Re: [Mesa-dev] [PATCH 09/11] nir: add lowering stage for user-clip-planes / clipdist

[Erik Faye-Lund]

On Tue, Sep 15, 2015 at 6:49 PM, Rob Clark  wrote:
> On Tue, Sep 15, 2015 at 12:39 PM, Erik Faye-Lund  wrote:
>> On Mon, Sep 14, 2015 at 11:53 AM, Erik Faye-Lund  wrote:
>>> On Sun, Sep 13, 2015 at 5:51 PM, Rob Clark  wrote:
 From: Rob Clark 

 The vertex shader lowering adds calculation for CLIPDIST, if needed
 (ie. user-clip-planes), and the frag shader lowering adds conditional
 kills based on CLIPDIST value (which should be treated as a normal
 interpolated varying by the driver).
>>>
>>> 
>>>
 +
 +/*
 + * FS lowering
 + */
 +
 +static void
 +lower_clip_fs(nir_function_impl *impl, unsigned ucp_enables,
 +  nir_variable **in)
 +{
 +   nir_ssa_def *clipdist[MAX_CLIP_PLANES];
 +   nir_builder b;
 +
 +   nir_builder_init(, impl);
 +   b.cursor = nir_before_cf_list(>body);
 +
 +   if (ucp_enables & 0x0f)
 +  load_clipdist_input(, in[0], [0]);
 +   if (ucp_enables & 0xf0)
 +  load_clipdist_input(, in[1], [4]);
 +
 +   for (int plane = 0; plane < MAX_CLIP_PLANES; plane++) {
 +  if (ucp_enables & (1 << plane)) {
 + nir_intrinsic_instr *discard;
 + nir_ssa_def *cond;
 +
 + cond = nir_flt(, clipdist[plane], nir_imm_float(, 0.0));
 +
 + discard = nir_intrinsic_instr_create(b.shader,
 +  nir_intrinsic_discard_if);
 + discard->src[0] = nir_src_for_ssa(cond);
 + nir_builder_instr_insert(, >instr);
>>>
>>> I think it's worth noting that this isn't *strictly* correct for
>>> multi-sampling, unless the shader is s run with per-sample shading
>>> (ala GL_ARB_sample_shading). Otherwise, all samples for a pixel will
>>> get the same discard-condition, leading to aliasing along the
>>> resulting edge.
>>>
>>> That being said, per-fragment clipping is better than no clipping, so
>>> it's clearly an improvement.
>>
>> So, in order to do this correctly for MSAA, I guess you'd need to use
>> SYSTEM_VALUE_SAMPLE_POS and FRAG_RESULT_SAMPLE_MASK, to perform
>> alpha-testing for each sample-point.
>
> I think it still involves being able to run the frag shader once per
> sample..  although blob does seem to expose OES_sample_shading so
> maybe that is possible?

No, that's the whole point of the above, to not have to run the entire
shader per sample, only the clipping-bit.

> I guess I'd care about it more once I supported MSAA ;-)
>
> (and tbh, all this effort was mostly just to get neverball to render
> correctly :-P)

Oh, I just meant that it might be neat to add to the commit message. I
wouldn't go ahead and implement this just yet.
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Re: [Mesa-dev] [PATCH 09/11] nir: add lowering stage for user-clip-planes / clipdist

[Erik Faye-Lund]

