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authorAlyssa Rosenzweig <[email protected]>2019-04-14 15:43:13 +0000
committerAlyssa Rosenzweig <[email protected]>2019-04-14 19:15:13 +0000
commit2ce4adefa5647ef853a6713e651134eb173dc6ea (patch)
tree8e41ccee8bb76539419636416ec9dd932a1868ea /src/compiler/nir
parent89b02bffcb452e1cb36dacded226d11e7e5ee713 (diff)
nir: Add nir_lower_viewport_transform
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! v3: Bikeshed continues. v4: Add to Makefile.sources (per Jason's comment). Bikeshed comment. Ian and Qiang's reviews are from v3, but no real functional changes from v4. Rob's review is from v4. Signed-off-by: Alyssa Rosenzweig <[email protected]> Suggested-by: Qiang Yu <[email protected]> Reviewed-by: Ian Romanick <[email protected]> Reviewed-by: Qiang Yu <[email protected]> Reviewed-by: Rob Clark <[email protected]>
Diffstat (limited to 'src/compiler/nir')
-rw-r--r--src/compiler/nir/meson.build1
-rw-r--r--src/compiler/nir/nir.h1
-rw-r--r--src/compiler/nir/nir_lower_viewport_transform.c102
3 files changed, 104 insertions, 0 deletions
diff --git a/src/compiler/nir/meson.build b/src/compiler/nir/meson.build
index 4e5039e28e0..d6e7b2cc167 100644
--- a/src/compiler/nir/meson.build
+++ b/src/compiler/nir/meson.build
@@ -152,6 +152,7 @@ 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 ad72a5c9222..4323f5e0413 100644
--- a/src/compiler/nir/nir.h
+++ b/src/compiler/nir/nir.h
@@ -3114,6 +3114,7 @@ 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..94b54524ab7
--- /dev/null
+++ b/src/compiler/nir/nir_lower_viewport_transform.c
@@ -0,0 +1,102 @@
+/*
+ * 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;
+
+ 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
+ */
+
+ 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);
+ }
+}