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FPGA VGA Glitch Problem

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nmcgnyksl

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Hello everyone,
I am trying to create a game on FPGA and to do so I need to use VGA. However there are glitches on the screen and I don't know what causes this problem. Help is much appriciated. I am posting the screen photo and the scynhonization code. I am using 640x480 60Hz. Thank you.
(Sorry for my english if there is any problem)

20150509_094845.jpg


Code Verilog - [expand]
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parameter hpix = 800;    // total horizontal pixels
parameter vpix = 525;   // total vertical pixels
parameter hlow = 96;        // first low signal of horizontal
parameter hbp = 144;        // end of back porch
parameter hfp = 784;        // start of front porch
parameter vlow = 2;     // first low vertical
parameter vbp = 35;     // back porch end
parameter vfp = 515;        // front porch start
 
    always @(posedge sclk)  //counting hreg vreg
                    begin
                        if (hreg < hpix-1)
                              hreg <= hreg+1;
                        else 
                           begin
                             hreg <=0;
                            if (vreg < vpix-1)
                        vreg <= vreg+1;
                        else 
                         vreg <=0;
                           end
                if(hreg>142)   //  generating creating screen map for sh<640 sv<480
                 sh <= hreg-143;
                else
                 sh <= hreg+657;
                 if(vreg>31)
                 sv <= vreg-32;
                else
                 sv <= vreg+491;
                    end
 
assign hsync = (hreg<hlow) ? 0:1;
assign vsync = (vreg<vlow) ? 0:1;

 
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