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

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Previously we were checking to see if the magnitude of determinant of the 
matrix to be inverted was less than 1.0e-8, which is a magic number possibly
plucked from Graphics Gems. After some discussion, it's been determined (ha)
that we can simply check to see if 1/det is finite and if so proceed.

BUG=222926
R=reed@google.com, shawnsingh@chromium.org

Author: jvanverth@google.com

Review URL: https://chromiumcodereview.appspot.com/22904003

git-svn-id: http://skia.googlecode.com/svn/trunk@10758 2bbb7eff-a529-9590-31e7-b0007b416f81
This commit is contained in:
commit-bot@chromium.org 2013-08-15 21:56:38 +00:00
parent 2822c9a92b
commit 7a3eeacd87
2 changed files with 32 additions and 3 deletions
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8
src/utils/SkMatrix44.cpp
View File

@ -529,13 +529,16 @@ bool SkMatrix44::invert(SkMatrix44* inverse) const {
// Calculate the determinant
double det = b00 * b11 - b01 * b10 + b02 * b09 + b03 * b08 - b04 * b07 + b05 * b06;
if (dabs(det) < TOO_SMALL_FOR_DETERMINANT) {
double invdet = 1.0 / det;
// If det is zero, we want to return false. However, we also want to return false
// if 1/det overflows to infinity (i.e. det is denormalized). Both of these are
// handled by checking that 1/det is finite.
if (!sk_float_isfinite(invdet)) {
return false;
}
if (NULL == inverse) {
return true;
}
double invdet = 1.0 / det;
b00 *= invdet;
b01 *= invdet;
@ -568,7 +571,6 @@ bool SkMatrix44::invert(SkMatrix44* inverse) const {
inverse->fMat[3][3] = SkDoubleToMScalar(a20 * b03 - a21 * b01 + a22 * b00);
inverse->dirtyTypeMask();
inverse->dirtyTypeMask();
return true;
}

27
tests/Matrix44Test.cpp
View File

@ -403,6 +403,33 @@ static void TestMatrix44(skiatest::Reporter* reporter) {
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-12, 3.0, 1.0e+12);
rot.setRotateDegreesAbout(0, 0, -1, 90);
mat.postConcat(rot);
mat.postTranslate(1.0e+12, 3.0, 1.0e-12);
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);