PPT: The Outline default Line Width value is one pixel not the zero

Description

I find the behavior in PowerPoint is different from the ECMA-376 document.

We can find the ECMA-376 document chapter 20.1.2.2.24 say that the Line Width is omitted, then a value of 0 is assumed.

But when we create a document with the Line Width is omitted, and the PowerPoint will show the shape Line Width as one pixel.

Information

• .NET Target: ALL
• DocumentFormat.OpenXml Version: ALL

Repro

https://github.com/lindexi/lindexi_gd/tree/173fbaf7c68023cf5064888bceeb197bd463538f/PptxDemo

  <p:sp>
    <p:nvSpPr>
      <p:cNvPr id="2" name="Rectangle 1" />
      <p:cNvSpPr />
      <p:nvPr />
    </p:nvSpPr>
    <p:spPr>
      <a:xfrm>
        <a:off x="5220072" y="1484784" />
        <a:ext cx="1440160" cy="1008112" />
      </a:xfrm>
      <a:prstGeom prst="rect"/>
      <a:ln w="0">
        <a:solidFill>
          <a:srgbClr val="565656" />
        </a:solidFill>
      </a:ln>
    </p:spPr>
  </p:sp>

And

  <p:sp>
    <p:nvSpPr>
      <p:cNvPr id="2" name="Rectangle 1" />
      <p:cNvSpPr />
      <p:nvPr />
    </p:nvSpPr>
    <p:spPr>
      <a:xfrm>
        <a:off x="5220072" y="1484784" />
        <a:ext cx="1440160" cy="1008112" />
      </a:xfrm>
      <a:prstGeom prst="rect"/>
      <a:ln>
        <a:solidFill>
          <a:srgbClr val="565656" />
        </a:solidFill>
      </a:ln>
    </p:spPr>
  </p:sp>

        private static void ReadShape(Shape shape)
        {
            var outline = shape.ShapeProperties?.GetFirstChild<Outline>();
            if (outline != null)
            {
                var lineWidth = outline.Width;
                var emu = new Emu(lineWidth);
                var pixel = emu.ToPixel();
                Console.WriteLine($"LineWidth {pixel.Value}");
            }
            else
            {
               
            }
        }

Observed

The outline.Width is null

Expected

I dot not know how to handle the PPT behavior is different from the ECMA-376 document

[lindexi]

@tomjebo Thank you.

[tomjebo]

@lindexi, the graphics team confirmed that this behavior mimics GDI/GDI+ library behavior and has likely been in early versions of Office. I’m proposing that we add a behavior note to [MS-OI29500] 2.1.1211 (that’s the section that describes our Office implementation for ISO 29500 20.1.2.2.24 ln (Outline)).

Some notes: A value of w=“0” is not the correct way to remove the outline from a shape. To remove the outline, use the <noFill> line property. As long as there is a fill of some kind (the default fill will be <solidFill>), the outline will be drawn. When w=“0” is specified in the XML or if you omit the w attribute and do not include <noFill>, the effect on Office will be to draw a 1 device unit outline on the shape. Office will also preload the Format Shape dialog with a width of “1 pt” but this will not be written to XML.

For the SDK, we should not default the Outline class’ Width property to 0 or 1. That is actually an application behavior of Office when rendering but is not persisted. For example, Office will show a width of 1 pt in the UI but it won’t write anything out unless the user explicitly sets/changes that or sets/changes some other property that mandates it like <solidFill>. Without those conditions, upon save, Office does not touch the <ln> element. So my understanding: if the w attribute is missing, calling Outline.Width should get a null object. In that case you’re application should behave as if a shape has an outline of one device unit. But it should not persist anything to the underlying XML unless an explicit change is required. I hope this is clear.