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`timescale 1ns / 1ps

//////////////////////////////////////////////////////////////////////////////////

// Company: 

// Engineer: Yann Vernier

// 

// Create Date:    21:37:32 02/19/2011 

// Design Name: 

// Module Name:    vector2scanline 

// Project Name: PDP-1

// Target Devices: Spartan 3A

// Tool versions: 

// Description: Converts vector data (exposed points) into raster video

//

// Dependencies: 

//

// Revision: 

// Revision 0.01 - File Created

// Additional Comments: 

//

//////////////////////////////////////////////////////////////////////////////////

module vector2scanline(

    input clk,

    input strobe,

    input [9:0] x,

    input [9:0] y,

    input [9:0] xout,

    input [9:0] yout,

         input newline,

         input newframe,

    output [7:0] pixel

    );

parameter X_WIDTH = 10;

parameter Y_WIDTH = 10;

parameter HIST_WIDTH = 10;

parameter AGE_WIDTH = 8;

reg [X_WIDTH+Y_WIDTH+AGE_WIDTH-1:0] exposures [(2**HIST_WIDTH)-1:0];

reg [X_WIDTH+Y_WIDTH+AGE_WIDTH-1:0] expr;

wire [X_WIDTH-1:0] expx;

wire [Y_WIDTH-1:0] expy;

wire [7:0] expi;

wire exposed;

reg [HIST_WIDTH-1:0] exprptr=0, expwptr=0;

// double-buffered; one gets wiped as it is displayed

// the other gets filled in with current exposures

reg [AGE_WIDTH-1:0] scanline0 [(2**X_WIDTH)-1:0];

reg [AGE_WIDTH-1:0] scanline1 [(2**X_WIDTH)-1:0];

reg [AGE_WIDTH-1:0] pixelout;

reg bufsel = 0;

wire [X_WIDTH-1:0] sl0w, sl1w;

always @(posedge clk) begin

        expr<=exposures[exprptr];

        if (!strobe) begin

                exprptr<=exprptr+1;

        end

end

assign expx = strobe?x:expr[X_WIDTH+Y_WIDTH+AGE_WIDTH-1:Y_WIDTH+AGE_WIDTH];

assign expy = strobe?y:expr[Y_WIDTH+AGE_WIDTH-1:AGE_WIDTH];

assign expi = strobe?(2**AGE_WIDTH)-1:expr[AGE_WIDTH-1:0];

assign exposed = expi!=0;

always @(posedge clk) begin

        // Feed incoming exposures into exposure buffer

        if (exposed) begin

                exposures[expwptr] <= {expx, expy, expy==yout?expi-1:expi};

                expwptr <= expwptr+1;

        end

end

assign sl0w=bufsel?expx:xout;

assign sl1w=bufsel?xout:expx;

always @(posedge clk) begin

        // Read out & wipe front buffer

        // Store exposures for current scanline as well

        if (expy==(y+1)) begin

                scanline0[sl0w] <= bufsel?expi:0;

                scanline1[sl1w] <= bufsel?0:expi;

                pixelout <= bufsel?scanline1[xout]:scanline0[xout];

        end

        if (newframe) begin

                bufsel <= ~bufsel;

        end

end

assign pixel = pixelout;

endmodule