Fix SkPaint::measureText for stroked hairline text

gm/glyph_pos.cpp

Index: gm/glyph_pos.cpp
diff --git a/gm/glyph_pos.cpp b/gm/glyph_pos.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..b0451016accaa71bc13a2d61b4d3db5a09cc212b
--- /dev/null
+++ b/gm/glyph_pos.cpp
@@ -0,0 +1,204 @@
+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "gm.h"
+#include "SkCanvas.h"
+#include "SkTypeface.h"
+
+/* This test tries to define the effect of using hairline strokes on text.
+ * Provides non-hairline images for reference and consistency checks.
+ * glyph_pos_(h/n)_(s/f/b)
+ *   -> test hairline/non-hairline stroke/fill/stroke+fill.
+ */
+static const SkScalar kTextHeight = 14.0f;
+static const char kText[] = "Proportional Hamburgefons #% fi";
+
+namespace skiagm {
+
+class GlyphPosGM : public GM {
+public:
+    GlyphPosGM(SkScalar strokeWidth, SkPaint::Style strokeStyle)
+        : fStrokeWidth(strokeWidth)
+        , fStrokeStyle(strokeStyle) {
+        }
+
+protected:
+    virtual uint32_t onGetFlags() const SK_OVERRIDE {
+        return kSkipTiled_Flag;
+    }
+
+    virtual SkString onShortName() SK_OVERRIDE {
+        SkString str("glyph_pos");
+        if (fStrokeWidth == 0.0f) {
+            str.append("_h"); // h == Hairline.
+        } else {
+            str.append("_n"); // n == Normal.
+        }
+        if (fStrokeStyle == SkPaint::kStroke_Style) {
+            str.append("_s");
+        } else if (fStrokeStyle == SkPaint::kFill_Style) {
+            str.append("_f");
+        } else {
+            str.append("_b"); // b == Both.
+        }
+        return str;
+    }
+
+    virtual SkISize onISize() { return SkISize::Make(800, 600); }
+
+    virtual void onDraw(SkCanvas* canvas) SK_OVERRIDE {
+        if (!fProp) {
+            fProp.reset(SkTypeface::CreateFromName("Helvetica", SkTypeface::kNormal));
+        }
+
+        // There's a black pixel at 40, 40 for reference.
+        canvas->drawPoint(40.0f, 40.0f, SK_ColorBLACK);
+
+        // Two reference images.
+        canvas->translate(50.0f, 50.0f);
+        drawTestCase(canvas, 1.0f);
+
+        canvas->translate(0.0f, 50.0f);
+        drawTestCase(canvas, 3.0f);
+
+        // Uniform scaling test.
+        canvas->translate(0.0f, 100.0f);
+        canvas->save();
+        canvas->scale(3.0f, 3.0f);
+        drawTestCase(canvas, 1.0f);
+        canvas->restore();
+
+        // Non-uniform scaling test.
+        canvas->translate(0.0f, 100.0f);
+        canvas->save();
+        canvas->scale(3.0f, 6.0f);
+        drawTestCase(canvas, 1.0f);
+        canvas->restore();
+
+        // Skew test.
+        canvas->translate(0.0f, 80.0f);
+        canvas->save();
+        canvas->scale(3.0f, 3.0f);
+        SkMatrix skew;
+        skew.setIdentity();
+        skew.setSkewX(SkScalarDiv(8.0f,
+                                  25.0f));
+        skew.setSkewY(SkScalarDiv(2.0f,
+                                  25.0f));
+        canvas->concat(skew);
+        drawTestCase(canvas, 1.0f);
+        canvas->restore();
+
+        // Perspective test.