On Mon, Sep 14, 2015 at 11:53 AM, Erik Faye-Lund  wrote:
> On Sun, Sep 13, 2015 at 5:51 PM, Rob Clark  wrote:
>> From: Rob Clark 
>>
>> The vertex shader lowering adds calculation for CLIPDIST, if needed
>> (ie. user-clip-planes), and the frag shader lowering adds conditional
>> kills based on CLIPDIST value (which should be treated as a normal
>> interpolated varying by the driver).
>
> 
>
>> +
>> +/*
>> + * FS lowering
>> + */
>> +
>> +static void
>> +lower_clip_fs(nir_function_impl *impl, unsigned ucp_enables,
>> +  nir_variable **in)
>> +{
>> +   nir_ssa_def *clipdist[MAX_CLIP_PLANES];
>> +   nir_builder b;
>> +
>> +   nir_builder_init(, impl);
>> +   b.cursor = nir_before_cf_list(>body);
>> +
>> +   if (ucp_enables & 0x0f)
>> +  load_clipdist_input(, in[0], [0]);
>> +   if (ucp_enables & 0xf0)
>> +  load_clipdist_input(, in[1], [4]);
>> +
>> +   for (int plane = 0; plane < MAX_CLIP_PLANES; plane++) {
>> +  if (ucp_enables & (1 << plane)) {
>> + nir_intrinsic_instr *discard;
>> + nir_ssa_def *cond;
>> +
>> + cond = nir_flt(, clipdist[plane], nir_imm_float(, 0.0));
>> +
>> + discard = nir_intrinsic_instr_create(b.shader,
>> +  nir_intrinsic_discard_if);
>> + discard->src[0] = nir_src_for_ssa(cond);
>> + nir_builder_instr_insert(, >instr);
>
> I think it's worth noting that this isn't *strictly* correct for
> multi-sampling, unless the shader is s run with per-sample shading
> (ala GL_ARB_sample_shading). Otherwise, all samples for a pixel will
> get the same discard-condition, leading to aliasing along the
> resulting edge.
>
> That being said, per-fragment clipping is better than no clipping, so
> it's clearly an improvement.

So, in order to do this correctly for MSAA, I guess you'd need to use
SYSTEM_VALUE_SAMPLE_POS and FRAG_RESULT_SAMPLE_MASK, to perform
alpha-testing for each sample-point.
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Re: [Mesa-dev] [PATCH 09/11] nir: add lowering stage for user-clip-planes / clipdist

[Ilia Mirkin]

On Tue, Sep 15, 2015 at 12:39 PM, Erik Faye-Lund  wrote:
> On Mon, Sep 14, 2015 at 11:53 AM, Erik Faye-Lund  wrote:
>> On Sun, Sep 13, 2015 at 5:51 PM, Rob Clark  wrote:
>>> From: Rob Clark 
>>>
>>> The vertex shader lowering adds calculation for CLIPDIST, if needed
>>> (ie. user-clip-planes), and the frag shader lowering adds conditional
>>> kills based on CLIPDIST value (which should be treated as a normal
>>> interpolated varying by the driver).
>>
>> 
>>
>>> +
>>> +/*
>>> + * FS lowering
>>> + */
>>> +
>>> +static void
>>> +lower_clip_fs(nir_function_impl *impl, unsigned ucp_enables,
>>> +  nir_variable **in)
>>> +{
>>> +   nir_ssa_def *clipdist[MAX_CLIP_PLANES];
>>> +   nir_builder b;
>>> +
>>> +   nir_builder_init(, impl);
>>> +   b.cursor = nir_before_cf_list(>body);
>>> +
>>> +   if (ucp_enables & 0x0f)
>>> +  load_clipdist_input(, in[0], [0]);
>>> +   if (ucp_enables & 0xf0)
>>> +  load_clipdist_input(, in[1], [4]);
>>> +
>>> +   for (int plane = 0; plane < MAX_CLIP_PLANES; plane++) {
>>> +  if (ucp_enables & (1 << plane)) {
>>> + nir_intrinsic_instr *discard;
>>> + nir_ssa_def *cond;
>>> +
>>> + cond = nir_flt(, clipdist[plane], nir_imm_float(, 0.0));
>>> +
>>> + discard = nir_intrinsic_instr_create(b.shader,
>>> +  nir_intrinsic_discard_if);
>>> + discard->src[0] = nir_src_for_ssa(cond);
>>> + nir_builder_instr_insert(, >instr);
>>
>> I think it's worth noting that this isn't *strictly* correct for
>> multi-sampling, unless the shader is s run with per-sample shading
>> (ala GL_ARB_sample_shading). Otherwise, all samples for a pixel will
>> get the same discard-condition, leading to aliasing along the
>> resulting edge.
>>
>> That being said, per-fragment clipping is better than no clipping, so
>> it's clearly an improvement.
>
> So, in order to do this correctly for MSAA, I guess you'd need to use
> SYSTEM_VALUE_SAMPLE_POS and FRAG_RESULT_SAMPLE_MASK, to perform
> alpha-testing for each sample-point.

