为什么OpenGL使用float而不是double? [英] Why does OpenGL use float rather than double?

问题描述

我想知道为什么OpenGL在功能上使用float而不是double. Double应该比float更准确.

I am wondering why OpenGL makes use of float rather than double in its functions. Double should be much more accurate than float.

推荐答案

过去，许多OpenGL函数确实具有double变体.例如， glMultMatrix 具有和d变体.其中大多数不再存在，但这与float与double无关. glMultMatrixd 和 glMultMatrixf在核心GL 3.1及更高版本中均已消失.

In the past, many OpenGL functions did have a double variant. glMultMatrix for example has f and d variations. Most of these don't exist anymore, but that has nothing to do with float vs. double. glMultMatrixd and glMultMatrixf are gone in core GL 3.1 and above.

在核心OpenGL 中，仍然存在具有double变体的函数.尽管有float版本(主要是为了与GL ES兼容引入的)，但glDepthRange需要double.有些功能不具有double变体，例如glBlendColor.

In core OpenGL, there are still functions that have double variants. glDepthRange takes double, though there is a float version (introduced mainly for GL ES compatibility). There are some functions that don't have double variants, like glBlendColor.

有时，OpenGL只是不一致.在其他时候，它只是遵循一个合理的原则:不对用户说谎.

Sometimes, OpenGL is just being inconsistent. Other times, it is simply following a reasonable principle: not lying to the user.

采用 glBlendColor .如果您可以将其传递为双精度值，则意味着浮点混合是以双精度精度进行的.由于它肯定不(在存在的任何硬件上)不存在，因此提供一种提供这种准确性的API对用户来说是一个默认的谎言.您正在将高精度值用于低精度操作.尽管glDepthRange的逻辑相同(没有双精度深度缓冲区不可用)，但它需要doubles.同样，不一致.

Take glBlendColor. If you could pass it double-precision values, that would imply that floating-point blending took place with double-precision accuracy. Since it most certainly does not (on any hardware that exists), providing an API that offers that accuracy is a tacit lie to the user. You're taking high-precision values to a low-precision operation. Though the same logic is true of glDepthRange (no double-precision depth buffers are not available), yet it takes doubles. So again, inconsistency.

glUniform* 函数集是一个更好的例子.他们将状态设置为当前程序对象.在GL 4.0之前，不存在double版本.为什么?因为那本来是谎言. GLSL 4.0之前的版本不允许您声明double，原因很简单，显而易见的原因是4.0之前的硬件无法实现它..如果硬件无法处理，则不允许用户创建double.

The glUniform* suite of functions is a much better example. They set state into the current program object. Until GL 4.0, the double versions did not exist. Why? Because that would have been a lie. GLSL pre-4.0 did not allow you to declare a double, for the simple and obvious reason that no pre-4.0 hardware could implement it. There's no point in allowing the user to create a double if the hardware couldn't handle it.

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