Moving blobs used as interpolation values between two images.

blend.shader

#define INTENSITY 6.5

float blob(vec2 uv, vec2 speed, float time) {
	// Compute a moving point
	vec2 point = vec2(
		sin(speed.x * time),
		cos(speed.y * time)
	);

	float d = 1.0 / distance(uv, point) / INTENSITY;
	
	return clamp(d, 0.0, 1.0);
}

void main(void) {
	// We might not need this, it should be provided by the context
	vec2 uv = -1.0 + 2.0 * (gl_FragCoord.xy / iResolution.xy);
	uv.y *= iResolution.y/iResolution.x;

	vec4 fg = texture2D(iChannel0, uv); // Sample blur 1
	vec4 bg = texture2D(iChannel1, uv); // Sample blur 2
	
	float d = 0.0; // Compute depth map
	d += blob(uv, vec2(0.7, 0.2), iGlobalTime);
	d += blob(uv, vec2(0.2, 0.3), iGlobalTime);
	d += blob(uv, vec2(0.3, 0.1), iGlobalTime);
	
	// Lerp between foreground+background
	vec4 color = mix(fg, bg, 1.0 - d);
	// DEBUG: color = vec4(d, d, d, 1.0);
	gl_FragColor = color;
}

blend2.shader

#define INTENSITY 0.1

float blob(vec2 uv, vec2 speed) {
	vec2 point = vec2(
		sin(speed.x * iGlobalTime),
		cos(speed.y * iGlobalTime)
	);

	return pow(distance(uv, point), 2.0) * INTENSITY;
}

void main(void) {
	// We might not need this, it should be provided by the context
	vec2 uv = (gl_FragCoord.xy / iResolution.xy) * vec2(1.0, -1.0);

	vec4 fg = texture2D(iChannel0, uv); // Sample blur 1
	vec4 bg = texture2D(iChannel1, uv); // Sample blur 2
	
	float d = 0.0; // Compute depth map
	d += blob(uv, vec2(1.7, 1.2));
	d += blob(uv, vec2(1.2, 1.3));
	d += blob(uv, vec2(1.3, 1.1));
	d = clamp(d, 0.0, 1.0);
	
	// Lerp between foreground+background
	vec4 color = mix(fg, bg, d);
	color = vec4(d, d, d, 1.0);
	gl_FragColor = color;	
}