Pass through mode uses the same compositing logic as REPLACE mode,
however, it's a special case of REPLACE, where the layer is already
composited against the backdrop. This allows us to take a few
shortcuts that aren't generally applicable to REPLACE mode.
Add a dedicated op class for pass through mode, derived from the
REPLACE mode op, implementing these shortcuts.
Commit 3635cf04ab moved the special
handling of bottom-layer compositing to GimpOperationLayerMode.
This required giving the op more control over the process()
function of its subclasses. As a temporary workaround, the commit
bypassed the subclasses entirely, using "gimp:layer-mode" for all
modes. This is the reckoning :)
Add a process() virtual function to GimpOperationLayerMode, which
its subclasses should override instead of
GeglOperationPointComposer3's process() functions. Reinstate the
subclasses (by returning the correct op in
gimp_layer_mode_get_oepration()), and have them override this
function.
Improve the way gimp_operation_layer_mode_process() dispatches to
the actual process function, to slightly lower its overhead and
fix some thread-safety issues.
Remove the "function" field of the layer-mode info array, and have
gimp_layer_mode_get_function() return the
GimpOperationLayerMode::process() function of the corresponding
op's class (caching the result, to keep it cheap.) This reduces
redundancy, allows us to make the ops' process() functions private,
and simplifies SSE dispatching (only used by NORMAL mode,
currently.)
Move the blend and composite functions of the non-specialized
layer modes to gimpoperationlayermode-{blend,composite}.[hc],
respectively, to improve code organization.
Move the SSE2 composite functions to a separate file, so that they
can be built as part of libapplayermodes_sse2, allowing
libapplayermodes to be built without SSE2 compiler flags. This
allows building GIMP with SSE acceleration enabled, while running
the resulting binary on a target with no SSE accelration.
Add a "blend_function" field to the layer-mode info array, and use
it to specify the blend function for the non-specialized modes.
This replaces the separate switch() statement that we used
previously.
Remove the "affected_region" field of the layer-mode info array.
We don't need it anymore, since we can go back to using
GimpOperationLayerMode's virtual get_affected_region() function.
Last but not least, a bunch of code cleanups and consistency
adjustments.
Merge mode lays the source layer on top of the destination, same as
normal mode, however, it assumes the source and destination are two
parts of an original whole, and are therefore mutually exclusive.
This is useful for blending cut & pasted content without artifacts,
or for replacing erased content in general.
... and get rid of the dedicated op. This gives us support for all
the blend/composite options for this mode.
Rename COLOR_ERASE to COLOR_ERASE_LEGACY, with perceptual blending/
compositing and immutable everything, and add a new COLOR_ERASE
mode, defaulting to linear blending/compositing, with mutable
everything. Modify affected code.
and to operations/layer-modes/, respectively.
Add gimp_layer_modes_init() which asserts on the correct order of the
GimpLayerModeInfo array, and switch to accessing the array directly in
gimp_layer_mode_info().
Some of the generic files still contain SSE2 code, in particular
gimpoperationlayermode.c. The reason why it often works without is that
native gcc will usually pre-define SSE macros by default.
To check this: gcc -dM -E - < /dev/null | grep SSE
Yet I had a case on a small netbook where the SSE macros were not
pre-defined even though supported. Consequently the build failed.
For operations needing to override default behavior sub-classes should still be
used.
This commit also enables pinligh, vividlight and linearlight blend mode modes
Implement a common utility function gimp_blend_composite that uses utility
functions for implementing layer modes, with separate (possibly SIMD) optimized
loops for blending and compositing, with configured linear TRC, perceptual
gamma TRC or even using CIE Lab as the space.
