History log of /frameworks/base/libs/hwui/GammaFontRenderer.cpp
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253f2c213f6ecda63b6872aee77bd30d5ec07c82 29-Sep-2016 Romain Guy <romainguy@google.com> Linear blending, step 1

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 clean up gamma / glyph cache properties

Change-Id: I75b1ac0cb55638bf787ffd3cf457483ae314f03b

Also fixes some INIT_LOGD logs

Change-Id: I212a71a1e7b366aea41f7c3c8cc169d509d6e4a2
6c15ffa196fc9b7724c189d833c3435d8db12266 02-Feb-2015 Chris Craik <ccraik@google.com> Refactoring of Program ownership/lifecycle, and WIP Glop rendering path

Change-Id: I2549032790bddbc048b0bccc224ed8f386b4517c
d41c4d8c732095ae99c955b6b82f7306633004b1 06-Jan-2015 Chris Craik <ccraik@google.com> Add overrides and switch to nullptr keyword for all files

Adds remaining missing overrides and nullptr usages, missed due to
an extreme failure in tool usage.

51d6a3db97bdd5315f1a17a4b447d10a92217b98 23-Dec-2014 Chris Craik <ccraik@google.com> Cleanup various clang warnings, use unique_ptrs in several places

Change-Id: I347904b25e51fcc7de14b1e72f1acd0f6ba26f3f
cf51a4199835e9604aa4c8b3854306f8fbabbf33 09-Apr-2013 Romain Guy <romainguy@google.com> Introduce PixelBuffer API to enable PBOs

PBOs (Pixel Buffer Objects) can be used on OpenGL ES 3.0 to perform
asynchronous texture uploads to free up the CPU. This change does not
enable the use of PBOs unless a specific property is set (Adreno drivers
have issues with PBOs at the moment, Mali drivers work just fine.)

This change also cleans up Font/FontRenderer a little bit and improves
a manual byte-by-byte copy.

On GL ES 2.0 devices, or when PBOs are disabled, a PixelBuffer instance
behaves like a simple byte array. The extra APIs introduced for PBOs
(map/unmap and bind/unbind) are pretty much no-ops for CPU pixel
buffers and won't introduce any significant overhead.

This change also fixes a bug with text drop shadows: if the drop
shadow is larger than the max texture size, the renderer would leave
the GL context in a bad state and generate 0x501 errors. This change
simply skips drop shadows if they are too large.

dfab50d8b97a90dca279b119ebe439f595616ffa 19-Jul-2012 Romain Guy <romainguy@google.com> Tweak text gamma correction

Change-Id: Icd3326e6a054d6020c3ed61c8459394bc87401dd
6e25e38e43f9e7f71397dfab7ed32c81c7bf7d46 19-Jul-2012 Romain Guy <romainguy@google.com> Add a new method for text gamma correction

To select the gamma correction method, adb shell setprop hwui.text_gamma_correction
with one of the following values:

lookup3
lookup

You can also control gamma correction using the following properties:

hwui.text_gamma
hwui.text_gamma.black_threshold
hwui.text_gamma.white_threshold

Change-Id: I47970b804d2c590c37d3da5008db094241579e25

To enable it, the system property ro.hwui.text_gamma_shader must be
set to true. For testing, DEBUG_FONT_RENDERER_FORCE_SHADER_GAMMA
can be set to 1 in libhwui/Debug.h.

Change-Id: If345c6b71b67ecf1ef2e8847b71f30f3ef251a27
b1d0a4ed21168fefcb82232c8f22cb95d60acb85 14-Jul-2012 Romain Guy <romainguy@google.com> Refactor GammaFontRenderer

This change is the first step to a shader-based text antialias
gamma correction.

Change-Id: I9eb02d4c56cb95d05219f712290c865b46141954
9a8245629d69d81e0b62e52970feaf9c02580e75 17-Dec-2011 Chet Haase <chet@google.com> De-allocate caches for large glyphs when trimming memory

Currently, font renderers eliminate some texture caches when
memory is trimmed. This change makes it go further by eliminating the
large-glyph caches for all font renderers. These caches are
only allocated as needed, but continue to consume large amounts of
memory (CPU and GPU) after that allocation. De-allocating this memory
on a trim operation should prevent background apps from holding onto
this memory in the possible case that they have allocated it by drawing
large glyphs.

Change-Id: Id7a3ab49b244e036b442d87252fb40aeca8fdb26
eca0ca2424afc1e98912405906edfc32f7733e16 04-Nov-2011 Romain Guy <romainguy@google.com> Memory optimizations for libhwui
Bug #5566149

Lazily initialize font renderers
Keep 60% of the texture cache when an app goes to the background
Delete least used font renderer when going to the background
Delete all font renderers on full memory trim

Change-Id: I3c2454d46dc1107ec0f0f72a9ce69cbbcc8825e7
c9855a53edfac818dc68714557185977556f849d 22-Jan-2011 Romain Guy <romainguy@google.com> Log only 1 line per process when using OpenGLRenderer.

Change-Id: Idbdd6b84f31301e58ed53e0d50fd61fece192dfa
b45c0c9774bd19a9dbe77d149abae4e124b08bf6 27-Aug-2010 Romain Guy <romainguy@google.com> Apply gamma correction to font rendering.

Change-Id: I1b05f40e356221b2a5eb9400e67d77ecd98ed6c4