Improve horizontal baseline detection.

src/core/SkScalerContext.cpp

 
 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #include "SkScalerContext.h"
@@ skipping 809 matching lines @@
     }
 
     // The 'remainingWithoutRotation' matrix GsA is the non-rotational part of A without the scale.
     if (GsA) {
         *GsA = GA;
          // G is rotational so reorders with the scale.
         GsA->preScale(SkScalarInvert(s->fX), SkScalarInvert(s->fY));
     }
 }
 
-SkAxisAlignment SkComputeAxisAlignmentForHText(const SkMatrix& matrix) {
-    SkASSERT(!matrix.hasPerspective());
+SkAxisAlignment SkScalerContext::computeAxisAlignmentForHText() {
+    // Why fPost2x2 can be used here.
+    // getSingleMatrix multiplies in getLocalMatrix, which consists of
+    // * fTextSize (a scale, which has no effect)
+    // * fPreScaleX (a scale in x, which has no effect)
+    // * fPreSkewX (has no effect, but would on vertical text alignment).
+    // In other words, making the text bigger, stretching it along the
+    // horizontal axis, or fake italicizing it does not move the baseline.

[herb_g, 2016/02/29 18:37:10]

italicizing; it does...

[bungeman-skia, 2016/02/29 19:21:20]

it actually has no effect on the horizontal baseline (which is the implied
baseline, since this is For'H'Text.

 
-    if (0 == matrix[SkMatrix::kMSkewY]) {
+    if (0 == fRec.fPost2x2[1][0]) {
+        // The x axis is mapped onto the x axis.
         return kX_SkAxisAlignment;
     }
-    if (0 == matrix[SkMatrix::kMSkewX]) {
+    if (0 == fRec.fPost2x2[0][0]) {
+        // The x axis is mapped onto the y axis.
         return kY_SkAxisAlignment;
     }
     return kNone_SkAxisAlignment;
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 
 class SkScalerContext_Empty : public SkScalerContext {
 public:
     SkScalerContext_Empty(SkTypeface* face, const SkDescriptor* desc)
@@ skipping 25 matching lines @@
 
 SkScalerContext* SkTypeface::createScalerContext(const SkDescriptor* desc,
                                                  bool allowFailure) const {
     SkScalerContext* c = this->onCreateScalerContext(desc);
 
     if (!c && !allowFailure) {
         c = new SkScalerContext_Empty(const_cast<SkTypeface*>(this), desc);
     }
     return c;
 }