Perhaps worth mentioning that a3xx doesn't *actually* support sample
shading, although it does appear to have a mode where a single
invocation can supply all the samples (but then you can only have a
single RT). Ultimately all it needs to do is be able to compute a
sample mask though, which *is* supported, but you'd need to do the
per-sample interp "by hand" (although afaik the IJ components are
provided... somewhere). a4xx brings real per-sample shading from what
I can tell though. No idea about vc4's capabilities.

This is all a bit moot of course since none of the relevant drivers
actually has support for even basic MSAA, nevermind sample shading.
However having a piglit test that covers this would be neat... I guess
you could clip a pixel in half and make sure that the resolved result
is some in-between color? Lots of implementation-dependent stuff going
on in there though.

  -ilia
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Re: [Mesa-dev] [PATCH 09/11] nir: add lowering stage for user-clip-planes / clipdist

[Rob Clark]

On Tue, Sep 15, 2015 at 12:39 PM, Erik Faye-Lund  wrote:
> On Mon, Sep 14, 2015 at 11:53 AM, Erik Faye-Lund  wrote:
>> On Sun, Sep 13, 2015 at 5:51 PM, Rob Clark  wrote:
>>> From: Rob Clark 
>>>
>>> The vertex shader lowering adds calculation for CLIPDIST, if needed
>>> (ie. user-clip-planes), and the frag shader lowering adds conditional
>>> kills based on CLIPDIST value (which should be treated as a normal
>>> interpolated varying by the driver).
>>
>> 
>>
>>> +
>>> +/*
>>> + * FS lowering
>>> + */
>>> +
>>> +static void
>>> +lower_clip_fs(nir_function_impl *impl, unsigned ucp_enables,
>>> +  nir_variable **in)
>>> +{
>>> +   nir_ssa_def *clipdist[MAX_CLIP_PLANES];
>>> +   nir_builder b;
>>> +
>>> +   nir_builder_init(, impl);
>>> +   b.cursor = nir_before_cf_list(>body);
>>> +
>>> +   if (ucp_enables & 0x0f)
>>> +  load_clipdist_input(, in[0], [0]);
>>> +   if (ucp_enables & 0xf0)
>>> +  load_clipdist_input(, in[1], [4]);
>>> +
>>> +   for (int plane = 0; plane < MAX_CLIP_PLANES; plane++) {
>>> +  if (ucp_enables & (1 << plane)) {
>>> + nir_intrinsic_instr *discard;
>>> + nir_ssa_def *cond;
>>> +
>>> + cond = nir_flt(, clipdist[plane], nir_imm_float(, 0.0));
>>> +
>>> + discard = nir_intrinsic_instr_create(b.shader,
>>> +  nir_intrinsic_discard_if);
>>> + discard->src[0] = nir_src_for_ssa(cond);
>>> + nir_builder_instr_insert(, >instr);
>>
>> I think it's worth noting that this isn't *strictly* correct for
>> multi-sampling, unless the shader is s run with per-sample shading
>> (ala GL_ARB_sample_shading). Otherwise, all samples for a pixel will
>> get the same discard-condition, leading to aliasing along the
>> resulting edge.
>>
>> That being said, per-fragment clipping is better than no clipping, so
>> it's clearly an improvement.
>
> So, in order to do this correctly for MSAA, I guess you'd need to use
> SYSTEM_VALUE_SAMPLE_POS and FRAG_RESULT_SAMPLE_MASK, to perform
> alpha-testing for each sample-point.

I think it still involves being able to run the frag shader once per
sample..  although blob does seem to expose OES_sample_shading so
maybe that is possible?

I guess I'd care about it more once I supported MSAA ;-)

(and tbh, all this effort was mostly just to get neverball to render
correctly :-P)

BR,
-R
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Re: [Mesa-dev] [PATCH 09/11] nir: add lowering stage for user-clip-planes / clipdist

[Erik Faye-Lund]

On Tue, Sep 15, 2015 at 6:49 PM, Ilia Mirkin  wrote:
> However having a piglit test that covers this would be neat... I guess
> you could clip a pixel in half and make sure that the resolved result
> is some in-between color? Lots of implementation-dependent stuff going
> on in there though.

