mesa/src/compiler/nir/nir_lower_wpos_ytransform.c

/*
 * Copyright © 2015 Red Hat
 *
 * 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.
 */

#include "nir.h"
#include "nir_builder.h"

/* Lower gl_FragCoord (and ddy) to account for driver's requested coordinate-
 * origin and pixel-center vs. shader.  If transformation is required, a
 * gl_FbWposYTransform uniform is inserted (with the specified state-slots)
 * and additional instructions are inserted to transform gl_FragCoord (and
 * ddy src arg).
 */

typedef struct {
   const nir_lower_wpos_ytransform_options *options;
   nir_builder b;
   nir_def *transform;
} lower_wpos_ytransform_state;

static nir_def *
get_transform(lower_wpos_ytransform_state *state)
{
   if (state->transform == NULL) {
      /* NOTE: name must be prefixed w/ "gl_" to trigger slot based
       * special handling in uniform setup:
       */
      nir_variable *var = nir_state_variable_create(state->b.shader,
                                                    glsl_vec4_type(),
                                                    "gl_FbWposYTransform",
                                                    state->options->state_tokens);

      var->data.how_declared = nir_var_hidden;
      state->b.cursor = nir_before_impl(nir_shader_get_entrypoint(state->b.shader));
      state->transform = nir_load_var(&state->b, var);
   }
   return state->transform;
}

static bool
emit_wpos_adjustment(lower_wpos_ytransform_state *state,
                     nir_intrinsic_instr *intr, bool invert,
                     float adjX, float adjY[2])
{
   nir_builder *b = &state->b;
   unsigned c = 0;
   if (nir_intrinsic_has_component(intr)) {
      c = nir_intrinsic_component(intr);
      /* this pass only alters the first two components */
      if (c > 1)
         return false;
   }

   if (c == 0 && intr->num_components == 1 && adjX == 0.0)
      return false;

   nir_def *wpostrans = get_transform(state);

   b->cursor = nir_after_instr(&intr->instr);
   nir_def *wpos[4] = { NULL };
   for (unsigned i = 0; i < intr->num_components; i++)
      wpos[i + c] = nir_channel(b, &intr->def, i);

   /* First, apply the coordinate shift: */
   if (wpos[0] && adjX)
      wpos[0] = nir_fadd_imm(b, wpos[0], adjX);

   if (wpos[1] && adjY[0] != adjY[1]) {
      /* Adjust the y coordinate by adjY[1] or adjY[0] respectively
       * depending on whether inversion is actually going to be applied
       * or not, which is determined by testing against the inversion
       * state variable used below, which will be either +1 or -1.
       */
      nir_def *cond = nir_flt_imm(b, nir_channel(b, wpostrans, invert ? 2 : 0), 0.0);
      nir_def *adj_temp = nir_bcsel(b, cond,
                                    nir_imm_float(b, adjY[0]),
                                    nir_imm_float(b, adjY[1]));

      wpos[1] = nir_fadd(b, wpos[1], adj_temp);
   } else if (wpos[1] && adjY[0]) {
      wpos[1] = nir_fadd_imm(b, wpos[1], adjY[0]);
   }

   if (wpos[1]) {
      /* Now the conditional y flip: STATE_FB_WPOS_Y_TRANSFORM.xy/zw will be
       * inversion/identity, or the other way around if we're drawing to an FBO.
       */
      unsigned base = invert ? 0 : 2;
      /* wpos.y = wpos.y * trans.x/z + trans.y/w */
      wpos[1] = nir_ffma(b, wpos[1], nir_channel(b, wpostrans, base),
                         nir_channel(b, wpostrans, base + 1));
   }

   nir_def *new_wpos = nir_vec(b, &wpos[c], intr->num_components);

   nir_def_rewrite_uses_after(&intr->def, new_wpos);

   return true;
}

static bool
lower_fragcoord(lower_wpos_ytransform_state *state, nir_intrinsic_instr *intr)
{
   const nir_lower_wpos_ytransform_options *options = state->options;
   const struct shader_info *info = &state->b.shader->info;
   float adjX = 0.0f;
   float adjY[2] = { 0.0f, 0.0f };
   bool invert = false;

