With linear blending turned off some textures were still
created as sRGB textures instead of linear textures.
Multi-stop gradients were not behaving properly on devices
with no support for float textures.
Gradients are now always interpolated in linear space
even if linear blending is off.
New functions to always force sRGB->linear->sRGB conversions.
Test: Manual testing
Bug: 29940137
Change-Id: Ie2f84ee2a65fd85570e88af813e841e0e625df6c
NOTE: Linear blending is currently disabled in this CL as the
feature is still a work in progress
Android currently performs all blending (any kind of linear math
on colors really) on gamma-encoded colors. Since Android assumes
that the default color space is sRGB, all bitmaps and colors
are encoded with the sRGB Opto-Electronic Conversion Function
(OECF, which can be approximated with a power function). Since
the power curve is not linear, our linear math is incorrect.
The result is that we generate colors that tend to be too dark;
this affects blending but also anti-aliasing, gradients, blurs,
etc.
The solution is to convert gamma-encoded colors back to linear
space before doing any math on them, using the sRGB Electo-Optical
Conversion Function (EOCF). This is achieved in different
ways in different parts of the pipeline:
- Using hardware conversions when sampling from OpenGL textures
or writing into OpenGL frame buffers
- Using software conversion functions, to translate app-supplied
colors to and from sRGB
- Using Skia's color spaces
Any type of processing on colors must roughly ollow these steps:
[sRGB input]->EOCF->[linear data]->[processing]->OECF->[sRGB output]
For the sRGB color space, the conversion functions are defined as
follows:
OECF(linear) :=
linear <= 0.0031308 ? linear * 12.92 : (pow(linear, 1/2.4) * 1.055) - 0.055
EOCF(srgb) :=
srgb <= 0.04045 ? srgb / 12.92 : pow((srgb + 0.055) / 1.055, 2.4)
The EOCF is simply the reciprocal of the OECF.
While it is highly recommended to use the exact sRGB conversion
functions everywhere possible, it is sometimes useful or beneficial
to rely on approximations:
- pow(x,2.2) and pow(x,1/2.2)
- x^2 and sqrt(x)
The latter is particularly useful in fragment shaders (for instance
to apply dithering in sRGB space), especially if the sqrt() can be
replaced with an inversesqrt().
Here is a fairly exhaustive list of modifications implemented
in this CL:
- Set TARGET_ENABLE_LINEAR_BLENDING := false in BoardConfig.mk
to disable linear blending. This is only for GLES 2.0 GPUs
with no hardware sRGB support. This flag is currently assumed
to be false (see note above)
- sRGB writes are disabled when entering a functor (WebView).
This will need to be fixed at some point
- Skia bitmaps are created with the sRGB color space
- Bitmaps using a 565 config are expanded to 888
- Linear blending is disabled when entering a functor
- External textures are not properly sampled (see below)
- Gradients are interpolated in linear space
- Texture-based dithering was replaced with analytical dithering
- Dithering is done in the quantization color space, which is
why we must do EOCF(OECF(color)+dither)
- Text is now gamma corrected differently depending on the luminance
of the source pixel. The asumption is that a bright pixel will be
blended on a dark background and the other way around. The source
alpha is gamma corrected to thicken dark on bright and thin
bright on dark to match the intended design of fonts. This also
matches the behavior of popular design/drawing applications
- Removed the asset atlas. It did not contain anything useful and
could not be sampled in sRGB without a yet-to-be-defined GL
extension
- The last column of color matrices is converted to linear space
because its value are added to linear colors
Missing features:
- Resource qualifier?
- Regeneration of goldeng images for automated tests
- Handle alpha8/grey8 properly
- Disable sRGB write for layers with external textures
Test: Manual testing while work in progress
Bug: 29940137
Change-Id: I6a07b15ab49b554377cd33a36b6d9971a15e9a0b
Also tune the parameters to match a better look designed by UX team.
For ambient part, the acos transformed alpha is not needed any more.
b/19370798
Change-Id: I20d2615d1be502eb900942ed756aecd1660dee48
Adds remaining missing overrides and nullptr usages, missed due to
an extreme failure in tool usage.
Change-Id: I56abd72975a3999ad13330003c348db40f59aebf
Remove Clang cutout for unused parameters. Fix warnings.
Remove Clang cutout for deprecated Skia function usage. Has been
fixed in the L push.
Change-Id: I7ea073ff67127cc1e14e798b655e2c50615fe8e7
bug:17405627
Previously, the input content to the color matrix computation was left
premultiplied. Since the color matrix could reduce the alpha channel,
the alpha was re-multiplied, but this was incomplete, and incorrect.
Instead, apply the color matrix in unpremultiplied space.
Change-Id: I87b8e03d2e228e6ded81f7bbfea952605d7a095c
bug:16852257
Use pow(alpha, 1.5) to avoid harsh edges on shadow alpha ramps.
Also adjusts shadow constants to compensate.
