src/compiler/nir/nir_lower_wpos_ytransform.c - platform/external/mesa3d - Git at Google

 /*
  * 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.
  */

 #include "nir.h"
 #include "nir_builder.h"
 #include "program/prog_instruction.h"

 /* Lower gl_FragCoord (and fddy) to account for driver's requested coordinate-
  * origin and pixel-center vs. shader.  If transformation is required, a
  * gl_FbWposYTransform uniform is inserted (with the specified state-slots)
  * and additional instructions are inserted to transform gl_FragCoord (and
  * fddy src arg).
  *
  * This is based on the logic in emit_wpos()/emit_wpos_adjustment() in TGSI
  * compiler.
  *
  * Run before nir_lower_io.
  */

 typedef struct {
    const nir_lower_wpos_ytransform_options *options;
    nir_shader   *shader;
    nir_builder   b;
    nir_variable *transform;
 } lower_wpos_ytransform_state;

 static nir_ssa_def *
 get_transform(lower_wpos_ytransform_state *state)
 {
    if (state->transform == NULL) {
       /* NOTE: name must be prefixed w/ "gl_" to trigger slot based
        * special handling in uniform setup:
        */
       nir_variable *var = nir_variable_create(state->shader,
                                               nir_var_uniform,
                                               glsl_vec4_type(),
                                               "gl_FbWposYTransform");

       var->num_state_slots = 1;
       var->state_slots = ralloc_array(var, nir_state_slot, 1);
       var->state_slots[0].swizzle = SWIZZLE_XYZW;
       memcpy(var->state_slots[0].tokens, state->options->state_tokens,
              sizeof(var->state_slots[0].tokens));

       state->transform = var;
    }
    return nir_load_var(&state->b, state->transform);
 }

 /* NIR equiv of TGSI CMP instruction: */
 static nir_ssa_def *
 nir_cmp(nir_builder *b, nir_ssa_def *src0, nir_ssa_def *src1, nir_ssa_def *src2)
 {
    return nir_bcsel(b, nir_flt(b, src0, nir_imm_float(b, 0.0)), src1, src2);
 }

 /* see emit_wpos_adjustment() in st_mesa_to_tgsi.c */
 static void
 emit_wpos_adjustment(lower_wpos_ytransform_state *state,
                      nir_intrinsic_instr *intr,
                      bool invert, float adjX, float adjY[2])
 {
    nir_builder *b = &state->b;
    nir_variable *fragcoord = intr->variables[0]->var;
    nir_ssa_def *wpostrans, *wpos_temp, *wpos_temp_y, *wpos_input;

    assert(intr->dest.is_ssa);

    b->cursor = nir_before_instr(&intr->instr);

    wpostrans = get_transform(state);
    wpos_input = nir_load_var(b, fragcoord);

    /* First, apply the coordinate shift: */
    if (adjX || adjY[0] || adjY[1]) {
       if (adjY[0] != adjY[1]) {
          /* Adjust the y coordinate by adjY[1] or adjY[0] respectively
           * depending on whether inversion is actually going to be applied
           * or not, which is determined by testing against the inversion
           * state variable used below, which will be either +1 or -1.
           */
          nir_ssa_def *adj_temp;

          adj_temp = nir_cmp(b,
                             nir_channel(b, wpostrans, invert ? 2 : 0),
                             nir_imm_vec4(b, adjX, adjY[0], 0.0f, 0.0f),
                             nir_imm_vec4(b, adjX, adjY[1], 0.0f, 0.0f));

          wpos_temp = nir_fadd(b, wpos_input, adj_temp);
       } else {
          wpos_temp = nir_fadd(b,
                               wpos_input,
                               nir_imm_vec4(b, adjX, adjY[0], 0.0f, 0.0f));
       }
       wpos_input = wpos_temp;
    } else {
       /* MOV wpos_temp, input[wpos]
        */
       wpos_temp = wpos_input;
    }

