GL: proper alloc of mip levels on texture alloc.

Not doing this prevents uploads on mip levels using texSubImage3D (texture arrays)

h3d/impl/GlDriver.hx

@@ -51,6 +51,8 @@ private extern class GL2 extends js.html.webgl.GL {
 	static inline var FUNC_MIN = 0x8007;
 	static inline var FUNC_MAX = 0x8008;
 	static inline var TEXTURE_LOD_BIAS : Int = 0x84FD;
+	static inline var TEXTURE_BASE_LEVEL = 0x813C;
+	static inline var TEXTURE_MAX_LEVEL = 0x813D;
 }
 private typedef Uniform = js.html.webgl.UniformLocation;
 private typedef Program = js.html.webgl.Program;
@@ -946,20 +948,26 @@ class GlDriver extends Driver {
 			return false;
 		}
 
-		if( t.flags.has(Cube) ) {
-			for( i in 0...6 ) {
-				gl.texImage2D(CUBE_FACES[i], 0, tt.internalFmt, tt.width, tt.height, 0, getChannels(tt), tt.pixelFmt, null);
-				if( checkError() ) break;
+		gl.texParameteri(bind, GL2.TEXTURE_BASE_LEVEL, 0);
+		gl.texParameteri(bind, GL2.TEXTURE_MAX_LEVEL, t.mipLevels-1);
+		for(mip in 0...t.mipLevels) {
+			var w = hxd.Math.imax(1, tt.width >> mip);
+			var h = hxd.Math.imax(1, tt.height >> mip);
+			if( t.flags.has(Cube) ) {
+				for( i in 0...6 ) {
+					gl.texImage2D(CUBE_FACES[i], mip, tt.internalFmt, w, h, 0, getChannels(tt), tt.pixelFmt, null);
+					if( checkError() ) break;
+				}
+			} else if( t.flags.has(IsArray) ) {
+				gl.texImage3D(bind, mip, tt.internalFmt, w, h, t.layerCount, 0, getChannels(tt), tt.pixelFmt, null);
+				checkError();
+			} else {
+				#if js
+				if( !t.format.match(S3TC(_)) )
+				#end
+				gl.texImage2D(bind, mip, tt.internalFmt, w, h, 0, getChannels(tt), tt.pixelFmt, null);
+				checkError();
 			}
-		} else if( t.flags.has(IsArray) ) {
-			gl.texImage3D(GL2.TEXTURE_2D_ARRAY, 0, tt.internalFmt, tt.width, tt.height, t.layerCount, 0, getChannels(tt), tt.pixelFmt, null);
-			checkError();
-		} else {
-			#if js
-			if( !t.format.match(S3TC(_)) )
-			#end
-			gl.texImage2D(bind, 0, tt.internalFmt, tt.width, tt.height, 0, getChannels(tt), tt.pixelFmt, null);
-			checkError();
 		}
 		restoreBind();