在OpenGL ES中绘制一个非常高分辨率的纹理对象（球体）

I'm drawing planets in OpenGL ES, and running into some interesting performance issues. The general question is: how best to render "hugely detailed" textures on a sphere?

我在OpenGL ES中绘制行星，并遇到一些有趣的性能问题。一般的问题是：如何最好地在球体上渲染“非常详细”的纹理？

(the sphere is guaranteed; I'm interested in sphere-specific optimizations)

（球体是有保证的;我对球体特定的优化感兴趣）

Base case:

基本情况：

Window is approx. 2048 x 1536 (e.g. iPad3)
窗口约。 2048 x 1536（例如iPad3）
Texture map for globe is 24,000 x 12,000 pixels (an area half the size of USA fits the full width of screen)
地球的纹理贴图是24,000 x 12,000像素（美国大小的一半区域适合屏幕的整个宽度）
Globe is displayed at everything from zoomed in (USA fills screen) to zoomed out (whole globe visible)
从放大（美国填充屏幕）到缩小（全球可见）的所有内容都显示地球仪
I need a MINIMUM of 3 texture layers (1 for the planet surface, 1 for day/night differences, 1 for user-interface (hilighting different regions)
我需要最少3个纹理层（1个用于行星表面，1个用于日/夜差异，1个用于用户界面（hilighting不同区域）
Some of the layers are animated (i.e. they have to load and drop their texture at runtime, rapidly)
一些层是动画的（即它们必须在运行时快速加载和删除它们的纹理）

Limitations:

限制：

top-end tablets are limited to 4096x4096 textures
*平板电脑限制为4096x4096纹理
top-end tablets are limited to 8 simultaneous texture units
*平板电脑限于8个同步纹理单元

Problems:

问题：

In total, it's naively 500 million pixels of texture data
总的来说，这是天真的500万像素的纹理数据
Splitting into smaller textures doesn't work well because devices only have 8 units; with only a single texture layer, I could split into 8 texture units and all textures would be less than 4096x4096 - but that only allows a single layer
分割成较小的纹理不能很好地工作，因为设备只有8个单位;只有一个纹理图层，我可以分成8个纹理单元，所有纹理都小于4096x4096 - 但这只允许单个图层
Rendering the layers as separate geometry works poorly because they need to be blended using fragment-shaders
将图层渲染为单独的几何图形效果很差，因为它们需要使用片段着色器进行混合

...at the moment, the only idea I have that sounds viable is:

......目前，我认为唯一可行的想法是：

split the sphere into NxM "pieces of sphere" and render each one as separate geometry
将球体分成NxM“球体块”并将每个球体渲染为单独的几何体
use mipmaps to render low-res textures when zoomed out
缩小时使用mipmap来渲染低分辨率纹理
...rely on simple culling to cut out most of them when zoomed in, and mipmapping to use small(er) textures when they can't be culled
...当放大时，依靠简单的剔除来切割大部分，并且当它们无法被剔除时，使用小的（呃）纹理进行mipmapping

...but it seems there ought to be an easier way / better options?

...但似乎应该有更简单的方法/更好的选择？

2 个解决方案

#1

Seems that there are no way to fit such huge textures in memory of mobile GPU, even into the iPad 3 one.

似乎没有办法在移动GPU的内存中安装如此巨大的纹理，甚至进入iPad 3。

So you have to stream texture data. The thing you need is called clipmap (popularized by id software with extended megatexture technology).

所以你必须传输纹理数据。你需要的东西叫做clipmap（由带有扩展megatexture技术的id软件推广）。

Please read about this here, there are links to docs describing technique: http://en.wikipedia.org/wiki/Clipmap

请在这里阅读，有链接到描述技术的文档：http：//en.wikipedia.org/wiki/Clipmap

#2

This is not easily done in ES, as there is no virtual texture extension (yet). You basically need to implement virtual texturing (some ES devices implement ARB_texture_array) and stream in the lowest resolution possible (view-dependent) for your sphere. That way, it is possible to do it all in a fragment shader, no geometry subdivision is required. See this presentation (and the paper) for details how this can be implemented.

这在ES中不容易完成，因为还没有虚拟纹理扩展。您基本上需要实现虚拟纹理（某些ES设备实现ARB_texture_array）并以可能的最低分辨率（视图相关）为您的球体进行流式传输。这样，可以在片段着色器中完成所有操作，不需要几何细分。有关如何实施此操作的详细信息，请参阅此演示文稿（和文章）。

If you do the math, it is simply impossible to stream 1 GB (24,000 x 12,000 pixels x 4 B) in real time. And it would be wasteful, too, as the user will never get to see it all at the same time.

如果进行数学计算，则无法实时传输1 GB（24,000 x 12,000像素x 4 B）。这也是浪费，因为用户永远不会同时看到它。

#1