src/glsl/nir/nir_lower_clip.c

   1 /*
   2  * Copyright © 2015 Red Hat
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining a
   5  * copy of this software and associated documentation files (the "Software"),
   6  * to deal in the Software without restriction, including without limitation
   7  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   8  * and/or sell copies of the Software, and to permit persons to whom the
   9  * Software is furnished to do so, subject to the following conditions:
  10  *
  11  * The above copyright notice and this permission notice (including the next
  12  * paragraph) shall be included in all copies or substantial portions of the
  13  * Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  16  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  18  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  19  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  20  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  21  * IN THE SOFTWARE.
  22  *
  23  * Authors:
  24  *    Rob Clark <robclark@freedesktop.org>
  25  */
  26
  27 #include "nir.h"
  28 #include "nir_builder.h"
  29
  30 #define MAX_CLIP_PLANES 8
  31
  32 /* Generates the lowering code for user-clip-planes, generating CLIPDIST
  33  * from UCP[n] + CLIPVERTEX or POSITION.  Additionally, an optional pass
  34  * for fragment shaders to insert conditional kill's based on the inter-
  35  * polated CLIPDIST
  36  *
  37  * NOTE: should be run after nir_lower_outputs_to_temporaries() (or at
  38  * least in scenarios where you can count on each output written once
  39  * and only once).
  40  */
  41
  42
  43 static nir_variable *
  44 create_clipdist_var(nir_shader *shader, unsigned drvloc,
  45                     bool output, gl_varying_slot slot)
  46 {
  47    nir_variable *var = rzalloc(shader, nir_variable);
  48
  49    var->data.driver_location = drvloc;
  50    var->type = glsl_vec4_type();
  51    var->data.mode = output ? nir_var_shader_out : nir_var_shader_in;
  52    var->name = ralloc_asprintf(var, "clipdist_%d", drvloc);
  53    var->data.index = 0;
  54    var->data.location = slot;
  55
  56    if (output) {
  57       exec_list_push_tail(&shader->outputs, &var->node);
  58       shader->num_outputs++; /* TODO use type_size() */
  59    }
  60    else {
  61       exec_list_push_tail(&shader->inputs, &var->node);
  62       shader->num_inputs++;  /* TODO use type_size() */
  63    }
  64    return var;
  65 }
  66
  67 static void
  68 store_clipdist_output(nir_builder *b, nir_variable *out, nir_ssa_def **val)
  69 {
  70    nir_intrinsic_instr *store;
  71
  72    store = nir_intrinsic_instr_create(b->shader, nir_intrinsic_store_output);
  73    store->num_components = 4;
  74    store->const_index[0] = out->data.driver_location;
  75    store->src[0].ssa = nir_vec4(b, val[0], val[1], val[2], val[3]);
  76    store->src[0].is_ssa = true;
  77    store->src[1] = nir_src_for_ssa(nir_imm_int(b, 0));
  78    nir_builder_instr_insert(b, &store->instr);
  79 }
  80
  81 static void
  82 load_clipdist_input(nir_builder *b, nir_variable *in, nir_ssa_def **val)
  83 {
  84    nir_intrinsic_instr *load;
  85
  86    load = nir_intrinsic_instr_create(b->shader, nir_intrinsic_load_input);
  87    load->num_components = 4;
  88    load->const_index[0] = in->data.driver_location;
  89    load->src[0] = nir_src_for_ssa(nir_imm_int(b, 0));
  90    nir_ssa_dest_init(&load->instr, &load->dest, 4, NULL);
  91    nir_builder_instr_insert(b, &load->instr);
  92
  93    val[0] = nir_channel(b, &load->dest.ssa, 0);
  94    val[1] = nir_channel(b, &load->dest.ssa, 1);
  95    val[2] = nir_channel(b, &load->dest.ssa, 2);
  96    val[3] = nir_channel(b, &load->dest.ssa, 3);
  97 }
  98
  99 struct find_output_state
 100 {
 101    unsigned drvloc;
 102    nir_ssa_def *def;
 103 };
 104
 105 static bool
 106 find_output_in_block(nir_block *block, void *void_state)
 107 {
 108    struct find_output_state *state = void_state;
 109    nir_foreach_instr(block, instr) {
 110
 111       if (instr->type == nir_instr_type_intrinsic) {
 112          nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
 113          if ((intr->intrinsic == nir_intrinsic_store_output) &&
 114              intr->const_index[0] == state->drvloc) {
 115             assert(state->def == NULL);
 116             assert(intr->src[0].is_ssa);
 117             assert(nir_src_as_const_value(intr->src[1]));
 118             state->def = intr->src[0].ssa;
 119
 120 #if !defined(DEBUG)
 121             /* for debug builds, scan entire shader to assert
 122              * if output is written multiple times.  For release
 123              * builds just assume all is well and bail when we
 124              * find first:
 125              */
 126             return false;
 127 #endif
 128          }
 129       }
 130    }
 131
 132    return true;
 133 }
 134
 135 /* TODO: maybe this would be a useful helper?
