Alpha blending

A fragment is eligible for alpha blending if it has passed the depth test. However, when depth testing is disabled, all fragments are eligible for alpha blending.

Alpha blending is enabled using the following line of code:

gl.enable(gl.BLEND);

For each eligible fragment the alpha blending operation reads the color present in the frame buffer for those fragment coordinates and creates a new color that is the result of a linear interpolation between the color previously calculated in the fragment shader (gl_FragColor) and the color already present in the frame buffer.

Note

Alpha blending is disabled by default in WebGL.

Blending function

With blending enabled, the next step is to define a blending function. This function will determine how the fragment colors coming from the object we are rendering (source) will be combined with the fragment colors already present in the frame buffer (destination).

We combine source and destination as follows:

Color Output = S * sW + D * dW

Here,

• S: source...