support updating only dirty CompressedArrayTexture layers

docs/api/en/textures/CompressedArrayTexture.html

@@ -61,14 +61,30 @@ <h3>[property:number wrapR]</h3>
 		<h3>[property:Object image]</h3>
 		<p>Overridden with a object containing width, height, and depth.</p>
 
+		<h3>[property:Set dirtyLayers]</h3>
+		<p>
+			A set of all dirty layers in the texture. See
+			[Page:CompressedTextureArray.addDirtyLayer addDirtyLayer].
+		</p>
+
 		<h3>[property:Boolean isCompressedArrayTexture]</h3>
 		<p>Read-only flag to check if a given object is of type [name].</p>
 
 		<h2>Methods</h2>
 
+		<h3>[method:addDirtyLayer addDirtyLayer]( layerIndex )</h3>
+		<p>
+			Describes that a specific layer of the texture needs to be updated.
+			Normally when [page:Texture.needsUpdate needsUpdate] is set to true, the
+			entire compressed texture array is sent to the GPU. Marking specific
+			layers will only transmit subsets of all mipmaps associated with a
+			specific depth in the array which is often much more performant. 
+		</p>
+
+		<h3>[method:clearDirtyLayers clearDirtyLayers]()</h3>
 		<p>
-			See the base [page:CompressedTexture CompressedTexture] class for common
-			methods.
+			Resets the dirty layers registry. See
+			[Page:CompressedTextureArray.addDirtyLayer addDirtyLayer].
 		</p>
 
 		<h2>Source</h2>

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.size > 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.clearDirtyLayers();
+
+										} 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

@@ -11,6 +11,20 @@ class CompressedArrayTexture extends CompressedTexture {
 		this.image.depth = depth;
 		this.wrapR = ClampToEdgeWrapping;
 
+		this.dirtyLayers = new Set();
+
+	}
+
+	addDirtyLayer( layerIndex ) {
+
+		this.dirtyLayers.add( layerIndex );
+
+	}
+
+	clearDirtyLayers() {
+
+		this.dirtyLayers.clear();
+
 	}
 
 }