1 Fonts and GM Tests 2 ================== 3 4 Overview 5 -------- 6 7 Each test in the gm directory draws a reference image. Their primary purpose is 8 to detect when images change unexpectedly, indicating that a rendering bug has 9 been introduced. 10 11 The gm tests have a secondary purpose: they detect when rendering is different 12 across platforms and configurations. 13 14 The dm \(Diamond Master\) tool supports flags that minimize or eliminate the 15 differences introduced by the font scaler native to each platform. 16 17 18 Portable fonts 19 -------------- 20 21 The most portable font format uses Skia to draw characters directly from paths, 22 and contains a idealized set of font metrics. This does not exercise platform 23 specific fonts at all, but does support specifying the font name, font size, 24 font style, and attributes like fakeBold. The paths are generated on a reference 25 platform \(currently a Mac\) and are stored as data in 26 'tools/test_font_data.cpp' . 27 28 To use portable fonts, pass '\-\-portableFonts' to dm. 29 30 31 Resource fonts 32 -------------- 33 34 The '\-\-resourceFonts' flag directs dm to use font files present in the resources 35 directory. By using the same font set on all buildbots, the generated gm images 36 become more uniform across platforms. 37 38 Today, the set of fonts used by gm, and present in my resources directory, 39 include: 40 41 * Courier New Bold Italic.ttf 42 * Courier New Bold.ttf 43 * Courier New Italic.ttf 44 * Courier New.ttf 45 * LiberationSans-Bold.ttf 46 * LiberationSans-BoldItalic.ttf 47 * LiberationSans-Italic.ttf 48 * LiberationSans-Regular.ttf 49 * Papyrus.ttc 50 * Pro W4.otf 51 * Times New Roman Bold Italic.ttf 52 * Times New Roman Bold.ttf 53 * Times New Roman Italic.ttf 54 * Times New Roman.ttf 55 56 57 System fonts 58 ------------ 59 60 If neither '\-\-portableFonts' nor '\-\-resourceFonts' is specified, dm uses the fonts 61 present on the system. Also, if '\-\-portableFonts' or '\-\-resourceFonts' is specified 62 and the desired font is not available, the native font lookup algorithm is 63 invoked. 64 65 66 GM font selection 67 ----------------- 68 69 Each gm specifies the typeface to use when drawing text. For now, to set the 70 portable typeface on the paint, call: 71 72 ~~~~ 73 sk_tool_utils::set_portable_typeface(SkPaint* , const char* name = nullptr, 74 SkTypeface::Style style = SkTypeface::kNormal ); 75 ~~~~ 76 77 To create a portable typeface, use: 78 79 ~~~~ 80 SkTypeface* typeface = sk_tool_utils::create_portable_typeface(const char* name, 81 SkTypeface::Style style); 82 ~~~~ 83 84 Eventually, both 'set_portable_typeface()' and 'create_portable_typeface()' will be 85 removed. Instead, a test-wide 'SkFontMgr' will be selected to choose portable 86 fonts or resource fonts. 87 88 89 Adding new fonts and glyphs to a GM 90 ----------------------------------- 91 92 If a font is missing from the portable data or the resource directory, the 93 system font is used instead. If a glyph is missing from the portable data, the 94 first character, usually a space, is drawn instead. 95 96 Running dm with '\-\-portableFonts' and '\-\-reportUsedChars' generates 97 'tools/test_font_data_chars.cpp', which describes the fonts and characters used by 98 all gm tests. Subsequently running the 'create_test_font' tool generates new paths 99 and writes them into 'tools/test_font_data.cpp' . 100 101 102 Future work 103 ----------- 104 105 The font set used by gm tests today is arbitrary and not intended to be 106 cross-platform. By choosing fonts without licensing issues, all bots can freely 107 contain the same fonts. By narrowing the font selection, the size of the test 108 font data will be more manageable. 109 110 Adding support for selecting from multiple font managers at runtime permits 111 removing manual typeface selection in the gm tests. Today, options to dm like 112 '\-\-pipe' fail with '\-\-portableFonts' because we're hard-coded to using the default 113 font manage when pictures are serialized. 114 115 Some gm tests explicitly always want to use system fonts and system metrics; 116 other gm tests use text only to label the drawing; yet other gm tests use text 117 to generate paths for testing. Additional discrimination is needed to 118 distinguish these cases. 119
