OpenGL 着色语言向后兼容性

Question

我注意到当 GLSL 版本低于 130 时，我的 GLSL 着色器无法编译。

拥有向后兼容的着色器源最关键的要素是什么？我不想完全向后兼容，但我想了解在 GLSL 低于 130 的 GPU 上运行简单(向前兼容)着色器的主要准则。

当然这个问题可以通过预处理器来解决

#if __VERSION__ < 130
#define VERTEX_IN attribute
#else
#define VERTER_IN in
#endif

但是可能有很多问题我忽略了。

Answer 1

最近的事件提出了这个老问题，我意识到我解决了这个问题。这并不容易，但它是一个成功的解决方案，许多基于它的着色器以及编译着色器源代码的驱动程序的数量都证明了这一点。

本质上，我使用了 GL_ARB_shading_language_include扩展(并且我还为那些未实现它的系统实现了源预处理器)，并且我最终定义了以下着色器包含源:

//  Copyright (C) 2011-2013 Luca Piccioni
// 
//  This program is free software: you can redistribute it and/or modify
//  it under the terms of the GNU General Public License as published by
//  the Free Software Foundation, either version 3 of the License, or
//  (at your option) any later version.
// 
//  This program is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//  GNU General Public License for more details.
// 
//  You should have received a copy of the GNU General Public License
//  along with this program.  If not, see <http://www.gnu.org/licenses/>.

// @BeginInterface

// Shader renderer

// Symbol defined if running on NVIDIA renderer.
#define DS_VENDOR_NVIDIA            1
// Symbol defined if running on ATI/AMD renderer.
#define DS_VENDOR_AMD               2
// Symbol defined if running on INTEL renderer
#define DS_VENDOR_INTEL             3

// Shader inputs and outputs keywords
//
// - ATTRIBUTE: used to mark a vertex shader inputs
// - SHADER_IN: used to mark a non-vertex shader inputs
// - SHADER_OUT: used to mark a non-fragment shader output
// - OUT: used to mark a fragment shader output
#if __VERSION__ >= 130

#define ATTRIBUTE in
#define SHADER_IN in
#define SHADER_OUT out
#define OUT out

#else

#define ATTRIBUTE attribute
#define SHADER_IN varying
#define SHADER_OUT varying
#define OUT

#endif

// Support array attributes
#if __VERSION__ >= 130

#define ARRAY_ATTRIBUTE(name, size) name[size]

#else

#define ARRAY_ATTRIBUTE(name, size) name[size]

#endif

// Uniform blocks
#if __VERSION__ >= 130

#define BEGIN_UNIFORM_BLOCK(name)   uniform name {

#define END_UNIFORM_BLOCK() };

#else

#define BEGIN_UNIFORM_BLOCK(name)

#define END_UNIFORM_BLOCK()

#endif

// Input and output blocks
#if __VERSION__ >= 150

#define BEGIN_INPUT_BLOCK(name) in name {
#define END_INPUT_BLOCK() };

#define BEGIN_OUTPUT_BLOCK(name) out name {
#define END_OUTPUT_BLOCK() };

#else

#define BEGIN_INPUT_BLOCK(name)
#define END_INPUT_BLOCK()

#define BEGIN_OUTPUT_BLOCK(name)
#define END_OUTPUT_BLOCK()

#endif

// Texturing functions
#if __VERSION__ >= 130

#define TEXTURE_2D texture
#define TEXTURE_3D texture
#define TEXTURE_RECT texture
#define TEXTURE_CUBE texture

#if __VERSION__ >= 150
#define TEXTURE_SIZE(sampler) textureSize(sampler)
#else
#define TEXTURE_SIZE(sampler) sampler ## _Size
#endif

#else

#define TEXTURE_2D texture2D
#define TEXTURE_3D texture3D
#define TEXTURE_RECT texture2DRect
#define TEXTURE_CUBE textureCube

#endif

// Invariance
#if __VERSION__ >= 120
#define INVARIANT invariant
#else
#define INVARIANT
#endif

// Attribute location
#if defined(GL_ARB_explicit_attrib_location)
#define LOCATION(loc)       layout(location = loc)
#else
#define LOCATION(loc)
#endif

// Geometry shader layout
#if __VERSION__ >= 150
#define GEOMETRY_LAYOUT_IN(from) layout (from) in
#define GEOMETRY_LAYOUT(to, max) layout (to, max_vertices = max) out
#else
#define GEOMETRY_LAYOUT_IN(from)
#define GEOMETRY_LAYOUT(to, max)
#endif

// @EndInterface

事实上，在着色器源代码之前包含着色器，框架可以在各种编译器上进行编译。当然，框架必须检测实际的系统功能并定义编译器参数，以便正确完成工作(考虑一下线着色器，因为线宽 > 1.0 已弃用)。

当然，着色器基础设施可以定义最低要求。一旦着色器需要 GLSL 1.50 或更高版本的核心配置文件，就不再需要上面包含的着色器。