 136  * NOTE: assumes each output is written exactly once (and unconditionally)
 137  * so if needed nir_lower_outputs_to_temporaries()
 138  */
 139 static nir_ssa_def *
 140 find_output(nir_shader *shader, unsigned drvloc)
 141 {
 142    struct find_output_state state = {
 143       .drvloc = drvloc,
 144    };
 145
 146    nir_foreach_function(shader, function) {
 147       if (function->impl) {
 148          nir_foreach_block_reverse(function->impl,
 149                                    find_output_in_block, &state);
 150       }
 151    }
 152
 153    return state.def;
 154 }
 155
 156 /*
 157  * VS lowering
 158  */
 159
 160 static void
 161 lower_clip_vs(nir_function_impl *impl, unsigned ucp_enables,
 162               nir_ssa_def *cv, nir_variable **out)
 163 {
 164    nir_ssa_def *clipdist[MAX_CLIP_PLANES];
 165    nir_builder b;
 166
 167    nir_builder_init(&b, impl);
 168
 169    /* NIR should ensure that, even in case of loops/if-else, there
 170     * should be only a single predecessor block to end_block, which
 171     * makes the perfect place to insert the clipdist calculations.
 172     *
 173     * NOTE: in case of early return's, these would have to be lowered
 174     * to jumps to end_block predecessor in a previous pass.  Not sure
 175     * if there is a good way to sanity check this, but for now the
 176     * users of this pass don't support sub-routines.
 177     */
 178    assert(impl->end_block->predecessors->entries == 1);
 179    b.cursor = nir_after_cf_list(&impl->body);
 180
 181    for (int plane = 0; plane < MAX_CLIP_PLANES; plane++) {
 182       if (ucp_enables & (1 << plane)) {
 183          nir_ssa_def *ucp =
 184             nir_load_system_value(&b, nir_intrinsic_load_user_clip_plane, plane);
 185
 186          /* calculate clipdist[plane] - dot(ucp, cv): */
 187          clipdist[plane] = nir_fdot4(&b, ucp, cv);
 188       }
 189       else {
 190          /* 0.0 == don't-clip == disabled: */
 191          clipdist[plane] = nir_imm_float(&b, 0.0);
 192       }
 193    }
 194
 195    if (ucp_enables & 0x0f)
 196       store_clipdist_output(&b, out[0], &clipdist[0]);
 197    if (ucp_enables & 0xf0)
 198       store_clipdist_output(&b, out[1], &clipdist[4]);
 199
 200    nir_metadata_preserve(impl, nir_metadata_dominance);
 201 }
 202
 203 /* ucp_enables is bitmask of enabled ucp's.  Actual ucp values are
 204  * passed in to shader via user_clip_plane system-values
 205  */
 206 void
 207 nir_lower_clip_vs(nir_shader *shader, unsigned ucp_enables)
 208 {
 209    int clipvertex = -1;
 210    int position = -1;
 211    int maxloc = -1;
 212    nir_ssa_def *cv;
 213    nir_variable *out[2] = { NULL };
 214
 215    if (!ucp_enables)
 216       return;
 217
 218    /* find clipvertex/position outputs: */
 219    nir_foreach_variable(var, &shader->outputs) {
 220       int loc = var->data.driver_location;
 221
 222       /* keep track of last used driver-location.. we'll be
 223        * appending CLIP_DIST0/CLIP_DIST1 after last existing
 224        * output:
 225        */
 226       maxloc = MAX2(maxloc, loc);
 227
 228       switch (var->data.location) {
 229       case VARYING_SLOT_POS:
 230          position = loc;
 231          break;
 232       case VARYING_SLOT_CLIP_VERTEX:
 233          clipvertex = loc;
 234          break;
 235       case VARYING_SLOT_CLIP_DIST0:
 236       case VARYING_SLOT_CLIP_DIST1:
 237          /* if shader is already writing CLIPDIST, then
 238           * there should be no user-clip-planes to deal
 239           * with.
