ee380a0c7d
Change-Id: Ifb2ca09b5d146eca796ce0e199720e8833848e13 Docs-Preview: https://skia.org/?cl=349401 Reviewed-on: https://skia-review.googlesource.com/c/skia/+/349401 Reviewed-by: Mike Reed <reed@google.com> Commit-Queue: Mike Reed <reed@google.com>
141 lines
5.3 KiB
Markdown
141 lines
5.3 KiB
Markdown
Tips & FAQ
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==========
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+ [Bitmap Subsetting](#bitmap-subsetting)
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+ [Capture a `.skp` file on a web page in Chromium](#skp-capture)
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+ [Capture a `.mskp` file on a web page in Chromium](#mskp-capture)
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+ [How to add hardware acceleration in Skia](#hw-acceleration)
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+ [Does Skia support Font hinting?](#font-hinting)
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+ [Does Skia shape text (kerning)?](#kerning)
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+ [How do I add drop shadow on text?](#text-shadow)
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* * *
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<span id="skp-capture">Capture a `.skp` file on a web page in Chromium</span>
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-----------------------------------------------------------------------------
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Use the script `experimental/tools/web_to_skp` , *or* do the following:
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1. Launch Chrome or Chromium with `--no-sandbox --enable-gpu-benchmarking`
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2. Open the JS console (Ctrl+Shift+J (Windows / Linux) or Cmd+Opt+J (MacOS))
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3. Execute: `chrome.gpuBenchmarking.printToSkPicture('/tmp')`
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This returns "undefined" on success.
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Open the resulting file in the [Skia Debugger](/dev/tools/debugger), rasterize it with `dm`,
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or use Skia's `viewer` to view it:
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<!--?prettify lang=sh?-->
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out/Release/dm --src skp --skps /tmp/layer_0.skp -w /tmp \
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--config 8888 gpu pdf --verbose
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ls -l /tmp/*/skp/layer_0.skp.*
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out/Release/viewer --skps /tmp --slide layer_0.skp
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* * *
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<span id="mskp-capture">Capture a `.mskp` file on a web page in Chromium</span>
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-------------------------------------------------------------------------------
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Multipage Skia Picture files capture the commands sent to produce PDFs
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and printed documents.
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Use the script `experimental/tools/web_to_mskp` , *or* do the following:
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1. Launch Chrome or Chromium with `--no-sandbox --enable-gpu-benchmarking`
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2. Open the JS console (Ctrl+Shift+J (Windows / Linux) or Cmd+Opt+J (MacOS))
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3. Execute: `chrome.gpuBenchmarking.printPagesToSkPictures('/tmp/filename.mskp')`
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This returns "undefined" on success.
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Open the resulting file in the [Skia Debugger](/dev/tools/debugger) or
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process it with `dm`.
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<!--?prettify lang=sh?-->
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experimental/tools/mskp_parser.py /tmp/filename.mskp /tmp/filename.mskp.skp
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ls -l /tmp/filename.mskp.skp
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# open filename.mskp.skp in the debugger.
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out/Release/dm --src mskp --mskps /tmp/filename.mskp -w /tmp \
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--config pdf --verbose
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ls -l /tmp/pdf/mskp/filename.mskp.pdf
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* * *
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<span id="hw-acceleration">How to add hardware acceleration in Skia</span>
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--------------------------------------------------------------------------
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There are two ways Skia takes advantage of specific hardware.
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1. Custom bottleneck routines
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There are sets of bottleneck routines inside the blits of Skia
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that can be replace on a platform in order to take advantage of
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specific CPU features. One such example is the NEON SIMD
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instructions on ARM v7 devices. See [src/opts/](https://skia.googlesource.com/skia/+/master/src/opts/)
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* * *
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<span id="font-hinting">Does Skia support Font hinting?</span>
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--------------------------------------------------------------
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Skia has a built-in font cache, but it does not know how to actually render font
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files like TrueType into its cache. For that it relies on the platform to
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supply an instance of `SkScalerContext`. This is Skia's abstract interface for
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communicating with a font scaler engine. In src/ports you can see support
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files for FreeType, macOS, and Windows GDI font engines. Other font
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engines can easily be supported in a like manner.
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* * *
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<span id="kerning">Does Skia shape text (kerning)?</span>
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---------------------------------------------------------
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Shaping is the process that translates a span of Unicode text into a span of
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positioned glyphs with the apropriate typefaces.
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Skia does not shape text. Skia provides interfaces to draw glyphs, but does
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not implement a text shaper. Skia's client's often use
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[HarfBuzz](http://www.freedesktop.org/wiki/Software/HarfBuzz/) to
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generate the glyphs and their positions, including kerning.
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[Here is an example of how to use Skia and HarfBuzz
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together](https://github.com/aam/skiaex). In the example, a
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`SkTypeface` and a `hb_face_t` are created using the same `mmap()`ed
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`.ttf` font file. The HarfBuzz face is used to shape unicode text into
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a sequence of glyphs and positions, and the `SkTypeface` can then be
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used to draw those glyphs.
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* * *
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<span id="text-shadow">How do I add drop shadow on text?</span>
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---------------------------------------------------------------
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<!--?prettify lang=cc?-->
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void draw(SkCanvas* canvas) {
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const SkScalar sigma = 1.65f;
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const SkScalar xDrop = 2.0f;
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const SkScalar yDrop = 2.0f;
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const SkScalar x = 8.0f;
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const SkScalar y = 52.0f;
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const SkScalar textSize = 48.0f;
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const uint8_t blurAlpha = 127;
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auto blob = SkTextBlob::MakeFromString("Skia", SkFont(nullptr, textSize));
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SkPaint paint;
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paint.setAntiAlias(true);
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SkPaint blur(paint);
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blur.setAlpha(blurAlpha);
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blur.setMaskFilter(SkMaskFilter::MakeBlur(kNormal_SkBlurStyle, sigma, 0));
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canvas->drawColor(SK_ColorWHITE);
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canvas->drawTextBlob(blob.get(), x + xDrop, y + yDrop, blur);
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canvas->drawTextBlob(blob.get(), x, y, paint);
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}
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<a href='https://fiddle.skia.org/c/@text_shadow'><img src='https://fiddle.skia.org/i/@text_shadow_raster.png'></a>
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* * *
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<div style="margin-bottom:99%"></div>
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