Alyssa Rosenzweig
91872c9c51
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io> Acked-by: Faith Ekstrand <faith.ekstrand@collabora.com> Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33722>
109 lines
4.5 KiB
C
109 lines
4.5 KiB
C
/*
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* Copyright (C) 2019 Alyssa Rosenzweig
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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
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* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
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* IN THE SOFTWARE.
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*/
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/* On some hardware (particularly, all current versions of Mali GPUs),
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* vertex shaders do not output gl_Position in world-space. Instead, they
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* output gl_Position in transformed screen space via the "pseudo"
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* position varying. Thus, this pass finds writes to gl_Position and
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* changes them to transformed writes, still to gl_Position. The
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* outputted screen space is still written back to VARYING_SLOT_POS,
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* which is semantically ambiguous but nevertheless a good match for
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* Gallium/NIR/Mali.
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*
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* Implements coordinate transformation as defined in section 12.5
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* "Coordinate Transformation" of the OpenGL ES 3.2 full specification.
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*
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* This pass must run before lower_vars/lower_io such that derefs are
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* still in place. This pass must run after lower_io_to_temporaries so
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* that the transformed position is not visible to user code.
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*/
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#include "nir/nir.h"
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#include "nir/nir_builder.h"
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/* Vulkan spec requires float accuracy to ~10^-5, so we need to differentiate
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* between W=0 and W=10^-5. Clamping 1/W to 2^15 gives a bit of margin on top
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* of this. */
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#define MAX_W_RECIP_ABS (float)(1l << 15)
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static bool
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lower_viewport_transform_instr(nir_builder *b, nir_intrinsic_instr *intr,
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void *data)
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{
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if (intr->intrinsic != nir_intrinsic_store_deref)
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return false;
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nir_variable *var = nir_intrinsic_get_var(intr, 0);
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if (var->data.mode != nir_var_shader_out ||
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var->data.location != VARYING_SLOT_POS)
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return false;
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b->cursor = nir_before_instr(&intr->instr);
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/* Grab the source and viewport */
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nir_def *input_point = intr->src[1].ssa;
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nir_def *scale = nir_load_viewport_scale(b);
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nir_def *offset = nir_load_viewport_offset(b);
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/* World space to normalised device coordinates to screen space */
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nir_def *w_recip = nir_frcp(b, nir_channel(b, input_point, 3));
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/* Clamp w_recip so that small w does not result in Inf or unacceptable
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* precision loss relative to clipping pre-transform. */
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w_recip = nir_fclamp(b, w_recip, nir_imm_float(b, -MAX_W_RECIP_ABS),
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nir_imm_float(b, MAX_W_RECIP_ABS));
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nir_def *ndc_point = nir_fmul(b, nir_trim_vector(b, input_point, 3),
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w_recip);
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nir_def *screen = nir_fadd(b, nir_fmul(b, ndc_point, scale),
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offset);
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/* gl_Position will be written out in screenspace xyz, with w set to
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* the reciprocal we computed earlier. The transformed w component is
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* then used for perspective-correct varying interpolation. The
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* transformed w component must preserve its original sign; this is
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* used in depth clipping computations
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*/
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nir_def *screen_space = nir_vec4(b,
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nir_channel(b, screen, 0),
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nir_channel(b, screen, 1),
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nir_channel(b, screen, 2),
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w_recip);
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nir_src_rewrite(&intr->src[1], screen_space);
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return true;
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}
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bool
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nir_lower_viewport_transform(nir_shader *shader)
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{
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assert((shader->info.stage == MESA_SHADER_VERTEX) || (shader->info.stage == MESA_SHADER_GEOMETRY) || (shader->info.stage == MESA_SHADER_TESS_EVAL));
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return nir_shader_intrinsics_pass(shader, lower_viewport_transform_instr,
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nir_metadata_control_flow,
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NULL);
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}
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