Shaders Help with tweaking a free shader's effects.

[Mauldini]

I'm really loving this CRT-style shader, released free by xygthrop3.
https://marketplace.yoyogames.com/assets/701/crt-pixel-shader

Is anyone familiar with writing/tweaking shader code?

The game I'm working on is very dark. I'd like to remove the default scan-lines (Both colored vertical lines and thin horizontal lines.) I could then draw my own from sprites.

• The vertical lines, pink and green, give my lighting a plaid-like texture.
• The horizontal lines produce awkward circular rings when bending the screen's edge.

A screenshot:


The border-fade and screen warp effects are awesome - those I'd like to keep intact.


Shader code:

Vertex tab:

attribute vec3 in_Position;
attribute vec4 in_Colour;
attribute vec2 in_TextureCoord;

varying vec2 v_vTexcoord;

void main()
{
    gl_Position = gm_Matrices[MATRIX_WORLD_VIEW_PROJECTION] * vec4(in_Position, 1.0);
    v_vTexcoord = in_TextureCoord;
}

Fragment tab:

varying vec2 v_vTexcoord;

uniform vec4 u_crt_sizes;
uniform float distortion;
uniform bool distort;
uniform bool border;

    #define TEX2D(c) pow(abs(texture2D(gm_BaseTexture, (c))), vec4(inputGamma))       
    float PI = 3.141592653589;
    float inputGamma = 2.4;
    float outputGamma = 2.8;
 
    vec4 scanlineWeights(float dist, vec4 col)
    {
        vec4 wid = 1.0 + 2.0 * pow(col, vec4(4.0));
        vec4 weights = vec4(dist * 3.333333);             
        return 0.51 * exp(-pow(abs(weights * sqrt(2.0 / wid)), wid)) / (0.18 + 0.06 * wid);
    }

    vec2 overscan = vec2(0.99, 0.99);
    vec2 aspect = vec2(u_crt_sizes.x/u_crt_sizes.x, u_crt_sizes.y/u_crt_sizes.x);
    float cornersize = 0.03;
    float cornersmooth = 80.0;
   
    float corner(vec2 coord)
    {
        coord = (coord - vec2(0.5)) * overscan + vec2(0.5);
        coord = min(coord, vec2(1.0)-coord) * aspect;
        vec2 cdist = vec2(cornersize);
        coord = (cdist - min(coord,cdist));
        float dist = sqrt(dot(coord,coord));
        return clamp((cdist.x-dist)*cornersmooth,0.0, 1.0);
    }

    vec2 radialDistortion(vec2 coord)
    {
        vec2 cc = coord - 0.5;
        float dist = dot(cc, cc) * distortion;
        return (coord + cc * (1.0 + dist) * dist);
    }
 
void main()
{
    vec2 one = 1.0 / u_crt_sizes.xy;
    vec2 _xy;
 
    if (distort == true)
        { _xy = radialDistortion(v_vTexcoord); }
    else
        { _xy = v_vTexcoord; }
     
    vec2 uv_ratio = fract(_xy * u_crt_sizes.xy) - vec2(0.5);

    float cval = corner(_xy);
 
    _xy = (floor(_xy * u_crt_sizes.xy) + vec2(0.5)) / u_crt_sizes.xy;
 
    vec4 coeffs = PI * vec4(1.0 + uv_ratio.x, uv_ratio.x, 1.0 - uv_ratio.x, 2.0 - uv_ratio.x);
    coeffs = max(abs(coeffs), 1e-6);
    coeffs = 2.0 * sin(coeffs) * sin(coeffs / 2.0) / (coeffs * coeffs);   
    coeffs /= dot(coeffs, vec4(1.0));

    vec4 col  = clamp(coeffs.x * TEX2D(_xy + vec2(-one.x, 0.0))   + coeffs.y * TEX2D(_xy)+ coeffs.z * TEX2D(_xy + vec2(one.x, 0.0)) + coeffs.w * TEX2D(_xy + vec2(2.0 * one.x, 0.0)),   0.0, 1.0);
    vec4 col2 = clamp(coeffs.x * TEX2D(_xy + vec2(-one.x, one.y)) + coeffs.y * TEX2D(_xy + vec2(0.0, one.y)) + coeffs.z * TEX2D(_xy + one)+ coeffs.w * TEX2D(_xy + vec2(2.0 * one.x, one.y)), 0.0, 1.0);

    vec4 weights  = scanlineWeights(abs(uv_ratio.y) , col);
    vec4 weights2 = scanlineWeights(1.0 - uv_ratio.y, col2);

    float mod_factor = v_vTexcoord.x * u_crt_sizes.z * u_crt_sizes.z / u_crt_sizes.z;
    vec3 dotMaskWeights = mix( vec3(1.05, 0.75, 1.05), vec3(0.75, 1.05, 0.75), floor(mod(mod_factor, 2.0)) );
 
    vec3 mul_res  = (col * weights + col2 * weights2).xyz;
    mul_res *= dotMaskWeights;
 
    if (border == true)
        { mul_res = pow(abs(mul_res), vec3(1.0 / (2.0 * inputGamma - outputGamma)))* vec3(cval); }
    else
        { mul_res = pow(abs(mul_res), vec3(1.0 / (2.0 * inputGamma - outputGamma))); }
 
    gl_FragColor = vec4(mul_res, 1.0);
}

Controller object code:

Create event:

// Store shader attributes.
uni_crt_sizes = shader_get_uniform(sh_CRT, "u_crt_sizes");
distort = shader_get_uniform(sh_CRT, "distort");
distortion = shader_get_uniform(sh_CRT, "distortion");
border = shader_get_uniform(sh_CRT, "border");
var_distort = true;
var_distortion_ammount = 0.2;
var_border = true;

Draw-GUI event:

// Enable shader.
shader_set(sh_CRT);

// No clue what this does.
//texture_set_stage(samp_CRT, tex_CRT);

// Configure shader.
shader_set_uniform_f(uni_crt_sizes, surface_width, surface_height, crt_surface_width, crt_surface_height);
shader_set_uniform_f(distort, var_distort); //combine 2
shader_set_uniform_f(distortion, var_distortion_ammount); //combine 2
shader_set_uniform_f(border, var_border); //combine 2

Thank you for your attention.