To incorporate a custom vertex attribute for the alpha value, utilize THREE.ShaderMaterial. Follow these steps for implementation:
1) Within the vertex shader, define an attribute float for the alpha value. Additionally, declare a varying float in both the vertex and fragment shaders.
Vertex shader:
attribute float customAlpha;
varying float vCustomAlpha;
Fragment shader:
varying float vCustomAlpha;
2) Link the alpha attribute value to the varying value in the vertex shader.
Vertex shader:
vCustomAlpha = customAlpha;
3) Once all calculations are complete, assign the varying alpha value to the alpha component of gl_FragColor.
Fragment shader:
gl_FragColor.a = vCustomAlpha;
4) On the host side, introduce an array equal to the total vertex count. Refer to the code snippet below -
var geometry = new THREE.BufferGeometry();
geometry.addAttribute('position', new THREE.BufferAttribute(vertices, 3));
var alphaCustomArray = [];
var alphaCustomArrayLength = vertices.length / 3;
for(var i = 0; i < alphaCustomArrayLength; i++) {
alphaCustomArray.push(0.5);
}
5) Add a specialized attribute for the alpha value within the geometry and update it using the generated array -
geometry.addAttribute('customAlpha', new THREE.BufferAttribute(new Float32Array(alphaCustomArray), 1));
6) Initialize a THREE.ShaderMaterial -
var newMaterial = new THREE.ShaderMaterial({
vertexColors: THREE.VertexColors,
side: THREE.DoubleSide,
transparent: true,
vertexShader: document.
getElementById('custom_vertex_shader').text,
fragmentShader: document.
getElementById('custom_fragment_shader').text
});
7) Generate the mesh with the defined geometry and material -
var customMesh = new THREE.Mesh(geometry, newMaterial);