iOS OpenGL ES 2.0 MultiTexturing Decal是半透明的

Question

我有一个添加广告牌四边形的功能，我可以在其中映射纹理。旋转时，此纹理在3D地球周围移动。我的drawInRect看起来像这样：

- (void)glkView:(GLKView *)view drawInRect:(CGRect)rect
{

    // Clear the buffer and prepare to draw
    glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    // Enable the Earth texture
    self.effect.texture2d0.name = _earthInfo.name;
    self.effect.texture2d0.target = _earthInfo.target;

    // Bind the earth vertex array
    glBindVertexArrayOES(_earthVertexArray);

    // Render the object with GLKit
    [self.effect prepareToDraw];

    // Draw elements from the index array and uv / vertex / normal info
    glDrawElements(GL_TRIANGLES,Earth_polygoncount*3,GL_UNSIGNED_SHORT,0);

    // Draw the SkyBox -- Draw skybox centered on eye position
//    _skyboxEffect.center = _eyePosition;
//    _skyboxEffect.transform.projectionMatrix = self.effect.transform.projectionMatrix;
//    _skyboxEffect.transform.modelviewMatrix = self.effect.transform.modelviewMatrix;
//    [_skyboxEffect prepareToDraw];
//    [_skyboxEffect draw];

    // Turn on Blending before displaying satellites
    // so that the satellite image ( which has alpha )
    // shows up OK
    glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
    glEnable(GL_BLEND);

    // Now billboard something
    [self createBillboardAtLat:35 andLon:-97];

    // Now billboard something
    [self createBillboardAtLat:0 andLon:0];

    // Now billboard something
    [self createBillboardAtLat:-65 andLon:-137];

}

在createBillboardAt函数中，我这样画：

// Create a billboard that always faces the camera
- (void)createBillboardAtLat:(float)lat andLon:(float)lon {

    ... Do stuff ....

    // Assign the new matrix to draw with - no translation
    self.effect.transform.modelviewMatrix = noTranslationInfo;

    // Render the object with GLKit
    [self.effect prepareToDraw];

    // Draw elements from the index array and uv / vertex / normal info
    glDrawElements(GL_TRIANGLES,Billboard_polygoncount*3,GL_UNSIGNED_SHORT,0);

    // Restore the original matrix
    self.effect.transform.modelviewMatrix = originalMat;

}

我在添加广告牌之前打开混合，但在某些方向上，用于卫星的纹理与Globe完美融合但不能相互融合。请看截图...我做错了什么？

我已经尝试了所有这些选项，但都没有工作 - 只有一颗（最重要的）卫星只能掠过其中一颗卫星 - 而不是两颗卫星。请帮忙！

    // Turn on Blending before displaying satellites
    // so that the satellite image ( which has alpha )
    // shows up OK
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
    glEnable(GL_BLEND);
    //glEnable(GL_DEPTH_TEST);
    //glDepthFunc(GL_LEQUAL);
    //glDepthMask(true);