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.
Calculates the dot product of the two input colors, and uses that
as the value for all the output color's components. Basically,
a per-pixel mono mixer.
Useful for custom desaturation, component extraction, and crazier
stuff (bump mapping!)
Include erase mode in the menu for layers and general paint tools.
This makes the eraser tool somewhat unnecessary, but allows for
interesting use cases (e.g., airbrush eraser, etc.)
... possibly due to small win32 stack
Limit the number of samples processed in one go by gimp_composite_blend()
so that we don't overflow the stack when we alloca() buffers on it.
... 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.
These are more general, and more expensive, versions of the non-
subtractive compositing functions. They are used with modes that
specify the SUBTRACTIVE flag. This doesn't affect anything yet, but
the next commit ports color-erase mode to a blendfun.
Most modes only modify the *color* of overlapping dest/src regions,
however, erase and color-erase may also reduce their *alpha*, i.e.,
eliminate some of the overlapping content. Flag these modes with
the new SUBTRACTIVE flag, as they require more general compositing
code. The next commit adds the said code.
The mode group switching combo box is hard to discover, until we use the
default group instead of legacy group as default - it is better to make legacy
resemble the full old set to.
which returns an array of modes in the order they would appear in a
GimpLayerModeContext's UI (like tool options or the layers dialog),
without the separators.
Use it in context-commands.c and layers-commands.c instead of static
(and outdated) arrays for the actions that cycle through modes.
Instead, add a gimp_layer_mode_get_format() function, which takes
the layer mode, composite space, and blend space, and returns the
I/O format.
Currently, we always use the composite space format as the I/O
format. This simplifies gimp_composite_blend(), and gives us
composite-space support for the "special" layer mode ops for free.
Replace the 'with-behind' and 'with-replace' properties with a
single 'context' property, and use it to select the included
layer modes, according to their context mask.
Add a dummy GIMP_LAYER_MODE_SEPARATOR value to the GimpLayerMode
enum, and use it to explicitly mark the menu separators in the
layer-mode group arrays; add separators to the layer-mode menu
accordingly.
Update the rest of the code to use 'context' instead of 'with-behind'
and 'with-replace'. In particular, in the layers and layer options
dialogs, select the right context based on whether or not the
selected layer is a group.
A bitmask, specifying in which contexts a layer mode is applicable.
Can be a combination of:
- LAYER: usable as a layer mode for actual layers.
- GROUP: usable as a layer mode for layer groups. Currently, all
modes that specify LAYER also specify GROUP, and vice versa,
but the planned pass-through mode will be GROUP only.
- PAINT: can be used as a paint mode.
- FADE: can be used for fading.
Add a 'context' field to _GimpLayerModeInfo, and provide context
masks to all the modes.
Use the context mask for validation when setting a layer's mode.
The next commit will use the mask when populating the layer mode
menus.
Add a "paint_composite_mode" field to GimpLayerModeInfo and set the
mode of the eraser to SRC_ATOP. Defaulting to SRC_OVER for all
painting didn't quite do it for all modes.
set all legacy modes to completely immutable and the LAB modes'
blend mode to immutable. Change GimpLayer setters and the UI
accordingly. Remove the LAB color spaces from the GUI, they can
only be used with the LAB blend modes anyway and not changed.
They can be affected by the same problem described in
commit 4c3a772cd8, although in the
case of SRC_ATOP, the affected pixels are always fully transparent.
When the source alpha is zero, we don't calculate the blended color,
so `comp[b]` can be infinite or NaN, in which case the expression
`in[ALPHA] * (comp[b] - layer[b])` is NaN, rather than the expected
value of zero.
