// retroDE_ps2 — tb_top_psmct32_tile_alpha_demo (Ch309)
//
// GS ALPHA mode expansion. The Ch305 3-primitive scene over a 2x2 tile grid, but
// P1 uses the ADDITIVE blend mode (Cv=((Cs-0)*FIX>>7)+Cd with FIX=0x80 => Cs+Cd
// clamped) instead of source-over, so two visibly-different blend equations coexist:
//   P0 blue bg : source-over (A=Cs,B=Cd,C=As,D=Cd, As=0x80 -> opaque blue).
//   P1 red     : ADDITIVE over the blue bg -> MAGENTA (255,0,255) (brighten/glow).
//   P2 white   : source-over translucent (A=0x40) -> light-blue over blue.
//
// PROOFS:
//   ADDITIVE  : the P1 region is MAGENTA (Cs+Cd clamped), not red -> additive + FIX work.
//   SOURCE-OVER preserved : P2 light-blue (127,127,255) over blue -> source-over unchanged.
//   DEPTH     : P2 occluded by P1 (Z 0x5800 < 0x6000) -> magenta shows, not blended.
//   IMAGE     : whole 32x32 matches the per-mode software reference.
//   GRID      : 4 tiles cleared (256 each) + 1024 flush; prim list = 3.

`timescale 1ns/1ps

module tb_top_psmct32_tile_alpha_demo;

    localparam int H_ACTIVE = 32, V_ACTIVE = 32;
    localparam int TP_CLEAR = 1;
    localparam real MARG = 0.08;
    localparam int Z0 = 'h5000, Z1 = 'h6000, Z2 = 'h5800, ZCLR = 'h4000;

    logic clk, rst_n;
    initial clk = 1'b0;
    always #5 clk = ~clk;

    logic        core_go;
    logic [7:0]  r, g, b;
    logic        hsync, vsync, de;
    logic        core_halt, dma_done_seen, frame_seen, raster_overflow;
    logic        frame_toggle, dma_done_toggle;

    top_psmct32_raster_demo_bram #(
        .H_ACTIVE(H_ACTIVE), .V_ACTIVE(V_ACTIVE),
        .VRAM_BYTES(16*1024), .PSMCT32_SWIZZLE(1'b0),
        .COMBINED_TAZ(1'b1), .TILE_LOCAL(1'b1), .TILE_COLS(2), .TILE_ROWS(2),
        .TILE_MULTIPRIM(1'b1), .TILE_PRIM_COUNT(3), .ALPHA_MODES_ENABLE(1'b1)
    ) dut (
        .clk(clk), .rst_n(rst_n), .core_go(core_go),
        .r(r), .g(g), .b(b), .hsync(hsync), .vsync(vsync), .de(de),
        .core_halt(core_halt), .dma_done_seen(dma_done_seen),
        .frame_seen(frame_seen), .raster_overflow(raster_overflow),
        .frame_toggle(frame_toggle), .dma_done_toggle(dma_done_toggle),
        .joy_a_pressed_i(1'b0), .joy_b_pressed_i(1'b0)
    );

    function automatic int tri_cls(input real px, input real py,
                                   input real ax, input real ay,
                                   input real bx, input real by,
                                   input real cx, input real cy);
        real d, wa, wb, wc;
        begin
            d  = (by-cy)*(ax-cx) + (cx-bx)*(ay-cy);
            wa = ((by-cy)*(px-cx) + (cx-bx)*(py-cy)) / d;
            wb = ((cy-ay)*(px-cx) + (ax-cx)*(py-cy)) / d;
            wc = 1.0 - wa - wb;
            if (wa>MARG && wb>MARG && wc>MARG)            tri_cls = 1;
            else if (wa<-MARG || wb<-MARG || wc<-MARG)    tri_cls = 0;
            else                                          tri_cls = 2;
        end
    endfunction
    // source-over channel: clamp(((cs-cd)*as>>>7)+cd)
    function automatic logic [7:0] sovr(input int cs, input int cd, input int aa);
        int t; begin t=((cs-cd)*aa)>>>7; t=t+cd; if(t<0)t=0; if(t>255)t=255; sovr=t[7:0]; end
    endfunction
    // additive channel (FIX=0x80): clamp(((cs-0)*128>>>7)+cd) = clamp(cs+cd)
    function automatic logic [7:0] addc(input int cs, input int cd);
        int t; begin t=((cs-0)*'h80)>>>7; t=t+cd; if(t<0)t=0; if(t>255)t=255; addc=t[7:0]; end
    endfunction

