1.越接近白色，越明亮
等比例缩放颜色，值越小越暗

#define PI 3.1415926

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

    vec3 orignal = vec3(1.0,1.0,0);

    orignal *= abs(sin(iTime));

    fragColor = vec4(orignal,1.0);
}

效果:

2.显示R通道

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    // 定义贴图坐标
    vec2 uv = fragCoord / iResolution.xy;
    // 采样贴图
    vec3 color = texture(iChannel0, uv).rgb;
    // 输出颜色
    fragColor = vec4(color, 1.0);
}

显示r通道

fragColor = vec4(vec3(color.r), 1.0);