This sample source code below shows how to implement Gaussian blur filter in OpenGL (WebGL) shading language. This is a popular algorithm in computer graphics that results in a blurry image.

## Source Code

The GL shader code below implements a **separable convolution** that we can use for a Gaussian filter image blur effect. The **GSLS code** convolve a one-dimensional kernel with coefficients once row-wise and once column-wise.

```
precision mediump float;
// our texture
uniform sampler2D u_image;
#define KERNEL_SIZE 15
uniform vec2 u_textureSize;
uniform int u_direction;
uniform float u_kernel[KERNEL_SIZE];
void main() {
vec2 textCoord = gl_FragCoord.xy / u_textureSize;
vec2 onePixel = ((u_direction == 0) ? vec2(1.0, 0.0) : vec2(0.0, 1.0)) / u_textureSize;
vec4 meanColor = vec4(0);
int ms = KERNEL_SIZE / 2;
for (int i = 0; i < KERNEL_SIZE; i++)
{
meanColor += texture2D(u_image, textCoord + onePixel*vec2(i - ms))*u_kernel[i];
}
gl_FragColor = meanColor;
}
```

The code accepts the following shader variables:

**u_image**– this is our source image**u_kernel**– the filtering Gaussian kernel as one-dimension floating point array**u_direction**– the filter direction –*horizontal*or*vertical*

## How it works?

The algorithm applies a smoothing effect to images using a **Gaussian filter**.

Let’s say we have an image source ready as an OpenGL/WebGL texture. The following steps then briefly describe how the algorithm works:

- Initially we must calculate a Gaussian kernel
- We then assign it to the uniform variable
**u_kernel** - Set the uniform parameter
**u_direction**– rows or columns - Execute the shader program for both directions

## Example Results

The following picture depicts an example output from the source code:

## Bonus Tip

In case you are looking for a pure Java Script solution then you may take a look at the Gaussian blur in plain JS. You can also take a look at how to apply various filters via SVG.

## Try it Online

You can explore the above algorithm in our free online image processing app.

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*See how it works in the browser!*

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