 240           */
 241          return;
 242       }
 243    }
 244
 245    if (clipvertex != -1)
 246       cv = find_output(shader, clipvertex);
 247    else if (position != -1)
 248       cv = find_output(shader, position);
 249    else
 250       return;
 251
 252    /* insert CLIPDIST outputs: */
 253    if (ucp_enables & 0x0f)
 254       out[0] =
 255          create_clipdist_var(shader, ++maxloc, true, VARYING_SLOT_CLIP_DIST0);
 256    if (ucp_enables & 0xf0)
 257       out[1] =
 258          create_clipdist_var(shader, ++maxloc, true, VARYING_SLOT_CLIP_DIST1);
 259
 260    nir_foreach_function(shader, function) {
 261       if (!strcmp(function->name, "main"))
 262          lower_clip_vs(function->impl, ucp_enables, cv, out);
 263    }
 264 }
 265
 266 /*
 267  * FS lowering
 268  */
 269
 270 static void
 271 lower_clip_fs(nir_function_impl *impl, unsigned ucp_enables,
 272               nir_variable **in)
 273 {
 274    nir_ssa_def *clipdist[MAX_CLIP_PLANES];
 275    nir_builder b;
 276
 277    nir_builder_init(&b, impl);
 278    b.cursor = nir_before_cf_list(&impl->body);
 279
 280    if (ucp_enables & 0x0f)
 281       load_clipdist_input(&b, in[0], &clipdist[0]);
 282    if (ucp_enables & 0xf0)
 283       load_clipdist_input(&b, in[1], &clipdist[4]);
 284
 285    for (int plane = 0; plane < MAX_CLIP_PLANES; plane++) {
 286       if (ucp_enables & (1 << plane)) {
 287          nir_intrinsic_instr *discard;
 288          nir_ssa_def *cond;
 289
 290          cond = nir_flt(&b, clipdist[plane], nir_imm_float(&b, 0.0));
 291
 292          discard = nir_intrinsic_instr_create(b.shader,
 293                                               nir_intrinsic_discard_if);
 294          discard->src[0] = nir_src_for_ssa(cond);
 295          nir_builder_instr_insert(&b, &discard->instr);
 296       }
 297    }
 298 }
 299
 300 /* insert conditional kill based on interpolated CLIPDIST
 301  */
 302 void
 303 nir_lower_clip_fs(nir_shader *shader, unsigned ucp_enables)
 304 {
 305    nir_variable *in[2];
 306    int maxloc = -1;
 307
 308    if (!ucp_enables)
 309       return;
 310
 311    nir_foreach_variable(var, &shader->inputs) {
 312       int loc = var->data.driver_location;
 313
 314       /* keep track of last used driver-location.. we'll be
 315        * appending CLIP_DIST0/CLIP_DIST1 after last existing
 316        * input:
 317        */
 318       maxloc = MAX2(maxloc, loc);
 319    }
 320
 321    /* The shader won't normally have CLIPDIST inputs, so we
 322     * must add our own:
 323     */
 324    /* insert CLIPDIST outputs: */
 325    if (ucp_enables & 0x0f)
 326       in[0] =
 327          create_clipdist_var(shader, ++maxloc, false,
 328                              VARYING_SLOT_CLIP_DIST0);
 329    if (ucp_enables & 0xf0)
 330       in[1] =
 331          create_clipdist_var(shader, ++maxloc, false,
 332                              VARYING_SLOT_CLIP_DIST1);
 333
 334    nir_foreach_function(shader, function) {
 335       if (!strcmp(function->name, "main"))
 336          lower_clip_fs(function->impl, ucp_enables, in);
 337    }
 338 }