 511.42859,652.36218 a 42.857143,17.142857 0 1 1 -85.71429,0 42.857143,17.142857 0 1 1 85.71429,0 z"
       transform="translate(0,-202)"
       id="ellipseObj"
       style="fill:#1d0075;fill-opacity:0.96808543;stroke:#000000;stroke-width:3.7420001;stroke-miterlimit:4;stroke-opacity:1;stroke-dasharray:none" />
    <path
       d="m 382.85714,235.21933 a 85.714287,34.285713 0 1 1 -171.42857,0 85.714287,34.285713 0 1 1 171.42857,0 z"
       transform="matrix(1.8089222,0,0,2.480639,-168.9369,-401.13206)"
       id="ellipsePath"
       style="fill:#1d0075;fill-opacity:0.02659577;stroke:#000000;stroke-width:3.7420001;stroke-miterlimit:4;stroke-opacity:1;stroke-dasharray:none" />
  </g>
</svg>


In order to animate the ellipseObj you can add the following code under the last path

<--in order to have an elliptic animation you have to copy-paste the path of the ellipsePath-->
 <animateMotion xlink:href="#ellipseObj"                     
       repeatCount="indefinite"
       dur="10s"
       path="382.85714,235.21933 a 85.714287,34.285713 0 1 1 -171.42857,0 85.714287,34.285713 0 1 1 171.42857,0 z" />
  • If you want you can erase the ellipsePath in order to display only the ellipseObj

7 Links

7.1 Official

Tutorials

7.2 Tutorials