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"
#include "program/prog_instruction.h"

/* Lower gl_FragCoord (and fddy) 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
 * fddy src arg).
 *
 * This is based on the logic in emit_wpos()/emit_wpos_adjustment() in TGSI
 * compiler.
 *
 * Run before nir_lower_io.
 */

typedef struct {
   const nir_lower_wpos_ytransform_options *options;
   nir_shader   *shader;
   nir_builder   b;
   nir_variable *transform;
} lower_wpos_ytransform_state;

static nir_ssa_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_variable_create(state->shader,
                                              nir_var_uniform,
                                              glsl_vec4_type(),
                                              "gl_FbWposYTransform");

      var->num_state_slots = 1;
      var->state_slots = ralloc_array(var, nir_state_slot, 1);
      var->state_slots[0].swizzle = SWIZZLE_XYZW;
      memcpy(var->state_slots[0].tokens, state->options->state_tokens,
             sizeof(var->state_slots[0].tokens));
      var->data.how_declared = nir_var_hidden;
      state->transform = var;
   }
   return nir_load_var(&state->b, state->transform);
}

/* NIR equiv of TGSI CMP instruction: */
static nir_ssa_def *
nir_cmp(nir_builder *b, nir_ssa_def *src0, nir_ssa_def *src1, nir_ssa_def *src2)
{
   return nir_bcsel(b, nir_flt(b, src0, nir_imm_float(b, 0.0)), src1, src2);
}

/* see emit_wpos_adjustment() in st_mesa_to_tgsi.c */
static void
emit_wpos_adjustment(lower_wpos_ytransform_state *state,
                     nir_intrinsic_instr *intr, nir_variable *fragcoord,
                     bool invert, float adjX, float adjY[2])
{
   nir_builder *b = &state->b;
   nir_ssa_def *wpostrans, *wpos_temp, *wpos_temp_y, *wpos_input;

   assert(intr->dest.is_ssa);

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

   wpostrans = get_transform(state);
   wpos_input = nir_load_var(b, fragcoord);

   /* First, apply the coordinate shift: */
   if (adjX || adjY[0] || adjY[1]) {
      if (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_ssa_def *adj_temp;

         adj_temp = nir_cmp(b,
                            nir_channel(b, wpostrans, invert ? 2 : 0),
                            nir_imm_vec4(b, adjX, adjY[0], 0.0f, 0.0f),
                            nir_imm_vec4(b, adjX, adjY[1], 0.0f, 0.0f));

         wpos_temp = nir_fadd(b, wpos_input, adj_temp);
      } else {
         wpos_temp = nir_fadd(b,
                              wpos_input,
                              nir_imm_vec4(b, adjX, adjY[0], 0.0f, 0.0f));
      }
      wpos_input = wpos_temp;
   } else {
      /* MOV wpos_temp, input[wpos]
       */
      wpos_temp = wpos_input;
   }

   /* 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.
    */
   if (invert) {
      /* wpos_temp.y = wpos_input * wpostrans.xxxx + wpostrans.yyyy */
      wpos_temp_y = nir_fadd(b, nir_fmul(b, nir_channel(b, wpos_temp, 1),
                                            nir_channel(b, wpostrans, 0)),
                                nir_channel(b, wpostrans, 1));
   } else {
      /* wpos_temp.y = wpos_input * wpostrans.zzzz + wpostrans.wwww */
      wpos_temp_y = nir_fadd(b, nir_fmul(b, nir_channel(b, wpos_temp, 1),
                                            nir_channel(b, wpostrans, 2)),
                                nir_channel(b, wpostrans, 3));
   }

   wpos_temp = nir_vec4(b,
                        nir_channel(b, wpos_temp, 0),
                        wpos_temp_y,
                        nir_channel(b, wpos_temp, 2),
                        nir_channel(b, wpos_temp, 3));

   nir_ssa_def_rewrite_uses(&intr->dest.ssa, nir_src_for_ssa(wpos_temp));
}

static void
lower_fragcoord(lower_wpos_ytransform_state *state,
                nir_intrinsic_instr *intr, nir_variable *fragcoord)
{
   const nir_lower_wpos_ytransform_options *options = state->options;
   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 (state->shader->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 (state->shader->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");
      }
   }

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

static void
lower_load_pointcoord(lower_wpos_ytransform_state *state,
                      nir_intrinsic_instr *intr)
{
   nir_builder *b = &state->b;
   b->cursor = nir_after_instr(&intr->instr);

   nir_ssa_def *pntc = &intr->dest.ssa;
   nir_ssa_def *transform = get_transform(state);
   nir_ssa_def *y = nir_channel(b, pntc, 1);
   /* The offset is 1 if we're flipping, 0 otherwise. */
   nir_ssa_def *offset = nir_fmax(b, nir_channel(b, transform, 2),
                                  nir_imm_float(b, 0.0));
   /* Flip the sign of y if we're flipping. */
   nir_ssa_def *scaled = nir_fmul(b, y, nir_channel(b, transform, 0));

