glsl background is black

OpenGL Development
#1

Hello Guys,
I recently started looking into GLSL and tried implementing an effect i found online.The effect worked but the background behind the effect is black. I want that only the effect is visible and not the black backgroung but instead the stuff thats already rendered. Im using LibGDX for the rendering. Here is the GLSL code so far:

#ifdef GL_ES
precision mediump float;
#endif

varying vec4 v_color;
varying vec2 v_texCoord0;

uniform sampler2D u_sampler2D;

uniform float time;
uniform vec2 mouse;
uniform vec2 resolution;


void main( void )
{
    vec4 color_original = texture2D(u_sampler2D, v_texCoord0) * v_color;
    
	vec2 uPos = ( gl_FragCoord.xy / resolution.xy );
	
	uPos.x -= 1.0;
	uPos.y -= 0.5;
	
	vec3 color = vec3(0.0);
	float vertColor = 2.0;
	for( float i = 0.0; i < 15.0; ++i )
	{
		float t = time * (0.9);
	
		uPos.y += sin( uPos.x*i + t+i/2.0 ) * 0.1;
		float fTemp = abs(1.0 / uPos.y / 100.0);
		vertColor += fTemp;
		color += vec3( fTemp*(10.0-i)/10.0, fTemp*i/10.0, pow(fTemp,1.5)*1.5 );
	}
	
	color_original.rgb = mix(color_original.rgb, color.rgb, 1.0);
	gl_FragColor = color_original;
}

Help is appreciated :slight_smile: