breakText on font

Bug: skia:
Change-Id: Iebf65b158a0b08ed8e65b77d9d0aeef8c159d5db
Reviewed-on: https://skia-review.googlesource.com/c/173770
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Mike Reed <reed@google.com>

include/core/SkFont.h

@@ -295,6 +295,9 @@ public:
      */
     bool containsText(const void* text, size_t byteLength, SkTextEncoding encoding) const;
 
+    size_t breakText(const void* text, size_t length, SkTextEncoding, SkScalar maxWidth,
+                     SkScalar* measuredWidth = nullptr) const;
+
     /** Returns the advance width of text.
         The advance is the normal distance to move before drawing additional text.
         Returns the bounding box of text if bounds is not nullptr.

src/core/SkFont.cpp

@@ -231,6 +231,55 @@ bool SkFont::containsText(const void* textData, size_t byteLength, SkTextEncodin
     return true;
 }
 
+size_t SkFont::breakText(const void* textD, size_t length, SkTextEncoding encoding,
+                         SkScalar maxWidth, SkScalar* measuredWidth) const {
+    if (0 == length || !(maxWidth > 0)) {
+        if (measuredWidth) {
+            *measuredWidth = 0;
+        }
+        return 0;
+    }
+    if (0 == fSize) {
+        if (measuredWidth) {
+            *measuredWidth = 0;
+        }
+        return length;
+    }
+
+    SkCanonicalizeFont canon(*this);
+    const SkFont& font = canon.getFont();
+    SkScalar scale = canon.getScale();
+
+    auto cache = SkStrikeCache::FindOrCreateStrikeWithNoDeviceExclusive(font);
+
+    const char* text = static_cast<const char*>(textD);
+    const char* stop = text + length;
+    auto glyphCacheProc = SkFontPriv::GetGlyphCacheProc(encoding, false);
+
+    if (scale) {
+        maxWidth /= scale;
+    }
+
+    SkScalar width = 0;
+    while (text < stop) {
+        const char* curr = text;
+        SkScalar x = glyphCacheProc(cache.get(), &text, stop).fAdvanceX;
+        if ((width += x) > maxWidth) {
+            width -= x;
+            text = curr;
+            break;
+        }
+    }
+
+    if (measuredWidth) {
+        if (scale) {
+            width *= scale;
+        }
+        *measuredWidth = width;
+    }
+    return text - stop + length;
+}
+
 static void set_bounds(const SkGlyph& g, SkRect* bounds) {
     bounds->set(SkIntToScalar(g.fLeft),
                 SkIntToScalar(g.fTop),

tests/PaintBreakTextTest.cpp

@@ -6,9 +6,23 @@
  */
 
 #include "SkAutoMalloc.h"
+#include "SkFont.h"
 #include "SkPaint.h"
 #include "Test.h"
 
+static size_t break_text(const SkPaint& paint, const void* text, size_t length, SkScalar maxw,
+                         SkScalar* measuredw, skiatest::Reporter* reporter) {
+    size_t n = paint.breakText(text, length, maxw, measuredw);
+    SkScalar measuredw2;
+    size_t n2 = SkFont::LEGACY_ExtractFromPaint(paint).breakText(text, length,
+                                     (SkTextEncoding)paint.getTextEncoding(), maxw, &measuredw2);
+    REPORTER_ASSERT(reporter, n == n2);
+    if (measuredw) {
+        REPORTER_ASSERT(reporter, *measuredw == measuredw2);
+    }
+    return n;
+}
+
 static void test_monotonic(skiatest::Reporter* reporter,
                            const SkPaint& paint,
                            const char* msg) {
@@ -21,7 +35,7 @@ static void test_monotonic(skiatest::Reporter* reporter,
     const SkScalar step = SkMaxScalar(width / 10, SK_Scalar1);
     for (SkScalar w = 0; w <= width; w += step) {
         SkScalar m;
-        const size_t n = paint.breakText(text, length, w, &m);
+        const size_t n = break_text(paint, text, length, w, &m, reporter);
 
         REPORTER_ASSERT(reporter, n <= length, msg);
         REPORTER_ASSERT(reporter, m <= width, msg);
@@ -51,7 +65,7 @@ static void test_eq_measure_text(skiatest::Reporter* reporter,
     const SkScalar width = paint.measureText(text, length);
 
     SkScalar mm;
-    const size_t length2 = paint.breakText(text, length, width, &mm);
+    const size_t length2 = break_text(paint, text, length, width, &mm, reporter);
     REPORTER_ASSERT(reporter, length2 == length, msg);
     REPORTER_ASSERT(reporter, mm == width, msg);
 }
@@ -67,7 +81,7 @@ static void test_long_text(skiatest::Reporter* reporter,
     const SkScalar width = paint.measureText(text, kSize);
 
     SkScalar mm;
-    const size_t length = paint.breakText(text, kSize, width, &mm);
+    const size_t length = break_text(paint, text, kSize, width, &mm, reporter);
     REPORTER_ASSERT(reporter, length == kSize, msg);
     REPORTER_ASSERT(reporter, mm == width, msg);
 }