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Improve skia text shaping & bounds calculation #103

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merged 3 commits into from
Aug 26, 2024
Merged

Improve skia text shaping & bounds calculation #103

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6d7b22f
Improve skia text shaping/bounds calculation
ckaiser Aug 17, 2024
51e69d7
Ceil the float spacing to avoid early cut-off of some glyphs
ckaiser Aug 20, 2024
d1dc97d
Whitespace bounds from space glyph
ckaiser Aug 22, 2024
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12 changes: 7 additions & 5 deletions text/skia_font.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -71,11 +71,13 @@ int SkiaFont::height() const

int SkiaFont::textLength(const std::string& str) const
{
return m_skFont.measureText(
str.c_str(),
str.size(),
SkTextEncoding::kUTF8,
nullptr);
return std::ceil(
m_skFont.measureText(
str.c_str(),
str.size(),
SkTextEncoding::kUTF8,
nullptr)
);
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}

float SkiaFont::measureText(const std::string& str,
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35 changes: 26 additions & 9 deletions text/skia_text_blob_shaper.cpp
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Expand Up @@ -34,7 +34,8 @@ class ShaperRunHandler final : public SkShaper::RunHandler {
const gfx::PointF& offset,
TextBlob::RunHandler* subHandler)
: m_builder(utf8Text, os::to_skia(offset))
, m_subHandler(subHandler) { }
, m_subHandler(subHandler)
, m_buffer() { }
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sk_sp<SkTextBlob> makeBlob() {
return m_builder.makeBlob();
Expand Down Expand Up @@ -131,17 +132,33 @@ TextBlobRef SkiaTextBlob::MakeWithShaper(
ASSERT(dynamic_cast<SkiaFont*>(font.get()));

SkFont skFont = static_cast<SkiaFont*>(font.get())->skFont();
auto skFontMgr = static_cast<SkiaFontMgr*>(fontMgr.get())->skFontMgr();
sk_sp<SkTextBlob> textBlob;
gfx::RectF bounds;
if (auto shaper = SkShaper::Make(
static_cast<SkiaFontMgr*>(fontMgr.get())->skFontMgr())) {
if (auto shaper = SkShaper::Make(skFontMgr)) {
ShaperRunHandler shaperHandler(text.c_str(), { 0, 0 }, handler);
shaper->shape(
text.c_str(), text.size(),
skFont,
true,
std::numeric_limits<float>::max(),
&shaperHandler);

auto bidiRun = SkShaper::MakeBiDiRunIterator(text.c_str(), text.size(), 0xfe);
constexpr SkFourByteTag tag = SkSetFourByteTag('Z', 'y', 'y', 'y');
auto scriptRun = SkShaper::MakeScriptRunIterator(text.c_str(), text.size(), tag);
auto languageRun = SkShaper::MakeStdLanguageRunIterator(text.c_str(), text.size());
auto fontRun = SkShaper::MakeFontMgrRunIterator(text.c_str(),
text.size(),
skFont,
skFontMgr,
"Arial", // Fallback
SkFontStyle::Normal(),
&*languageRun);

shaper->shape(text.c_str(),
text.size(),
*fontRun,
*bidiRun,
*scriptRun,
*languageRun,
std::numeric_limits<float>::max(),
&shaperHandler);

Comment on lines +141 to +161
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It looks like MakeBiDiRunIterator and MakeScriptRunIterator functions are legacy too.

Probably we could do something similar to SkShaperPrimitive::shape() (using values instead of smart pointers for each run iterator):

void SkShaperPrimitive::shape(const char* utf8,
                              size_t utf8Bytes,
                              const SkFont& font,
                              bool leftToRight,
                              SkScalar width,
                              RunHandler* handler) const {
    std::unique_ptr<FontRunIterator> fontRuns(
            MakeFontMgrRunIterator(utf8, utf8Bytes, font, nullptr));
    if (!fontRuns) {
        return;
    }
    // bidi, script, and lang are all unused so we can construct them with empty data.
    TrivialBiDiRunIterator bidi{0, 0};
    TrivialScriptRunIterator script{0, 0};
    TrivialLanguageRunIterator lang{nullptr, 0};
    return this->shape(utf8, utf8Bytes, *fontRuns, bidi, script, lang, nullptr, 0, width, handler);
}

Anyway I tried to replace with these iterators and didn't work (I got a crash), so there is something I'm missing here.

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I'll look into it, it's very strange that we're getting different behaviors per-platform

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Oh in this case your code worked on Linux 👍 I was just commenting this because it might be better if we avoid calling those legacy Make*RunIterator functions and create those iterators in the stack directly.

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The thing is that we need to use these functions because they have different implementations depending on what's available, so on a platform without harfbuzz or on a compile without it, it'll use a trivial one - etc. If we don't use them we'd have to include that logic ourselves.

The legacy stuff is kind of interesting too because the only place where that SK_DISABLE_LEGACY_SKSHAPER_FUNCTIONS is declared is in the Bazel compile scripts, not in the GN ones, so it's not even possible to disable these functions for anyone building aseprite atm. I think it's probably ok to keep using them for now.

textBlob = shaperHandler.makeBlob();
bounds = shaperHandler.bounds();
}
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6 changes: 4 additions & 2 deletions text/text_blob.cpp
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Expand Up @@ -69,10 +69,12 @@ gfx::RectF TextBlob::RunInfo::getGlyphBounds(const size_t i) const
if (bounds.isEmpty()) {
FontMetrics metrics;
font->metrics(&metrics);
bounds.w = metrics.avgCharWidth;
bounds.h = -metrics.capHeight;
// avgCharWidth can be 0, so we grab the next most useful thing, the height
bounds.w = metrics.avgCharWidth > 0 ? metrics.avgCharWidth : metrics.xHeight;
bounds.h = 1.0;
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I'm not sure about this one, xHeight is the height of the lowercase x character. It feels wrong to use this value as the whitespace width (and hard coding 1.0 as the height).

To test this we can use the text_shape which is a mini text editor, put the cursor at a whitespace to test the whitespace bounds.

We should be able to set bounds.w = the advance in X axis for whitespaces, but I'm not sure where to find this value on Skia.

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Yeah this one's the most contentious change, the hardcoded 1 was to try and fix a specific bug of things being too tall in some circumstances, it should not stay like this. I need to look into more of the documentation

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I'm trying a new approach with just the normal " " character glyph bounds and it looks to behave correctly - at least more consistently than attempting to use FontMetrics. I think the ideal solution would be to shape the entire set of glyphs in one go with skia using getWidthsBounds but that'd mean a full refactor of how the runs are working currently.

}

ASSERT(!bounds.isEmpty());
bounds.offset(positions[i].x,
positions[i].y);
if (offsets) {
Expand Down
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