   /* Based on logic in emit_wpos():
    *
    * Query the pixel center conventions supported by the pipe driver and set
    * adjX, adjY to help out if it cannot handle the requested one internally.
    *
    * The bias of the y-coordinate depends on whether y-inversion takes place
    * (adjY[1]) or not (adjY[0]), which is in turn dependent on whether we are
    * drawing to an FBO (causes additional inversion), and whether the pipe
    * driver origin and the requested origin differ (the latter condition is
    * stored in the 'invert' variable).
    *
    * For height = 100 (i = integer, h = half-integer, l = lower, u = upper):
    *
    * center shift only:
    * i -> h: +0.5
    * h -> i: -0.5
    *
    * inversion only:
    * l,i -> u,i: ( 0.0 + 1.0) * -1 + 100 = 99
    * l,h -> u,h: ( 0.5 + 0.0) * -1 + 100 = 99.5
    * u,i -> l,i: (99.0 + 1.0) * -1 + 100 = 0
    * u,h -> l,h: (99.5 + 0.0) * -1 + 100 = 0.5
    *
    * inversion and center shift:
    * l,i -> u,h: ( 0.0 + 0.5) * -1 + 100 = 99.5
    * l,h -> u,i: ( 0.5 + 0.5) * -1 + 100 = 99
    * u,i -> l,h: (99.0 + 0.5) * -1 + 100 = 0.5
    * u,h -> l,i: (99.5 + 0.5) * -1 + 100 = 0
    */

   if (info->fs.origin_upper_left) {
      /* Fragment shader wants origin in upper-left */
      if (options->fs_coord_origin_upper_left) {
         /* the driver supports upper-left origin */
      } else if (options->fs_coord_origin_lower_left) {
         /* the driver supports lower-left origin, need to invert Y */
         invert = true;
      } else {
         UNREACHABLE("invalid options");
      }
   } else {
      /* Fragment shader wants origin in lower-left */
      if (options->fs_coord_origin_lower_left) {
         /* the driver supports lower-left origin */
      } else if (options->fs_coord_origin_upper_left) {
         /* the driver supports upper-left origin, need to invert Y */
         invert = true;
      } else {
         UNREACHABLE("invalid options");
      }
   }

   if (info->fs.pixel_center_integer) {
      /* Fragment shader wants pixel center integer */
      if (options->fs_coord_pixel_center_integer) {
         /* the driver supports pixel center integer */
         adjY[1] = 1.0f;
      } else if (options->fs_coord_pixel_center_half_integer) {
         /* the driver supports pixel center half integer, need to bias X,Y */
         adjX = -0.5f;
         adjY[0] = -0.5f;
         adjY[1] = 0.5f;
      } else {
         UNREACHABLE("invalid options");
      }
   } else {
      /* Fragment shader wants pixel center half integer */
      if (options->fs_coord_pixel_center_half_integer) {
         /* the driver supports pixel center half integer */
      } else if (options->fs_coord_pixel_center_integer) {
         /* the driver supports pixel center integer, need to bias X,Y */
         adjX = adjY[0] = adjY[1] = 0.5f;
      } else {
         UNREACHABLE("invalid options");
      }
   }

   return emit_wpos_adjustment(state, intr, invert, adjX, adjY);
}

/* turns 'ddy(p)' into 'ddy(fmul(p, transform.x))' */
static bool
lower_ddy(lower_wpos_ytransform_state *state, nir_intrinsic_instr *ddy)
{
   nir_builder *b = &state->b;
   nir_def *wpostrans = get_transform(state);

   b->cursor = nir_before_instr(&ddy->instr);

   nir_def *p = ddy->src[0].ssa;
   nir_def *trans = nir_f2fN(b, nir_channel(b, wpostrans, 0), p->bit_size);
   nir_def *pt = nir_fmul(b, p, trans);

   nir_src_rewrite(&ddy->src[0], pt);

