Vulkan spec

cglm/docs/source/troubleshooting.rst

@@ -0,0 +1,99 @@
+.. default-domain:: C
+
+Troubleshooting
+================================================================================
+
+It is possible that you may sometimes get crashes or wrong results.
+Follow these topics
+
+Memory Allocation:
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Recall that **cglm** does not alloc any memory on the heap.
+cglm functions work like memcpy; they copy data from src,
+make calculations, then copy the result to dest.
+
+You are responsible for allocation of **src** and **dest** parameters.
+
+Alignment:
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+**vec4** and **mat4** types require 16 byte alignment.
+These types are marked with the align attribute to let the compiler know about this
+requirement.
+
+Since MSVC (Windows) throws this error:
+
+**"formal parameter with requested alignment of 16 won't be aligned"**
+
+The alignment attribute has been commented out for MSVC
+
+.. code-block:: c
+
+   #if defined(_MSC_VER)
+   #  define CGLM_ALIGN(X) /* __declspec(align(X)) */
+   #else
+   #  define CGLM_ALIGN(X) __attribute((aligned(X)))
+   #endif.
+
+So MSVC may not know about alignment requirements when creating variables.
+The interesting thing is that, if I remember correctly, Visual Studio 2017
+doesn't throw the above error. So we may uncomment that line for Visual Studio 2017,
+you may do it yourself.
+
+**This MSVC issue is still in TODOs.**
+
+**UPDATE:** Starting with v0.4.5, cglm provides an option to disable the alignment requirement.
+Also, alignment is disabled for older msvc versions by default. Now alignment is only required in Visual Studio 2017 version 15.6+ if the CGLM_ALL_UNALIGNED macro is not defined.
+
+Crashes, Invalid Memory Access:
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Most likely, you are trying to write to an invalid memory location.
+
+You may have used a wrong function for what you want to do.
+
+For example, you may have called a **glm_vec4_** function for a **vec3** data type.
+It will try to write 32 bytes, but since **vec3** is 24 bytes, it should throw
+a memory access error or exit the app without saying anything.
+
+**UPDATE - IMPORTANT:** 
+
+  | On MSVC or some other compilers, if alignment is enabled (default) then double check alignment requirements if you got a crash.
+
+  | If you send GLM_VEC4_ONE or similar macros directly to a function, it may crash.
+  | Because the compiler may not apply alignment as defined on **typedef** to that macro while passing it (on stack) to a function.
+
+Wrong Results:
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Again, you may have used a wrong function.
+
+For instance if you use **glm_normalize()** or **glm_vec3_normalize()** for a **vec4**,
+it will assume that the passed param is a **vec3**, and will normalize it for **vec3**.
+Since you need a **vec4** to be normalized in your case, you will get wrong results.
+
+Accessing a vec4 type with vec3 functions is valid, you will not get any error, exception or crash.
+You only get wrong results if you don't know what you are doing!
+
+So be careful, when your IDE (Xcode, Visual Studio ...) tries to autocomplete function names, READ IT :)
+
+**Also implementation may be wrong, please let us know by creating an issue on Github.**
+
+BAD_ACCESS : Thread 1: EXC_BAD_ACCESS (code=EXC_I386_GPFLT) or Similar Errors/Crashes
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This is a similar issue with alignment. For instance if you compiled **cglm** with 
+AVX (**-mavx**, intentionally or not) and if you use **cglm** in an environment that doesn't 
+support AVX (or if AVX is disabled intentionally) e.g. environment that max support SSE2/3/4, 
+then you probably get **BAD ACCESS** or similar...
+
+Because if you compile **cglm** with AVX it aligns **mat4** with 32 byte boundary, 
+and your project aligns that as a 16 byte boundary...
+
+Check alignment, supported vector extension, or simd in **cglm** and linked projects...
+
+Other Issues?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+**Please let us know by creating an issue on Github.**