    int  clear_cw_tile [0:1][0:1];
    int  flush_emits;
    bit  saw_prim_count_3;
    initial begin
        for (int rr=0;rr<2;rr++) for (int cc=0;cc<2;cc++) clear_cw_tile[rr][cc]=0;
        flush_emits=0; saw_prim_count_3=1'b0;
    end
    always_ff @(posedge clk) if (rst_n) begin
        if (dut.u_gs.tile_phase==TP_CLEAR && dut.u_gs.tile_color_we) begin
            int cc, rr; cc=int'(dut.u_gs.tile_col_r); rr=int'(dut.u_gs.tile_row_r);
            if (cc<2 && rr<2) clear_cw_tile[rr][cc] <= clear_cw_tile[rr][cc] + 1;
        end
        if (dut.u_gs.raster_pixel_emit) flush_emits <= flush_emits + 1;
        if (dut.u_gs.raster_active && (int'(dut.u_gs.prim_count_r)==3)) saw_prim_count_3 <= 1'b1;
    end

    logic [7:0] cap_r[0:V_ACTIVE-1][0:H_ACTIVE-1], cap_g[0:V_ACTIVE-1][0:H_ACTIVE-1], cap_b[0:V_ACTIVE-1][0:H_ACTIVE-1];
    logic       cap_de[0:V_ACTIVE-1][0:H_ACTIVE-1];
    bit capture_armed;
    initial begin
        for (int y=0;y<V_ACTIVE;y++) for (int x=0;x<H_ACTIVE;x++) begin cap_r[y][x]=0;cap_g[y][x]=0;cap_b[y][x]=0;cap_de[y][x]=0; end
        capture_armed=1'b0;
    end
    logic [31:0] hcnt_d, vcnt_d;
    always_ff @(posedge clk) begin
        if (!rst_n) begin hcnt_d<=0; vcnt_d<=0; end
        else begin hcnt_d<=32'(dut.u_pcrtc.hcnt); vcnt_d<=32'(dut.u_pcrtc.vcnt); end
    end
    always_ff @(posedge clk) begin
        if (rst_n && capture_armed && de && (vcnt_d<V_ACTIVE) && (hcnt_d<H_ACTIVE)) begin
            cap_r[vcnt_d][hcnt_d]<=r; cap_g[vcnt_d][hcnt_d]<=g; cap_b[vcnt_d][hcnt_d]<=b; cap_de[vcnt_d][hcnt_d]<=1'b1;
        end
    end

    int errors, n_match, n_check, n_seam, n_magenta, n_lblue;

    initial begin
        errors=0; n_match=0; n_check=0; n_seam=0; n_magenta=0; n_lblue=0;
        rst_n=1'b0; core_go=1'b0;
        repeat(4) @(posedge clk); rst_n=1'b1; repeat(8) @(posedge clk);
        @(negedge clk); core_go=1'b1; @(negedge clk); core_go=1'b0;
        wait (core_halt==1'b1); repeat(4) @(posedge clk);
        wait (dma_done_seen==1'b1); repeat(10) @(posedge clk);
        if (dut.xfer_busy==1'b1) wait (dut.xfer_busy==1'b0);
        @(posedge dut.u_gs.raster_active);
        @(negedge dut.u_gs.raster_active);
        repeat(10) @(posedge clk);
        @(posedge dut.u_pcrtc.end_of_frame); @(posedge clk); capture_armed=1'b1;
        @(posedge dut.u_pcrtc.end_of_frame); @(posedge clk); capture_armed=1'b0;

        for (int rr=0;rr<2;rr++) for (int cc=0;cc<2;cc++)
            if (clear_cw_tile[rr][cc] != 256) begin
                $error("[tal] tile(col=%0d,row=%0d) cleared %0d (want 256)", cc, rr, clear_cw_tile[rr][cc]); errors++;
            end
        if (flush_emits != 4*256) begin $error("[tal] flush emitted %0d (want %0d)", flush_emits, 4*256); errors++; end
        if (!saw_prim_count_3)     begin $error("[tal] prim_count_r never == 3"); errors++; end

