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  * Sample positions:
  28  *   2 6 a e
  29  * 2   0
  30  * 6       1
  31  * a 2
  32  * e     3
  33  */
  34 static const uint32_t
  35 brw_multisample_positions_4x[] = { 0xae2ae662 };
  36
  37 /**
  38  * Sample positions are based on a solution to the "8 queens" puzzle.
  39  * Rationale: in a solution to the 8 queens puzzle, no two queens share
  40  * a row, column, or diagonal.  This is a desirable property for samples
  41  * in a multisampling pattern, because it ensures that the samples are
  42  * relatively uniformly distributed through the pixel.
  43  *
  44  * There are several solutions to the 8 queens puzzle (see
  45  * http://en.wikipedia.org/wiki/Eight_queens_puzzle).  This solution was
  46  * chosen because it has a queen close to the center; this should
  47  * improve the accuracy of centroid interpolation, since the hardware
  48  * implements centroid interpolation by choosing the centermost sample
  49  * that overlaps with the primitive being drawn.
  50  *
  51  * Note: from the Ivy Bridge PRM, Vol2 Part1 p304 (3DSTATE_MULTISAMPLE:
  52  * Programming Notes):
  53  *
  54  *     "When programming the sample offsets (for NUMSAMPLES_4 or _8 and
  55  *     MSRASTMODE_xxx_PATTERN), the order of the samples 0 to 3 (or 7
  56  *     for 8X) must have monotonically increasing distance from the
  57  *     pixel center. This is required to get the correct centroid
  58  *     computation in the device."
  59  *
  60  * Sample positions:
  61  *   1 3 5 7 9 b d f
  62  * 1     5
  63  * 3           2
  64  * 5               6
  65  * 7 4
  66  * 9       0
  67  * b             3
  68  * d         1
  69  * f   7
  70  */
  71 static const uint32_t
  72 brw_multisample_positions_8x[] = { 0xdbb39d79, 0x3ff55117 };