Make SkMatrix44::invert() check for finite 1/det instead of magic value

tests/Matrix44Test.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "Test.h"
 #include "SkMatrix44.h"
 
@@ skipping 385 matching lines @@
     mat.setScale(3, 3, 3);
     rot.setRotateDegreesAbout(0, 0, -1, 90);
     mat.postConcat(rot);
     REPORTER_ASSERT(reporter, mat.invert(NULL));
     mat.invert(&inverse);
     iden1.setConcat(mat, inverse);
     REPORTER_ASSERT(reporter, is_identity(iden1));
     iden2.setConcat(inverse, mat);
     REPORTER_ASSERT(reporter, is_identity(iden2));
 
+    // test tiny-valued matrix inverse
+    mat.reset();
+    mat.setScale(1.0e-12, 1.0e-12, 1.0e-12);
+    rot.setRotateDegreesAbout(0, 0, -1, 90);
+    mat.postConcat(rot);
+    mat.postTranslate(1.0e-12, 1.0e-12, 1.0e-12);
+    REPORTER_ASSERT(reporter, mat.invert(NULL));
+    mat.invert(&inverse);
+    iden1.setConcat(mat, inverse);
+    REPORTER_ASSERT(reporter, is_identity(iden1));
+    
+    // test mixed-valued matrix inverse
+    mat.reset();
+    mat.setScale(1.0e-11, 3.0, 1.0e+11);
+    rot.setRotateDegreesAbout(0, 0, -1, 90);
+    mat.postConcat(rot);
+    mat.postTranslate(1.0e+11, 3.0, 1.0e-11);
+    REPORTER_ASSERT(reporter, mat.invert(NULL));
+    mat.invert(&inverse);
+    iden1.setConcat(mat, inverse);
+    REPORTER_ASSERT(reporter, is_identity(iden1));
+    
+    // test degenerate matrix
+    mat.reset();
+    mat.set3x3(1.0, 1.0, 0.0, 1.0, 0.0, 0.0, 0.0, 1.0, 0.0);
+    REPORTER_ASSERT(reporter, !mat.invert(NULL));
+    
     // test rol/col Major getters
     {
         mat.setTranslate(2, 3, 4);
         float dataf[16];
         double datad[16];
 
         mat.asColMajorf(dataf);
         assert16<float>(reporter, dataf,
                  1, 0, 0, 0,
                  0, 1, 0, 0,
@@ skipping 28 matching lines @@
     test_transpose(reporter);
     test_get_set_double(reporter);
     test_set_row_col_major(reporter);
     test_translate(reporter);
     test_scale(reporter);
     test_map2(reporter);
 }
 
 #include "TestClassDef.h"
 DEFINE_TESTCLASS("Matrix44", Matrix44TestClass, TestMatrix44)