99 lines
4.1 KiB
C
99 lines
4.1 KiB
C
/*
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* Copyright © 2020 Valve Corporation
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*
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* Permission is hereby granted, free of charge, to any person obtaining a
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* copy of this software and associated documentation files (the "Software"),
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* to deal in the Software without restriction, including without limitation
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* the rights to use, copy, modify, merge, publish, distribute, sublicense,
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* and/or sell copies of the Software, and to permit persons to whom the
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* Software is furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice (including the next
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* paragraph) shall be included in all copies or substantial portions of the
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* Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
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* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*/
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#ifndef __FREEDRENO_GUARDBAND_H__
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#define __FREEDRENO_GUARDBAND_H__
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#include <assert.h>
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#include <math.h>
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#include <stdbool.h>
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static inline unsigned
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fd_calc_guardband(float offset, float scale, bool is_a3xx)
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{
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/* On a3xx, the viewport max is 4k and the docs say the max guardband
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* width is 8k. That is, GRAS cannot handle triangle coordinates more than
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* 8k, positive or negative. On a4xx+ the viewport width was bumped to
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* 16k, and so the guardband width was necessarily also bumped. Note that
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* the numbers here should correspond to
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* VkPhysicalDeviceLimits::viewportBoundsRange in Vulkan.
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*/
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const float gb_min = is_a3xx ? -8192. : -32768.;
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const float gb_max = is_a3xx ? 8191. : 32767.;
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/* Clipping happens in normalized device coordinates, so we have to
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* transform gb_min and gb_max to ndc using the inverse of the viewport
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* transform. Avoid flipping min and max by using the absolute value of
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* the scale.
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*/
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const float gb_min_ndc = (gb_min - offset) / fabsf(scale);
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const float gb_max_ndc = (gb_max - offset) / fabsf(scale);
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/* There's only one GB_ADJ field, so presumably the guardband is
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* [-GB_ADJ, GB_ADJ] like on Radeon. It's always safe to make the
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* guardband smaller, so we have to take the min to get the largest range
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* contained in [gb_min_ndc, gb_max_ndc].
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*/
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const float gb_adj = fminf(-gb_min_ndc, gb_max_ndc);
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/* The viewport should always be contained in the guardband. */
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assert(gb_adj >= 1.0);
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/* frexp returns an unspecified value if given an infinite value, which
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* can happen if scale == 0.
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*/
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if (isinf(gb_adj))
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return 0x1ff;
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/* Convert gb_adj to 3.6 floating point, rounding down since it's always
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* safe to make the guard band smaller (but not the other way around!).
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*
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* Note: After converting back to a float, the value the blob returns here
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* is sometimes a little smaller than the value we return. This seems to
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* happen around the boundary between two different rounded values. For
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* example, using the a6xx blob:
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*
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* min | width | unrounded gb_adj | blob result | mesa result
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* ------------------------------------------------------------
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* 0 | 510 | 127.498 | 127. | 127.
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* 0 | 511 | 127.247 | 126. | 127.
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* 0 | 512 | 126.996 | 126. | 126.
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*
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* The guardband must be 32767 wide, since that's what the blob reports
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* for viewportBoundsRange, so I'm guessing that they're rounding slightly
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* more conservatively somehow.
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*/
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int gb_adj_exp;
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float gb_adj_mantissa = frexpf(gb_adj, &gb_adj_exp);
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assert(gb_adj_exp > 0);
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/* Round non-representable numbers down to the largest possible number. */
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if (gb_adj_exp > 8)
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return 0x1ff;
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return ((gb_adj_exp - 1) << 6) |
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((unsigned)truncf(gb_adj_mantissa * (1 << 7)) - (1 << 6));
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}
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#endif /* __FREEDRENO_GUARDBAND_H__ */
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