Fix uncleared uniforms bug

src/drawables/drawable-descriptor.ts

@@ -52,6 +52,8 @@ export interface DrawableDescriptor {
    *
    * For each step, a shader will be generated. And at runtime the closes matching
    * shader will be used to render a given part of the scene.
+   *
+   * Must contain 0 as a value.
    */
   shaderCombinationSteps: Array<number>;
 

src/drawables/drawable.ts

@@ -33,6 +33,7 @@ export abstract class Drawable {
    */
   protected abstract getObjectToSerialize(transform2d: mat2d, transform1d: number): any;
 
+  /** @internal */
   public serializeToUniforms(
     uniforms: any,
     transform2d: mat2d,