31.1.3 WMF format limitations
WMF graphics are like scripts for the Windows GDI. A WMF graphic can include vector elements (as in FrameMaker native graphics), text, and bitmaps (with up to 24-bit resolution). You can import WMF graphics into FrameMaker, where they are seen as Frame Vector facets. However, FrameMaker special-ungroup command Esc g U does not make it possible to edit a WMF graphic.
In WinHelp, WMF graphics can cause system crashes on Windows 9x or Windows ME; see §8.6.2 Avoiding the GDI resource leak for more information.
The WMF graphic format has limitations:
Bezier curves become polylines
Cropped images show all in WinHelp
Bezier curves become polylines
WMF does not support Bezier curves (smoothed polylines in FrameMaker). WMF does support ellipses and elliptic arcs, with radii or chords available for the arcs. Bezier curves are represented by polyline segments. When Mif2Go converts FrameMaker vector graphics to WMF, Mif2Go generates the polyline segments; but some segments might be only one pixel long, if that is what it takes to emulate a Bezier display. The segmented polylines are indistinguishable from the original Bezier curves when viewed on screen. There is a difference in print, but you would have to use a magnifier to see it.
For dashed lines and other non-solid lines, MicroSoft code for WMF images sets line thickness to 1 (one), which is nominally 1.0 twip (1/20 pt) or 0.01 mm. This value is affected by scaling, so you always get the thinnest line drawable. If you try to use a different thickness for a non-solid line, you get the thickness you specified, but the line becomes solid. However, when you specify Mif2Go native graphics export to WMF, Mif2Go preserves the line style rather than the line width. To preserve both line style and line width, you would have to specify FrameMaker graphics export instead, and convert the image to a BMP instead of to a WMF. See §31.2.5 Converting graphics with FrameMaker export filters.
Cropped images show all in WinHelp
WMF does not support cropping. In FrameMaker, you can use the anchored frame to crop a large graphic to the area of interest. This does not work at all in WinHelp. Although you see the part you want in WinHelp, the rest of the image is also visible, running right over any nearby text or other graphics. This is true of both bitmaps and vectors. We advise cropping bitmaps to the actual displayed area before importing them into FrameMaker, even if you are importing by reference.
WMF cannot embed fonts, and so relies on the viewing application to have the fonts available for rendering. If Windows substitutes another font with different metrics, the result can be quite ugly. WMF has no concept of text frames with flowing content. Instead, each line is an independent text line that cannot include any font-property changes, such as bold or subscript. Such changes require starting a new text line; however, you do not know where the last segment ended (one of the key differences between WMF and direct Windows GDI calls), so you must compute the position based on your own estimate of the font metrics. A miscalculation (or a different font) can result in big gaps, or in overlapping text.
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