119 lines
3.9 KiB
Markdown
119 lines
3.9 KiB
Markdown
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Fonts and GM Tests
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==================
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Overview
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--------
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Each test in the gm directory draws a reference image. Their primary purpose is
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to detect when images change unexpectedly, indicating that a rendering bug has
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been introduced.
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The gm tests have a secondary purpose: they detect when rendering is different
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across platforms and configurations.
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The dm \(Diamond Master\) tool supports flags that minimize or eliminate the
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differences introduced by the font scaler native to each platform.
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Portable fonts
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--------------
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The most portable font format uses Skia to draw characters directly from paths,
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and contains a idealized set of font metrics. This does not exercise platform
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specific fonts at all, but does support specifying the font name, font size,
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font style, and attributes like fakeBold. The paths are generated on a reference
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platform \(currently a Mac\) and are stored as data in
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'tools/test_font_data.cpp' .
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To use portable fonts, pass '\-\-portableFonts' to dm.
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Resource fonts
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--------------
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The '\-\-resourceFonts' flag directs dm to use font files present in the resources
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directory. By using the same font set on all buildbots, the generated gm images
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become more uniform across platforms.
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Today, the set of fonts used by gm, and present in my resources directory,
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include:
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* Courier New Bold Italic.ttf
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* Courier New Bold.ttf
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* Courier New Italic.ttf
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* Courier New.ttf
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* LiberationSans-Bold.ttf
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* LiberationSans-BoldItalic.ttf
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* LiberationSans-Italic.ttf
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* LiberationSans-Regular.ttf
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* Papyrus.ttc
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* Pro W4.otf
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* Times New Roman Bold Italic.ttf
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* Times New Roman Bold.ttf
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* Times New Roman Italic.ttf
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* Times New Roman.ttf
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System fonts
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------------
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If neither '\-\-portableFonts' nor '\-\-resourceFonts' is specified, dm uses the fonts
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present on the system. Also, if '\-\-portableFonts' or '\-\-resourceFonts' is specified
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and the desired font is not available, the native font lookup algorithm is
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invoked.
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GM font selection
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-----------------
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Each gm specifies the typeface to use when drawing text. For now, to set the
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portable typeface on the paint, call:
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~~~~
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sk_tool_utils::set_portable_typeface(SkPaint* , const char* name = NULL,
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SkTypeface::Style style = SkTypeface::kNormal );
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~~~~
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To create a portable typeface, use:
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~~~~
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SkTypeface* typeface = sk_tool_utils::create_portable_typeface(const char* name,
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SkTypeface::Style style);
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~~~~
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Eventually, both 'set_portable_typeface()' and 'create_portable_typeface()' will be
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removed. Instead, a test-wide 'SkFontMgr' will be selected to choose portable
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fonts or resource fonts.
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Adding new fonts and glyphs to a GM
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-----------------------------------
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If a font is missing from the portable data or the resource directory, the
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system font is used instead. If a glyph is missing from the portable data, the
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first character, usually a space, is drawn instead.
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Running dm with '\-\-portableFonts' and '\-\-reportUsedChars' generates
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'tools/test_font_data_chars.cpp', which describes the fonts and characters used by
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all gm tests. Subsequently running the 'create_test_font' tool generates new paths
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and writes them into 'tools/test_font_data.cpp' .
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Future work
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-----------
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The font set used by gm tests today is arbitrary and not intended to be
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cross-platform. By choosing fonts without licensing issues, all bots can freely
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contain the same fonts. By narrowing the font selection, the size of the test
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font data will be more manageable.
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Adding support for selecting from multiple font managers at runtime permits
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removing manual typeface selection in the gm tests. Today, options to dm like
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'\-\-pipe' fail with '\-\-portableFonts' because we're hard-coded to using the default
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font manage when pictures are serialized.
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Some gm tests explicitly always want to use system fonts and system metrics;
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other gm tests use text only to label the drawing; yet other gm tests use text
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to generate paths for testing. Additional discrimination is needed to
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distinguish these cases.
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