Change-Id: I5869956d7d292db2a8e496bc320084b6d64c3fb7
bug:16804363
Since dist can be in the 1000s of pixels, and length() may square it
in its current precision, scale the value down significantly first,
since final precision isn't very important.
Change-Id: Id20f7a49d6171355c8e242442c2b5083f746dca3
bug:4351353
bug:8185479
Point tessellation is similar to line special case, except that we
only tessellate one point (as a circle or rect) and duplicate it
across other instances.
Additionally:
Fixes square caps for AA=false lines
Cleanup in CanvasCompare, disabling interpolation on zoomed-in
comparison view
Change-Id: I0756fcc4b20f77878fed0d8057297c80e82ed9dc
The counter can be enabled by setting the system property called
debug.hwui.overdraw to the string "count". If the string is set
to "show", overdraw will be highlighted on screen instead of
printing out a simple counter.
Change-Id: I9a9c970d54bffab43138bbb7682f6c04bc2c40bd
This is a more elegant way to sample from a float alpha texture.
Instead of sampling from the red channel in the fragment shader
we can set the alpha channel swizzle to redirect it to the
red channel. This lets us sample from the alpha channel in the
fragment shader and get the correct value.
Change-Id: I95bbf7a82964e1bf42c0fee1b782b6bdbbcef618
Float textures offer better precision for dithering.
In addition this change removes two uniforms from gradient shaders.
These uniforms were used to dither gradients but their value is
a build time constant. Instead we hardcode the value directly in
the shader source at compile time.
Change-Id: I05e9fd3eef93771843bbd91b453274452dfaefee
Add a key manipulation that makes black text/paths use the standard
simple bitmap/patch shader, since they are the same. Previously we'd
create a separate shader for each because the keys differed, even
though the shaders were functionally equivalent.
Also fixes some issues around setting DEBUG_PROGRAM
Change-Id: I0c77c684d58da03501ee9ab8239c7d4a70fd6b5c
This change adds a new property called "debug.hwui.show_stencil_clip"
that accepts the following values:
- "highlight", colorizes in green any drawing command that's tested
against a non-rectangular clip region
- "region", shows the non-rectangular clip region in blue every time
it is used
- "hide", default value, nothing is shown
Change-Id: I83c8602310edc4aaeb8b905371cdd185b17d32b5
bug:7117155
bug:8114304
Currently used for lines (with and without AA) and arcs with useCenter=false
Also removes 0.375, 0.375 offset for AA lines
Change-Id: Ic8ace418739344db1e2814edf65253fe7448b0b0
Bug #7239634
This change passes two matrices to the vertex shader instead of one.
We used to compute the final MVP matrix on the CPU to minimize the
number of operations in the vertex shaders. Shader compilers are
however smart enough to perform this optimization for us. Since we
need the MV matrix to properly compute gradients dithering, this
change splits the MVP matrix into two. This has the advantage of
removing one matrix multiplication per drawing operation on the
CPU.
The SGX 540 shader compiler produces the same number of instructions
in both cases. There is no penalty hit with having two matrices
instead of one. We also send so few vertices per frame that it
does not matter very much.
Change-Id: I17d47ac4772615418e0e1885b97493d31435a936
Bug #7222476
There were two issues:
- Blending was ignored with color filters
- The addition vector of a color filter was treated as integer values
instead of float values
Change-Id: Id94065704a30ee8aaaa5724a9f3a3cff7c50ced7
It's faster to compute a dither calculation in the vertex shader and use
a varying (letting the GPU interpolate the fragment values) than to perform
that calculation in the fragment shader as part of a texture lookup.
Issue #7207600 Prime mr1 shader performance issues
Issue #7158326 Bad framerates on MR1 (Mako, Manta, Prime)
Change-Id: I15789582a6e9e2d8b9dd22aa5b0f72f0ba1cce7f
Modulation is normally enabled in a shader when drawing with an alpha
mask (A8 texture.) Modulation is used to do one of two things:
- Colorize the primitive (to draw text in red for instance)
- Apply extra translucency (50% translucent circle filled with a bitmap)
The current implementation has four issues:
1. Unnecessary work is performed by assigning the modulation color
to vec4 fragColor early in the shader
2. The modulation color's alpha is applied twice when the primitive
is drawn with an SkShader
3. The decision to modulate is wrong and triggers when any of the
RGB channels is < 1.0. Only the alpha channel needs to be taken
into account to make the decision
4. Gamma correction is not applied properly
This change addresses all four issues above.
Change-Id: I73fcc74efc4b094bf2d1b835f10ffaa2ea4b9eb9
Instead of calculating opacity from relative position in the shader, use a
shader varying to do this computation for us.
bug:5045101
Also adds a test to HwAccelerationTest to show incorrect antialiasing in
scaled drawAARect / boundarySize calculation.
Change-Id: Icdc41acb01dc10ce354834f8389a5aed2f439162
