[Mesa-dev] [PATCH 08/12] i965/fs: Add support for gl_Layer input

[Ian Romanick]

On 01/24/2014 10:51 PM, Chris Forbes wrote:
> This is a bit unusual -- we want to treat it as an input on the GLSL
> side rather than a `system value` oddball. However, it doesn't get a
> real slot in the VUE layout -- earlier shader stages write it into the
> vertex header, and it appears in the FS payload packed into some R0.0
> bits.

This has the same problems as gl_ViewportIndex.  See my reply to the
next patch.

> Signed-off-by: Chris Forbes <chrisf at ijw.co.nz>
> ---
>  src/mesa/drivers/dri/i965/brw_fs.cpp         | 22 ++++++++++++++++++++++
>  src/mesa/drivers/dri/i965/brw_fs.h           |  1 +
>  src/mesa/drivers/dri/i965/brw_fs_visitor.cpp |  2 ++
>  3 files changed, 25 insertions(+)
> 
> diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
> index 1e6c3e0..17d5237 100644
> --- a/src/mesa/drivers/dri/i965/brw_fs.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
> @@ -1272,6 +1272,28 @@ fs_visitor::emit_samplemaskin_setup(ir_variable *ir)
>     return reg;
>  }
>  
> +fs_reg *
> +fs_visitor::emit_layer_setup(ir_variable *ir)
> +{
> +   /* The value for gl_Layer is provided in bits 26:16 of R0.0. */
> +
> +   /* These bits are actually present on all Gen4+ h/w, but until GS is enabled
> +    * on earlier platforms we don't expect to get here on anything earlier
> +    * than Gen7.
> +    */
> +   assert(brw->gen >= 7);
> +
> +   this->current_annotation = "gl_Layer";
> +   fs_reg *reg = new(this->mem_ctx) fs_reg(this, ir->type);
> +   fs_reg temp = fs_reg(this, glsl_type::int_type);
> +   emit(BRW_OPCODE_SHR, temp,
> +         fs_reg(retype(brw_vec1_grf(0, 0), BRW_REGISTER_TYPE_D)),
> +         fs_reg(brw_imm_d(16)));
> +   emit(BRW_OPCODE_AND, *reg, temp,
> +         fs_reg(brw_imm_d(0x7ff)));
> +   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 2ccb8c4..e04c341 100644
> --- a/src/mesa/drivers/dri/i965/brw_fs.h
> +++ b/src/mesa/drivers/dri/i965/brw_fs.h
> @@ -345,6 +345,7 @@ public:
>     fs_reg *emit_samplepos_setup(ir_variable *ir);
>     fs_reg *emit_sampleid_setup(ir_variable *ir);
>     fs_reg *emit_samplemaskin_setup(ir_variable *ir);
> +   fs_reg *emit_layer_setup(ir_variable *ir);
>     fs_reg *emit_general_interpolation(ir_variable *ir);
>     void emit_interpolation_setup_gen4();
>     void emit_interpolation_setup_gen6();
> diff --git a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
> index d88d24c..e949f4b 100644
> --- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
> @@ -61,6 +61,8 @@ fs_visitor::visit(ir_variable *ir)
>  	 reg = emit_fragcoord_interpolation(ir);
>        } else if (!strcmp(ir->name, "gl_FrontFacing")) {
>  	 reg = emit_frontfacing_interpolation(ir);
> +      } else if (!strcmp(ir->name, "gl_Layer")) {
> +         reg = emit_layer_setup(ir);
>        } else {
>  	 reg = emit_general_interpolation(ir);
>        }
>