        // reference: P0 source-over (blue) -> P1 ADDITIVE (red) -> P2 source-over (white)
        for (int py=0; py<V_ACTIVE; py++) begin
            for (int px=0; px<H_ACTIVE; px++) begin
                int c0, c1, c2, zz; logic [7:0] cr, cg, cb, er, eg, eb;
                c0 = tri_cls(real'(px),real'(py),  1, 1, 30, 1, 15,30);
                c1 = tri_cls(real'(px),real'(py),  8, 3, 22, 3, 15,20);
                c2 = tri_cls(real'(px),real'(py),  7, 9, 23, 9, 15,28);
                if (c0==2 || c1==2 || c2==2) begin er=8'hxx; eg=8'hxx; eb=8'hxx; end
                else begin
                    cr=0; cg=128; cb=0; zz=ZCLR;
                    if (c0==1 && Z0>=zz) begin cr=sovr(0,cr,'h80);   cg=sovr(0,cg,'h80);   cb=sovr(255,cb,'h80); zz=Z0; end  // blue src-over
                    if (c1==1 && Z1>=zz) begin cr=addc(255,cr);      cg=addc(0,cg);        cb=addc(0,cb);        zz=Z1; end  // red ADDITIVE
                    if (c2==1 && Z2>=zz) begin cr=sovr(255,cr,'h40); cg=sovr(255,cg,'h40); cb=sovr(255,cb,'h40); zz=Z2; end  // white src-over
                    er=cr; eg=cg; eb=cb;
                end

                if (er!==8'hxx && cap_de[py][px]) begin
                    n_check++;
                    if (er==8'hFF && eg==8'h00 && eb==8'hFF) n_magenta++;   // additive red over blue
                    if (er==8'h7F && eg==8'h7F && eb==8'hFF) n_lblue++;     // source-over white over blue
                    if (cap_r[py][px]===er && cap_g[py][px]===eg && cap_b[py][px]===eb) begin
                        n_match++;
                        if (px==15||px==16||py==15||py==16) n_seam++;
                    end else begin
                        if (errors<14) $error("[tal] (%0d,%0d) got(%02x,%02x,%02x) exp(%02x,%02x,%02x) [c0%0d c1%0d c2%0d]",
                                              px,py,cap_r[py][px],cap_g[py][px],cap_b[py][px],er,eg,eb,c0,c1,c2);
                        errors++;
                    end
                end
            end
        end

        if (n_check < 200)      begin $error("[tal] too few checkable pixels (%0d)", n_check); errors++; end
        if (n_match != n_check) begin $error("[tal] image match %0d/%0d (alpha-mode error)", n_match, n_check); errors++; end
        if (n_magenta < 10)     begin $error("[tal] ADDITIVE (magenta) region thin (%0d) — additive not proven", n_magenta); errors++; end
        if (n_lblue   < 10)     begin $error("[tal] source-over (light-blue) thin (%0d) — src-over regressed?", n_lblue); errors++; end
        if (n_seam    < 15)     begin $error("[tal] too few SEAM matches (%0d)", n_seam); errors++; end
        if (!core_halt)         begin $error("core_halt low"); errors++; end
        if (raster_overflow)    begin $error("raster_overflow"); errors++; end

        $display("[tb_top_psmct32_tile_alpha_demo] clears=[%0d %0d %0d %0d] flush=%0d prim3=%0b match=%0d/%0d seam=%0d | magenta=%0d lblue=%0d errors=%0d",
                 clear_cw_tile[0][0],clear_cw_tile[0][1],clear_cw_tile[1][0],clear_cw_tile[1][1],
                 flush_emits, saw_prim_count_3, n_match, n_check, n_seam, n_magenta, n_lblue, errors);
        if (errors==0) $display("[tb_top_psmct32_tile_alpha_demo] PASS");
        else           $display("[tb_top_psmct32_tile_alpha_demo] FAIL");
        $finish;
    end

    initial begin #300000000; $error("[tb_top_psmct32_tile_alpha_demo] TIMEOUT"); $finish; end
endmodule : tb_top_psmct32_tile_alpha_demo