    /* Now the conditional y flip: STATE_FB_WPOS_Y_TRANSFORM.xy/zw will be
     * inversion/identity, or the other way around if we're drawing to an FBO.
     */
    if (invert) {
       /* wpos_temp.y = wpos_input * wpostrans.xxxx + wpostrans.yyyy */
       wpos_temp_y = nir_fadd(b, nir_fmul(b, nir_channel(b, wpos_temp, 1),
                                             nir_channel(b, wpostrans, 0)),
                                 nir_channel(b, wpostrans, 1));
    } else {
       /* wpos_temp.y = wpos_input * wpostrans.zzzz + wpostrans.wwww */
       wpos_temp_y = nir_fadd(b, nir_fmul(b, nir_channel(b, wpos_temp, 1),
                                             nir_channel(b, wpostrans, 2)),
                                 nir_channel(b, wpostrans, 3));
    }

    wpos_temp = nir_vec4(b,
                         nir_channel(b, wpos_temp, 0),
                         wpos_temp_y,
                         nir_channel(b, wpos_temp, 2),
                         nir_channel(b, wpos_temp, 3));

    nir_ssa_def_rewrite_uses(&intr->dest.ssa, nir_src_for_ssa(wpos_temp));
 }

 static void
 lower_fragcoord(lower_wpos_ytransform_state *state, nir_intrinsic_instr *intr)
 {
    const nir_lower_wpos_ytransform_options *options = state->options;
    nir_variable *fragcoord = intr->variables[0]->var;
    float adjX = 0.0f;
    float adjY[2] = { 0.0f, 0.0f };
    bool invert = false;

    /* Based on logic in emit_wpos():
     *
     * Query the pixel center conventions supported by the pipe driver and set
     * adjX, adjY to help out if it cannot handle the requested one internally.
     *
     * The bias of the y-coordinate depends on whether y-inversion takes place
     * (adjY[1]) or not (adjY[0]), which is in turn dependent on whether we are
     * drawing to an FBO (causes additional inversion), and whether the pipe
     * driver origin and the requested origin differ (the latter condition is
     * stored in the 'invert' variable).
     *
     * For height = 100 (i = integer, h = half-integer, l = lower, u = upper):
     *
     * center shift only:
     * i -> h: +0.5
     * h -> i: -0.5
     *
     * inversion only:
     * l,i -> u,i: ( 0.0 + 1.0) * -1 + 100 = 99
     * l,h -> u,h: ( 0.5 + 0.0) * -1 + 100 = 99.5
     * u,i -> l,i: (99.0 + 1.0) * -1 + 100 = 0
     * u,h -> l,h: (99.5 + 0.0) * -1 + 100 = 0.5
     *
     * inversion and center shift:
     * l,i -> u,h: ( 0.0 + 0.5) * -1 + 100 = 99.5
     * l,h -> u,i: ( 0.5 + 0.5) * -1 + 100 = 99
     * u,i -> l,h: (99.0 + 0.5) * -1 + 100 = 0.5
     * u,h -> l,i: (99.5 + 0.5) * -1 + 100 = 0
     */

    if (fragcoord->data.origin_upper_left) {
       /* Fragment shader wants origin in upper-left */
       if (options->fs_coord_origin_upper_left) {
          /* the driver supports upper-left origin */
       } else if (options->fs_coord_origin_lower_left) {
          /* the driver supports lower-left origin, need to invert Y */
          invert = true;
       } else {
          unreachable("invalid options");
       }
    } else {
       /* Fragment shader wants origin in lower-left */
       if (options->fs_coord_origin_lower_left) {
          /* the driver supports lower-left origin */
       } else if (options->fs_coord_origin_upper_left) {
          /* the driver supports upper-left origin, need to invert Y */
          invert = true;
       } else {
          unreachable("invalid options");
       }
    }

    if (fragcoord->data.pixel_center_integer) {
       /* Fragment shader wants pixel center integer */
       if (options->fs_coord_pixel_center_integer) {
          /* the driver supports pixel center integer */
          adjY[1] = 1.0f;
       } else if (options->fs_coord_pixel_center_half_integer) {
          /* the driver supports pixel center half integer, need to bias X,Y */
          adjX = -0.5f;
          adjY[0] = -0.5f;
          adjY[1] = 0.5f;
       } else {
          unreachable("invalid options");
       }
    } else {
       /* Fragment shader wants pixel center half integer */
       if (options->fs_coord_pixel_center_half_integer) {
          /* the driver supports pixel center half integer */
       } else if (options->fs_coord_pixel_center_integer) {
          /* the driver supports pixel center integer, need to bias X,Y */
          adjX = adjY[0] = adjY[1] = 0.5f;
       } else {
          unreachable("invalid options");
       }
    }

    emit_wpos_adjustment(state, intr, invert, adjX, adjY);
 }

 /* turns 'fddy(p)' into 'fddy(fmul(p, transform.x))' */
 static void
 lower_fddy(lower_wpos_ytransform_state *state, nir_alu_instr *fddy)
 {
    nir_builder *b = &state->b;
    nir_ssa_def *p, *pt, *trans;

    b->cursor = nir_before_instr(&fddy->instr);

    p = nir_ssa_for_alu_src(b, fddy, 0);
    trans = get_transform(state);
    pt = nir_fmul(b, p, nir_channel(b, trans, 0));

    nir_instr_rewrite_src(&fddy->instr,
                          &fddy->src[0].src,
                          nir_src_for_ssa(pt));

    for (unsigned i = 0; i < 4; i++)
       fddy->src[0].swizzle[i] = MIN2(i, pt->num_components - 1);
 }

