[Mesa-dev] [PATCH V2 08/12] i965: Add FS backend for builtin gl_SampleID
Anuj Phogat
anuj.phogat at gmail.com
Tue Oct 29 00:26:56 CET 2013
On Mon, Oct 28, 2013 at 3:23 PM, Paul Berry <stereotype441 at gmail.com> wrote:
> On 25 October 2013 16:45, Anuj Phogat <anuj.phogat at gmail.com> wrote:
>
>> V2:
>> - Update comments
>> - Make changes to support simd16 mode.
>> - Add compute_sample_id variables in brw_wm_prog_key
>> - Add a special backend instruction to compute sample_id.
>>
>> Signed-off-by: Anuj Phogat <anuj.phogat at gmail.com>
>> ---
>> src/mesa/drivers/dri/i965/brw_defines.h | 1 +
>> src/mesa/drivers/dri/i965/brw_fs.cpp | 49
>> ++++++++++++++++++++++++++
>> src/mesa/drivers/dri/i965/brw_fs.h | 7 ++++
>> src/mesa/drivers/dri/i965/brw_fs_generator.cpp | 27 ++++++++++++++
>> src/mesa/drivers/dri/i965/brw_fs_visitor.cpp | 2 ++
>> src/mesa/drivers/dri/i965/brw_wm.c | 6 ++++
>> src/mesa/drivers/dri/i965/brw_wm.h | 1 +
>> 7 files changed, 93 insertions(+)
>>
>> diff --git a/src/mesa/drivers/dri/i965/brw_defines.h
>> b/src/mesa/drivers/dri/i965/brw_defines.h
>> index 5ba9d45..f3c994b 100644
>> --- a/src/mesa/drivers/dri/i965/brw_defines.h
>> +++ b/src/mesa/drivers/dri/i965/brw_defines.h
>> @@ -788,6 +788,7 @@ enum opcode {
>> FS_OPCODE_VARYING_PULL_CONSTANT_LOAD_GEN7,
>> FS_OPCODE_MOV_DISPATCH_TO_FLAGS,
>> FS_OPCODE_DISCARD_JUMP,
>> + FS_OPCODE_SET_SAMPLE_ID,
>> FS_OPCODE_SET_SIMD4X2_OFFSET,
>> FS_OPCODE_PACK_HALF_2x16_SPLIT,
>> FS_OPCODE_UNPACK_HALF_2x16_SPLIT_X,
>> diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp
>> b/src/mesa/drivers/dri/i965/brw_fs.cpp
>> index 0f8213e..5773c6f 100644
>> --- a/src/mesa/drivers/dri/i965/brw_fs.cpp
>> +++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
>> @@ -1176,6 +1176,55 @@ fs_visitor::emit_samplepos_setup(ir_variable *ir)
>> return reg;
>> }
>>
>> +fs_reg *
>> +fs_visitor::emit_sampleid_setup(ir_variable *ir)
>> +{
>> + assert(brw->gen >= 6);
>> +
>> + this->current_annotation = "compute sample id";
>> + fs_reg *reg = new(this->mem_ctx) fs_reg(this, ir->type);
>> +
>> + if (c->key.compute_sample_id) {
>> + fs_reg t1 = fs_reg(this, glsl_type::int_type);
>> + fs_reg t2 = fs_reg(this, glsl_type::int_type);
>> + t2.type = BRW_REGISTER_TYPE_UW;
>> +
>> + /* The PS will be run in MSDISPMODE_PERSAMPLE. For example with
>> + * 8x multisampling, subspan 0 will represent sample N (where N
>> + * is 0, 2, 4 or 6), subspan 1 will represent sample 1, 3, 5 or
>> + * 7. We can find the value of N by looking at R0.0 bits 7:6
>> + * ("Starting Sample Pair Index (SSPI)") and multiplying by two
>> + * (since samples are always delivered in pairs). That is, we
>> + * compute 2*((R0.0 & 0xc0) >> 6) == (R0.0 & 0xc0) >> 5. Then
>> + * we need to add N to the sequence (0, 0, 0, 0, 1, 1, 1, 1) in
>> + * case of SIMD8 and sequence (0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2,
>> + * 2, 3, 3, 3, 3) in case of SIMD16. We compute this sequence by
>> + * populating a temporary variable with the sequence (0, 1, 2, 3),
>> + * and then reading from it using vstride=1, width=4, hstride=0.
>> + * These computations hold good for 4x multisampling as well.
