106 lines
4.3 KiB
ReStructuredText
106 lines
4.3 KiB
ReStructuredText
Getting Started
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================================
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Types:
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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**cglm** uses **glm** prefix for all functions e.g. glm_lookat. You can see supported types in common header file:
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.. code-block:: c
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:linenos:
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typedef float vec2[2];
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typedef float vec3[3];
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typedef int ivec3[3];
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typedef CGLM_ALIGN_IF(16) float vec4[4];
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typedef vec4 versor;
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typedef vec3 mat3[3];
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#ifdef __AVX__
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typedef CGLM_ALIGN_IF(32) vec4 mat4[4];
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#else
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typedef CGLM_ALIGN_IF(16) vec4 mat4[4];
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#endif
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As you can see types don't store extra informations in favor of space.
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You can send these values e.g. matrix to OpenGL directly without casting or calling a function like *value_ptr*
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Alignment Is Required:
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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**vec4** and **mat4** requires 16 (32 for **mat4** if AVX is enabled) byte alignment because **vec4** and **mat4** operations are vectorized by SIMD instructions (SSE/AVX/NEON).
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**UPDATE:**
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By starting v0.4.5 cglm provides an option to disable alignment requirement, it is enabled as default
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| Check :doc:`opt` page for more details
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Also alignment is disabled for older msvc verisons as default. Now alignment is only required in Visual Studio 2017 version 15.6+ if CGLM_ALL_UNALIGNED macro is not defined.
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Allocations:
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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*cglm* doesn't alloc any memory on heap. So it doesn't provide any allocator.
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You must allocate memory yourself. You should alloc memory for out parameters too if you pass pointer of memory location. When allocating memory, don't forget that **vec4** and **mat4** require alignment.
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**NOTE:** Unaligned **vec4** and unaligned **mat4** operations will be supported in the future. Check todo list.
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Because you may want to multiply a CGLM matrix with external matrix.
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There is no guarantee that non-CGLM matrix is aligned. Unaligned types will have *u* prefix e.g. **umat4**
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Array vs Struct:
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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*cglm* uses arrays for vector and matrix types. So you can't access individual
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elements like vec.x, vec.y, vec.z... You must use subscript to access vector elements
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e.g. vec[0], vec[1], vec[2].
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Also I think it is more meaningful to access matrix elements with subscript
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e.g **matrix[2][3]** instead of **matrix._23**. Since matrix is array of vectors,
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vectors are also defined as array. This makes types homogeneous.
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**Return arrays?**
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Since C doesn't support return arrays, cglm also doesn't support this feature.
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Function design:
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.. image:: cglm-intro.png
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:width: 492px
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:height: 297px
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:align: center
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cglm provides a few way to call a function to do same operation.
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* Inline - *glm_, glm_u*
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* Pre-compiled - *glmc_, glmc_u*
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For instance **glm_mat4_mul** is inline (all *glm_* functions are inline), to make it non-inline (pre-compiled),
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call it as **glmc_mat4_mul** from library, to use unaligned version use **glm_umat4_mul** (todo).
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Most functions have **dest** parameter for output. For instance mat4_mul func looks like this:
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.. code-block:: c
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CGLM_INLINE
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void
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glm_mat4_mul(mat4 m1, mat4 m2, mat4 dest)
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The dest parameter is out parameter. Result will be stored in **dest**.
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Also in this case matrix multiplication order is dest = m1 * m2.
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* Changing parameter order will change the multiplication order.
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* You can pass all parameter same (this is similar to m1 `*=` m1), you can pass **dest** as m1 or m2 (this is similar to m1 `*=` m2)
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**v** postfix in function names
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-------------------------------
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You may see **v** postfix in some function names, v stands for vector.
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For instance consider a function that accepts three parameters x, y, z.
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This function may be overloaded by **v** postfix to accept vector (vec3) instead of separate parameters.
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In some places the v means that it will be apply to a vector.
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**_to** postfix in function names
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---------------------------------
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*_to* version of function will store the result in specified parameter instead of in-out parameter.
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Some functions don't have _to prefix but they still behave like this e.g. glm_mat4_mul.
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