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 "midgard/midgard_compile.h"
  28 #include "compiler/nir/nir_builder.h"
  29 //#include "gallium/auxiliary/nir/nir_lower_blend.h"
  30
  31 /*
  32  * Implements the command stream portion of programmatic blend shaders.
  33  *
  34  * On Midgard, common blending operations are accelerated by the fixed-function
  35  * blending pipeline. Panfrost supports this fast path via the code in
  36  * pan_blending.c. Nevertheless, uncommon blend modes (including some seemingly
  37  * simple modes present in ES2) require "blend shaders", a special internal
  38  * shader type used for programmable blending.
  39  *
  40  * Blend shaders operate during the normal blending time, but they bypass the
  41  * fixed-function blending pipeline and instead go straight to the Midgard
  42  * shader cores. The shaders themselves are essentially just fragment shaders,
  43  * making heavy use of uint8 arithmetic to manipulate RGB values for the
  44  * framebuffer.
  45  *
  46  * As is typical with Midgard, shader binaries must be accompanied by
  47  * information about the first tag (ORed with the bottom nibble of address,
  48  * like usual) and work registers. Work register count is specified in the
  49  * blend descriptor, as well as in the coresponding fragment shader's work
  50  * count. This suggests that blend shader invocation is tied to fragment shader
  51  * execution.
  52  *
  53  * ---
  54  *
  55  * As for blend shaders, they use the standard ISA.
  56  *
  57  * The source pixel colour, including alpha, is preloaded into r0 as a vec4 of
  58  * float32.
  59  *
  60  * The destination pixel colour must be loaded explicitly via load/store ops.
  61  * TODO: Investigate.
  62  *
  63  * They use fragment shader writeout; however, instead of writing a vec4 of
  64  * float32 for RGBA encoding, we writeout a vec4 of uint8, using 8-bit imov
  65  * instead of 32-bit fmov. The net result is that r0 encodes a single uint32
  66  * containing all four channels of the color.  Accordingly, the blend shader
  67  * epilogue has to scale all four channels by 255 and then type convert to a
  68  * uint8.
  69  *
  70  * ---
  71  *
  72  * Blend shaders hardcode constants. Naively, this requires recompilation each
  73  * time the blend color changes, which is a performance risk. Accordingly, we
  74  * 'cheat' a bit: instead of loading the constant, we compile a shader with a
  75  * dummy constant, exporting the offset to the immediate in the shader binary,
  76  * storing this generic binary and metadata in the CSO itself at CSO create
  77  * time.
  78  *
  79  * We then hot patch in the color into this shader at attachment / color change
  80  * time, allowing for CSO create to be the only expensive operation
  81  * (compilation).
  82  */
  83
  84 static nir_ssa_def *
  85 nir_blending_f(const struct pipe_rt_blend_state *blend, nir_builder *b,
  86                 nir_ssa_def *s_src, nir_ssa_def *s_dst, nir_ssa_def *s_con)
  87 {
  88         /* Stub, to be replaced by the real implementation when that is
  89          * upstream (pending on a rewrite to be Gallium agnostic) */
  90
  91         return s_src;
  92 }
  93
  94 void
  95 panfrost_make_blend_shader(struct panfrost_context *ctx, struct panfrost_blend_state *cso, const struct pipe_blend_color *blend_color)
  96 {
  97         const struct pipe_rt_blend_state *blend = &cso->base.rt[0];
  98         mali_ptr *out = &cso->blend_shader;
  99
 100         /* Build the shader */
 101
 102         nir_shader *shader = nir_shader_create(NULL, MESA_SHADER_FRAGMENT, &midgard_nir_options, NULL);
 103         nir_function *fn = nir_function_create(shader, "main");
 104         nir_function_impl *impl = nir_function_impl_create(fn);
 105
 106         /* Create the blend variables */
 107
 108         nir_variable *c_src = nir_variable_create(shader, nir_var_shader_in, glsl_vector_type(GLSL_TYPE_FLOAT, 4), "gl_Color");
 109         nir_variable *c_dst = nir_variable_create(shader, nir_var_shader_in, glsl_vector_type(GLSL_TYPE_FLOAT, 4), "gl_SecondaryColor");
 110         nir_variable *c_out = nir_variable_create(shader, nir_var_shader_out, glsl_vector_type(GLSL_TYPE_FLOAT, 4), "gl_FragColor");
 111         nir_variable *c_con = nir_variable_create(shader, nir_var_uniform, glsl_vector_type(GLSL_TYPE_FLOAT, 4), "constant");
 112
 113         c_src->data.location = VARYING_SLOT_COL0;
 114         c_dst->data.location = VARYING_SLOT_COL1;
 115         c_out->data.location = FRAG_RESULT_COLOR;
 116
 117         /* Setup nir_builder */
 118
 119         nir_builder _b;
 120         nir_builder *b = &_b;
 121         nir_builder_init(b, impl);
 122         b->cursor = nir_before_block(nir_start_block(impl));
 123
 124         /* Setup inputs */
 125
 126         nir_ssa_def *s_src = nir_load_var(b, c_src);
 127         nir_ssa_def *s_dst = nir_load_var(b, c_dst);
 128         nir_ssa_def *s_con = nir_load_var(b, c_con);
 129
 130         /* Build a trivial blend shader */
 131         nir_store_var(b, c_out, nir_blending_f(blend, b, s_src, s_dst, s_con), 0xFF);
 132
 133         nir_print_shader(shader, stdout);
 134
 135         /* Compile the built shader */
 136
 137         midgard_program program;
 138         midgard_compile_shader_nir(shader, &program, true);
 139
 140
 141         /* Upload the shader */
 142
 143         int size = program.compiled.size;
 144         uint8_t *dst = program.compiled.data;
 145
 146         /* Hot patch in constant color */
 147
 148         if (program.blend_patch_offset >= 0) {
 149                 float *hot_color = (float *) (dst + program.blend_patch_offset);
 150
 151                 for (int c = 0; c < 4; ++c)
 152                         hot_color[c] = blend_color->color[c];
 153         }
 154
 155         *out = panfrost_upload(&ctx->shaders, dst, size, true) | program.first_tag;
 156
 157         /* We need to switch to shader mode */
 158         cso->has_blend_shader = true;
 159
 160         /* At least two work registers are needed due to an encoding quirk */
 161         cso->blend_work_count = MAX2(program.work_register_count, 2);
 162 }