src/gallium/docs/source/cso/blend.rst

   1 .. _blend:
   2
   3 Blend
   4 =====
   5
   6 This state controls blending of the final fragments into the target rendering
   7 buffers.
   8
   9 Blend Factors
  10 -------------
  11
  12 The blend factors largely follow the same pattern as their counterparts
  13 in other modern and legacy drawing APIs.
  14
  15 Dual source blend factors are supported for up to 1 MRT, although
  16 you can advertise > 1 MRT, the stack cannot handle them for a few reasons.
  17 There is no definition on how the 1D array of shader outputs should be mapped
  18 to something that would be a 2D array (location, index). No current hardware
  19 exposes > 1 MRT, and we should revisit this issue if anyone ever does.
  20
  21 Logical Operations
  22 ------------------
  23
  24 Logical operations, also known as logicops, lops, or rops, are supported.
  25 Only two-operand logicops are available. When logicops are enabled, all other
  26 blend state is ignored, including per-render-target state, so logicops are
  27 performed on all render targets.
  28
  29 .. warning::
  30    The blend_enable flag is ignored for all render targets when logical
  31    operations are enabled.
  32
  33 For a source component `s` and destination component `d`, the logical
  34 operations are defined as taking the bits of each channel of each component,
  35 and performing one of the following operations per-channel:
  36
  37 * ``CLEAR``: 0
  38 * ``NOR``: :math:`\lnot(s \lor d)`
  39 * ``AND_INVERTED``: :math:`\lnot s \land d`
  40 * ``COPY_INVERTED``: :math:`\lnot s`
  41 * ``AND_REVERSE``: :math:`s \land \lnot d`
  42 * ``INVERT``: :math:`\lnot d`
  43 * ``XOR``: :math:`s \oplus d`
  44 * ``NAND``: :math:`\lnot(s \land d)`
  45 * ``AND``: :math:`s \land d`
  46 * ``EQUIV``: :math:`\lnot(s \oplus d)`
  47 * ``NOOP``: :math:`d`
  48 * ``OR_INVERTED``: :math:`\lnot s \lor d`
  49 * ``COPY``: :math:`s`
  50 * ``OR_REVERSE``: :math:`s \lor \lnot d`
  51 * ``OR``: :math:`s \lor d`
  52 * ``SET``: 1
  53
  54 .. note::
  55    The logical operation names and definitions match those of the OpenGL API,
  56    and are similar to the ROP2 and ROP3 definitions of GDI. This is
  57    intentional, to ease transitions to Gallium.
  58
  59 Members
  60 -------
  61
  62 These members affect all render targets.
  63
  64 dither
  65 %%%%%%
  66
  67 Whether dithering is enabled.
  68
  69 .. note::
  70    Dithering is completely implementation-dependent. It may be ignored by
  71    drivers for any reason, and some render targets may always or never be
  72    dithered depending on their format or usage flags.
  73
  74 logicop_enable
  75 %%%%%%%%%%%%%%
  76
  77 Whether the blender should perform a logicop instead of blending.
  78
  79 logicop_func
  80 %%%%%%%%%%%%
  81
  82 The logicop to use. One of ``PIPE_LOGICOP``.
  83
  84 independent_blend_enable
  85    If enabled, blend state is different for each render target, and
  86    for each render target set in the respective member of the rt array.
  87    If disabled, blend state is the same for all render targets, and only
  88    the first member of the rt array contains valid data.
  89 rt
  90    Contains the per-rendertarget blend state.
  91 alpha_to_coverage
  92    If enabled, the fragment's alpha value is used to override the fragment's
  93    coverage mask.  The coverage mask will be all zeros if the alpha value is
  94    zero.  The coverage mask will be all ones if the alpha value is one.
  95    Otherwise, the number of bits set in the coverage mask will be proportional
  96    to the alpha value.  Note that this step happens regardless of whether
  97    multisample is enabled or the destination buffer is multisampled.
  98 alpha_to_one
  99    If enabled, the fragment's alpha value will be set to one.  As with
 100    alpha_to_coverage, this step happens regardless of whether multisample
 101    is enabled or the destination buffer is multisampled.
 102
 103
 104 Per-rendertarget Members
 105 ------------------------
 106
 107 blend_enable
 108    If blending is enabled, perform a blend calculation according to blend
 109    functions and source/destination factors. Otherwise, the incoming fragment
 110    color gets passed unmodified (but colormask still applies).
 111 rgb_func
 112    The blend function to use for rgb channels. One of PIPE_BLEND.
 113 rgb_src_factor
 114    The blend source factor to use for rgb channels. One of PIPE_BLENDFACTOR.
 115 rgb_dst_factor
 116    The blend destination factor to use for rgb channels. One of PIPE_BLENDFACTOR.
 117 alpha_func
 118    The blend function to use for the alpha channel. One of PIPE_BLEND.
 119 alpha_src_factor
 120    The blend source factor to use for the alpha channel. One of PIPE_BLENDFACTOR.
 121 alpha_dst_factor
 122    The blend destination factor to use for alpha channel. One of PIPE_BLENDFACTOR.
 123 colormask
 124    Bitmask of which channels to write. Combination of PIPE_MASK bits.