I think this would simply be a matter of drawing a white triangle on a
black background both with clipping and pre-clipped, and verify that
the result is the same. Perhaps even using a few differently sub-pixel
jittered triangles.
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Re: [Mesa-dev] [PATCH 09/11] nir: add lowering stage for user-clip-planes / clipdist

[Ilia Mirkin]

On Tue, Sep 15, 2015 at 1:09 PM, Erik Faye-Lund  wrote:
> On Tue, Sep 15, 2015 at 6:49 PM, Ilia Mirkin  wrote:
>> However having a piglit test that covers this would be neat... I guess
>> you could clip a pixel in half and make sure that the resolved result
>> is some in-between color? Lots of implementation-dependent stuff going
>> on in there though.
>
> I think this would simply be a matter of drawing a white triangle on a
> black background both with clipping and pre-clipped, and verify that
> the result is the same. Perhaps even using a few differently sub-pixel
> jittered triangles.

Right, but sample positions are implementation-defined. Although I
guess you could retrieve those positions and pre-clip yourself...
However the resolve is also implementation-defined I think, so there's
no good way to know what the resulting color would be. However you
could ensure that it was neither white nor black.
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Re: [Mesa-dev] [PATCH 09/11] nir: add lowering stage for user-clip-planes / clipdist

[Erik Faye-Lund]

On Tue, Sep 15, 2015 at 6:49 PM, Ilia Mirkin  wrote:
> On Tue, Sep 15, 2015 at 12:39 PM, Erik Faye-Lund  wrote:
>> On Mon, Sep 14, 2015 at 11:53 AM, Erik Faye-Lund  wrote:
>>> On Sun, Sep 13, 2015 at 5:51 PM, Rob Clark  wrote:
 From: Rob Clark 

 The vertex shader lowering adds calculation for CLIPDIST, if needed
 (ie. user-clip-planes), and the frag shader lowering adds conditional
 kills based on CLIPDIST value (which should be treated as a normal
 interpolated varying by the driver).
>>>
>>> 
>>>
 +
 +/*
 + * FS lowering
 + */
 +
 +static void
 +lower_clip_fs(nir_function_impl *impl, unsigned ucp_enables,
 +  nir_variable **in)
 +{
 +   nir_ssa_def *clipdist[MAX_CLIP_PLANES];
 +   nir_builder b;
 +
 +   nir_builder_init(, impl);
 +   b.cursor = nir_before_cf_list(>body);
 +
 +   if (ucp_enables & 0x0f)
 +  load_clipdist_input(, in[0], [0]);
 +   if (ucp_enables & 0xf0)
 +  load_clipdist_input(, in[1], [4]);
 +
 +   for (int plane = 0; plane < MAX_CLIP_PLANES; plane++) {
 +  if (ucp_enables & (1 << plane)) {
 + nir_intrinsic_instr *discard;
 + nir_ssa_def *cond;
 +
 + cond = nir_flt(, clipdist[plane], nir_imm_float(, 0.0));
 +
 + discard = nir_intrinsic_instr_create(b.shader,
 +  nir_intrinsic_discard_if);
 + discard->src[0] = nir_src_for_ssa(cond);
 + nir_builder_instr_insert(, >instr);
>>>
>>> I think it's worth noting that this isn't *strictly* correct for
>>> multi-sampling, unless the shader is s run with per-sample shading
>>> (ala GL_ARB_sample_shading). Otherwise, all samples for a pixel will
>>> get the same discard-condition, leading to aliasing along the
>>> resulting edge.
>>>
>>> That being said, per-fragment clipping is better than no clipping, so
>>> it's clearly an improvement.
>>
>> So, in order to do this correctly for MSAA, I guess you'd need to use
>> SYSTEM_VALUE_SAMPLE_POS and FRAG_RESULT_SAMPLE_MASK, to perform
>> alpha-testing for each sample-point.
>
> Ultimately all it needs to do is be able to compute a
> sample mask though, which *is* supported, but you'd need to do the
> per-sample interp "by hand" (although afaik the IJ components are
> provided... somewhere).