>> + */
>> + emit(BRW_OPCODE_AND, t1,
>> + fs_reg(retype(brw_vec1_grf(0, 0), BRW_REGISTER_TYPE_D)),
>> + fs_reg(brw_imm_d(0xc0)));
>> + emit(BRW_OPCODE_SHR, t1, t1, fs_reg(5));
>> + /* This works for both SIMD8 and SIMD16 */
>> + emit(MOV(t2, brw_imm_v(0x3210)));
>>
>
> These three instructions need to be emitted with force_writemask_all =
> true, just in case the fragment shader is dispatched with channel 0
> disabled.
>
Isn't this covered by calling brw_set_mask_control(p, BRW_MASK_DISABLE) in
fs_generator::generate_set_sample_id() function?
>
>
+ /* This special instruction takes care of setting vstride=1,
>> + * width=4, hstride=0 of t2 during an ADD instruction.
>> + */
>> + emit(FS_OPCODE_SET_SAMPLE_ID, *reg, t1, t2);
>>
>
> I don't believe this will work, because type conversions can only be done
> in MOV instructions. reg and t1 are UD, but FS_OPCODE_SET_SAMPLE_ID is
> going to cast t2 as UW. Have you tried running this code in the simulator
> to see if it complains?
>
Initially, I wasn't sure either. But after looking at PRM, ADD instruction
seems to allow src and dst registers to be B, W or D types. I also verified
this on simulator.
>From Ivybridge PRM vol. 4, part 3, page 147:
Src Types Dst Type
*B, *W, *D *B, *W, *D
*B, *W, *D F
F F
DF DF
It's same for SNB.
>
> I believe what you need to do is use a MOV to copy the (0, 1, 2, 3)
> sequence to a full-size UD register, and then do the ADD as a final
> instruction.
>
I tried to avoid this extra instruction.
>
> (Note that the reason this wasn't necessary in blorp is that blorp uses UW
> for a lot of its temporary registers, so in the corresponding blorp code
> there's no type conversion going on).
>
>
>> + }
>> + else {
>>
>
> Style nit-pick: generally we put "} else {" on a single line.
>
ok.
>
>
>> + /* As per GL_ARB_sample_shading specification:
>> + * "When rendering to a non-multisample buffer, or if multisample
>> + * rasterization is disabled, gl_SampleID will always be zero."
>> + */
>> + emit(BRW_OPCODE_MOV, *reg, fs_reg(0));
>> + }
>> +
>> + return reg;
>> +}
>> +
>> fs_reg
>> fs_visitor::fix_math_operand(fs_reg src)
>> {
>> diff --git a/src/mesa/drivers/dri/i965/brw_fs.h
>> b/src/mesa/drivers/dri/i965/brw_fs.h
>> index db5df39..8a1a414 100644
>> --- a/src/mesa/drivers/dri/i965/brw_fs.h
>> +++ b/src/mesa/drivers/dri/i965/brw_fs.h
>> @@ -334,6 +334,7 @@ public:
>> bool is_centroid);
>> fs_reg *emit_frontfacing_interpolation(ir_variable *ir);
>> fs_reg *emit_samplepos_setup(ir_variable *ir);
>> + fs_reg *emit_sampleid_setup(ir_variable *ir);
>> fs_reg *emit_general_interpolation(ir_variable *ir);
>> void emit_interpolation_setup_gen4();
>> void emit_interpolation_setup_gen6();
>> @@ -538,6 +539,12 @@ private:
>> struct brw_reg index,
>> struct brw_reg offset);
>> void generate_mov_dispatch_to_flags(fs_inst *inst);
>> +
>> + void generate_set_sample_id(fs_inst *inst,
>> + struct brw_reg dst,
>> + struct brw_reg src0,
>> + struct brw_reg src1);
>> +
>> void generate_set_simd4x2_offset(fs_inst *inst,
>> struct brw_reg dst,
>> struct brw_reg offset);
>> diff --git a/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
>> b/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
>> index fa15f7b..4f15ed7 100644
>> --- a/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
>> +++ b/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
>> @@ -1024,6 +1024,29 @@ fs_generator::generate_set_simd4x2_offset(fs_inst
>> *inst,
>> brw_pop_insn_state(p);
>> }
>>
>> +/* Sets vstride=1, width=4, hstride=0 of register src1 during
>> + * the ADD instruction.