+        canvas->translate(0.0f, 80.0f);
+        canvas->save();
+        SkMatrix perspective;
+        perspective.setIdentity();
+        perspective.setPerspX(-SkScalarDiv(SK_Scalar1, 340.0f));
+        perspective.setSkewX(SkScalarDiv(8.0f,
+                                         25.0f));
+        perspective.setSkewY(SkScalarDiv(2.0f,
+                                         25.0f));
+
+
+        canvas->concat(perspective);
+        drawTestCase(canvas, 1.0f);
+        canvas->restore();
+    }
+
+    void drawTestCase(SkCanvas* canvas, SkScalar textScale) {
+        SkPaint paint;
+        paint.setColor(SK_ColorBLACK);
+        paint.setAntiAlias(true);
+        paint.setTextSize(kTextHeight * textScale);
+        paint.setTypeface(fProp);
+        paint.setDevKernText(true);
+        paint.setStrokeWidth(fStrokeWidth);
+        paint.setStyle(fStrokeStyle);
+
+        // This demonstrates that we can not measure the text if there's a device transform. The
+        // canvas total matrix will end up being a device transform.
+        bool drawRef = !(canvas->getTotalMatrix().getType() &
+                         ~(SkMatrix::kIdentity_Mask | SkMatrix::kTranslate_Mask));
+
+        SkRect bounds;
+        if (drawRef) {
+            SkScalar advance = paint.measureText(kText, sizeof(kText) - 1, &bounds);
+
+            paint.setStrokeWidth(0.0f);
+            paint.setStyle(SkPaint::kStroke_Style);
+
+            // Green box is the measured text bounds.
+            paint.setColor(SK_ColorGREEN);
+            canvas->drawRect(bounds, paint);
+
+            // Red line is the measured advance from the 0,0 of the text position.
+            paint.setColor(SK_ColorRED);
+            canvas->drawLine(0.0f, 0.0f, advance, 0.0f, paint);
+        }
+
+        // Black text is the testcase, eg. the text.
+        paint.setColor(SK_ColorBLACK);
+        paint.setStrokeWidth(fStrokeWidth);
+        paint.setStyle(fStrokeStyle);
+        canvas->drawText(kText, sizeof(kText) - 1, 0.0f, 0.0f, paint);
+
+        if (drawRef) {
+            SkScalar widths[sizeof(kText) - 1];
+            paint.getTextWidths(kText, sizeof(kText) - 1, widths, NULL);
+
+            paint.setStrokeWidth(0.0f);
+            paint.setStyle(SkPaint::kStroke_Style);
+
+            // Magenta lines are the positions for the characters.
+            paint.setColor(SK_ColorMAGENTA);
+            SkScalar w = bounds.x();
+            for (size_t i = 0; i < sizeof(kText) - 1; ++i) {
+                canvas->drawLine(w, 0.0f, w, 5.0f, paint);
+                w += widths[i];
+            }
+        }
+    }
+
+private:
+    SkAutoTUnref<SkTypeface> fProp;
+    SkScalar fStrokeWidth;
+    SkPaint::Style fStrokeStyle;
+
+    typedef GM INHERITED;
+};
+
+//////////////////////////////////////////////////////////////////////////////
+
+static GM* GlyphPosHairlineStrokeAndFillFactory(void*) {
+    return new GlyphPosGM(0.0f, SkPaint::kStrokeAndFill_Style);
+}
+static GM* GlyphPosStrokeAndFillFactory(void*) {
+    return new GlyphPosGM(1.2f, SkPaint::kStrokeAndFill_Style);
+}
+static GM* GlyphPosHairlineStrokeFactory(void*) {
+    return new GlyphPosGM(0.0f, SkPaint::kStroke_Style);
+}
+static GM* GlyphPosStrokeFactory(void*) {
+    return new GlyphPosGM(1.2f, SkPaint::kStroke_Style);
+}
+static GM* GlyphPosHairlineFillFactory(void*) {
+    return new GlyphPosGM(0.0f, SkPaint::kFill_Style);
+}
+static GM* GlyphPosFillFactory(void*) {
+    return new GlyphPosGM(1.2f, SkPaint::kFill_Style);
+}
+
+static GMRegistry reg1(GlyphPosHairlineStrokeAndFillFactory);
+static GMRegistry reg2(GlyphPosStrokeAndFillFactory);
+static GMRegistry reg3(GlyphPosHairlineStrokeFactory);
+static GMRegistry reg4(GlyphPosStrokeFactory);
+static GMRegistry reg5(GlyphPosHairlineFillFactory);
+static GMRegistry reg6(GlyphPosFillFactory);
+
+
+}