Oculus 裂谷 + 点精灵 + 点大小衰减

我正在编写一个支持 Oculus Rfit 的小项目，我使用点精灵来渲染我的粒子。我根据点精灵与顶点着色器中"相机"的距离来计算点精灵的大小（以像素为单位）。在默认屏幕（而不是在 Rift 上）绘图时，大小可以完美运行，但是当我切换到 Rift 时，我注意到以下现象：

左眼上的颗粒很小，并且尺寸会很快减小。 右眼上的颗粒很大，大小不会改变。

截图：裂痕禁用：https://i.stack.imgur.com/03l3o.jpg启用裂缝：https://i.stack.imgur.com/4tswC.jpg

下面是顶点着色器：

#version 120
attribute vec3 attr_pos;
attribute vec4 attr_col;
attribute float attr_size;
uniform mat4 st_view_matrix;
uniform mat4 st_proj_matrix;
uniform vec2 st_screen_size;
varying vec4 color;
void main()
{
    vec4 local_pos = vec4(attr_pos, 1.0);
    vec4 eye_pos = st_view_matrix * local_pos;
    vec4 proj_vector = st_proj_matrix * vec4(attr_size, 0.0, eye_pos.z, eye_pos.w);
    float proj_size = st_screen_size.x * proj_vector.x / proj_vector.w;
    gl_PointSize = proj_size;
    gl_Position = st_proj_matrix * eye_pos;
    color = attr_col;
}

st_screen_size制服是视口的大小。由于我在 Rift 上渲染时使用单个 frambuffer（每只眼睛 1 个一半），因此st_screen_size的值应该是 （frabuffer_width/2.0， frambuffer_height）。

这是我的抽奖电话：

    /*Drawing starts with a call to ovrHmd_BeginFrame.*/
    ovrHmd_BeginFrame(game::engine::ovr_data.hmd, 0);
    /*Start drawing onto our texture render target.*/
    game::engine::ovr_rtarg.bind();
    glClearColor(0, 0, 0, 1);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
   //Update the particles.
    game::engine::nuc_manager->update(dt, get_msec());
    /*for each eye... */
    for(unsigned int i = 0 ; i < 2 ; i++){
        ovrEyeType eye = game::engine::ovr_data.hmd->EyeRenderOrder[i];
        /* -- Viewport Transformation --
         * Setup the viewport to draw in the left half of the framebuffer when we're
         * rendering the left eye's view (0, 0, width / 2.0, height), and in the right half
         * of the frambuffer for the right eye's view (width / 2.0, 0, width / 2.0, height)
         */
        int fb_width = game::engine::ovr_rtarg.get_fb_width();
        int fb_height = game::engine::ovr_rtarg.get_fb_height();
        glViewport(eye == ovrEye_Left ? 0 : fb_width / 2, 0, fb_width / 2, fb_height);
      //Send the Viewport size to the shader.
      set_unistate("st_screen_size", Vector2(fb_width /2.0 , fb_height));
        /* -- Projection Transformation --
         * We'll just have to use the projection matrix supplied but he oculus SDK for this eye.
         * Note that libovr matrices are the transpose of what OpenGL expects, so we have to
         * send the transposed ovr projection matrix to the shader.*/
        proj = ovrMatrix4f_Projection(game::engine::ovr_data.hmd->DefaultEyeFov[eye], 0.01, 40000.0, true);
      Matrix4x4 proj_mat;
      memcpy(proj_mat[0], proj.M, 16 * sizeof(float));
      //Send the Projection matrix to the shader.
      set_projection_matrix(proj_mat);
        /* --view/camera tranformation --
         * We need to construct a view matrix by combining all the information provided by
         * the oculus SDK, about the position and orientation of the user's head in the world.
         */
         pose[eye] = ovrHmd_GetHmdPosePerEye(game::engine::ovr_data.hmd, eye);
         camera->reset_identity();
         camera->translate(Vector3(game::engine::ovr_data.eye_rdesc[eye].HmdToEyeViewOffset.x,
          game::engine::ovr_data.eye_rdesc[eye].HmdToEyeViewOffset.y,
          game::engine::ovr_data.eye_rdesc[eye].HmdToEyeViewOffset.z));
         /*Construct a quaternion from the data of the oculus SDK and rotate the view matrix*/
         Quaternion q = Quaternion(pose[eye].Orientation.w, pose[eye].Orientation.x,
                                   pose[eye].Orientation.y, pose[eye].Orientation.z);
         camera->rotate(q.inverse().normalized());

         /*Translate the view matrix with the positional tracking*/
         camera->translate(Vector3(-pose[eye].Position.x, -pose[eye].Position.y, -pose[eye].Position.z));
       camera->rotate(Vector3(0, 1, 0), DEG_TO_RAD(theta));
       //Send the View matrix to the shader.
       set_view_matrix(*camera);

         game::engine::active_stage->render(STAGE_RENDER_SKY | STAGE_RENDER_SCENES | STAGE_RENDER_GUNS |
          STAGE_RENDER_ENEMIES | STAGE_RENDER_PROJECTILES, get_msec());
         game::engine::nuc_manager->render(RENDER_PSYS, get_msec());
       game::engine::active_stage->render(STAGE_RENDER_COCKPIT, get_msec());
    }
    /* After drawing both eyes into the texture render target, revert to drawing directly to the display,
     * and we call ovrHmd_EndFrame, to let the Oculus SDK draw both images properly, compensated for lens
     * distortion and chromatic abberation onto the HMD screen.
     */
    game::engine::ovr_rtarg.unbind();
    ovrHmd_EndFrame(game::engine::ovr_data.hmd, pose, &game::engine::ovr_data.fb_ovr_tex[0].Texture);

这个问题已经困扰了我很多天了......我觉得我已经走到了死胡同。我可以用广告牌四边形.....但我不想轻易放弃:)加点精灵更快。在 Rift 上渲染时，基于距离的点大小衰减背后的数学会发生变化吗？我不是考虑到什么吗？数学不是（至少）我的强项。:)任何见解将不胜感激！

PS：如果需要有关我发布的代码的任何其他信息，我很乐意提供。