src/gallium/drivers/panfrost/pan_blend_shaders.c

   1 /*
   2  * © Copyright 2018 Alyssa Rosenzweig
   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
  25 #include <stdio.h>
  26 #include "pan_blend_shaders.h"
  27 #include "pan_util.h"
  28 #include "midgard/midgard_compile.h"
  29 #include "compiler/nir/nir_builder.h"
  30 #include "nir/nir_lower_blend.h"
  31 #include "gallium/auxiliary/util/u_blend.h"
  32 #include "util/u_memory.h"
  33
  34 /*
  35  * Implements the command stream portion of programmatic blend shaders.
  36  *
  37  * On Midgard, common blending operations are accelerated by the fixed-function
  38  * blending pipeline. Panfrost supports this fast path via the code in
  39  * pan_blending.c. Nevertheless, uncommon blend modes (including some seemingly
  40  * simple modes present in ES2) require "blend shaders", a special internal
  41  * shader type used for programmable blending.
  42  *
  43  * Blend shaders operate during the normal blending time, but they bypass the
  44  * fixed-function blending pipeline and instead go straight to the Midgard
  45  * shader cores. The shaders themselves are essentially just fragment shaders,
  46  * making heavy use of uint8 arithmetic to manipulate RGB values for the
  47  * framebuffer.
  48  *
  49  * As is typical with Midgard, shader binaries must be accompanied by
  50  * information about the first tag (ORed with the bottom nibble of address,
  51  * like usual) and work registers. Work register count is specified in the
  52  * blend descriptor, as well as in the coresponding fragment shader's work
  53  * count. This suggests that blend shader invocation is tied to fragment shader
  54  * execution.
  55  *
  56  * ---
  57  *
  58  * As for blend shaders, they use the standard ISA.
  59  *
  60  * The source pixel colour, including alpha, is preloaded into r0 as a vec4 of
  61  * float32.
  62  *
  63  * The destination pixel colour must be loaded explicitly via load/store ops.
  64  * TODO: Investigate.
  65  *
  66  * They use fragment shader writeout; however, instead of writing a vec4 of
  67  * float32 for RGBA encoding, we writeout a vec4 of uint8, using 8-bit imov
  68  * instead of 32-bit fmov. The net result is that r0 encodes a single uint32
  69  * containing all four channels of the color.  Accordingly, the blend shader
  70  * epilogue has to scale all four channels by 255 and then type convert to a
  71  * uint8.
  72  *
  73  * ---
  74  *
  75  * Blend shaders hardcode constants. Naively, this requires recompilation each
  76  * time the blend color changes, which is a performance risk. Accordingly, we
  77  * 'cheat' a bit: instead of loading the constant, we compile a shader with a
  78  * dummy constant, exporting the offset to the immediate in the shader binary,
  79  * storing this generic binary and metadata in the CSO itself at CSO create
  80  * time.
  81  *
  82  * We then hot patch in the color into this shader at attachment / color change
  83  * time, allowing for CSO create to be the only expensive operation
  84  * (compilation).
