Add function to get both min and max scale factors from matrix

R=reed@google.com, jvanverth@google.com

Author: bsalomon@google.com

Review URL: https://codereview.chromium.org/298473002

git-svn-id: http://skia.googlecode.com/svn/trunk@14804 2bbb7eff-a529-9590-31e7-b0007b416f81

3 files changed, 104 insertions, 28 deletions

diff --git a/include/core/SkMatrix.h b/include/core/SkMatrix.h
index d52ab67f8c..7aa079ebda 100644
--- a/include/core/SkMatrix.h
+++ b/include/core/SkMatrix.h
@@ -563,22 +563,29 @@ public:
     SK_TO_STRING_NONVIRT()
 
     /**
-     * Calculates the minimum scaling factor of the matrix. If the matrix has
-     * perspective -1 is returned.
+     * Calculates the minimum scaling factor of the matrix as computed from the SVD of the upper
+     * left 2x2. If the matrix has perspective -1 is returned.
      *
      * @return minumum scale factor
      */
     SkScalar getMinScale() const;
 
     /**
-     * Calculates the maximum scale factor of the matrix. If the matrix has
-     * perspective -1 is returned.
+     * Calculates the maximum scaling factor of the matrix as computed from the SVD of the upper
+     * left 2x2. If the matrix has perspective -1 is returned.
      *
      * @return maximum scale factor
      */
     SkScalar getMaxScale() const;
 
     /**
+     * Gets both the min and max scale factors. The min scale factor is scaleFactors[0] and the max
+     * is scaleFactors[1]. If the matrix has perspective false will be returned and scaleFactors
+     * will be unchanged.
+     */
+    bool getMinMaxScales(SkScalar scaleFactors[2]) const;
+        
+    /**
      *  Return a reference to a const identity matrix
      */
     static const SkMatrix& I();
diff --git a/src/core/SkMatrix.cpp b/src/core/SkMatrix.cpp
index 483c6c83e4..40f6e5298d 100644
--- a/src/core/SkMatrix.cpp
+++ b/src/core/SkMatrix.cpp
@@ -1451,27 +1451,40 @@ bool SkMatrix::setPolyToPoly(const SkPoint src[], const SkPoint dst[],
 
 ///////////////////////////////////////////////////////////////////////////////
 
-enum MinOrMax {
-    kMin_MinOrMax,
-    kMax_MinOrMax
+enum MinMaxOrBoth {
+    kMin_MinMaxOrBoth,
+    kMax_MinMaxOrBoth,
+    kBoth_MinMaxOrBoth
 };
 