SYSTEM_VALUE_SAMPLE_POS could be lowered to a uniform array. You just
need to know where the hardware sampling points are.

And you could use screen-space derivatives for the per-sample interp.

So yeah, the *real* hardware-support needed is just being able to
write a sample-mask from the fragment shader.
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Re: [Mesa-dev] [PATCH 09/11] nir: add lowering stage for user-clip-planes / clipdist

[Rob Clark]

On Tue, Sep 15, 2015 at 12:49 PM, Rob Clark  wrote:
> On Tue, Sep 15, 2015 at 12:39 PM, Erik Faye-Lund  wrote:
>> On Mon, Sep 14, 2015 at 11:53 AM, Erik Faye-Lund  wrote:
>>> On Sun, Sep 13, 2015 at 5:51 PM, Rob Clark  wrote:
 From: Rob Clark 

 The vertex shader lowering adds calculation for CLIPDIST, if needed
 (ie. user-clip-planes), and the frag shader lowering adds conditional
 kills based on CLIPDIST value (which should be treated as a normal
 interpolated varying by the driver).
>>>
>>> 
>>>
 +
 +/*
 + * FS lowering
 + */
 +
 +static void
 +lower_clip_fs(nir_function_impl *impl, unsigned ucp_enables,
 +  nir_variable **in)
 +{
 +   nir_ssa_def *clipdist[MAX_CLIP_PLANES];
 +   nir_builder b;
 +
 +   nir_builder_init(, impl);
 +   b.cursor = nir_before_cf_list(>body);
 +
 +   if (ucp_enables & 0x0f)
 +  load_clipdist_input(, in[0], [0]);
 +   if (ucp_enables & 0xf0)
 +  load_clipdist_input(, in[1], [4]);
 +
 +   for (int plane = 0; plane < MAX_CLIP_PLANES; plane++) {
 +  if (ucp_enables & (1 << plane)) {
 + nir_intrinsic_instr *discard;
 + nir_ssa_def *cond;
 +
 + cond = nir_flt(, clipdist[plane], nir_imm_float(, 0.0));
 +
 + discard = nir_intrinsic_instr_create(b.shader,
 +  nir_intrinsic_discard_if);
 + discard->src[0] = nir_src_for_ssa(cond);
 + nir_builder_instr_insert(, >instr);
>>>
>>> I think it's worth noting that this isn't *strictly* correct for
>>> multi-sampling, unless the shader is s run with per-sample shading
>>> (ala GL_ARB_sample_shading). Otherwise, all samples for a pixel will
>>> get the same discard-condition, leading to aliasing along the
>>> resulting edge.
>>>
>>> That being said, per-fragment clipping is better than no clipping, so
>>> it's clearly an improvement.
>>
>> So, in order to do this correctly for MSAA, I guess you'd need to use
>> SYSTEM_VALUE_SAMPLE_POS and FRAG_RESULT_SAMPLE_MASK, to perform
>> alpha-testing for each sample-point.
>
> I think it still involves being able to run the frag shader once per
> sample..  although blob does seem to expose OES_sample_shading so
> maybe that is possible?

(or rather, a4xx blob does, a3xx doesn't)

> I guess I'd care about it more once I supported MSAA ;-)
>
> (and tbh, all this effort was mostly just to get neverball to render
> correctly :-P)
>
> BR,
> -R
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Re: [Mesa-dev] [PATCH 09/11] nir: add lowering stage for user-clip-planes / clipdist

[Erik Faye-Lund]

On Tue, Sep 15, 2015 at 7:12 PM, Ilia Mirkin  wrote:
> On Tue, Sep 15, 2015 at 1:09 PM, Erik Faye-Lund  wrote:
>> On Tue, Sep 15, 2015 at 6:49 PM, Ilia Mirkin  wrote:
>>> However having a piglit test that covers this would be neat... I guess
>>> you could clip a pixel in half and make sure that the resolved result
>>> is some in-between color? Lots of implementation-dependent stuff going
>>> on in there though.
>>
>> I think this would simply be a matter of drawing a white triangle on a
>> black background both with clipping and pre-clipped, and verify that
>> the result is the same. Perhaps even using a few differently sub-pixel
>> jittered triangles.
>
> Right, but sample positions are implementation-defined. Although I
> guess you could retrieve those positions and pre-clip yourself...

