{"id":99955,"date":"2018-10-12T07:00:00","date_gmt":"2018-10-12T21:00:00","guid":{"rendered":"https:\/\/blogs.msdn.microsoft.com\/oldnewthing\/?p=99955"},"modified":"2019-03-13T00:22:02","modified_gmt":"2019-03-13T07:22:02","slug":"20181012-00","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/oldnewthing\/20181012-00\/?p=99955","title":{"rendered":"Why doesn’t GetTextExtentPoint return the correct extent for strings containing tabs?"},"content":{"rendered":"

A customer reported that the Get­Text­Extent­Point<\/code> and Get­Text­Extent­Point32<\/code> functions do not return the correct extents for strings that contain tabs. The documentation does say that they do not support carriage return and linefeed, but nothing about tabs. <\/p>\n

The Text­Out<\/code> and Get­Text­Extent­Point<\/code> functions do not interpret control characters. They take the string you pass, convert the code points to glyphs, string the glyphs together, and display or measure the result. <\/p>\n

They don’t move the virtual carriage to the “left margin” when they encounter a U+000D CARRIAGE RETURN, or move it down by the “line height” when they encounter a U+000A LINE FEED, or forward to the next “tab stop”, when they encounter a U+0009 CHARACTER TABULATION, or to the left by “some distance” when they encounter a U+0008 BACKSPACE,¹ or clear the “screen” when they encounter a U+000C FORM FEED, or change the “typewriter ribbon color” when they encounter U+000E SHIFT IN and U+000F SHIFT OUT, or beep the speaker when they encounter a U+0007 BELL. <\/p>\n

At best, you’ll get the graphics for the various control characters, like ␉ for the horizontal tab, but more likely you’ll get ugly black boxes. <\/p>\n

If you want to render text with tabs, use Tabbed­Text­Out<\/code>. If you want to measure text with tabs, use Get­Tabbed­Text­Extent<\/code>. The Draw­Text<\/code> function can both render and measure, and it also supports carriage returns and line feeds. <\/p>\n

Still no luck with backspace, changing the typewriter ribbon color, clearing the screen, or beeping the speaker, though. For those you’re on your own. <\/p>\n

¹ What would that even mean if you backspaced beyond the start of the string? Does this mean you could have a string whose extent is negative? <\/p>\n","protected":false},"excerpt":{"rendered":"

It doesn’t do carriage control.<\/p>\n","protected":false},"author":1069,"featured_media":111744,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1],"tags":[25],"class_list":["post-99955","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-oldnewthing","tag-code"],"acf":[],"blog_post_summary":"

It doesn’t do carriage control.<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/99955","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/users\/1069"}],"replies":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/comments?post=99955"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/99955\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media\/111744"}],"wp:attachment":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media?parent=99955"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/categories?post=99955"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/tags?post=99955"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}