src/compiler/nir/nir_lower_bitmap.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 FROM,
  20  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  21  * SOFTWARE.
  22  */
  23
  24 #include "nir.h"
  25 #include "nir_builder.h"
  26
  27 /* Lower glBitmap().
  28  *
  29  * This is based on the logic in st_get_bitmap_shader() in TGSI compiler.
  30  * From st_cb_bitmap.c:
  31  *
  32  *    glBitmaps are drawn as textured quads.  The user's bitmap pattern
  33  *    is stored in a texture image.  An alpha8 texture format is used.
  34  *    The fragment shader samples a bit (texel) from the texture, then
  35  *    discards the fragment if the bit is off.
  36  *
  37  *    Note that we actually store the inverse image of the bitmap to
  38  *    simplify the fragment program.  An "on" bit gets stored as texel=0x0
  39  *    and an "off" bit is stored as texel=0xff.  Then we kill the
  40  *    fragment if the negated texel value is less than zero.
  41  *
  42  * Note that the texture format will be, according to what driver supports,
  43  * in order of preference (with swizzle):
  44  *
  45  *    I8_UNORM - .xxxx
  46  *    A8_UNORM - .000x
  47  *    L8_UNORM - .xxx1
  48  *
  49  * If L8_UNORM, options->swizzle_xxxx is true.  Otherwise we can just use
  50  * the .w comp.
  51  *
  52  * Run before nir_lower_io.
  53  */
  54
  55 static nir_variable *
  56 get_texcoord(nir_shader *shader)
  57 {
  58    nir_variable *texcoord =
  59       nir_find_variable_with_location(shader, nir_var_shader_in,
  60                                       VARYING_SLOT_TEX0);
  61    /* otherwise create it: */
  62    if (texcoord == NULL) {
  63       texcoord = nir_variable_create(shader,
  64                                      nir_var_shader_in,
  65                                      glsl_vec4_type(),
  66                                      "gl_TexCoord");
  67       texcoord->data.location = VARYING_SLOT_TEX0;
  68    }
  69
  70    return texcoord;
  71 }
  72
  73 static void
  74 lower_bitmap(nir_shader *shader, nir_builder *b,
  75              const nir_lower_bitmap_options *options)
  76 {
  77    nir_ssa_def *texcoord;
  78    nir_tex_instr *tex;
  79    nir_ssa_def *cond;
  80    nir_intrinsic_instr *discard;
  81
  82    texcoord = nir_load_var(b, get_texcoord(shader));
  83
  84    const struct glsl_type *sampler2D =
  85       glsl_sampler_type(GLSL_SAMPLER_DIM_2D, false, false, GLSL_TYPE_FLOAT);
  86
  87    nir_variable *tex_var =
  88       nir_variable_create(shader, nir_var_uniform, sampler2D, "bitmap_tex");
  89    tex_var->data.binding = options->sampler;
  90    tex_var->data.explicit_binding = true;
  91    tex_var->data.how_declared = nir_var_hidden;
  92
  93    nir_deref_instr *tex_deref = nir_build_deref_var(b, tex_var);
  94
  95    tex = nir_tex_instr_create(shader, 3);
  96    tex->op = nir_texop_tex;
  97    tex->sampler_dim = GLSL_SAMPLER_DIM_2D;
  98    tex->coord_components = 2;
  99    tex->dest_type = nir_type_float;
 100    tex->src[0].src_type = nir_tex_src_texture_deref;
 101    tex->src[0].src = nir_src_for_ssa(&tex_deref->dest.ssa);
 102    tex->src[1].src_type = nir_tex_src_sampler_deref;
 103    tex->src[1].src = nir_src_for_ssa(&tex_deref->dest.ssa);
 104    tex->src[2].src_type = nir_tex_src_coord;
 105    tex->src[2].src =
 106       nir_src_for_ssa(nir_channels(b, texcoord,
 107                                    (1 << tex->coord_components) - 1));
 108
 109    nir_ssa_dest_init(&tex->instr, &tex->dest, 4, 32, NULL);
 110    nir_builder_instr_insert(b, &tex->instr);
 111
 112    /* kill if tex != 0.0.. take .x or .w channel according to format: */
 113    cond = nir_f2b(b, nir_channel(b, &tex->dest.ssa,
 114                   options->swizzle_xxxx ? 0 : 3));
 115
 116    discard = nir_intrinsic_instr_create(shader, nir_intrinsic_discard_if);
 117    discard->src[0] = nir_src_for_ssa(cond);
 118    nir_builder_instr_insert(b, &discard->instr);
 119
 120    shader->info.fs.uses_discard = true;
 121 }
 122
 123 static void
 124 lower_bitmap_impl(nir_function_impl *impl,
 125                   const nir_lower_bitmap_options *options)
 126 {
 127    nir_builder b;
 128
 129    nir_builder_init(&b, impl);
 130    b.cursor = nir_before_cf_list(&impl->body);
 131
 132    lower_bitmap(impl->function->shader, &b, options);
 133
 134    nir_metadata_preserve(impl, nir_metadata_block_index |
 135                                nir_metadata_dominance);
 136 }
 137
 138 void
 139 nir_lower_bitmap(nir_shader *shader,
 140                  const nir_lower_bitmap_options *options)
 141 {
 142    assert(shader->info.stage == MESA_SHADER_FRAGMENT);
 143
 144    lower_bitmap_impl(nir_shader_get_entrypoint(shader), options);
 145 }