OpenGL ES 3.0 和 APPLE_clip_distance 扩展 [英] OpenGL ES 3.0 and APPLE_clip_distance extension

问题描述

根据本文档APPLE_clip_distance 扩展存在于 OpenGL ES 3.0 和 iPhone 6+ 硬件上.我试图通过首先在代码中启用它然后在着色器中使用来使用它.

According to this document APPLE_clip_distance extension is present on OpenGL ES 3.0 and iPhone 6+ hardware. I'm trying to use this by first enabling it in code and then using in the shader.

我可以通过执行查询最大数量的裁剪平面

I can query the maximum number of clipping planes by doing

GLint i;
glGetIntegerv(GL_MAX_CLIP_DISTANCES_APPLE, &i);
printf("i: %d\n", i);

这会打印出 8.

当尝试在着色器中使用它时:

When trying to use this in the shader like this:

const mediump int gl_MaxClipDistances = 8;
out highp float gl_ClipDistance[gl_MaxClipDistances];

我收到以下错误:

ERROR: 0:24: Identifier name 'gl_MaxClipDistances' cannot start with 'gl_'
ERROR: 0:25: Use of undeclared identifier 'gl_MaxClipDistances'
ERROR: 0:33: Use of undeclared identifier 'gl_ClipDistance'

本文档 描述了扩展，就我而言理解它，由于我使用的是 ES 3.0，我应该重新声明剪辑距离数组:

This document describes the extension and as far as I understand it I'm supposed to redeclare the clip distance array due to the fact that I'm using ES 3.0:

(1) GLSL 300 doesn't support unsized arrays, how should gl_ClipDistance
be sized?

  RESOLVED: For maximal compatibility, it works like ES2/desktop,
  remaining unsized until sized by direct access or explicitly
  redeclared.  Language describing this behavior must be added to the
  extension specification since it's gone from the base language
  specification.

也是这样声明的:

out highp float gl_ClipDistance[];

给出这个错误:

ERROR: 0:25: Unsized array 'gl_ClipDistance' requires sized initializer under GLSL 300
ERROR: 0:33: Use of undeclared identifier 'gl_ClipDistance'

有人有这个扩展的工作示例吗?

Does somebody have a working example of this extension?

推荐答案

你需要做的一件事是在你的着色器代码中指定它依赖于这个扩展.靠近顶点着色器的开头，在#version之后，添加对应的#extension指令:

One thing you need to do is specify in your shader code that it relies on this extension. Close to the start of the vertex shader, after the #version, add the corresponding #extension directive:

#version 300 es
#extension GL_APPLE_clip_distance : require

然后，按照我阅读扩展规范的方式，您使用如下所示的声明来调整 gl_ClipDistance 的大小:

Then, the way I read the extension spec, you use a declaration looking like this to size gl_ClipDistance:

out highp float gl_ClipDistance[4];

其中常量与您要使用的裁剪平面的数量相匹配.请注意，与问题中发布的代码不同，您不重新定义gl_MaxClipDistances.一旦您需要扩展，就应该已经定义了常量.

where the constant matches the number of clip planes you want to use. Note that, unlike the code posted in the question, you do not redefine gl_MaxClipDistances. Once you require the extension, the constant should already be defined.

如果您想使用最大支持数量的剪裁平面，您可以使用常量:

You can use the constant if you want to use the maximum supported number of clip planes:

out highp float gl_ClipDistance[gl_MaxClipDistances];

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