   /* Reassemble the vector. */
   nir_ssa_def *flipped_pntc = nir_vec2(b,
                                        nir_channel(b, pntc, 0),
                                        nir_fadd(b, offset, scaled));

   nir_ssa_def_rewrite_uses_after(&intr->dest.ssa, nir_src_for_ssa(flipped_pntc),
                                  flipped_pntc->parent_instr);
}

/* turns 'fddy(p)' into 'fddy(fmul(p, transform.x))' */
static void
lower_fddy(lower_wpos_ytransform_state *state, nir_alu_instr *fddy)
{
   nir_builder *b = &state->b;
   nir_ssa_def *p, *pt, *trans;

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

   p = nir_ssa_for_alu_src(b, fddy, 0);
   trans = get_transform(state);
   pt = nir_fmul(b, p, nir_channel(b, trans, 0));

   nir_instr_rewrite_src(&fddy->instr,
                         &fddy->src[0].src,
                         nir_src_for_ssa(pt));

   for (unsigned i = 0; i < 4; i++)
      fddy->src[0].swizzle[i] = MIN2(i, pt->num_components - 1);
}

/* Multiply interp_deref_at_offset's offset by transform.x to flip it. */
static void
lower_interp_deref_at_offset(lower_wpos_ytransform_state *state,
                           nir_intrinsic_instr *interp)
{
   nir_builder *b = &state->b;
   nir_ssa_def *offset;
   nir_ssa_def *flip_y;

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

   offset = nir_ssa_for_src(b, interp->src[1], 2);
   flip_y = nir_fmul(b, nir_channel(b, offset, 1),
                        nir_channel(b, get_transform(state), 0));
   nir_instr_rewrite_src(&interp->instr, &interp->src[1],
                         nir_src_for_ssa(nir_vec2(b, nir_channel(b, offset, 0),
                                                     flip_y)));
}

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

   nir_ssa_def *pos = &intr->dest.ssa;
   nir_ssa_def *scale = nir_channel(b, get_transform(state), 0);
   nir_ssa_def *neg_scale = nir_channel(b, get_transform(state), 2);
   /* Either y or 1-y for scale equal to 1 or -1 respectively. */
   nir_ssa_def *flipped_y =
               nir_fadd(b, nir_fmax(b, neg_scale, nir_imm_float(b, 0.0)),
                        nir_fmul(b, nir_channel(b, pos, 1), scale));
   nir_ssa_def *flipped_pos = nir_vec2(b, nir_channel(b, pos, 0), flipped_y);

   nir_ssa_def_rewrite_uses_after(&intr->dest.ssa, nir_src_for_ssa(flipped_pos),
                                  flipped_pos->parent_instr);
}

static void
lower_wpos_ytransform_block(lower_wpos_ytransform_state *state, nir_block *block)
{
   nir_foreach_instr_safe(instr, block) {
      if (instr->type == nir_instr_type_intrinsic) {
         nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
         if (intr->intrinsic == 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_shader_in &&
                 var->data.location == VARYING_SLOT_POS) ||
                (var->data.mode == nir_var_system_value &&
                 var->data.location == SYSTEM_VALUE_FRAG_COORD)) {
               /* gl_FragCoord should not have array/struct derefs: */
               lower_fragcoord(state, intr, var);
            } else if (var->data.mode == nir_var_system_value &&
                       var->data.location == SYSTEM_VALUE_SAMPLE_POS) {
               lower_load_sample_pos(state, intr);
            } else if (var->data.mode == nir_var_shader_in &&
                       var->data.location == VARYING_SLOT_PNTC &&
                       state->shader->options->lower_wpos_pntc) {
               lower_load_pointcoord(state, intr);
            }
         } else if (intr->intrinsic == nir_intrinsic_load_frag_coord) {
            lower_fragcoord(state, intr, NULL);
         } else if (intr->intrinsic == nir_intrinsic_load_sample_pos) {
            lower_load_sample_pos(state, intr);
         } else if (intr->intrinsic == nir_intrinsic_interp_deref_at_offset) {
            lower_interp_deref_at_offset(state, intr);
         }
      } else if (instr->type == nir_instr_type_alu) {
         nir_alu_instr *alu = nir_instr_as_alu(instr);
         if (alu->op == nir_op_fddy ||
             alu->op == nir_op_fddy_fine ||
             alu->op == nir_op_fddy_coarse)
            lower_fddy(state, alu);
      }
   }
}

static void
lower_wpos_ytransform_impl(lower_wpos_ytransform_state *state, nir_function_impl *impl)
{
   nir_builder_init(&state->b, impl);

   nir_foreach_block(block, impl) {
      lower_wpos_ytransform_block(state, block);
   }
   nir_metadata_preserve(impl, nir_metadata_block_index |
                               nir_metadata_dominance);
}

bool
nir_lower_wpos_ytransform(nir_shader *shader,
                          const nir_lower_wpos_ytransform_options *options)
{
   lower_wpos_ytransform_state state = {
      .options = options,
      .shader = shader,
   };

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

   nir_foreach_function(function, shader) {
      if (function->impl)
         lower_wpos_ytransform_impl(&state, function->impl);
   }

   return state.transform != NULL;
}