帮我评估这个选角 [英] Help me evaluate this casting
问题描述
我在PowerVR网格绘图代码中发现了这一点,但我真的不知道如何阅读.
I found this in the PowerVR mesh drawing code and I don't really know how to read it.
&((unsigned short*)0)[3 * mesh.sBoneBatches.pnBatchOffset[batchNum]]
这是怎么回事?这是对void的引用,将其转换为无符号短指针,然后偏移(3 * mesh(etc ...)+ batchNum)吗?真伤了我的脑筋.
What is going on here? Is this a reference to void cast as an unsigned short pointer and then offset by (3*mesh(etc...) + batchNum)? It's breaking my brain.
可以在glDrawElements调用的上下文中找到它:
It's found in the context of a glDrawElements call:
glDrawElements(GL_TRIANGLES, i32Tris * 3, GL_UNSIGNED_SHORT,
&((unsigned short*)0)[3 * mesh.sBoneBatches.pnBatchOffset[batchNum]]);
推荐答案
让我们由内而外.
(unsigned short*)0
这会将0
强制转换为无符号的短指针.这将用于计算内存偏移量,该内存偏移量是根据无符号short的大小计算的.
This is casting 0
to an unsigned short pointer. This will be used for computing a memory offset, computed in terms of the size of an unsigned short.
3 * mesh.sBoneBatches.pnBatchOffset[batchNum]
这大概是某些三角形批次在内存中的偏移量.三角形由3个短裤组成,因此看起来它们以三角形的数量存储偏移量,然后乘以3即可得到短裤的数量.
This is, presumably, the offset in memory of some batch of triangles. A triangle is composed of 3 shorts, so it looks like they are storing an offset in terms of numbers of triangles, and then multiplying by 3 to get the number of shorts.
((unsigned short*)0)[3 * mesh.sBoneBatches.pnBatchOffset[batchNum]]
现在使用该0
指针查找给定偏移量的存储位置.通常,这将返回该内存位置的值,但是他们希望将指针传递给glDrawElements,因此请使用&
运算符获取指向该内存位置的指针:
This is now using that 0
pointer to find the memory location of the given offset. This would normally return the value of that memory location, but they want a pointer to pass into glDrawElements, so the use the &
operator to get a pointer to that memory location:
&((unsigned short*)0)[3 * mesh.sBoneBatches.pnBatchOffset[batchNum]]
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