>> + */
>> +void
>> +fs_generator::generate_set_sample_id(fs_inst *inst,
>> + struct brw_reg dst,
>> + struct brw_reg src0,
>> + struct brw_reg src1)
>> +{
>> + assert(dst.type == BRW_REGISTER_TYPE_D ||
>> + dst.type == BRW_REGISTER_TYPE_UD);
>> + assert(src0.type == BRW_REGISTER_TYPE_D ||
>> + src0.type == BRW_REGISTER_TYPE_UD);
>> + if (dispatch_width == 16)
>> + dst = vec16(dst);
>> + brw_push_insn_state(p);
>> + brw_set_compression_control(p, BRW_COMPRESSION_NONE);
>> + brw_set_mask_control(p, BRW_MASK_DISABLE);
>> + brw_ADD(p, dst, src0, stride(retype(brw_vec1_reg(src1.file, src1.nr,
>> 0),
>> + BRW_REGISTER_TYPE_UW), 1, 4, 0));
>>
> + brw_pop_insn_state(p);
>> +}
>> +
>> /**
>> * Change the register's data type from UD to W, doubling the strides in
>> order
>> * to compensate for halving the data type width.
>> @@ -1553,6 +1576,10 @@ fs_generator::generate_code(exec_list
>> *instructions)
>> generate_set_simd4x2_offset(inst, dst, src[0]);
>> break;
>>
>> + case FS_OPCODE_SET_SAMPLE_ID:
>> + generate_set_sample_id(inst, dst, src[0], src[1]);
>> + break;
>> +
>> case FS_OPCODE_PACK_HALF_2x16_SPLIT:
>> generate_pack_half_2x16_split(inst, dst, src[0], src[1]);
>> break;
>> diff --git a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
>> b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
>> index 51972fe..7a6a0b5 100644
>> --- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
>> +++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
>> @@ -129,6 +129,8 @@ fs_visitor::visit(ir_variable *ir)
>> } else if (ir->mode == ir_var_system_value) {
>> if (!strcmp(ir->name, "gl_SamplePosition")) {
>> reg = emit_samplepos_setup(ir);
>> + } else if (!strcmp(ir->name, "gl_SampleID")) {
>> + reg = emit_sampleid_setup(ir);
>>
>
> As in the previous patch, I believe you can just use ir->location rather
> than doing a strcmp on the name.
>
yeah that's easy to use.
> }
>> }
>>
>> diff --git a/src/mesa/drivers/dri/i965/brw_wm.c
>> b/src/mesa/drivers/dri/i965/brw_wm.c
>> index d2a5a9f..afb62fb 100644
>> --- a/src/mesa/drivers/dri/i965/brw_wm.c
>> +++ b/src/mesa/drivers/dri/i965/brw_wm.c
>> @@ -367,6 +367,7 @@ static void brw_wm_populate_key( struct brw_context
>> *brw,
>> GLuint lookup = 0;
>> GLuint line_aa;
>> bool program_uses_dfdy = fp->program.UsesDFdy;
>> + bool multisample_fbo = ctx->DrawBuffer->Visual.samples > 1;
>>
>> memset(key, 0, sizeof(*key));
>>
>> @@ -489,6 +490,11 @@ static void brw_wm_populate_key( struct brw_context
>> *brw,
>> _mesa_get_min_invocations_per_fragment(ctx, &fp->program) > 1 &&
>> fp->program.Base.SystemValuesRead & SYSTEM_BIT_SAMPLE_POS;
>>
>> + key->compute_sample_id =
>> + multisample_fbo &&
>> + ctx->Multisample.Enabled &&
>> + fp->program.Base.SystemValuesRead & SYSTEM_BIT_SAMPLE_ID;
>>
>
> I always forget the precedence rules between & and &&. Can we put
> parenthesis around (fp->program.Base.SystemValuesRead &
> SYSTEM_BIT_SAMPLE_ID) just to be on the safe side?
>
I'll put the braces for clarity.
>
>
+
>> /* BRW_NEW_VUE_MAP_GEOM_OUT */
>> if (brw->gen < 6 || _mesa_bitcount_64(fp->program.Base.InputsRead &
>> BRW_FS_VARYING_INPUT_MASK) > 16)
>> diff --git a/src/mesa/drivers/dri/i965/brw_wm.h
>> b/src/mesa/drivers/dri/i965/brw_wm.h
>> index eb740ad..f5823f4 100644
>> --- a/src/mesa/drivers/dri/i965/brw_wm.h
>> +++ b/src/mesa/drivers/dri/i965/brw_wm.h
>> @@ -66,6 +66,7 @@ struct brw_wm_prog_key {
>> GLuint render_to_fbo:1;
>> GLuint clamp_fragment_color:1;
>> GLuint compute_pos_offset:1;
>> + GLuint compute_sample_id:1;
>> GLuint line_aa:2;
>> GLuint high_quality_derivatives:1;
>>
>> --
>> 1.8.1.4
>>
>>
>
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