DAY18：阅读纹理内存之Layered Textures

3.2.11.1.3. 16-Bit Floating-Point Textures

The 16-bit floating-point or half format supported by CUDA arrays is the same as the IEEE 754-2008 binary2 format.

CUDA C does not support a matching data type, but provides intrinsic functions【内联函数】 to convert to and from the 32-bit floating-point format via the unsigned short type: __float2half_rn(float) and __half2float(unsigned short). These functions are only supported in device code. Equivalent functions【等价函数】 for the host code can be found in the OpenEXR library, for example.

16-bit floating-point components are promoted to 32 bit float during texture fetching before any filtering is performed.

A channel description for the 16-bit floating-point format can be created by calling one of the cudaCreateChannelDescHalf*() functions.

3.2.11.1.4. Layered Textures

A one-dimensional or two-dimensional layered texture (also known as texture array in Direct3D and array texture in OpenGL) is a texture made up of a sequence of layers, all of which are regular textures of same dimensionality, size, and data type.

A one-dimensional layered texture is addressed using an integer index and a floating-point texture coordinate; the index denotes a layer within the sequence and the coordinate addresses a texel within that layer. A two-dimensional layered texture is addressed using an integer index and two floating-point texture coordinates; the index denotes a layer within the sequence and the coordinates address a texel within that layer.

A layered texture can only be a CUDA array by calling cudaMalloc3DArray() with the cudaArrayLayered flag (and a height of zero for one-dimensional layered texture).

Layered textures are fetched using the device functions described in tex1DLayered(), tex1DLayered(), tex2DLayered(), and tex2DLayered(). Texture filtering (see Texture Fetching) is done only within a layer, not across layers.

Layered textures are only supported on devices of compute capability 2.0 and higher.

本文备注/经验分享：

16-Bit Floating-Point Textures 这部分内容因为我们从来没用过，所以没有好补充的...

 Layered Textures——

这个等于纹理数组(某种意义上)，和普通的3D的CUDA Array不同。这个层和层之间是独立的。插值的时候不跨层。 而存储的时候也*可能*每层存储为单独的像2D的纹理那样的布局(4个元素临近在一起)，而不是3D那样的8个。例如说, 你有一堆图片的时候，例如PhotoShop之类的软件可以用来做多个图层。 可以总是看成是一堆图层的。而直接的3D纹理会导致层与层之前有关系，而这个只是一堆图片而已。

A one-dimensional layered texture is addressed using an integer index and a floating-point texture coordinate; the index denotes a layer within the sequence and the coordinate addresses a texel within that layer. 这个是1D的, 和2D一个道理, 纹理内部(一张图片内部你可以理解)坐标是float的。而层的坐标是整数的，例如: 第3层, 第2层图片，而不会像是普通的2D(相比1D的layered的)或者3D纹理(相比2D的Layered)那样，虽然大家都是2个坐标和3个坐标。 但含有Layered的字样的纹理最后一个坐标不是纹理内部的, 而是代表层次，因为我们普通的2D和3D的可以随时插值, 允许最后一个坐标是1.2, 3.4这种浮点值，而Layered的最后一个坐标是整数值，这首先暗示里这个纹理不同, 最后一个坐标不是纹理内部的坐标, 也不能用来插值，其次说明不存在层次间的关系, 没有第1.5层之类的说法。我建议你总是将Layered的理解成纹理数组，这样好理解很多。

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