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fix animated webp background handling

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We were using WEBP_FF_BACKGROUND_COLOR as the background colour, but
that's not correct, it should always be zero (transparent).
WEBP_FF_BACKGROUND_COLOR is there just as a hint when flattening down to
plain RGB.
This commit is contained in:
John Cupitt 2019-04-24 18:18:21 +01:00
parent 0102a10b49
commit 4a9db0e83f
1 changed files with 12 additions and 42 deletions
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54
libvips/foreign/webp2vips.c
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@ -15,6 +15,8 @@
* - add animated read
* 19/4/19
* - could memleak on some read errors
* 24/4/19
* - fix bg handling in animations
*/
/*
@ -102,10 +104,6 @@ typedef struct {
int frame_width;
int frame_height;
/* Background colour as an ink we can paint with.
*/
guint32 background;
/* TRUE for RGBA.
*/
int alpha;
@ -191,14 +189,6 @@ vips_image_paint_area( VipsImage *image, const VipsRect *r, const VipsPel *ink )
}
}
static void
vips_image_paint( VipsImage *image, const VipsPel *ink )
{
VipsRect area = { 0, 0, image->Xsize, image->Ysize };
vips_image_paint_area( image, &area, ink );
}
/* Blend two guint8.
*/
#define BLEND( X, aX, Y, aY, scale ) \
@ -386,21 +376,6 @@ const VipsWebPNames vips__webp_names[] = {
};
const int vips__n_webp_names = VIPS_NUMBER( vips__webp_names );
/* libwebp supplies things like background as B, G, R, A, but we need RGBA
* order for libvips.
*/
static guint32
bgra2rgba( guint32 x )
{
VipsPel pixel[4];
*((guint32 *) &pixel) = x;
VIPS_SWAP( VipsPel, pixel[0], pixel[2] );
x = *((guint32 *) &pixel);
return( x );
}
static int
read_header( Read *read, VipsImage *out )
{
@ -444,16 +419,6 @@ read_header( Read *read, VipsImage *out )
read->frame_count = WebPDemuxGetI( read->demux,
WEBP_FF_FRAME_COUNT );
/* background is in B, G, R, A byte order, but we need
* R, G, B, A for libvips.
*
* background is only relevant for animations. For
* single-frame webp, we want to just return the RGBA in the
* file. We just leave bg as 0 and blend with that.
*/
read->background = bgra2rgba( WebPDemuxGetI( read->demux,
WEBP_FF_BACKGROUND_COLOR ) );
#ifdef DEBUG
printf( "webp2vips: animation\n" );
printf( "webp2vips: loop_count = %d\n", loop_count );
@ -537,8 +502,6 @@ read_header( Read *read, VipsImage *out )
if( vips_image_write_prepare( read->frame ) )
return( -1 );
vips_image_paint( read->frame, (VipsPel *) &read->background );
vips_image_init_fields( out,
read->width, read->height,
read->alpha ? 4 : 3,
@ -626,12 +589,19 @@ read_next_frame( Read *read )
/* Dispose from the previous frame.
*/
if( read->dispose_method == WEBP_MUX_DISPOSE_BACKGROUND )
if( read->dispose_method == WEBP_MUX_DISPOSE_BACKGROUND ) {
/* We must clear the pixels occupied by this webp frame (not
* the whole of the read frame) to the background colour.
* the whole of the read frame) to 0 (transparent).
*
* We do not clear to WEBP_FF_BACKGROUND_COLOR. That's only
* used to composite down to RGB. Perhaps we
* should attach background as metadata.
*/
guint32 zero = 0;
vips_image_paint_area( read->frame,
&read->dispose_rect, (VipsPel *) &read->background );
&read->dispose_rect, (VipsPel *) &zero );
}
/* Note this frame's dispose for next time.
*/