如何在 glsl 中编写 cga 着色器？

Question

如何编写将调色板限制为 4 种颜色并将原始颜色与这些颜色（青色、品红色、黑色、白色）相匹配的 CGA 着色器？？

我正在开发 Game Maker Studio Professional，它实际上允许使用着色器编写顶点和片段代码

我已经在 yoyogames 社区和 openGl 论坛中问过这个问题

有人这样回答我：

varying vec2 v_vTexcoord;
varying vec4 v_vColour;

const mat3 rgb_to_wcm = mat3(1,-1, 0,  1, 0,-1, -1, 1, 1);

void main()
{
    vec4 rgba = v_vColour * texture2D(gm_BaseTexture, v_vTexcoord);
    vec3 wcm = rgb_to_wcm * rgba.rgb;
    vec3 rgb = dot(wcm,vec3(1,1,1)) < 0.5
        ? vec3(0,0,0)
        : wcm.x > wcm.y
            ? (wcm.x > wcm.z ? vec3(1,1,1) : vec3(1,0,1))
            : (wcm.y > wcm.z ? vec3(0,1,1) : vec3(1,0,1));
    gl_FragColor = vec4(rgb, rgba.a);
}

它有效，但不是 return cga 调色板，它 return 黑白（非灰度）

我该怎么办？

Answer 1

非常感谢我用不同的方式做了，也许更简单

https://www.shadertoy.com/view/MdlyDH

//   ▄████████    ▄██████▄     ▄████████ 
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//  ███         ▄███          ███    ███ 
//  ███        ▀▀███ ████▄  ▀███████████ 
//  ███    █▄    ███    ███   ███    ███ 
//  ███    ███   ███    ███   ███    ███ 
//  ████████▀    ████████▀    ███    █▀  
// 

/*

////only for game maker studio////

varying vec2 v_vTexcoord;
varying vec4 v_vColour;

varying vec2 fragCoord;
//you have to put varying vec2 fragCoord also in the vertex shader
//after write in the last row of the local scope of the vertex shader: fragCoord = in_Position.xy

uniform vec2 iResolution;
uniform float iGlobalTime;

//palette 0 is not cga but gameboy, I put it as bonus
uniform int palette;
uniform float gamma;

*/

// rgb to float
// rgb to float = rgb / 255

// 0 = 0.0
// 85 = 0.333
// 170 = 0.666
// 255 = 1.0

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    vec2 uv = fragCoord.xy / iResolution.xy;

    vec3 c = vec3(0.0);
    float alpha = 1.0;

    //only for shadertoy
    int palette = 2; //the number between 0 and 6 change palette
    float gamma = 1.5; //the gamma change the threshold of the palette swapper

    //c = texture2D(gm_BaseTexture,uv).rgb;
    c = texture(iChannel0,uv).rgb;

    c.r = pow(abs(c.r),gamma);
    c.g = pow(abs(c.g),gamma);
    c.b = pow(abs(c.b),gamma);

    vec3 col1 = vec3(0.0);
    vec3 col2 = vec3(0.0);
    vec3 col3 = vec3(0.0);
    vec3 col4 = vec3(0.0);

    if(palette == 0) {
        col1 = vec3(0.612,0.725,0.086);
        col2 = vec3(0.549,0.667,0.078);
        col3 = vec3(0.188,0.392,0.188);
        col4 = vec3(0.063,0.247,0.063);
    }
    if(palette == 1) {
        col1 = vec3(0.0);
        col2 = vec3(0.0,0.666,0.666);
        col3 = vec3(0.666,0.0,0.666);
        col4 = vec3(0.666,0.666,0.666);
    }
    if(palette == 2) {
        col1 = vec3(0.0);
        col2 = vec3(0.333,1.0,1.0);
        col3 = vec3(1.0,0.333,1.0);
        col4 = vec3(1.0);
    }
    if(palette == 3) {
        col1 = vec3(0.0);
        col2 = vec3(0.0,0.666,0.0);
        col3 = vec3(0.666,0.0,0.0);
        col4 = vec3(0.666,0.333,0.0);
    }
    if(palette == 4) {
        col1 = vec3(0.0);
        col2 = vec3(0.333,1.0,0.333);
        col3 = vec3(1.0,0.333,0.333);
        col4 = vec3(1.0,1.0,0.333);
    }
    if(palette == 5) {
        col1 = vec3(0.0);
        col2 = vec3(0.0,0.666,0.666);
        col3 = vec3(0.666,0.0,0.0);
        col4 = vec3(0.666,0.666,0.666);
    }
    if(palette == 6) {
        col1 = vec3(0.0);
        col2 = vec3(0.333,0.666,0.666);
        col3 = vec3(1.0,0.333,0.333);
        col4 = vec3(1.0);
    }

    float dist1 = length(c - col1);
    float dist2 = length(c - col2);
    float dist3 = length(c - col3);
    float dist4 = length(c - col4);

    float d = min(dist1,dist2);
    d = min(d,dist3);
    d = min(d,dist4);

    if(d == dist1) {
        c = col1;
    }
    else if(d == dist2) {
        c = col2;
    }
    else if(d == dist3) {
        c = col3;
    }
    else {
        c = col4;
    }

    //gl_FragColor = vec4(c,alpha).rgba;
    fragColor = vec4(c,alpha).rgba;
}

这里我还包括了将这个 shadertoy 着色器转换为 game maker studio 着色器的方法，因为在 game maker studio 中没有统一的时间和分辨率来进行时间编辑和 vec2 uv

我还包括了所有 cga 调色板的评论右调色板和一个 gameboy 调色板的奖励调色板 0

我还包括了从 rgb 255 值到无法转换的浮点数的转换

这里唯一的问题是它不能反转颜色或改变调色板中颜色的位置，它采用原始源并输出 4 种颜色，这是唯一的差距。

如何在 glsl 中编写 cga 着色器？

how to write a cga shader in glsl?

glsl

shader

fragment-shader

game-maker

gml