-template <MinOrMax MIN_OR_MAX> SkScalar get_scale_factor(SkMatrix::TypeMask typeMask,
-                                                         const SkScalar m[9]) {
+template <MinMaxOrBoth MIN_MAX_OR_BOTH> bool get_scale_factor(SkMatrix::TypeMask typeMask,
+                                                              const SkScalar m[9],
+                                                              SkScalar results[/*1 or 2*/]) {
     if (typeMask & SkMatrix::kPerspective_Mask) {
-        return -1;
+        return false;
     }
     if (SkMatrix::kIdentity_Mask == typeMask) {
-        return 1;
+        results[0] = SK_Scalar1;
+        if (kBoth_MinMaxOrBoth == MIN_MAX_OR_BOTH) {
+            results[1] = SK_Scalar1;
+        }
+        return true;
     }
     if (!(typeMask & SkMatrix::kAffine_Mask)) {
-        if (kMin_MinOrMax == MIN_OR_MAX) {
-             return SkMinScalar(SkScalarAbs(m[SkMatrix::kMScaleX]),
-                                SkScalarAbs(m[SkMatrix::kMScaleY]));
+        if (kMin_MinMaxOrBoth == MIN_MAX_OR_BOTH) {
+             results[0] = SkMinScalar(SkScalarAbs(m[SkMatrix::kMScaleX]),
+                                      SkScalarAbs(m[SkMatrix::kMScaleY]));
+        } else if (kMax_MinMaxOrBoth == MIN_MAX_OR_BOTH) {
+             results[0] = SkMaxScalar(SkScalarAbs(m[SkMatrix::kMScaleX]),
+                                      SkScalarAbs(m[SkMatrix::kMScaleY]));
         } else {
-             return SkMaxScalar(SkScalarAbs(m[SkMatrix::kMScaleX]),
-                                SkScalarAbs(m[SkMatrix::kMScaleY]));
+            results[0] = SkScalarAbs(m[SkMatrix::kMScaleX]);
+            results[1] = SkScalarAbs(m[SkMatrix::kMScaleY]);
+             if (results[0] > results[1]) {
+                 SkTSwap(results[0], results[1]);
+             }
         }
+        return true;
     }
     // ignore the translation part of the matrix, just look at 2x2 portion.
     // compute singular values, take largest or smallest abs value.
@@ -1487,35 +1500,62 @@ template <MinOrMax MIN_OR_MAX> SkScalar get_scale_factor(SkMatrix::TypeMask type
     // l^2 - (a + c)l + (ac-b^2)
     // solve using quadratic equation (divisor is non-zero since l^2 has 1 coeff
     // and roots are guaranteed to be pos and real).
-    SkScalar chosenRoot;
     SkScalar bSqd = b * b;
     // if upper left 2x2 is orthogonal save some math
     if (bSqd <= SK_ScalarNearlyZero*SK_ScalarNearlyZero) {
-        if (kMin_MinOrMax == MIN_OR_MAX) {
-            chosenRoot = SkMinScalar(a, c);
+        if (kMin_MinMaxOrBoth == MIN_MAX_OR_BOTH) {
+            results[0] = SkMinScalar(a, c);
+        } else if (kMax_MinMaxOrBoth == MIN_MAX_OR_BOTH) {
+            results[0] = SkMaxScalar(a, c);
         } else {
-            chosenRoot = SkMaxScalar(a, c);
+            results[0] = a;
+            results[1] = c;
+            if (results[0] > results[1]) {
+                SkTSwap(results[0], results[1]);
+            }
         }
     } else {
         SkScalar aminusc = a - c;
         SkScalar apluscdiv2 = SkScalarHalf(a + c);
         SkScalar x = SkScalarHalf(SkScalarSqrt(aminusc * aminusc + 4 * bSqd));
-        if (kMin_MinOrMax == MIN_OR_MAX) {
-            chosenRoot = apluscdiv2 - x;
+        if (kMin_MinMaxOrBoth == MIN_MAX_OR_BOTH) {
+            results[0] = apluscdiv2 - x;
+        } else if (kMax_MinMaxOrBoth == MIN_MAX_OR_BOTH) {
+            results[0] = apluscdiv2 + x;
         } else {
-            chosenRoot = apluscdiv2 + x;
+            results[0] = apluscdiv2 - x;
+            results[1] = apluscdiv2 + x;
         }
     }
-    SkASSERT(chosenRoot >= 0);
-    return SkScalarSqrt(chosenRoot);
+    SkASSERT(results[0] >= 0);
+    results[0] = SkScalarSqrt(results[0]);
+    if (kBoth_MinMaxOrBoth == MIN_MAX_OR_BOTH) {
+        SkASSERT(results[1] >= 0);
+        results[1] = SkScalarSqrt(results[1]);
+    }
+    return true;
 }
 
 SkScalar SkMatrix::getMinScale() const {
-    return get_scale_factor<kMin_MinOrMax>(this->getType(), fMat);
+    SkScalar factor;
+    if (get_scale_factor<kMin_MinMaxOrBoth>(this->getType(), fMat, &factor)) {
+        return factor;
+    } else {
+        return -1;
+    }
 }
 
 SkScalar SkMatrix::getMaxScale() const {
-    return get_scale_factor<kMax_MinOrMax>(this->getType(), fMat);
+    SkScalar factor;
+    if (get_scale_factor<kMax_MinMaxOrBoth>(this->getType(), fMat, &factor)) {
+        return factor;
+    } else {
+        return -1;
+    }
+}
+
+bool SkMatrix::getMinMaxScales(SkScalar scaleFactors[2]) const {
+    return get_scale_factor<kBoth_MinMaxOrBoth>(this->getType(), fMat, scaleFactors);
 }
 
 static void reset_identity_matrix(SkMatrix* identity) {
diff --git a/tests/MatrixTest.cpp b/tests/MatrixTest.cpp
index 1897554bc8..9c7a520369 100644
--- a/tests/MatrixTest.cpp
+++ b/tests/MatrixTest.cpp
@@ -120,43 +120,67 @@ static void test_flatten(skiatest::Reporter* reporter, const SkMatrix& m) {
 }
 
 static void test_matrix_min_max_scale(skiatest::Reporter* reporter) {
+    SkScalar scales[2];
+    bool success;
+
     SkMatrix identity;
     identity.reset();
     REPORTER_ASSERT(reporter, SK_Scalar1 == identity.getMinScale());
     REPORTER_ASSERT(reporter, SK_Scalar1 == identity.getMaxScale());
+    success = identity.getMinMaxScales(scales);
+    REPORTER_ASSERT(reporter, success && SK_Scalar1 == scales[0] && SK_Scalar1 == scales[1]);
 
