mirror of https://gitlab.freedesktop.org/mesa/mesa
125 lines
4.7 KiB
ReStructuredText
125 lines
4.7 KiB
ReStructuredText
.. _blend:
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Blend
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=====
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This state controls blending of the final fragments into the target rendering
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buffers.
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Blend Factors
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-------------
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The blend factors largely follow the same pattern as their counterparts
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in other modern and legacy drawing APIs.
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Dual source blend factors are supported for up to 1 MRT, although
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you can advertise > 1 MRT, the stack cannot handle them for a few reasons.
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There is no definition on how the 1D array of shader outputs should be mapped
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to something that would be a 2D array (location, index). No current hardware
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exposes > 1 MRT, and we should revisit this issue if anyone ever does.
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Logical Operations
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------------------
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Logical operations, also known as logicops, LOPs, or ROPs, are supported.
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Only two-operand logicops are available. When logicops are enabled, all other
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blend state is ignored, including per-render-target state, so logicops are
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performed on all render targets.
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.. warning::
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The blend_enable flag is ignored for all render targets when logical
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operations are enabled.
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For a source component ``s`` and destination component ``d``, the logical
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operations are defined as taking the bits of each channel of each component,
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and performing one of the following operations per-channel:
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================== =========================
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Operation Equation
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================== =========================
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``CLEAR`` :math:`0`
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``NOR`` :math:`\lnot(s \lor d)`
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``AND_INVERTED`` :math:`\lnot s \land d`
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``COPY_INVERTED`` :math:`\lnot s`
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``AND_REVERSE`` :math:`s \land \lnot d`
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``INVERT`` :math:`\lnot d`
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``XOR`` :math:`s \oplus d`
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``NAND`` :math:`\lnot(s \land d)`
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``AND`` :math:`s \land d`
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``EQUIV`` :math:`\lnot(s \oplus d)`
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``NOOP`` :math:`d`
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``OR_INVERTED`` :math:`\lnot s \lor d`
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``COPY`` :math:`s`
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``OR_REVERSE`` :math:`s \lor \lnot d`
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``OR`` :math:`s \lor d`
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``SET`` :math:`1`
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================== =========================
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.. note::
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The logical operation names and definitions match those of the OpenGL API,
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and are similar to the ROP2 and ROP3 definitions of GDI. This is
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intentional, to ease transitions to Gallium.
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Members
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-------
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These members affect all render targets.
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dither
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Whether dithering is enabled.
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.. note::
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Dithering is completely implementation-dependent. It may be ignored by
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drivers for any reason, and some render targets may always or never be
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dithered depending on their format or usage flags.
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logicop_enable
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Whether the blender should perform a logicop instead of blending.
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logicop_func
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The logicop to use. One of ``PIPE_LOGICOP``.
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independent_blend_enable
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If enabled, blend state is different for each render target, and
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for each render target set in the respective member of the rt array.
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If disabled, blend state is the same for all render targets, and only
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the first member of the rt array contains valid data.
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rt
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Contains the per-rendertarget blend state.
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alpha_to_coverage
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If enabled, the fragment's alpha value is used to override the fragment's
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coverage mask. The coverage mask will be all zeros if the alpha value is
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zero. The coverage mask will be all ones if the alpha value is one.
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Otherwise, the number of bits set in the coverage mask will be proportional
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to the alpha value. Note that this step happens regardless of whether
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multisample is enabled or the destination buffer is multisampled.
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alpha_to_one
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If enabled, the fragment's alpha value will be set to one. As with
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alpha_to_coverage, this step happens regardless of whether multisample
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is enabled or the destination buffer is multisampled.
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max_rt
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The index of the max render target (irrespective of whether independent
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blend is enabled), i.e. the number of MRTs minus one. This is provided
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so that the driver can avoid the overhead of programming unused MRTs.
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Per-rendertarget Members
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------------------------
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blend_enable
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If blending is enabled, perform a blend calculation according to blend
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functions and source/destination factors. Otherwise, the incoming fragment
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color gets passed unmodified (but colormask still applies).
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rgb_func
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The blend function to use for RGB channels. One of PIPE_BLEND.
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rgb_src_factor
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The blend source factor to use for RGB channels. One of PIPE_BLENDFACTOR.
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rgb_dst_factor
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The blend destination factor to use for RGB channels. One of PIPE_BLENDFACTOR.
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alpha_func
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The blend function to use for the alpha channel. One of PIPE_BLEND.
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alpha_src_factor
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The blend source factor to use for the alpha channel. One of PIPE_BLENDFACTOR.
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alpha_dst_factor
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The blend destination factor to use for alpha channel. One of PIPE_BLENDFACTOR.
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colormask
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Bitmask of which channels to write. Combination of PIPE_MASK bits.
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