 /* Multiply interp_var_at_offset's offset by transform.x to flip it. */
 static void
 lower_interp_var_at_offset(lower_wpos_ytransform_state *state,
                            nir_intrinsic_instr *interp)
 {
    nir_builder *b = &state->b;
    nir_ssa_def *offset;
    nir_ssa_def *flip_y;

    b->cursor = nir_before_instr(&interp->instr);

    offset = nir_ssa_for_src(b, interp->src[0], 2);
    flip_y = nir_fmul(b, nir_channel(b, offset, 1),
                         nir_channel(b, get_transform(state), 0));
    nir_instr_rewrite_src(&interp->instr, &interp->src[0],
                          nir_src_for_ssa(nir_vec2(b, nir_channel(b, offset, 0),
                                                      flip_y)));
 }

 static void
 lower_load_sample_pos(lower_wpos_ytransform_state *state,
                       nir_intrinsic_instr *intr)
 {
    nir_builder *b = &state->b;
    b->cursor = nir_after_instr(&intr->instr);

    nir_ssa_def *pos = &intr->dest.ssa;
    nir_ssa_def *scale = nir_channel(b, get_transform(state), 0);
    nir_ssa_def *neg_scale = nir_channel(b, get_transform(state), 2);
    /* Either y or 1-y for scale equal to 1 or -1 respectively. */
    nir_ssa_def *flipped_y =
                nir_fadd(b, nir_fmax(b, neg_scale, nir_imm_float(b, 0.0)),
                         nir_fmul(b, nir_channel(b, pos, 1), scale));
    nir_ssa_def *flipped_pos = nir_vec2(b, nir_channel(b, pos, 0), flipped_y);

    nir_ssa_def_rewrite_uses_after(&intr->dest.ssa, nir_src_for_ssa(flipped_pos),
                                   flipped_pos->parent_instr);
 }

 static void
 lower_wpos_ytransform_block(lower_wpos_ytransform_state *state, nir_block *block)
 {
    nir_foreach_instr_safe(instr, block) {
       if (instr->type == nir_instr_type_intrinsic) {
          nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
          if (intr->intrinsic == nir_intrinsic_load_var) {
             nir_deref_var *dvar = intr->variables[0];
             nir_variable *var = dvar->var;

             if (var->data.mode == nir_var_shader_in &&
                 var->data.location == VARYING_SLOT_POS) {
                /* gl_FragCoord should not have array/struct deref's: */
                assert(dvar->deref.child == NULL);
                lower_fragcoord(state, intr);
             } else if (var->data.mode == nir_var_system_value &&
                        var->data.location == SYSTEM_VALUE_SAMPLE_POS) {
                assert(dvar->deref.child == NULL);
                lower_load_sample_pos(state, intr);
             }
          } else if (intr->intrinsic == nir_intrinsic_interp_var_at_offset) {
             lower_interp_var_at_offset(state, intr);
          }
       } else if (instr->type == nir_instr_type_alu) {
          nir_alu_instr *alu = nir_instr_as_alu(instr);
          if (alu->op == nir_op_fddy ||
              alu->op == nir_op_fddy_fine ||
              alu->op == nir_op_fddy_coarse)
             lower_fddy(state, alu);
       }
    }
 }

 static void
 lower_wpos_ytransform_impl(lower_wpos_ytransform_state *state, nir_function_impl *impl)
 {
    nir_builder_init(&state->b, impl);

    nir_foreach_block(block, impl) {
       lower_wpos_ytransform_block(state, block);
    }
    nir_metadata_preserve(impl, nir_metadata_block_index |
                                nir_metadata_dominance);
 }

 bool
 nir_lower_wpos_ytransform(nir_shader *shader,
                           const nir_lower_wpos_ytransform_options *options)
 {
    lower_wpos_ytransform_state state = {
       .options = options,
       .shader = shader,
    };

    assert(shader->stage == MESA_SHADER_FRAGMENT);

    nir_foreach_function(function, shader) {
       if (function->impl)
          lower_wpos_ytransform_impl(&state, function->impl);
    }

    return state.transform != NULL;
 }
	/*
	* 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.
	*/

