TextureMerger

TextureMerger is a lightweight client-side Javascript library that generates a texture atlas from provided Three.js textures and calculates the UV coordinates for each texture inside the atlas.

TextureMerger produces power-of-two textures, so the atlas generated by TextureMerger can be compressed.

Ported from TextureMerger class of ROYGBIV Engine.

What can you do with it?

You can pack your textures into one big texture, share the texture uniform across different meshes to gain performance. You can also pack different textures of a single mesh (emissive texture, displacement texture etc.) into a one texture for only one mesh.

Example

Check out this live example.

In this example a single Texture Atlas is shared by 4 different meshes, however each of these meshes look like they have a separate texture mapped.

Usage

Include the library in your HTML

<script src="path_to_TextureMerger.js"></script>

Merge your Textures

var texture1, texture2, texture3; // Both instances of THREE.Texture
loadTextures(); // Your texture loading logic

var textureMerger = new TextureMerger({
	texture1: texture1,
	texture2: texture2,
	texture3: texture3
});

var atlas = textureMerger.mergedTexture;
var ranges = textureMerger.ranges;
console.log(ranges);

Prints:

{
	texture1: {startU: 0, endU: 0.25, startV: 1, endV: 0.6},
	texture1: {startU: ..., endU: ..., startV: ..., endV: ...},
	texture1: {startU: ..., endU: ..., startV: ..., endV: ...}
}

In your shader

Pass textureMerger.mergedTexture to your shader as a Texture uniform. Pass the range of related texture as an attribute or uniform (attribute makes more sense as it's not dynamic):

For gl.POINTS

float coordX = ((gl_PointCoord.x) * (endU - startU)) + startU;
float coordY = ((1.0 - gl_PointCoord.y) * (endV - startV)) + startV;
vec4 textureColor = texture2D(texture, vec2(coordX, coordY));

For the rest:

// affine transformation on original UV of a vertex
float coordX = (uv.x * (endU - startU) + startU);
float coordY = (uv.y * (startV - endV) + endV);
vec4 textureColor = texture2D(texture, vec2(coordX, coordY));

Prevent Texture Bleeding

Texture Bleeding is a common problem for visual applications that rely on Texture Atlases. In order to overcome this problem you can use Half-texel edge correction method:

In your vertex shader:

// Instead of the original uvCoordinates, pass the return value
// of this function to your Fragment Shader.
// uvCoordinates: [startU, startV, endU, endV]
vec4 fixTextureBleeding(vec4 uvCoordinates){
	// TEXTURE_SIZE is the size of each Atlas entry.
	// For instance if you created a Texture Atlas from 128x128
	// textures, TEXTURE_SIZE would be 128.
	float offset = 0.5 / float(TEXTURE_SIZE);
	return vec4(uvCoordinates[0] + offset, uvCoordinates[1] - offset, uvCoordinates[2] - offset, uvCoordinates[3] + offset);
}

License

TextureMerger uses MIT license.

glivera / TextureMerger