No need to do that, I think. Clipping happens earlier in the OpenGL
pipeline than rasterization, so a user-clipped triangle and a
pre-clipped triangle should produce exactly the same result.

There is of course a chance of some variance in the calculations,
though. So perhaps it'd be better to do a user-clipped triangle vs a
near-plane clipped triangle one. Those are defined to be clipped in
the same pipeline-stage, and should yield the same result.

> However the resolve is also implementation-defined I think, so there's
> no good way to know what the resulting color would be. However you
> could ensure that it was neither white nor black.

Yeah, that's why I'm suggesting comparing two renderings that should
give the same result instead.
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Re: [Mesa-dev] [PATCH 09/11] nir: add lowering stage for user-clip-planes / clipdist

[Rob Clark]

On Tue, Sep 15, 2015 at 1:10 PM, Erik Faye-Lund  wrote:
>> I guess I'd care about it more once I supported MSAA ;-)
>>
>> (and tbh, all this effort was mostly just to get neverball to render
>> correctly :-P)
>
> Oh, I just meant that it might be neat to add to the commit message. I
> wouldn't go ahead and implement this just yet.


yeah, fair enough, I'll add something to the commit msg
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Re: [Mesa-dev] [PATCH 09/11] nir: add lowering stage for user-clip-planes / clipdist

[Erik Faye-Lund]

On Sun, Sep 13, 2015 at 5:51 PM, Rob Clark  wrote:
> From: Rob Clark 
>
> The vertex shader lowering adds calculation for CLIPDIST, if needed
> (ie. user-clip-planes), and the frag shader lowering adds conditional
> kills based on CLIPDIST value (which should be treated as a normal
> interpolated varying by the driver).



> +
> +/*
> + * FS lowering
> + */
> +
> +static void
> +lower_clip_fs(nir_function_impl *impl, unsigned ucp_enables,
> +  nir_variable **in)
> +{
> +   nir_ssa_def *clipdist[MAX_CLIP_PLANES];
> +   nir_builder b;
> +
> +   nir_builder_init(, impl);
> +   b.cursor = nir_before_cf_list(>body);
> +
> +   if (ucp_enables & 0x0f)
> +  load_clipdist_input(, in[0], [0]);
> +   if (ucp_enables & 0xf0)
> +  load_clipdist_input(, in[1], [4]);
> +
> +   for (int plane = 0; plane < MAX_CLIP_PLANES; plane++) {
> +  if (ucp_enables & (1 << plane)) {
> + nir_intrinsic_instr *discard;
> + nir_ssa_def *cond;
> +
> + cond = nir_flt(, clipdist[plane], nir_imm_float(, 0.0));
> +
> + discard = nir_intrinsic_instr_create(b.shader,
> +  nir_intrinsic_discard_if);
> + discard->src[0] = nir_src_for_ssa(cond);
> + nir_builder_instr_insert(, >instr);

I think it's worth noting that this isn't *strictly* correct for
multi-sampling, unless the shader is s run with per-sample shading
(ala GL_ARB_sample_shading). Otherwise, all samples for a pixel will
get the same discard-condition, leading to aliasing along the
resulting edge.

That being said, per-fragment clipping is better than no clipping, so
it's clearly an improvement.
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[Mesa-dev] [PATCH 09/11] nir: add lowering stage for user-clip-planes / clipdist

[Rob Clark]

From: Rob Clark 

The vertex shader lowering adds calculation for CLIPDIST, if needed
(ie. user-clip-planes), and the frag shader lowering adds conditional
kills based on CLIPDIST value (which should be treated as a normal
interpolated varying by the driver).