  85  */
  86
  87 static nir_lower_blend_options
  88 nir_make_options(const struct pipe_blend_state *blend, unsigned i)
  89 {
  90         nir_lower_blend_options options;
  91
  92         if (blend->logicop_enable) {
  93             options.logicop_enable = true;
  94             options.logicop_func = blend->logicop_func;
  95             return options;
  96         }
  97
  98         options.logicop_enable = false;
  99
 100         /* If blend is disabled, we just use replace mode */
 101
 102         nir_lower_blend_channel rgb = {
 103                 .func = BLEND_FUNC_ADD,
 104                 .src_factor = BLEND_FACTOR_ZERO,
 105                 .invert_src_factor = true,
 106                 .dst_factor = BLEND_FACTOR_ZERO,
 107                 .invert_dst_factor = false
 108         };
 109
 110         nir_lower_blend_channel alpha = rgb;
 111
 112         if (blend->rt[i].blend_enable) {
 113                 rgb.func = util_blend_func_to_shader(blend->rt[i].rgb_func);
 114                 rgb.src_factor = util_blend_factor_to_shader(blend->rt[i].rgb_src_factor);
 115                 rgb.dst_factor = util_blend_factor_to_shader(blend->rt[i].rgb_dst_factor);
 116                 rgb.invert_src_factor = util_blend_factor_is_inverted(blend->rt[i].rgb_src_factor);
 117                 rgb.invert_dst_factor = util_blend_factor_is_inverted(blend->rt[i].rgb_dst_factor);
 118
 119                 alpha.func = util_blend_func_to_shader(blend->rt[i].alpha_func);
 120                 alpha.src_factor = util_blend_factor_to_shader(blend->rt[i].alpha_src_factor);
 121                 alpha.dst_factor = util_blend_factor_to_shader(blend->rt[i].alpha_dst_factor);
 122                 alpha.invert_src_factor = util_blend_factor_is_inverted(blend->rt[i].alpha_src_factor);
 123                 alpha.invert_dst_factor = util_blend_factor_is_inverted(blend->rt[i].alpha_dst_factor);
 124         }
 125
 126         options.rgb = rgb;
 127         options.alpha = alpha;
 128
 129         options.colormask = blend->rt[i].colormask;
 130
 131         return options;
 132 }
 133
 134 struct panfrost_blend_shader
 135 panfrost_compile_blend_shader(
 136         struct panfrost_context *ctx,
 137         struct pipe_blend_state *cso,
 138         enum pipe_format format,
 139         unsigned rt)
 140 {
 141         struct panfrost_screen *screen = pan_screen(ctx->base.screen);
 142         struct panfrost_blend_shader res;
 143
 144         res.ctx = ctx;
 145
 146         /* Build the shader */
 147
 148         nir_shader *shader = nir_shader_create(NULL, MESA_SHADER_FRAGMENT, &midgard_nir_options, NULL);
 149         nir_function *fn = nir_function_create(shader, "main");
 150         nir_function_impl *impl = nir_function_impl_create(fn);
 151
 152         /* Create the blend variables */
 153
 154         nir_variable *c_src = nir_variable_create(shader, nir_var_shader_in, glsl_vector_type(GLSL_TYPE_FLOAT, 4), "gl_Color");
 155         nir_variable *c_out = nir_variable_create(shader, nir_var_shader_out, glsl_vector_type(GLSL_TYPE_FLOAT, 4), "gl_FragColor");
 156
 157         c_src->data.location = VARYING_SLOT_COL0;
 158         c_out->data.location = FRAG_RESULT_COLOR;
 159
 160         /* Setup nir_builder */
 161
 162         nir_builder _b;
 163         nir_builder *b = &_b;
 164         nir_builder_init(b, impl);
 165         b->cursor = nir_before_block(nir_start_block(impl));
 166
 167         /* Setup inputs */
 168
 169         nir_ssa_def *s_src = nir_load_var(b, c_src);
 170
 171         /* Build a trivial blend shader */
 172         nir_store_var(b, c_out, s_src, 0xFF);
 173
 174         nir_lower_blend_options options =
 175                 nir_make_options(cso, rt);
 176         NIR_PASS_V(shader, nir_lower_blend, options);
 177
 178         NIR_PASS_V(shader, nir_lower_framebuffer, format, screen->gpu_id);
 179
 180         /* Compile the built shader */
 181
 182         midgard_program program;
 183         midgard_compile_shader_nir(shader, &program, true, rt, screen->gpu_id, false);
 184
 185         /* Allow us to patch later */
 186         res.patch_index = program.blend_patch_offset;
 187         res.first_tag = program.first_tag;
 188         res.size = program.compiled.size;
 189         res.buffer = program.compiled.data;
 190
 191         return res;
 192 }