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
am: b2e36d7939
* commit 'b2e36d7939610de538a6ec95a821b61b365b3073':
Use LUT for computing final shadow alpha
Change-Id: Ia17e3b93e9ade0633aee5a1e9edd60b92dd1e062
Full GLES error checking layer via -include
trickery. Change DEBUG_OPENGL to a level system.
HIGH = every GL call is error checked
MODERATE = checkpointing at interesting spots
LOW = only asserts there are no errors at the end of a frame
or when the FBO changes
NONE = AIN'T GOT NO TIME FOR ERRORS GOTTA GO FAST!
Change-Id: Ibe81aae93d942059c4ddf1cbb11c828b7ce4c10b
When there is not enough space and we cannot delete any
Texture in TextureCache to secure space, a new Texture is
created over and over again for the same SkBitmap and
there is the case that it is not deleted.
This patch avoids such cases.
Change-Id: Ic5353995e6d0716c31fe3bb49c60ec1a71574643
Signed-off-by: Dohyun Lee <leedhyun11@gmail.com>
DeferredLayerUpdater always did a post to delete itself, which
would result in the test thinking it had leaked an object since
it wasn't deleted when it returned. Fix this by deleting immediately
if we're already on the right thread.
Remove RenderState's requireGlContext assert as it's now
covered by GpuMemoryTracker, which is also more test friendly.
RenderState's assert required an actual EGL context, which we
don't mock away in unit tests.
Change-Id: Ic23eb54e7151355f7acca483d7464350c9d6a87f
bug:20063841
Restores old SkShader matrix behavior from before the Glop refactor.
Many drawing operations draw without sending the canvas transform to
the GL shader. In such cases, we need to adapt the matrix sent to the
SkShader logic to invert the canvas transform that's built into
the mesh.
Change-Id: I42b6f59df36ce46436322b95bf9ad2140795ee58
bug:21431334
Should be explicitly passing target through, to ensure
GL_EXTERNAL_OES textures are bound correctly.
Change-Id: I997672ae292ea7fc016c02a59a3c7c8358ecfe0b
bug:19967854
Separate properties from Caches, into static, RenderThread-only class.
Also rewrites the means for java to set properties to correctly handle
threading, and adds an override for profile bars so that SysUi doesn't clutter
the screen with them.
Change-Id: I6e21a96065f52b9ecc49d1a126244804ba106fa9
