opaque和transparent下blending都为alphaBlending的疑问

[yj7810520113]

renderEntity中，无论对于opaque还是transparent pass，blending均为 alphaBlending，这个blending默认值是有什么目的吗？

function getOpaqueRenderState() {
    return Cesium.RenderState.fromCache({
        cull : {
            enabled : false
        },
        depthTest : {
            enabled : true,
            func : Cesium.DepthFunction.LESS_OR_EQUAL
        },
        blending : Cesium.BlendingState.ALPHA_BLEND
    });
}

function getTransparentRenderState() {
    return Cesium.RenderState.fromCache({
        cull : {
            enabled : true
        },
        depthTest : {
            enabled : true,
            func : Cesium.DepthFunction.LESS_OR_EQUAL
        },
        blending : Cesium.BlendingState.ALPHA_BLEND
    });
}

对比3DTiles中

function getTranslucentRenderState(renderState) {
  var rs = clone(renderState, true);
  rs.cull.enabled = false;
  rs.depthTest.enabled = true;
  rs.depthMask = false;
  rs.blending = BlendingState.ALPHA_BLEND;
  rs.stencilTest = StencilConstants.setCesium3DTileBit();
  rs.stencilMask = StencilConstants.CESIUM_3D_TILE_MASK;

  return RenderState.fromCache(rs);
}

function getOpaqueRenderState(renderState) {
  var rs = clone(renderState, true);
  rs.stencilTest = StencilConstants.setCesium3DTileBit();
  rs.stencilMask = StencilConstants.CESIUM_3D_TILE_MASK;

  return RenderState.fromCache(rs);
}