1.shadertoy代码

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    // Normalized pixel coordinates (from 0 to 1)
    vec2 uv = fragCoord/iResolution.xy;
    uv -= 0.5;

    //将uv的x坐标进行放大
    uv.x *= iResolution.x / iResolution.y;

    uv = abs(uv);
    float c = dot(uv,vec2(1,1));
    vec3 col = vec3(0.0);
    col += step(c,0.5);
    fragColor = vec4(vec3(c),1.0);
}

越靠近中点，点积越接近0

2 四边形

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    // Normalized pixel coordinates (from 0 to 1)
    vec2 uv = fragCoord/iResolution.xy;
    uv -= 0.5;

    //将uv的x坐标进行放大
    uv.x *= iResolution.x / iResolution.y;

    uv = abs(uv);
    float c = dot(uv,vec2(1,1));
    vec3 col = vec3(0.0);
    col += step(c,0.5);
    fragColor = vec4(col,1.0);
}