config_host/config_skia.h.in | 11 ++++++++---
vcl/skia/salbmp.cxx | 8 +++++++-
2 files changed, 15 insertions(+), 4 deletions(-)
New commits:
commit 6edf8fb2b21aec0295fc71c5bfdd9cd14556e323
Author: Luboš Luňák <l.lu...@collabora.com>
AuthorDate: Wed Sep 23 10:50:57 2020 +0200
Commit: Luboš Luňák <l.lu...@collabora.com>
CommitDate: Wed Sep 23 12:21:40 2020 +0200
clarifications on the use of SKIA_USE_BITMAP32
Change-Id: Ia2f80c3dc6ac3e0b16993dde588a4987ce98aa81
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/103235
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lu...@collabora.com>
diff --git a/config_host/config_skia.h.in b/config_host/config_skia.h.in
index ba3d3c6c0a07..db103238d4fc 100644
--- a/config_host/config_skia.h.in
+++ b/config_host/config_skia.h.in
@@ -8,19 +8,24 @@ are the same.
#ifndef CONFIG_SKIA_H
#define CONFIG_SKIA_H
-// This a setting that should be set manually and it affects LO
+// This is a setting that should be set manually and it affects LO
// code rather than Skia itself. It basically controls setting
-// BackendCapabilities::mbSupportsBitmap32.
+// BackendCapabilities::mbSupportsBitmap32, i.e. whether one LO bitmap
+// contains all the 32bits of an image including the alpha (premultiplied).
+//
// Since Skia does not natively support 24bpp, the preferred setup is
// that the setting should be enabled, it makes the code faster and cleaner.
+//
// Unfortunately VCL historically splits alpha into a whole separate
// bitmap and works with 24bpp+8bpp, which is generally more complicated,
// more error-prone and just worse, but that's how LO code has been
// written and so there are many places in LO that expect this and
// do not work correctly with true 32bpp bitmaps.
+//
// So ultimately the 24+8 split should be dumped (preferably in all of LO,
// not just the Skia-related code), but until all of LO works correctly
-// with 32bpp disabling this will avoid such breakages.
+// with 32bpp keep this disabled in order to avoid such breakages.
+
//#define SKIA_USE_BITMAP32 1
#define SKIA_USE_BITMAP32 0
diff --git a/vcl/skia/salbmp.cxx b/vcl/skia/salbmp.cxx
index d7399855a3ec..379f53bb032d 100644
--- a/vcl/skia/salbmp.cxx
+++ b/vcl/skia/salbmp.cxx
@@ -466,10 +466,12 @@ SkBitmap SkiaSalBitmap::GetAsSkBitmap() const
const size_t bytes = mPixelsSize.Height() * mScanlineSize;
std::unique_ptr<sal_uInt8[]> data(new sal_uInt8[bytes]);
memcpy(data.get(), mBuffer.get(), bytes);
+ // The bitmap's alpha matters only if SKIA_USE_BITMAP32 is set,
otherwise
+ // the alpha is in a separate bitmap.
#if SKIA_USE_BITMAP32
SkAlphaType alphaType = kPremul_SkAlphaType;
#else
- SkAlphaType alphaType = kUnpremul_SkAlphaType;
+ SkAlphaType alphaType = kOpaque_SkAlphaType;
#endif
if (!bitmap.installPixels(
SkImageInfo::MakeS32(mPixelsSize.Width(),
mPixelsSize.Height(), alphaType),
@@ -917,6 +919,10 @@ void SkiaSalBitmap::EnsureBitmapData()
// Try to fill mBuffer from mImage.
assert(mImage->colorType() == kN32_SkColorType);
SkiaZone zone;
+ // Use kUnpremul_SkAlphaType to make Skia convert from premultiplied alpha
when reading
+ // from the SkImage, in case there is any alpha involved. If converting to
bpp<32 formats,
+ // we will ignore the alpha when converting to mBuffer. Unless bpp==32 and
SKIA_USE_BITMAP32,
+ // in which case keep the format, since SKIA_USE_BITMAP32 implies
premultiplied alpha.
SkAlphaType alphaType = kUnpremul_SkAlphaType;
#if SKIA_USE_BITMAP32
if (mBitCount == 32)
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