The following GL extensions provide support for shaders CM:
-GL_OES_texture_float_linear makes GL_RGB32F linear filterable.
-GL ES 3.0 provides Texture3D support in GL API.
-GL_OES_texture_3D provides sampler3D support in ESSL 1.00.
If abovesaid is supported then renderer sets flag WESTON_CAP_COLOR_OPS
which means that all fields in struct weston_color_transform are
supported, for example, 1DLUT and 3DLUT.
Use GL_OES_texture_3D to implement 3DLUT function which
uses trilinear interpolation for pixel processing or bypass as is.
Quote from https://nick-shaw.github.io/cinematiccolor/luts-and-transforms.html
"3D LUTs have long been embraced by color scientists and are one of
the tools commonly used for gamut mapping. In fact, 3D LUTs are used
within ICC profiles to model the complex device behaviors necessary
for accurate color image reproduction".
Quote from https://developer.nvidia.com/gpugems/gpugems2/part-iii-high-quality-rendering/
chapter-24-using-lookup-tables-accelerate-color
is about interpolation: "By generating intermediate results based
on a weighted average of the eight corners of the bounding cube,
this algorithm is typically sufficient for color processing,
and it is implemented in graphics hardware".
Signed-off-by: Vitaly Prosyak <vitaly.prosyak@amd.com>
This makes weston_color_transform object be able to express
three-channel one-dimensional look-up table transformations. They are
useful for applying EOTF and EOTF^-1 mapping, or, gamma curves. They
will also be useful in optimizing a following 3D LUT tap distribution
once support for 3D LUT is added.
The code added here translates from the lut_3x1d fill_in() interface to
a GL texture to be used with SHADER_COLOR_CURVE_LUT_3x1D for
weston_surfaces.
It demonstrates how renderer data is attached to weston_color_transform
and cached.
GL_OES_texture_float_linear is required to be able to use bilinear
texture filtering with 32-bit floating-point textures, used for the LUT.
As the size of the LUT depends on what implements it, lut_3x1d fill_in()
interface is a callback to the color management component to ask for an
arbitrary size. For GL-renderer this is not important as it can easily
realize any LUT size, but when DRM-backend wants to offload the EOTF^-1
mapping to KMS (GAMMA_LUT), the LUT size comes from KMS.
Nothing actually implements lut_3x1d fill_in() yet, that will come in a
later patch.
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Vitaly Prosyak
Pekka Paalanen