Here we show how to enable transparency for glTF-compliant PBR, Cycles and Eevee materials in Blender. Blender 2.7 Internal materials are not discussed since they are deprecated and are not recommended for use.

Blended vs Masked

Being a real-time 3D engine, Verge3D offers two main methods to handle transparent objects: alpha blending and alpha clipping (usually with an image mask). Blending enables combining a translucent foreground color with a background color, using the foreground color's alpha as blending factor. Clipping, on the other hand, simply discards all pixels with alpha less than some predefined threshold (usually 0.5).
Blending enables for smooth transitions, generally looks nicer but computationally more expensive than clipping. It may also produce z-sorting artifacts when polygons appear to be rendered in wrong order. Clipping works best for visualizing numerous small objects (such as grass or tree leaves). It also produces hard edges without any transitions which may be aliased.

Alpha Add (aka No Depth Writes)

Verge3D also offers a special mode for disabling writing to the depth buffer while rendering. This results in polygons being excluded from pixel depth comparison. Such polygons are composited in additive manner, which sometimes can help get rid of blending artifacts.

Rendering Order (aka Z-index)

Verge3D does not perform sorting of polygons inside objects, but rather performs sorting between objects. This provides correct blending in most cases but sometimes one may need to forcibly change the rendering order for an object.
To modify the rendering order for a particular object, change the numeric field in the Verge3D settings panel. The smaller the index, the earlier the object will be rendered.
So, if you have a transparent, continuous object in the rear and want other transparent objects in the front to render correctly, set some negative value as the rendering order of the rear object.

Transparency for glTF-compliant PBR Materials

In order to enable transparency for such materials, add alpha mask information to the alpha channel of the base color texture. Then connect texture's alpha channel with the Alpha input of the Verge3D PBR node.
Use the AlphaMode slider to change the transparency type: 0 will enable blending, 1 - masking.

Transparency for Cycles Materials

In Cycles, transparency can be enabled by using a combination of the Transparent BSDF and the Mix Shader nodes. Be sure to also turn on the Transparency checkbox on the Verge3D settings panel. Use the transparency type selector to switch between blending and masking modes.
The factor in the Mix Shader node can be used to define the alpha value. You can also connect this input with a texture containing alpha information in its RGB or alpha channels.
Use the Alpha Add Transparency checkbox to enable the additive mode.

Transparency for Eevee Materials

Similar to Cycles, transparency for Eevee materials can be enabled by using a combination of the Transparent BSDF and the Mix Shader nodes. The factor in the Mix Shader node can be used to define the alpha value - you can directly specify a value or create a dependency from some other nodes such as Fresnel for more realistic look.
Use the Blend Mode dropdown to choose between transparency modes.