	#include "nir.h"
	#include "nir_builder.h"
	#include "program/prog_instruction.h"

	/* Lower gl_FragCoord (and fddy) to account for driver's requested coordinate-
	* origin and pixel-center vs. shader. If transformation is required, a
	* gl_FbWposYTransform uniform is inserted (with the specified state-slots)
	* and additional instructions are inserted to transform gl_FragCoord (and
	* fddy src arg).
	*
	* This is based on the logic in emit_wpos()/emit_wpos_adjustment() in TGSI
	* compiler.
	*
	* Run before nir_lower_io.
	*/

	typedef struct {
	const nir_lower_wpos_ytransform_options *options;
	nir_shader *shader;
	nir_builder b;
	nir_variable *transform;
	} lower_wpos_ytransform_state;

	static nir_ssa_def *
	get_transform(lower_wpos_ytransform_state *state)
	{
	if (state->transform == NULL) {
	/* NOTE: name must be prefixed w/ "gl_" to trigger slot based
	* special handling in uniform setup:
	*/
	nir_variable *var = nir_variable_create(state->shader,
	nir_var_uniform,
	glsl_vec4_type(),
	"gl_FbWposYTransform");

	var->num_state_slots = 1;
	var->state_slots = ralloc_array(var, nir_state_slot, 1);
	var->state_slots[0].swizzle = SWIZZLE_XYZW;
	memcpy(var->state_slots[0].tokens, state->options->state_tokens,
	sizeof(var->state_slots[0].tokens));

	state->transform = var;
	}
	return nir_load_var(&state->b, state->transform);
	}

	/* NIR equiv of TGSI CMP instruction: */
	static nir_ssa_def *
	nir_cmp(nir_builder b, nir_ssa_def src0, nir_ssa_def src1, nir_ssa_def src2)
	{
	return nir_bcsel(b, nir_flt(b, src0, nir_imm_float(b, 0.0)), src1, src2);
	}

	/* see emit_wpos_adjustment() in st_mesa_to_tgsi.c */
	static void
	emit_wpos_adjustment(lower_wpos_ytransform_state *state,
	nir_intrinsic_instr *intr,
	bool invert, float adjX, float adjY[2])
	{
	nir_builder *b = &state->b;
	nir_variable *fragcoord = intr->variables[0]->var;
	nir_ssa_def wpostrans, wpos_temp, wpos_temp_y, wpos_input;

	assert(intr->dest.is_ssa);

	b->cursor = nir_before_instr(&intr->instr);

	wpostrans = get_transform(state);
	wpos_input = nir_load_var(b, fragcoord);

	/* First, apply the coordinate shift: */
	if (adjX \|\| adjY[0] \|\| adjY[1]) {
	if (adjY[0] != adjY[1]) {
	/* Adjust the y coordinate by adjY[1] or adjY[0] respectively
	* depending on whether inversion is actually going to be applied
	* or not, which is determined by testing against the inversion
	* state variable used below, which will be either +1 or -1.
	*/
	nir_ssa_def *adj_temp;

	adj_temp = nir_cmp(b,
	nir_channel(b, wpostrans, invert ? 2 : 0),
	nir_imm_vec4(b, adjX, adjY[0], 0.0f, 0.0f),
	nir_imm_vec4(b, adjX, adjY[1], 0.0f, 0.0f));

	wpos_temp = nir_fadd(b, wpos_input, adj_temp);
	} else {
	wpos_temp = nir_fadd(b,
	wpos_input,
	nir_imm_vec4(b, adjX, adjY[0], 0.0f, 0.0f));
	}
	wpos_input = wpos_temp;
	} else {
	/* MOV wpos_temp, input[wpos]
	*/
	wpos_temp = wpos_input;
	}

	/* Now the conditional y flip: STATE_FB_WPOS_Y_TRANSFORM.xy/zw will be
	* inversion/identity, or the other way around if we're drawing to an FBO.
	*/
	if (invert) {
	/* wpos_temp.y = wpos_input * wpostrans.xxxx + wpostrans.yyyy */
	wpos_temp_y = nir_fadd(b, nir_fmul(b, nir_channel(b, wpos_temp, 1),
	nir_channel(b, wpostrans, 0)),
	nir_channel(b, wpostrans, 1));
	} else {
	/* wpos_temp.y = wpos_input * wpostrans.zzzz + wpostrans.wwww */
	wpos_temp_y = nir_fadd(b, nir_fmul(b, nir_channel(b, wpos_temp, 1),
	nir_channel(b, wpostrans, 2)),
	nir_channel(b, wpostrans, 3));
	}

	wpos_temp = nir_vec4(b,
	nir_channel(b, wpos_temp, 0),
	wpos_temp_y,
	nir_channel(b, wpos_temp, 2),
	nir_channel(b, wpos_temp, 3));

	nir_ssa_def_rewrite_uses(&intr->dest.ssa, nir_src_for_ssa(wpos_temp));
	}

	static void
	lower_fragcoord(lower_wpos_ytransform_state state, nir_intrinsic_instr intr)
	{
	const nir_lower_wpos_ytransform_options *options = state->options;
	nir_variable *fragcoord = intr->variables[0]->var;
	float adjX = 0.0f;
	float adjY[2] = { 0.0f, 0.0f };
	bool invert = false;

	/* Based on logic in emit_wpos():
	*
	* Query the pixel center conventions supported by the pipe driver and set
	* adjX, adjY to help out if it cannot handle the requested one internally.
	*
	* The bias of the y-coordinate depends on whether y-inversion takes place
	* (adjY[1]) or not (adjY[0]), which is in turn dependent on whether we are
	* drawing to an FBO (causes additional inversion), and whether the pipe
	* driver origin and the requested origin differ (the latter condition is
	* stored in the 'invert' variable).
	*
	* For height = 100 (i = integer, h = half-integer, l = lower, u = upper):
	*
	* center shift only:
	* i -> h: +0.5
	* h -> i: -0.5
	*
	* inversion only:
	* l,i -> u,i: ( 0.0 + 1.0) * -1 + 100 = 99
	* l,h -> u,h: ( 0.5 + 0.0) * -1 + 100 = 99.5
	* u,i -> l,i: (99.0 + 1.0) * -1 + 100 = 0
	* u,h -> l,h: (99.5 + 0.0) * -1 + 100 = 0.5
	*
	* inversion and center shift:
	* l,i -> u,h: ( 0.0 + 0.5) * -1 + 100 = 99.5
	* l,h -> u,i: ( 0.5 + 0.5) * -1 + 100 = 99
	* u,i -> l,h: (99.0 + 0.5) * -1 + 100 = 0.5
	* u,h -> l,i: (99.5 + 0.5) * -1 + 100 = 0
	*/

	if (fragcoord->data.origin_upper_left) {
	/* Fragment shader wants origin in upper-left */
	if (options->fs_coord_origin_upper_left) {
	/* the driver supports upper-left origin */
	} else if (options->fs_coord_origin_lower_left) {
	/* the driver supports lower-left origin, need to invert Y */
	invert = true;
	} else {
	unreachable("invalid options");
	}
	} else {
	/* Fragment shader wants origin in lower-left */
	if (options->fs_coord_origin_lower_left) {
	/* the driver supports lower-left origin */
	} else if (options->fs_coord_origin_upper_left) {
	/* the driver supports upper-left origin, need to invert Y */
	invert = true;
	} else {
	unreachable("invalid options");
	}
	}

	if (fragcoord->data.pixel_center_integer) {
	/* Fragment shader wants pixel center integer */
	if (options->fs_coord_pixel_center_integer) {
	/* the driver supports pixel center integer */
	adjY[1] = 1.0f;
	} else if (options->fs_coord_pixel_center_half_integer) {
	/* the driver supports pixel center half integer, need to bias X,Y */
	adjX = -0.5f;
	adjY[0] = -0.5f;
	adjY[1] = 0.5f;
	} else {
	unreachable("invalid options");
	}
	} else {
	/* Fragment shader wants pixel center half integer */
	if (options->fs_coord_pixel_center_half_integer) {
	/* the driver supports pixel center half integer */
	} else if (options->fs_coord_pixel_center_integer) {
	/* the driver supports pixel center integer, need to bias X,Y */
	adjX = adjY[0] = adjY[1] = 0.5f;
	} else {
	unreachable("invalid options");
	}
	}

	emit_wpos_adjustment(state, intr, invert, adjX, adjY);
	}

	/* turns 'fddy(p)' into 'fddy(fmul(p, transform.x))' */
	static void
	lower_fddy(lower_wpos_ytransform_state state, nir_alu_instr fddy)
	{
	nir_builder *b = &state->b;
	nir_ssa_def p, pt, *trans;

	b->cursor = nir_before_instr(&fddy->instr);

	p = nir_ssa_for_alu_src(b, fddy, 0);
	trans = get_transform(state);
	pt = nir_fmul(b, p, nir_channel(b, trans, 0));

	nir_instr_rewrite_src(&fddy->instr,
	&fddy->src[0].src,
	nir_src_for_ssa(pt));

	for (unsigned i = 0; i < 4; i++)
	fddy->src[0].swizzle[i] = MIN2(i, pt->num_components - 1);
	}

	/* Multiply interp_var_at_offset's offset by transform.x to flip it. */
	static void
	lower_interp_var_at_offset(lower_wpos_ytransform_state *state,
	nir_intrinsic_instr *interp)
	{
	nir_builder *b = &state->b;
	nir_ssa_def *offset;
	nir_ssa_def *flip_y;

	b->cursor = nir_before_instr(&interp->instr);

	offset = nir_ssa_for_src(b, interp->src[0], 2);
	flip_y = nir_fmul(b, nir_channel(b, offset, 1),
	nir_channel(b, get_transform(state), 0));
	nir_instr_rewrite_src(&interp->instr, &interp->src[0],
	nir_src_for_ssa(nir_vec2(b, nir_channel(b, offset, 0),
	flip_y)));
	}

	static void
	lower_load_sample_pos(lower_wpos_ytransform_state *state,
	nir_intrinsic_instr *intr)
	{
	nir_builder *b = &state->b;
	b->cursor = nir_after_instr(&intr->instr);

	nir_ssa_def *pos = &intr->dest.ssa;
	nir_ssa_def *scale = nir_channel(b, get_transform(state), 0);
	nir_ssa_def *neg_scale = nir_channel(b, get_transform(state), 2);
	/* Either y or 1-y for scale equal to 1 or -1 respectively. */
	nir_ssa_def *flipped_y =
	nir_fadd(b, nir_fmax(b, neg_scale, nir_imm_float(b, 0.0)),
	nir_fmul(b, nir_channel(b, pos, 1), scale));
	nir_ssa_def *flipped_pos = nir_vec2(b, nir_channel(b, pos, 0), flipped_y);

	nir_ssa_def_rewrite_uses_after(&intr->dest.ssa, nir_src_for_ssa(flipped_pos),
	flipped_pos->parent_instr);
	}

	static void
	lower_wpos_ytransform_block(lower_wpos_ytransform_state state, nir_block block)
	{
	nir_foreach_instr_safe(instr, block) {
	if (instr->type == nir_instr_type_intrinsic) {
	nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
	if (intr->intrinsic == nir_intrinsic_load_var) {
	nir_deref_var *dvar = intr->variables[0];
	nir_variable *var = dvar->var;

	if (var->data.mode == nir_var_shader_in &&
	var->data.location == VARYING_SLOT_POS) {
	/* gl_FragCoord should not have array/struct deref's: */
	assert(dvar->deref.child == NULL);
	lower_fragcoord(state, intr);
	} else if (var->data.mode == nir_var_system_value &&
	var->data.location == SYSTEM_VALUE_SAMPLE_POS) {
	assert(dvar->deref.child == NULL);
	lower_load_sample_pos(state, intr);
	}
	} else if (intr->intrinsic == nir_intrinsic_interp_var_at_offset) {
	lower_interp_var_at_offset(state, intr);
	}
	} else if (instr->type == nir_instr_type_alu) {
	nir_alu_instr *alu = nir_instr_as_alu(instr);
	if (alu->op == nir_op_fddy \|\|
	alu->op == nir_op_fddy_fine \|\|
	alu->op == nir_op_fddy_coarse)
	lower_fddy(state, alu);
	}
	}
	}

	static void
	lower_wpos_ytransform_impl(lower_wpos_ytransform_state state, nir_function_impl impl)
	{
	nir_builder_init(&state->b, impl);

	nir_foreach_block(block, impl) {
	lower_wpos_ytransform_block(state, block);
	}
	nir_metadata_preserve(impl, nir_metadata_block_index \|
	nir_metadata_dominance);
	}

	bool
	nir_lower_wpos_ytransform(nir_shader *shader,
	const nir_lower_wpos_ytransform_options *options)
	{
	lower_wpos_ytransform_state state = {
	.options = options,
	.shader = shader,
	};

	assert(shader->stage == MESA_SHADER_FRAGMENT);

	nir_foreach_function(function, shader) {
	if (function->impl)
	lower_wpos_ytransform_impl(&state, function->impl);
	}

	return state.transform != NULL;
	}