On 21 May 2012 18:00, Ian Romanick <i...@freedesktop.org> wrote:
> On 05/11/2012 11:03 AM, Paul Berry wrote:
>
>> This patch modifies the function brw_blorp_blit_program::texel_**fetch()
>> to emit the SI (sample index) argument to the SAMPLE_LD message when
>> reading from a sample index other than zero.
>>
>> Previously we were using the ugly hack of configuring multisampled
>> source surfaces as single-sampled, and accessing sample indices other
>> than zero by swizzling the texture coordinates in the WM program.
>> ---
>> src/mesa/drivers/dri/i965/brw_**blorp.cpp | 7 +---
>> src/mesa/drivers/dri/i965/brw_**blorp_blit.cpp | 45
>> ++++++++++++++++---------
>> 2 files changed, 31 insertions(+), 21 deletions(-)
>>
>> diff --git a/src/mesa/drivers/dri/i965/**brw_blorp.cpp
>> b/src/mesa/drivers/dri/i965/**brw_blorp.cpp
>> index 8e22511..f6aff44 100644
>> --- a/src/mesa/drivers/dri/i965/**brw_blorp.cpp
>> +++ b/src/mesa/drivers/dri/i965/**brw_blorp.cpp
>> @@ -57,19 +57,16 @@ brw_blorp_surface_info::set(**struct
>> intel_mipmap_tree *mt,
>> unsigned int level, unsigned int layer)
>> {
>> brw_blorp_mip_info::set(mt, level, layer);
>> + this->num_samples = mt->num_samples;
>>
>> if (mt->format == MESA_FORMAT_S8) {
>> /* The miptree is a W-tiled stencil buffer. Surface states can't
>> be set
>> * up for W tiling, so we'll need to use Y tiling and have the WM
>> - * program swizzle the coordinates. Furthermore, we need to set
>> up the
>> - * surface state as single-sampled, because the memory layout of
>> related
>> - * samples doesn't match between W and Y tiling.
>> + * program swizzle the coordinates.
>> */
>> this->map_stencil_as_y_tiled = true;
>> - this->num_samples = 0;
>> } else {
>> this->map_stencil_as_y_tiled = false;
>> - this->num_samples = mt->num_samples;
>> }
>> }
>>
>> diff --git a/src/mesa/drivers/dri/i965/**brw_blorp_blit.cpp
>> b/src/mesa/drivers/dri/i965/**brw_blorp_blit.cpp
>> index d3ab0ba..e985fad 100644
>> --- a/src/mesa/drivers/dri/i965/**brw_blorp_blit.cpp
>> +++ b/src/mesa/drivers/dri/i965/**brw_blorp_blit.cpp
>> @@ -220,6 +220,8 @@ enum sampler_message_arg
>> SAMPLER_MESSAGE_ARG_V_FLOAT,
>> SAMPLER_MESSAGE_ARG_U_INT,
>> SAMPLER_MESSAGE_ARG_V_INT,
>> + SAMPLER_MESSAGE_ARG_SI_INT,
>> + SAMPLER_MESSAGE_ARG_ZERO_INT,
>> };
>>
>> /**
>> @@ -435,14 +437,6 @@ brw_blorp_blit_program::**compile(struct
>> brw_context *brw,
>> GLuint *program_size)
>> {
>> /* Sanity checks */
>> - if (key->src_tiled_w) {
>> - /* If the source image is W tiled, then tex_samples must be 0.
>> - * Otherwise, after conversion between W and Y tiling, there's no
>> - * guarantee that the sample index will be 0.
>> - */
>> - assert(key->tex_samples == 0);
>> - }
>> -
>> if (key->dst_tiled_w) {
>> /* If the destination image is W tiled, then dst_samples must be 0.
>> * Otherwise, after conversion between W and Y tiling, there's no
>> @@ -920,13 +914,15 @@ brw_blorp_blit_program::**sample()
>> void
>> brw_blorp_blit_program::texel_**fetch()
>> {
>> - static const sampler_message_arg args[2] = {
>> + static const sampler_message_arg args[5] = {
>> SAMPLER_MESSAGE_ARG_U_INT,
>> - SAMPLER_MESSAGE_ARG_V_INT
>> + SAMPLER_MESSAGE_ARG_V_INT,
>> + SAMPLER_MESSAGE_ARG_ZERO_INT, /* R */
>> + SAMPLER_MESSAGE_ARG_ZERO_INT, /* LOD */
>> + SAMPLER_MESSAGE_ARG_SI_INT
>> };
>>
>> - assert(s_is_zero);
>> - texture_lookup(GEN5_SAMPLER_**MESSAGE_SAMPLE_LD, args,
>> ARRAY_SIZE(args));
>> + texture_lookup(GEN5_SAMPLER_**MESSAGE_SAMPLE_LD, args, s_is_zero ? 2
>> : 5);
>> }
>>
>> void
>> @@ -960,6 +956,15 @@ brw_blorp_blit_program::**texture_lookup(GLuint
>> msg_type,
>> case SAMPLER_MESSAGE_ARG_V_INT:
>> expand_to_32_bits(Y, mrf);
>> break;
>> + case SAMPLER_MESSAGE_ARG_SI_INT:
>> + if (s_is_zero)
>> + brw_MOV(&func, mrf, brw_imm_ud(0));
>> + else
>> + expand_to_32_bits(S, mrf);
>> + break;
>>
>
> It seems like up above you've guaranteed that you won't see
> SAMPLER_MESSAGE_ARG_SI_INT when s_is_zero. Is this extra check necessary?
>
You're certainly right for Gen6. On Gen7 it's necessary, though, because
on Gen7, when downsampling, the fragment shader has to grab all N samples
(using N texel fetches) and blend them manually. When it's grabbing sample
0, we will see SAMPLER_MESSAGE_ARG_SI_INT with s_is_zero=true.
I'll add a comment above the "if (s_is_zero)" line to explain why it's
necessary.
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