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Diffstat (limited to 'doc/expert/pre_cove')
| -rw-r--r-- | doc/expert/pre_cove | 32 |
1 files changed, 32 insertions, 0 deletions
diff --git a/doc/expert/pre_cove b/doc/expert/pre_cove new file mode 100644 index 0000000..c5cf45e --- /dev/null +++ b/doc/expert/pre_cove @@ -0,0 +1,32 @@ +@Section + @Title { "@HCover" and "@VCover" } + @Tag { hcover } +@Begin +@PP +hcover. @Index { @@HCover symbol } +vcover. @Index { @@VCover symbol } +The @@VCover symbol vertically scales its right parameter so that it +covers every object that shares its row mark. For example, +@ID @Code "@VCover ( 45d @Rotate Hello @VCover )" +produces +@ID @ShowHMark { @VCover ( 45d @Rotate Hello @VCover ) } +The row mark has been added to show clearly where it lies. This should be +compared with +@ID @Code "@VScale ( 45d @Rotate Hello @VScale )" +which produces +@ID @ShowHMark { @VScale ( 45d @Rotate Hello @VScale ) } +Scaling abandons mark alignment and so is able to exactly cover the +rest of the row, whereas covering preserves mark alignment and so +is obliged in general to more than cover the rest of the row. +@PP +If the parameter of @@VCover has zero vertical size, this is taken +to mean that covering is not required after all and the @@VCover is +silently ignored. If however the parameter has non-zero size above +the mark but zero size below, or vice versa, this is taken to be an error +since scaling cannot make the parameter cover the rest of the row. +@PP +@@HCover is similar, horizontally covering all objects that share +its column mark. Neither symbol works well near galley targets, +because the scale factor to apply is determined before any galley +flushing takes place. +@End @Section |