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Avoid overflow in PictureTransformPoint. Fix PictureTransformIsIdentity. 

PictureTransformPoint computes homogeneous coordinates internally, but fails
to handle intermediate values larger than 16.16. Use 64 bit intermediate
values while computing the final result at 16.16 and only complain if that
result is too large.

PictureTransformIsIdentity was completely wrong -- it was not checking for
identity transforms at all.
This commit is contained in:
Keith Packard 2008-03-21 02:35:28 -07:00
parent 6fe9c15731
commit fa6a1df209
2 changed files with 22 additions and 41 deletions
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58
render/matrix.c
View File

@ -50,6 +50,8 @@ PictureTransformInitIdentity (PictTransformPtr matrix)
matrix->matrix[i][i] = F(1);
}
typedef xFixed_32_32 xFixed_34_30;
_X_EXPORT Bool
PictureTransformPoint3d (PictTransformPtr transform,
PictVectorPtr vector)
@ -78,7 +80,6 @@ PictureTransformPoint3d (PictTransformPtr transform,
return TRUE;
}
_X_EXPORT Bool
PictureTransformPoint (PictTransformPtr transform,
PictVectorPtr vector)
@ -86,30 +87,27 @@ PictureTransformPoint (PictTransformPtr transform,
PictVector result;
int i, j;
xFixed_32_32 partial;
xFixed_48_16 v;
xFixed_34_30 v[3];
xFixed_48_16 quo;
for (j = 0; j < 3; j++)
{
v = 0;
v[j] = 0;
for (i = 0; i < 3; i++)
{
partial = ((xFixed_48_16) transform->matrix[j][i] *
(xFixed_48_16) vector->vector[i]);
v += partial >> 16;
partial = ((xFixed_32_32) transform->matrix[j][i] *
(xFixed_32_32) vector->vector[i]);
v[j] += partial >> 2;
}
if (v > MAX_FIXED_48_16 || v < MIN_FIXED_48_16)
return FALSE;
result.vector[j] = (xFixed) v;
}
if (!result.vector[2])
if (!v[2])
return FALSE;
for (j = 0; j < 2; j++)
{
partial = (xFixed_48_16) result.vector[j] << 16;
v = partial / result.vector[2];
if (v > MAX_FIXED_48_16 || v < MIN_FIXED_48_16)
quo = v[j] / (v[2] >> 16);
if (quo > MAX_FIXED_48_16 || quo < MIN_FIXED_48_16)
return FALSE;
vector->vector[j] = (xFixed) v;
vector->vector[j] = (xFixed) quo;
}
vector->vector[2] = xFixed1;
return TRUE;
@ -296,29 +294,15 @@ within_epsilon (xFixed a, xFixed b, xFixed epsilon)
_X_EXPORT Bool
PictureTransformIsIdentity(PictTransform *t)
{
return (IsUnit (t->matrix[0][0]) &&
IsUnit (t->matrix[0][1]) &&
IsInt (t->matrix[0][2]) &&
IsUnit (t->matrix[1][0]) &&
IsUnit (t->matrix[1][1]) &&
IsInt (t->matrix[1][2]) &&
IsZero (t->matrix[2][0]) &&
IsZero (t->matrix[2][1]) &&
IsOne (t->matrix[2][2]));
}
_X_EXPORT Bool
PictureTransformIsUnit(PictTransform *t)
{
return (IsSame (t->matrix[0][0],t->matrix[1][1]) &&
return (IsSame (t->matrix[0][0], t->matrix[1][1]) &&
IsSame (t->matrix[0][0], t->matrix[2][2]) &&
!IsZero (t->matrix[0][0]) &&
!IsZero (t->matrix[0][0]) &&
IsZero (t->matrix[0][1]) &&
IsZero (t->matrix[0][2]) &&
IsZero (t->matrix[1][0]) &&
IsZero (t->matrix[1][2]) &&
IsZero (t->matrix[2][0]) &&
IsZero (t->matrix[2][1]));
IsZero (t->matrix[0][2]) &&
IsZero (t->matrix[1][0]) &&
IsZero (t->matrix[1][2]) &&
IsZero (t->matrix[2][0]) &&
IsZero (t->matrix[2][1]));
}
_X_EXPORT Bool
@ -334,11 +318,11 @@ PictureTransformIsScale(PictTransform *t)
IsZero (t->matrix[2][0]) &&
IsZero (t->matrix[2][1]) &&
IsOne (t->matrix[2][2]));
!IsZero (t->matrix[2][2]));
}
_X_EXPORT Bool
PictureTransformIsTranslate(PictTransform *t)
PictureTransformIsIntTranslate(PictTransform *t)
{
return ( IsOne (t->matrix[0][0]) &&
IsZero (t->matrix[0][1]) &&

5
render/picturestr.h
View File

@ -733,14 +733,11 @@ PictureTransformInvert (PictTransformPtr dst, const PictTransformPtr src);
Bool
PictureTransformIsIdentity(PictTransform *t);
Bool
PictureTransformIsUnit(PictTransform *t);
Bool
PictureTransformIsScale(PictTransform *t);
Bool
PictureTransformIsTranslate (PictTransform *t);
PictureTransformIsIntTranslate (PictTransform *t);
Bool
PictureTransformIsInverse(PictTransform *t, PictTransform *i);