I am pleased to announce that I have a guide to accessibility available to download from VisionUp and I will be presenting a webcast on the subject on 26th September 2019. Registration is now open at the following link : Introducing Accessibility in Visio.
The Web Content Access Guidelines (WCAG) 2.0 provides the current recommendations for making web content accessible to users with vision impairment, but how do you test if your Visio shapes pass? There are several web sites out there that provide this capability, but all of them require the HEX values, rather than the RGB or HSL that Visio provides natively. Therefore, I have created a Visio callout shape that can be associated with a target shape to report on the values of each of its main color elements, and provides hyperlinks to automatically check the contrast ratio on WebAIM.
The colour formats that can be selected from either the Shape Data window or the right mouse menu are:
One of the ways that Visio supports accessibility is to provide text that is read out by a screen reader, such as Windows Narrator or JAWS. This Alt Text can be set using Format Shape / Size & Properties tab using the Title and Description text boxes. The Title is the initial text that is read out when a shape is attentioned, and the Description will only read out if the user pauses. The Description text box only allows 255 characters to be entered and displayed, but this is not actually the limit!
Visio defaults to tabbing from shape to shape in the order that the shapes are added to the page. However, this can end up with an illogical order if you are trying to navigate a diagram with the keyboard, which is often an accessibility requirement. Fortunately, Visio provides a Diagram Navigation pane so that the tab order can be changed, but how does it do it? The following short video shows how the navigation order, displayed as numbers in each shape, is assigned a value as soon as the order is edited.
Accessibility is important in my current project, so understanding how this happens was important to understand, and to surface this order to JavaScript, as we want to list the shapes in a logical order too.
I managed this by adding a User.visNavOrder to the master shape of all the significant masters, and a hidden Shape Data row, labelled “Navigation Order“. This has the following formula for its value:
I wrote about ensuring high contrast between text and the background of Visio shapes in my last article. The RGB values actually came from an imported SharePoint list that has a lookup to a list that contains the RGB values of named colours. Having solved how to display the correct text colour for high contrast in Visio, I wanted to the same in a SharePoint column, but first I had to learn how to use the RGB values to format the background colour.
My good friend Chris Roth, aka VisGuy, has already produced Visio ShapeSheet formulas to convert RGB values to Hex values. so I adaptively re-used his idea to create a formula that I could use in a SharePoint calculated column, called Hex.
First, I compressed his multiple User-defined Cells rows into a single formula:
I am working on a project where I need to ensure high contrast of the text in the Visio shapes for accessibility. At first, I attempted to write my own formula but a colleague pointed my to a website that confirms if the contrast is acceptable ( contrast-ratio.com ), and showed me that a few of my examples failed. So the search was on for a better formula than my own. This lead me to a Stack Exchange answer with just what I was looking for (Formula for Color Contrast between Text and Background). All I needed to do was to convert this into a ShapeSheet formula or two, and then I could apply it to the text inside the shapes.
Any text created with Data Graphic Text Callouts cannot have the high contrast formula applied to because they can be moved independent of the background. However any text added with Insert / Field inside the shape changes between black and white with respect to the FillForegnd value in its background.
Following the article above, it is necessary to calculate the lightness, L, of the FillForegnd, and then to check if black or white text is going to provide satisfactory contrast.