     SkMatrix scale;
     scale.setScale(SK_Scalar1 * 2, SK_Scalar1 * 4);
     REPORTER_ASSERT(reporter, SK_Scalar1 * 2 == scale.getMinScale());
     REPORTER_ASSERT(reporter, SK_Scalar1 * 4 == scale.getMaxScale());
+    success = scale.getMinMaxScales(scales);
+    REPORTER_ASSERT(reporter, success && SK_Scalar1 * 2 == scales[0] && SK_Scalar1 * 4 == scales[1]);
 
     SkMatrix rot90Scale;
     rot90Scale.setRotate(90 * SK_Scalar1);
     rot90Scale.postScale(SK_Scalar1 / 4, SK_Scalar1 / 2);
     REPORTER_ASSERT(reporter, SK_Scalar1 / 4 == rot90Scale.getMinScale());
     REPORTER_ASSERT(reporter, SK_Scalar1 / 2 == rot90Scale.getMaxScale());
+    success = rot90Scale.getMinMaxScales(scales);
+    REPORTER_ASSERT(reporter, success && SK_Scalar1 / 4  == scales[0] && SK_Scalar1 / 2 == scales[1]);
 
     SkMatrix rotate;
     rotate.setRotate(128 * SK_Scalar1);
-    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(SK_Scalar1, rotate.getMinScale() ,SK_ScalarNearlyZero));
+    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(SK_Scalar1, rotate.getMinScale(), SK_ScalarNearlyZero));
     REPORTER_ASSERT(reporter, SkScalarNearlyEqual(SK_Scalar1, rotate.getMaxScale(), SK_ScalarNearlyZero));
+    success = rotate.getMinMaxScales(scales);
+    REPORTER_ASSERT(reporter, success);
+    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(SK_Scalar1, scales[0], SK_ScalarNearlyZero));
+    REPORTER_ASSERT(reporter, SkScalarNearlyEqual(SK_Scalar1, scales[1], SK_ScalarNearlyZero));
 
     SkMatrix translate;
     translate.setTranslate(10 * SK_Scalar1, -5 * SK_Scalar1);
     REPORTER_ASSERT(reporter, SK_Scalar1 == translate.getMinScale());
     REPORTER_ASSERT(reporter, SK_Scalar1 == translate.getMaxScale());
+    success = translate.getMinMaxScales(scales);
+    REPORTER_ASSERT(reporter, success && SK_Scalar1 == scales[0] && SK_Scalar1 == scales[1]);
 
     SkMatrix perspX;
     perspX.reset();
     perspX.setPerspX(SkScalarToPersp(SK_Scalar1 / 1000));
     REPORTER_ASSERT(reporter, -SK_Scalar1 == perspX.getMinScale());
     REPORTER_ASSERT(reporter, -SK_Scalar1 == perspX.getMaxScale());
+    // Verify that getMinMaxScales() doesn't update the scales array on failure.
+    scales[0] = -5;
+    scales[1] = -5;
+    success = perspX.getMinMaxScales(scales);
+    REPORTER_ASSERT(reporter, !success && -5 * SK_Scalar1 == scales[0] && -5 * SK_Scalar1  == scales[1]);
 
     SkMatrix perspY;
     perspY.reset();
     perspY.setPerspY(SkScalarToPersp(-SK_Scalar1 / 500));
     REPORTER_ASSERT(reporter, -SK_Scalar1 == perspY.getMinScale());
     REPORTER_ASSERT(reporter, -SK_Scalar1 == perspY.getMaxScale());
+    scales[0] = -5;
+    scales[1] = -5;
+    success = perspY.getMinMaxScales(scales);
+    REPORTER_ASSERT(reporter, !success && -5 * SK_Scalar1 == scales[0] && -5 * SK_Scalar1  == scales[1]);
 
     SkMatrix baseMats[] = {scale, rot90Scale, rotate,
                            translate, perspX, perspY};
@@ -180,6 +204,11 @@ static void test_matrix_min_max_scale(skiatest::Reporter* reporter) {
         REPORTER_ASSERT(reporter, (minScale < 0) == (maxScale < 0));
         REPORTER_ASSERT(reporter, (maxScale < 0) == mat.hasPerspective());
 
+        SkScalar scales[2];
+        bool success = mat.getMinMaxScales(scales);
+        REPORTER_ASSERT(reporter, success == !mat.hasPerspective());
+        REPORTER_ASSERT(reporter, !success || (scales[0] == minScale && scales[1] == maxScale));
+
         if (mat.hasPerspective()) {
             m -= 1; // try another non-persp matrix
             continue;