On 4/8/19 5:34 AM, Thomas Helland wrote:
> man. 8. apr. 2019 kl. 06:30 skrev Alyssa Rosenzweig <aly...@rosenzweig.io>:
>>
>> On Mali hardware (supported by Panfrost and Lima), the fixed-function
>> transformation from world-space to screen-space coordinates is done in
>> the vertex shader prior to writing out the gl_Position varying, rather
>> than in dedicated hardware. This commit adds a shared NIR pass for
>> implementing coordinate transformation and lowering gl_Position writes
>> into screen-space gl_Position writes.
>>
>> v2: Run directly on derefs before io/vars are lowered to cleanup the
>> code substantially. Thank you to Qiang for this suggestion!
>>
>> Signed-off-by: Alyssa Rosenzweig <aly...@rosenzweig.io>
>> Suggested-by: Qiang Yu <yuq...@gmail.com>
>> Cc: Jason Ekstrand <ja...@jlekstrand.net>
>> Cc: Eric Anholt <e...@anholt.net>
>> ---
>> src/compiler/nir/meson.build | 1 +
>> src/compiler/nir/nir.h | 1 +
>> .../nir/nir_lower_viewport_transform.c | 98 +++++++++++++++++++
>> 3 files changed, 100 insertions(+)
>> create mode 100644 src/compiler/nir/nir_lower_viewport_transform.c
>>
>> diff --git a/src/compiler/nir/meson.build b/src/compiler/nir/meson.build
>> index c65f2ff62ff..c274361bdc4 100644
>> --- a/src/compiler/nir/meson.build
>> +++ b/src/compiler/nir/meson.build
>> @@ -151,6 +151,7 @@ files_libnir = files(
>> 'nir_lower_vars_to_ssa.c',
>> 'nir_lower_var_copies.c',
>> 'nir_lower_vec_to_movs.c',
>> + 'nir_lower_viewport_transform.c',
>> 'nir_lower_wpos_center.c',
>> 'nir_lower_wpos_ytransform.c',
>> 'nir_lower_bit_size.c',
>> diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
>> index bc72d8f83f5..0f6ed734efa 100644
>> --- a/src/compiler/nir/nir.h
>> +++ b/src/compiler/nir/nir.h
>> @@ -3124,6 +3124,7 @@ void nir_lower_io_to_scalar(nir_shader *shader,
>> nir_variable_mode mask);
>> void nir_lower_io_to_scalar_early(nir_shader *shader, nir_variable_mode
>> mask);
>> bool nir_lower_io_to_vector(nir_shader *shader, nir_variable_mode mask);
>>
>> +void nir_lower_viewport_transform(nir_shader *shader);
>> bool nir_lower_uniforms_to_ubo(nir_shader *shader, int multiplier);
>>
>> typedef struct nir_lower_subgroups_options {
>> diff --git a/src/compiler/nir/nir_lower_viewport_transform.c
>> b/src/compiler/nir/nir_lower_viewport_transform.c
>> new file mode 100644
>> index 00000000000..9646b72c053
>> --- /dev/null
>> +++ b/src/compiler/nir/nir_lower_viewport_transform.c
>> @@ -0,0 +1,98 @@
>> +/*
>> + * Copyright (C) 2019 Alyssa Rosenzweig
>> + *
>> + * Permission is hereby granted, free of charge, to any person obtaining a
>> + * copy of this software and associated documentation files (the
>> "Software"),
>> + * to deal in the Software without restriction, including without limitation
>> + * the rights to use, copy, modify, merge, publish, distribute, sublicense,
>> + * and/or sell copies of the Software, and to permit persons to whom the
>> + * Software is furnished to do so, subject to the following conditions:
>> + *
>> + * The above copyright notice and this permission notice (including the next
>> + * paragraph) shall be included in all copies or substantial portions of the
>> + * Software.
>> + *
>> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
>> OR
>> + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
>> + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
>> + * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
>> OTHER
>> + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
>> + * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
>> DEALINGS
>> + * IN THE SOFTWARE.
>> + */
>> +
>> +/* On some hardware (particularly, all current versions of Mali GPUs),
>> + * vertex shaders do not output gl_Position in world-space. Instead, they
>> + * output gl_Position in transformed screen space via the "pseudo"
>> + * position varying. Thus, this pass finds writes to gl_Position and
>> + * changes them to transformed writes, still to gl_Position. The
>> + * outputted screen space is still written back to VARYING_SLOT_POS,
>> + * which is semantically ambiguous but nevertheless a good match for
>> + * Gallium/NIR/Mali.
>> + *
>> + * Implements coordinate transformation as defined in section 12.5
>> + * "Coordinate Transformation" of the OpenGL ES 3.2 full specification.
>> + *
>> + * This pass must run before lower_vars/lower_io such that derefs are
>> + * still in place.
>> + */
>> +
>> +#include "nir/nir.h"
>> +#include "nir/nir_builder.h"
>> +
>> +void
>> +nir_lower_viewport_transform(nir_shader *shader)
>> +{
>> + assert(shader->info.stage == MESA_SHADER_VERTEX);
>> +
>> + nir_foreach_function(func, shader) {
>> + nir_foreach_block(block, func->impl) {
>> + nir_foreach_instr_safe(instr, block) {
>> + if (instr->type != nir_instr_type_intrinsic) continue;
>> +
>> + nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
>> + if (intr->intrinsic != nir_intrinsic_store_deref) continue;
>> +
>> + nir_variable *var = nir_intrinsic_get_var(intr, 0);
>> + if (var->data.location != VARYING_SLOT_POS) continue;
>> +
>
> I believe it's agreement in mesa that the if ( ... ) should be on one line,
> and the continue, return, etc should be on a new one.
>
> Regards,
> Thomas Helland
>
>> + nir_builder b;
>> + nir_builder_init(&b, func->impl);
>> + b.cursor = nir_before_instr(instr);
>> +
>> + /* Grab the source and viewport */
>> + nir_ssa_def *input_point = nir_ssa_for_src(&b, intr->src[1], 4);
>> + nir_ssa_def *scale = nir_load_viewport_scale(&b);
>> + nir_ssa_def *offset = nir_load_viewport_offset(&b);
>> +
>> + /* World space to normalised device coordinates to screen space
>> */
>> +
>> + nir_ssa_def *w_recip = nir_frcp(&b, nir_channel(&b,
>> input_point, 3));
>> +
>> + nir_ssa_def *ndc_point = nir_fmul(&b,
>> + nir_channels(&b, input_point, 0x7), w_recip);
>> +
>> + nir_ssa_def *screen = nir_fadd(&b,
>> + nir_fmul(&b, ndc_point, scale), offset);
>> +
>> + /* gl_Position will be written out in screenspace xyz, with w
>> set to
>> + * the reciprocal we computed earlier. The transformed w
>> component is
>> + * then used for perspective-correct varying interpolation. The
>> + * transformed w component must preserve its original sign;
>> this is
>> + * used in depth clipping computations */
As an even smaller nit to pick... the */ of a multi-line comment should
be on its own line.
>> +
>> + nir_ssa_def *screen_space = nir_vec4(&b,
>> + nir_channel(&b, screen, 0),
>> + nir_channel(&b, screen, 1),
>> + nir_channel(&b, screen, 2),
>> + w_recip);
>> +
>> + nir_instr_rewrite_src(instr, &intr->src[1],
>> + nir_src_for_ssa(screen_space));
>> + }
>> + }
>> +
>> + nir_metadata_preserve(func->impl, nir_metadata_block_index |
>> + nir_metadata_dominance);
>> + }
>> +}
>> --
>> 2.20.1
>>
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