Code
precision mediump float;
uniform vec2 m; // mouse
uniform float t; // time
uniform vec2 r; // resolution
uniform sampler2D smp; // prev scene
void main(void){
const vec4 color1 = vec4(0.0, 0.18, 0.28, 1.0); // 下
const vec4 color2 = vec4(0.0, 0.0, 0.0, 1.0); // 上
float percent = 1.0 - (gl_FragCoord.y / r.y);
gl_FragColor = color1 * percent + color2 * (1.0 - percent);
}