add helper to create fancy underlines

src/core/SkGlyphCache.cpp

Index: src/core/SkGlyphCache.cpp
diff --git a/src/core/SkGlyphCache.cpp b/src/core/SkGlyphCache.cpp
index 1512dbf0e5dd0a627369e74d32ce804945dd6bfc..56836524a993bb36eca90f4a4f29527b95921c1a 100644
--- a/src/core/SkGlyphCache.cpp
+++ b/src/core/SkGlyphCache.cpp
@@ -224,6 +224,170 @@ const SkPath* SkGlyphCache::findPath(const SkGlyph& glyph) {
     return glyph.fPath;
 }
 
+#include "../pathops/SkPathOpsCubic.h"
+#include "../pathops/SkPathOpsQuad.h"
+
+static bool quad_in_bounds(const SkScalar* pts, const SkScalar bounds[2]) {
+    SkScalar min = SkTMin(SkTMin(pts[0], pts[2]), pts[4]);
+    if (bounds[1] < min) {
+        return false;
+    }
+    SkScalar max = SkTMax(SkTMax(pts[0], pts[2]), pts[4]);
+    return bounds[0] < max;
+}
+
+static bool cubic_in_bounds(const SkScalar* pts, const SkScalar bounds[2]) {
+    SkScalar min = SkTMin(SkTMin(SkTMin(pts[0], pts[2]), pts[4]), pts[6]);
+    if (bounds[1] < min) {
+        return false;
+    }
+    SkScalar max = SkTMax(SkTMax(SkTMax(pts[0], pts[2]), pts[4]), pts[6]);
+    return bounds[0] < max;
+}
+
+static void offset_results(const SkGlyph::Intercept* intercept, SkScalar scale, SkScalar xPos,
+                           SkScalar* array, int* count) {
+    if (array) {
+        array += *count;
+        for (int index = 0; index < 2; index++) {
+            *array++ = intercept->fInterval[index] * scale + xPos;
+        }
+    }
+    *count += 2;
+}
+
+static void add_interval(SkScalar val, SkGlyph::Intercept* intercept) {
+    intercept->fInterval[0] = SkTMin(intercept->fInterval[0], val);
+    intercept->fInterval[1] = SkTMax(intercept->fInterval[1], val);
+}
+
+static void add_points(const SkPoint* pts, int ptCount, const SkScalar bounds[2], 
+        bool yAxis, SkGlyph::Intercept* intercept) {
+    for (int i = 0; i < ptCount; ++i) {
+        SkScalar val = *(&pts[i].fY - yAxis);
+        if (bounds[0] < val && val < bounds[1]) {
+            add_interval(*(&pts[i].fX + yAxis), intercept);
+        }
+    }
+}
+
+static void add_line(const SkPoint pts[2], SkScalar axis, bool yAxis,
+                     SkGlyph::Intercept* intercept) {
+    SkScalar t = yAxis ? (axis - pts[0].fX) / (pts[1].fX - pts[0].fX)
+            : (axis - pts[0].fY) / (pts[1].fY - pts[0].fY);
+    if (0 <= t && t < 1) {   // this handles divide by zero above
+        add_interval(yAxis ? pts[0].fY + t * (pts[1].fY - pts[0].fY)
+            : pts[0].fX + t * (pts[1].fX - pts[0].fX), intercept);
+    }
+}
+
+static void add_quad(const SkPoint pts[2], SkScalar axis, bool yAxis,
+                     SkGlyph::Intercept* intercept) {
+    SkDQuad quad;
+    quad.set(pts);
+    double roots[2];
+    int count = yAxis ? quad.verticalIntersect(axis, roots)
+            : quad.horizontalIntersect(axis, roots);
+    while (--count >= 0) {
+        SkPoint pt = quad.ptAtT(roots[count]).asSkPoint();
+        add_interval(*(&pt.fX + yAxis), intercept);
+    }
+}
+
+static void add_cubic(const SkPoint pts[3], SkScalar axis, bool yAxis,
+                      SkGlyph::Intercept* intercept) {
+    SkDCubic cubic;
+    cubic.set(pts);
+    double roots[3];
+    int count = yAxis ? cubic.verticalIntersect(axis, roots)
+            : cubic.horizontalIntersect(axis, roots);
+    while (--count >= 0) {
+        SkPoint pt = cubic.ptAtT(roots[count]).asSkPoint();
