support updating only dirty CompressedArrayTexture layers

docs/api/en/textures/CompressedArrayTexture.html

@@ -61,6 +61,20 @@ <h3>[property:number wrapR]</h3>
 		<h3>[property:Object image]</h3>
 		<p>Overridden with a object containing width, height, and depth.</p>
 
+		<h3>[property:Boolean layerNeedsUpdate]</h3>
+		<p>
+			Specifies that a specific layer of the texture needs to be updated. Unlike
+			[page:Texture.needsUpdate needsUpdate] which sends the entire compressed
+			texture array to the GPU, marking specific layers will only transmit
+			subsets of all mipmaps associated with a specific depth in the array.
+		</p>
+
+		<h3>[property:Array dirtyLayers]</h3>
+		<p>
+			A list of all dirty layers in the texture. See
+			[Page:CompressedTextureArray.layerNeedsUpdate layerNeedsUpdate].
+		</p>
+
 		<h3>[property:Boolean isCompressedArrayTexture]</h3>
 		<p>Read-only flag to check if a given object is of type [name].</p>
 

src/renderers/webgl/WebGLTextures.js

@@ -820,7 +820,22 @@ function WebGLTextures( _gl, extensions, state, properties, capabilities, utils,
 
 									if ( dataReady ) {
 
-										state.compressedTexSubImage3D( _gl.TEXTURE_2D_ARRAY, i, 0, 0, 0, mipmap.width, mipmap.height, image.depth, glFormat, mipmap.data, 0, 0 );
+										if ( texture.dirtyLayers.length > 0 ) {
+
+											for ( const layerIndex of texture.dirtyLayers ) {
+
+												const layerSize = mipmap.width * mipmap.height;
+												state.compressedTexSubImage3D( _gl.TEXTURE_2D_ARRAY, i, 0, 0, layerIndex, mipmap.width, mipmap.height, 1, glFormat, mipmap.data.slice( layerSize * layerIndex, layerSize * ( layerIndex + 1 ) ), 0, 0 );
+
+											}
+
+											texture.dirtyLayers = [];
+
+										} else {
+
+											state.compressedTexSubImage3D( _gl.TEXTURE_2D_ARRAY, i, 0, 0, 0, mipmap.width, mipmap.height, image.depth, glFormat, mipmap.data, 0, 0 );
+
+										}
 
 									}
 

src/textures/CompressedArrayTexture.js

@@ -10,6 +10,14 @@ class CompressedArrayTexture extends CompressedTexture {
 		this.isCompressedArrayTexture = true;
 		this.image.depth = depth;
 		this.wrapR = ClampToEdgeWrapping;
+		this.dirtyLayers = [];
+
+	}
+
+	set layerNeedsUpdate( layerIndex ) {
+
+		this.needsUpdate = true;
+		this.dirtyLayers.push( layerIndex );
 
 	}