Re: Tables - can't get the address of value

[r3c]

When im creating the faces, i know their exact number, but to speedup the 
rendering, I want to merge them by their common texture. I dont know the number 
of the merged faces, so I have to make one [loop trough all the 
faces](https://github.com/JDragan/CoreQ3BSP/blob/a9242fed0e603628b8c1e901a258a34edb899ad7/src/coreBSP.nim#L93)
 and find the number of unique texture/lightmap combinations.

Then from this number i have the size of the render data (number of merged 
faces) Then I do another loop to fill the data.

With tables I dont have to do that, I can do that in the first loop

Re: Tables - can't get the address of value

[demotomohiro]

From: 
[https://nim-lang.org/docs/manual.html#statements-and-expressions-the-addr-operator](https://nim-lang.org/docs/manual.html#statements-and-expressions-the-addr-operator)

> The addr operator returns the address of an l-value.

From: 
[https://nim-lang.org/docs/manual.html#procedures-var-return-type](https://nim-lang.org/docs/manual.html#procedures-var-return-type)

> A proc, converter or iterator may return a var type which means that the 
> returned value is an l-value and can be modified by the caller:

In other words, when a return type is not a var type, it is not an l-value.

From: 
[https://nim-lang.org/docs/tables.html#%5B%5D%2CTable%5BA%2CB%5D%2CA](https://nim-lang.org/docs/tables.html#%5B%5D%2CTable%5BA%2CB%5D%2CA)
 
[https://nim-lang.org/docs/tables.html#%5B%5D%2CTable%5BA%2CB%5D%2CA_2](https://nim-lang.org/docs/tables.html#%5B%5D%2CTable%5BA%2CB%5D%2CA_2)

> proc `[]`[A, B](t: Table[A, B]; key: A): B
> 
> proc `[]`[A, B](t: var Table[A, B]; key: A): var B

So in your `CreateBuffers` proc, `proc `[]`[A, B](t: Table[A, B]; key: A): B` 
is called and it doesn't return var type. You can get an address only from an 
l-value. That is why you cannt use `unsafeAddr` in your code.

You can not access `seq[0]` when the lenght of the sequence is 0.

I think your code shoulde be like: 


proc CreateBuffers*(obj: var RenderableObject) {.inline.} =
# # #
  glBufferData(GL_ARRAY_BUFFER, obj.vertices_tbl[f].len*sizeof(GLfloat), if 
obj.vertices_tbl[f].len == 0: nil else: obj.vertices_tbl[f][0].unsafeAddr, 
GL_STATIC_DRAW)


Run

> if I pass it with var like obj: var RenderableObject it works, but that kinda 
> defeats the purpose of using tables and its very slow

I don't understand neither why you are using tables in your code nor why `var` 
defeats the purpose of using tables only from your code.

Tables - can't get the address of value

[r3c]

I use table in type like: 


type
  RenderableObject* = object
vertices_tbl*: Table[int, seq[float32]]
indices_tbl*: Table[int, seq[uint32]]

# init
var FACE : RenderableObject
FACE.vertices_tbl = initTable[int, seq[float32]]()
FACE.indices_tbl  = initTable[int, seq[uint32]]()

#init the seq
proc CreateFace(f: int, pos: int) =
  if not hasKey(FACE.vertices_tbl, pos):
FACE.vertices_tbl[pos] = @[]
FACE.indices_tbl[pos] = @[]


Run

but in OpenGL function where i specify the container 


proc CreateBuffers*(obj: RenderableObject) {.inline.} =
# # #
  glBufferData(GL_ARRAY_BUFFER, obj.vertices_tbl[f].len*sizeof(GLfloat), 
obj.vertices_tbl[f][0].unsafeAddr, GL_STATIC_DRAW)
# # #


Run

It says it cant get the address.

Is it because its not yet initialized? if I pass it with var like _obj: var 
RenderableObject_ it works, but that kinda defeats the purpose and its very slow