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. 125