Signed-off-by: Rob Clark 
---
 src/glsl/Makefile.sources |   1 +
 src/glsl/nir/nir.h|   3 +
 src/glsl/nir/nir_lower_clip.c | 341 ++
 3 files changed, 345 insertions(+)
 create mode 100644 src/glsl/nir/nir_lower_clip.c

diff --git a/src/glsl/Makefile.sources b/src/glsl/Makefile.sources
index da7fdf9..5d98b7b 100644
--- a/src/glsl/Makefile.sources
+++ b/src/glsl/Makefile.sources
@@ -35,6 +35,7 @@ NIR_FILES = \
nir/nir_live_variables.c \
nir/nir_lower_alu_to_scalar.c \
nir/nir_lower_atomics.c \
+   nir/nir_lower_clip.c \
nir/nir_lower_global_vars_to_local.c \
nir/nir_lower_load_const_to_scalar.c \
nir/nir_lower_locals_to_regs.c \
diff --git a/src/glsl/nir/nir.h b/src/glsl/nir/nir.h
index 3f693b1..1e91ab5 100644
--- a/src/glsl/nir/nir.h
+++ b/src/glsl/nir/nir.h
@@ -1824,6 +1824,9 @@ void nir_lower_system_values(nir_shader *shader);
 void nir_lower_tex_projector(nir_shader *shader);
 void nir_lower_idiv(nir_shader *shader);
 
+void nir_lower_clip_vs(nir_shader *shader, unsigned ucp_enables);
+void nir_lower_clip_fs(nir_shader *shader, unsigned ucp_enables);
+
 void nir_lower_atomics(nir_shader *shader);
 void nir_lower_to_source_mods(nir_shader *shader);
 
diff --git a/src/glsl/nir/nir_lower_clip.c b/src/glsl/nir/nir_lower_clip.c
new file mode 100644
index 000..b278aa2
--- /dev/null
+++ b/src/glsl/nir/nir_lower_clip.c
@@ -0,0 +1,341 @@
+/*
+ * Copyright © 2015 Red Hat
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ *
+ * Authors:
+ *Rob Clark 
+ */
+
+#include "nir.h"
+#include "nir_builder.h"
+
+#define MAX_CLIP_PLANES 8
+
+/* Generates the lowering code for user-clip-planes, generating CLIPDIST
+ * from UCP[n] + CLIPVERTEX or POSITION.  Additionally, an optional pass
+ * for fragment shaders to insert conditional kill's based on the inter-
+ * polated CLIPDIST
+ *
+ * NOTE: should be run after nir_lower_outputs_to_temporaries() (or at
+ * least in scenarios where you can count on each output written once
+ * and only once).
+ */
+
+
+static nir_variable *
+create_clipdist_var(nir_shader *shader, unsigned drvloc,
+bool output, gl_varying_slot slot)
+{
+   nir_variable *var = rzalloc(shader, nir_variable);
+
+   var->data.driver_location = drvloc;
+   var->type = glsl_vec4_type();
+   var->data.mode = output ? nir_var_shader_out : nir_var_shader_in;
+   var->name = ralloc_asprintf(var, "clipdist_%d", drvloc);
+   var->data.index = 0;
+   var->data.location = slot;
+
+   if (output) {
+  exec_list_push_tail(>outputs, >node);
+   }
+   else {
+  exec_list_push_tail(>inputs, >node);
+   }
+   return var;
+}
+
+static void
+store_clipdist_output(nir_builder *b, nir_variable *out, nir_ssa_def **val)
+{
+   nir_intrinsic_instr *store;
+
+   store = nir_intrinsic_instr_create(b->shader, nir_intrinsic_store_output);
+   store->num_components = 4;
+   store->const_index[0] = out->data.driver_location;
+   store->src[0].ssa = nir_vec4(b, val[0], val[1], val[2], val[3]);
+   store->src[0].is_ssa = true;
+   nir_builder_instr_insert(b, >instr);
+}
+
+static void
+load_clipdist_input(nir_builder *b, nir_variable *in, nir_ssa_def **val)
+{
+   nir_intrinsic_instr *load;
+
+   load = nir_intrinsic_instr_create(b->shader, nir_intrinsic_load_input);
+   load->num_components = 4;
+   load->const_index[0] = in->data.driver_location;
+   nir_ssa_dest_init(>instr, >dest, 4, NULL);
+   nir_builder_instr_insert(b, >instr);
+
+   val[0] = nir_channel(b, >dest.ssa, 0);
+   val[1] = nir_channel(b,