src/mesa/drivers/dri/i965/brw_multisample_state.h

   1 /*
   2  * Copyright © 2013 Intel Corporation
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining a
   5  * copy of this software and associated documentation files (the "Software"),
   6  * to deal in the Software without restriction, including without limitation
   7  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   8  * and/or sell copies of the Software, and to permit persons to whom the
   9  * Software is furnished to do so, subject to the following conditions:
  10  *
  11  * The above copyright notice and this permission notice (including the next
  12  * paragraph) shall be included in all copies or substantial portions of the
  13  * Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  16  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  18  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  19  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  20  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  21  * IN THE SOFTWARE.
  22  */
  23
  24 #include <stdint.h>
  25
  26 /**
  27  * 1x MSAA has a single sample at the center: (0.5, 0.5) -> (0x8, 0x8).
  28  *
  29  * 2x MSAA sample positions are (0.25, 0.25) and (0.75, 0.75):
  30  *   4 c
  31  * 4 0
  32  * c   1
  33  */
  34 static const uint32_t
  35 brw_multisample_positions_1x_2x = 0x0088cc44;
  36
  37 /**
  38  * Sample positions:
  39  *   2 6 a e
  40  * 2   0
  41  * 6       1
  42  * a 2
  43  * e     3
  44  */
  45 static const uint32_t
  46 brw_multisample_positions_4x = 0xae2ae662;
  47
  48 /**
  49  * Sample positions are based on a solution to the "8 queens" puzzle.
  50  * Rationale: in a solution to the 8 queens puzzle, no two queens share
  51  * a row, column, or diagonal.  This is a desirable property for samples
  52  * in a multisampling pattern, because it ensures that the samples are
  53  * relatively uniformly distributed through the pixel.
  54  *
  55  * There are several solutions to the 8 queens puzzle (see
  56  * http://en.wikipedia.org/wiki/Eight_queens_puzzle).  This solution was
  57  * chosen because it has a queen close to the center; this should
  58  * improve the accuracy of centroid interpolation, since the hardware
  59  * implements centroid interpolation by choosing the centermost sample
  60  * that overlaps with the primitive being drawn.
  61  *
  62  * Note: from the Ivy Bridge PRM, Vol2 Part1 p304 (3DSTATE_MULTISAMPLE:
  63  * Programming Notes):
  64  *
  65  *     "When programming the sample offsets (for NUMSAMPLES_4 or _8 and
  66  *     MSRASTMODE_xxx_PATTERN), the order of the samples 0 to 3 (or 7
  67  *     for 8X) must have monotonically increasing distance from the
  68  *     pixel center. This is required to get the correct centroid
  69  *     computation in the device."
  70  *
  71  * Sample positions:
  72  *   1 3 5 7 9 b d f
  73  * 1     5
  74  * 3           2
  75  * 5               6
  76  * 7 4
  77  * 9       0
  78  * b             3
  79  * d         1
  80  * f   7
  81  */
  82 static const uint32_t
  83 brw_multisample_positions_8x[] = { 0xdbb39d79, 0x3ff55117 };