Babylon.js/src/Shaders/convolution.fragment.fx

// Samplers
varying vec2 vUV;
uniform sampler2D textureSampler;

uniform vec2 screenSize;
uniform float kernel[9];

void main(void)
{
	vec2 onePixel = vec2(1.0, 1.0) / screenSize;
	vec4 colorSum =
		texture2D(textureSampler, vUV + onePixel * vec2(-1, -1)) * kernel[0] +
		texture2D(textureSampler, vUV + onePixel * vec2(0, -1)) * kernel[1] +
		texture2D(textureSampler, vUV + onePixel * vec2(1, -1)) * kernel[2] +
		texture2D(textureSampler, vUV + onePixel * vec2(-1, 0)) * kernel[3] +
		texture2D(textureSampler, vUV + onePixel * vec2(0, 0)) * kernel[4] +
		texture2D(textureSampler, vUV + onePixel * vec2(1, 0)) * kernel[5] +
		texture2D(textureSampler, vUV + onePixel * vec2(-1, 1)) * kernel[6] +
		texture2D(textureSampler, vUV + onePixel * vec2(0, 1)) * kernel[7] +
		texture2D(textureSampler, vUV + onePixel * vec2(1, 1)) * kernel[8];

	float kernelWeight =
		kernel[0] +
		kernel[1] +
		kernel[2] +
		kernel[3] +
		kernel[4] +
		kernel[5] +
		kernel[6] +
		kernel[7] +
		kernel[8];

	if (kernelWeight <= 0.0) {
		kernelWeight = 1.0;
	}

	gl_FragColor = vec4((colorSum / kernelWeight).rgb, 1);
}