+        add_interval(*(&pt.fX + yAxis), intercept);
+    }
+}
+
+static const SkGlyph::Intercept* match_bounds(const SkGlyph* glyph, const SkScalar bounds[2]) {
+    const SkGlyph::Intercept* intercept = glyph->fIntercept;
+    while (intercept) {
+        if (bounds[0] == intercept->fBounds[0] && bounds[1] == intercept->fBounds[1]) {
+            return intercept;
+        }
+        intercept = intercept->fNext;
+    }
+    return nullptr;
+}
+
+void SkGlyphCache::findIntercepts(const SkScalar bounds[2], SkScalar scale, SkScalar xPos,
+        bool yAxis, SkGlyph* glyph, SkScalar* array, int* count) {
+    const SkGlyph::Intercept* match = match_bounds(glyph, bounds);
+
+    if (match) {
+        if (match->fInterval[0] < match->fInterval[1]) {
+            offset_results(match, scale, xPos, array, count);
+        }
+        return;
+    }
+
+    SkGlyph::Intercept* intercept =
+            (SkGlyph::Intercept* ) fGlyphAlloc.allocThrow(sizeof(SkGlyph::Intercept));
+    intercept->fNext = glyph->fIntercept;
+    intercept->fBounds[0] = bounds[0];
+    intercept->fBounds[1] = bounds[1];
+    intercept->fInterval[0] = SK_ScalarMax;
+    intercept->fInterval[1] = SK_ScalarMin;
+    glyph->fIntercept = intercept;
+    const SkPath* path = glyph->fPath;
+    const SkRect& pathBounds = path->getBounds();
+    if (*(&pathBounds.fBottom - yAxis) < bounds[0] || bounds[1] < *(&pathBounds.fTop - yAxis)) {
+        return;
+    }
+    SkPath::Iter iter(*path, false);
+    SkPoint pts[4];
+    SkPath::Verb verb;
+    while (SkPath::kDone_Verb != (verb = iter.next(pts))) {
+        switch (verb) {
+            case SkPath::kMove_Verb:
+                break;
+            case SkPath::kLine_Verb:
+                add_line(pts, bounds[0], yAxis, intercept);
+                add_line(pts, bounds[1], yAxis, intercept);
+                add_points(pts, 2, bounds, yAxis, intercept);
+                break;
+            case SkPath::kQuad_Verb:
+                if (!quad_in_bounds(&pts[0].fY - yAxis, bounds)) {
+                    break;
+                }
+                add_quad(pts, bounds[0], yAxis, intercept);
+                add_quad(pts, bounds[1], yAxis, intercept);
+                add_points(pts, 3, bounds, yAxis, intercept);
+                break;
+            case SkPath::kConic_Verb:
+                SkASSERT(0);  // no support for text composed of conics
+                break;
+            case SkPath::kCubic_Verb:
+                if (!cubic_in_bounds(&pts[0].fY - yAxis, bounds)) {
+                    break;
+                }
+                add_cubic(pts, bounds[0], yAxis, intercept);
+                add_cubic(pts, bounds[1], yAxis, intercept);
+                add_points(pts, 4, bounds, yAxis, intercept);
+                break;
+            case SkPath::kClose_Verb:
+                break;
+            default:
+                SkASSERT(0);
+                break;
+        }
+    }
+    if (intercept->fInterval[0] >= intercept->fInterval[1]) {
+        intercept->fInterval[0] = SK_ScalarMax;
+        intercept->fInterval[1] = SK_ScalarMin;
+        return;
+    }
+    offset_results(intercept, scale, xPos, array, count);
+}
+
 void SkGlyphCache::dump() const {
     const SkTypeface* face = fScalerContext->getTypeface();
     const SkScalerContextRec& rec = fScalerContext->getRec();