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all tested and working 

revised formula for in/out/dest-in/dest-out, for vector and scalar paths

see https://github.com/libvips/libvips/issues/1301
This commit is contained in:
John Cupitt 2019-05-08 18:16:40 +01:00
parent 447e0f3ea2
commit d5ca1ddfd4
1 changed files with 27 additions and 18 deletions
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45
libvips/conversion/composite.cpp
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@ -13,6 +13,8 @@
* - don't stop on first non-transparent image [felixbuenemann, GDmac]
* 6/12/18
* - do our own subimage positioning
* 8/5/19
* - revise in/out/dest-in/dest-out to make smoother alpha
*/
/*
@ -461,14 +463,18 @@ vips_composite_base_blend( VipsCompositeBase *composite,
case VIPS_BLEND_MODE_IN:
aR = aA * aB;
for( int b = 0; b < bands; b++ )
B[b] = A[b];
// if aA == 0, then aR == 0 and so B will already be 0
if( aA != 0 )
for( int b = 0; b < bands; b++ )
B[b] = A[b] * aR / aA;
break;
case VIPS_BLEND_MODE_OUT:
aR = aA * (1 - aB);
for( int b = 0; b < bands; b++ )
B[b] = A[b];
// if aA == 0, then aR == 0 and so B will already be 0
if( aA != 0 )
for( int b = 0; b < bands; b++ )
B[b] = A[b] * aR / aA;
break;
case VIPS_BLEND_MODE_ATOP:
@ -493,11 +499,18 @@ vips_composite_base_blend( VipsCompositeBase *composite,
case VIPS_BLEND_MODE_DEST_IN:
aR = aA * aB;
// B = B
if( aB != 0 )
for( int b = 0; b < bands; b++ )
B[b] *= aR / aB;
break;
case VIPS_BLEND_MODE_DEST_OUT:
aR = (1 - aA) * aB;
// B = B
// if aB is 0, then B is already 0
if( aB != 0 )
for( int b = 0; b < bands; b++ )
B[b] *= aR / aB;
break;
case VIPS_BLEND_MODE_DEST_ATOP:
@ -676,8 +689,8 @@ vips_composite_base_blend3( VipsCompositeBase *composite,
/* See https://www.cairographics.org/operators for a nice summary of
* the operators and their meaning.
*
* Some operators need the unpremultiplied values, so we have to do an
* extra unpremultiply/premultiply.
* Some operators need the unpremultiplied values (eg. dest-in), so
* we have to do an extra unpremultiply/premultiply.
*/
switch( mode ) {
@ -701,18 +714,14 @@ vips_composite_base_blend3( VipsCompositeBase *composite,
case VIPS_BLEND_MODE_IN:
aR = aA * aB;
// we want to set B = A, but A has been premultiplied against
// aA ... we must undo that premul and redo against aR
// if aA == 0, then aR == 0 and so B will be set to 0
// if aA == 0, then aR == 0 and so B will already be 0
if( aA != 0 )
B = A * aR / aA;
break;
case VIPS_BLEND_MODE_OUT:
aR = aA * (1 - aB);
// we want to set B = A, but A has been premultiplied against
// aA ... we must undo that premul and redo against aR
// if aA == 0, then aR == 0 and so B will be set to 0
// if aA == 0, then aR == 0 and so B will already be 0
if( aA != 0 )
B = A * aR / aA;
break;
@ -736,17 +745,17 @@ vips_composite_base_blend3( VipsCompositeBase *composite,
case VIPS_BLEND_MODE_DEST_IN:
aR = aA * aB;
// we need to simply copy B over, but B is premultiplied
// against aB ... we must unpremultiply and premultiply
// against aR instead
// if aB is 0, then B is 0 too
//if( aB != 0 )
//B *= aR / aB;
// if aB is 0, then B is already 0
if( aB != 0 )
B *= aR / aB;
break;
case VIPS_BLEND_MODE_DEST_OUT:
aR = (1 - aA) * aB;
// B = B
// if aB is 0, then B is already 0
if( aB != 0 )
B *= aR / aB;
break;
case VIPS_BLEND_MODE_DEST_ATOP: