/*
 * Copyright 2010 Marek Olšák <maraeo@gmail.com>
 * SPDX-License-Identifier: MIT
 */

/**
 * The two-sided stencil reference value fallback for r3xx-r4xx chips.
 * These chips support two-sided stencil functions but they do not support
 * a two-sided reference value.
 *
 * The functions below split every draw call which uses the two-sided
 * reference value into two draw calls -- the first one renders front faces
 * and the second renders back faces with the other reference value.
 */

#include "r300_context.h"
#include "r300_reg.h"

struct r300_stencilref_context {
    pipe_draw_func draw_vbo;

    uint32_t rs_cull_mode;
    uint32_t zb_stencilrefmask;
    uint8_t ref_value_front;
};

static bool r300_stencilref_needed(struct r300_context *r300)
{
    struct r300_dsa_state *dsa = (struct r300_dsa_state*)r300->dsa_state.state;

    return dsa->two_sided_stencil_ref ||
           (dsa->two_sided &&
            r300->stencil_ref.ref_value[0] != r300->stencil_ref.ref_value[1]);
}

/* Set drawing for front faces. */
static void r300_stencilref_begin(struct r300_context *r300)
{
    struct r300_stencilref_context *sr = r300->stencilref_fallback;
    struct r300_rs_state *rs = (struct r300_rs_state*)r300->rs_state.state;
    struct r300_dsa_state *dsa = (struct r300_dsa_state*)r300->dsa_state.state;

    /* Save state. */
    sr->rs_cull_mode = rs->cb_main[rs->cull_mode_index];
    sr->zb_stencilrefmask = dsa->stencil_ref_mask;
    sr->ref_value_front = r300->stencil_ref.ref_value[0];

    /* We *cull* pixels, therefore no need to mask out the bits. */
    rs->cb_main[rs->cull_mode_index] |= R300_CULL_BACK;

    r300_mark_atom_dirty(r300, &r300->rs_state);
}

/* Set drawing for back faces. */
static void r300_stencilref_switch_side(struct r300_context *r300)
{
    struct r300_stencilref_context *sr = r300->stencilref_fallback;
    struct r300_rs_state *rs = (struct r300_rs_state*)r300->rs_state.state;
    struct r300_dsa_state *dsa = (struct r300_dsa_state*)r300->dsa_state.state;

    rs->cb_main[rs->cull_mode_index] = sr->rs_cull_mode | R300_CULL_FRONT;
    dsa->stencil_ref_mask = dsa->stencil_ref_bf;
    r300->stencil_ref.ref_value[0] = r300->stencil_ref.ref_value[1];

    r300_mark_atom_dirty(r300, &r300->rs_state);
    r300_mark_atom_dirty(r300, &r300->dsa_state);
}

/* Restore the original state. */
static void r300_stencilref_end(struct r300_context *r300)
{
    struct r300_stencilref_context *sr = r300->stencilref_fallback;
    struct r300_rs_state *rs = (struct r300_rs_state*)r300->rs_state.state;
    struct r300_dsa_state *dsa = (struct r300_dsa_state*)r300->dsa_state.state;

    /* Restore state. */
    rs->cb_main[rs->cull_mode_index] = sr->rs_cull_mode;
    dsa->stencil_ref_mask = sr->zb_stencilrefmask;
    r300->stencil_ref.ref_value[0] = sr->ref_value_front;

    r300_mark_atom_dirty(r300, &r300->rs_state);
    r300_mark_atom_dirty(r300, &r300->dsa_state);
}

static void r300_stencilref_draw_vbo(struct pipe_context *pipe,
                                     const struct pipe_draw_info *info,
                                     unsigned drawid_offset,
                                     const struct pipe_draw_indirect_info *indirect,
                                     const struct pipe_draw_start_count_bias *draws,
                                     unsigned num_draws)
{
    struct r300_context *r300 = r300_context(pipe);
    struct r300_stencilref_context *sr = r300->stencilref_fallback;

    if (!r300_stencilref_needed(r300)) {
        sr->draw_vbo(pipe, info, drawid_offset, NULL, draws, num_draws);
    } else {
        r300_stencilref_begin(r300);
        sr->draw_vbo(pipe, info, drawid_offset, NULL, draws, num_draws);
        r300_stencilref_switch_side(r300);
        sr->draw_vbo(pipe, info, drawid_offset, NULL, draws, num_draws);
        r300_stencilref_end(r300);
    }
}

void r300_plug_in_stencil_ref_fallback(struct r300_context *r300)
{
    r300->stencilref_fallback = CALLOC_STRUCT(r300_stencilref_context);

    /* Save original draw function. */
    r300->stencilref_fallback->draw_vbo = r300->context.draw_vbo;

    /* Override the draw function. */
    r300->context.draw_vbo = r300_stencilref_draw_vbo;
}