   return true;
}

/* Multiply interp_deref_at_offset's or load_barycentric_at_offset's offset
 * by transform.x to flip it.
 */
static bool
lower_interp_deref_or_load_baryc_at_offset(lower_wpos_ytransform_state *state,
                                           nir_intrinsic_instr *intr,
                                           unsigned offset_src)
{
   nir_builder *b = &state->b;
   nir_def *wpostrans = get_transform(state);

   b->cursor = nir_before_instr(&intr->instr);

   nir_def *offset = intr->src[offset_src].ssa;
   nir_def *flip_y = nir_fmul(b, nir_channel(b, offset, 1),
                              nir_channel(b, wpostrans, 0));
   offset = nir_vector_insert_imm(b, offset, flip_y, 1);
   nir_src_rewrite(&intr->src[offset_src], offset);

   return true;
}

static bool
lower_load_sample_pos(lower_wpos_ytransform_state *state,
                      nir_intrinsic_instr *intr)
{
   nir_builder *b = &state->b;
   nir_def *wpostrans = get_transform(state);
   b->cursor = nir_after_instr(&intr->instr);

   nir_def *pos = &intr->def;
   nir_def *scale = nir_channel(b, wpostrans, 0);
   nir_def *neg_scale = nir_channel(b, wpostrans, 2);
   /* Either y or 1-y for scale equal to 1 or -1 respectively. */
   nir_def *flipped_y = nir_ffma(b, nir_channel(b, pos, 1), scale,
                                 nir_fmax(b, neg_scale, nir_imm_float(b, 0.0)));
   nir_def *flipped_pos = nir_vector_insert_imm(b, pos, flipped_y, 1);

   nir_def_rewrite_uses_after(&intr->def, flipped_pos);

   return true;
}

static bool
lower_wpos_ytransform_instr(nir_builder *b, nir_intrinsic_instr *intr,
                            void *data)
{
   lower_wpos_ytransform_state *state = data;
   state->b = *b;

   switch (intr->intrinsic) {
   case nir_intrinsic_load_deref: {
      nir_deref_instr *deref = nir_src_as_deref(intr->src[0]);
      nir_variable *var = nir_deref_instr_get_variable(deref);
      if (var->data.mode == nir_var_system_value &&
          var->data.location == SYSTEM_VALUE_FRAG_COORD) {
         /* gl_FragCoord should not have array/struct derefs: */
         return lower_fragcoord(state, intr);
      } else if (var->data.mode == nir_var_system_value &&
                 var->data.location == SYSTEM_VALUE_SAMPLE_POS) {
         return lower_load_sample_pos(state, intr);
      }
      return false;
   }
   case nir_intrinsic_load_interpolated_input: {
      nir_io_semantics sem = nir_intrinsic_io_semantics(intr);
      if (sem.location == VARYING_SLOT_POS)
         return lower_fragcoord(state, intr);
      return false;
   }
   case nir_intrinsic_load_frag_coord:
      return lower_fragcoord(state, intr);
   case nir_intrinsic_load_sample_pos:
      return lower_load_sample_pos(state, intr);
   case nir_intrinsic_interp_deref_at_offset:
      return lower_interp_deref_or_load_baryc_at_offset(state, intr, 1);
   case nir_intrinsic_load_barycentric_at_offset:
      return lower_interp_deref_or_load_baryc_at_offset(state, intr, 0);
   case nir_intrinsic_ddy:
   case nir_intrinsic_ddy_fine:
   case nir_intrinsic_ddy_coarse:
      return lower_ddy(state, intr);
   default:
      return false;
   }
}

bool
nir_lower_wpos_ytransform(nir_shader *shader,
                          const nir_lower_wpos_ytransform_options *options)
{
   assert(shader->info.io_lowered);

   lower_wpos_ytransform_state state = {
      .options = options,
   };

   assert(shader->info.stage == MESA_SHADER_FRAGMENT);

   return nir_shader_intrinsics_pass(shader,
                                     lower_wpos_ytransform_instr,
                                     nir_metadata_control_flow,
                                     &state);
}