Three.js (GLSL) basic bloom shader

bloom.fragment.glsl

// THREEjs build-in uniforms and attributes (Fragment)

// uniform mat4 viewMatrix - camera.matrixWorldInverse
// uniform vec3 cameraPosition - camera position in world space

varying vec2 vUv;

uniform sampler2D albedo;

void main() {
	vec4 col = vec4(0);
	// Current texture coordinate
	vec2 texel = vUv;
	vec4 pixel = vec4(texture2D(albedo, texel));

	// Mean spread value
	float pixelWidth = 0.1;
    float pixelHeight = 0.1;
    // Dim factor
    float dim = 0.75;

	if (pixel.a < 1.0) {
		// Glow is based on the alpha value
		float glow = pixel.a * ((pixelWidth + pixelHeight) / 2.0);

		vec4 bloom = vec4(0);	// The vector to contain the new, "bloomed" colour values

		// Apply a horrible version of "mean filter"
		// Horrible because GLSL needs constants for loop initializations
		bloom += (texture2D(albedo, vec2(texel.x, texel.y)) - dim);
		bloom += (texture2D(albedo, vec2(texel.x - glow, texel.y - glow)) - dim);
		bloom += (texture2D(albedo, vec2(texel.x + glow, texel.y + glow)) - dim);
		bloom += (texture2D(albedo, vec2(texel.x + glow, texel.y - glow)) - dim);
		bloom += (texture2D(albedo, vec2(texel.x - glow, texel.y + glow)) - dim);
		bloom += (texture2D(albedo, vec2(texel.x + glow, texel.y)) - dim);
		bloom += (texture2D(albedo, vec2(texel.x - glow, texel.y)) - dim);
		bloom += (texture2D(albedo, vec2(texel.x, texel.y + glow)) - dim);
		bloom += (texture2D(albedo, vec2(texel.x, texel.y - glow)) - dim);

		// Clamp the value between a 0.0 to 1.0 range
		bloom = clamp(bloom / 9.0, 0.0, 1.0);

		col = pixel + bloom;
	} else {
		col = vec4(pixel.rgb, 1.0);
	}

	gl_FragColor = col;
}

bloom.vertex.glsl

// THREEjs build-in uniforms and attributes (Vertex)

// uniform mat4 modelMatrix - object.matrixWorld
// uniform mat4 modelViewMatrix - camera.matrixWorldInverse * object.matrixWorld
// uniform mat4 projectionMatrix - camera.projectionMatrix
// uniform mat4 viewMatrix - camera.matrixWorldInverse
// uniform mat3 normalMatrix - inverse transpose of modelViewMatrix
// uniform vec3 cameraPosition - camera position in world space
// attribute vec3 position - vertex position
// attribute vec3 normal - vertex normal
// attribute vec2 uv - uv
// attribute vec2 uv2 - uv2

varying vec2 vUv;

void main()
{
	vUv = uv;

	gl_Position = projectionMatrix * modelViewMatrix * vec4(position, 1.0);
}