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Dyn. 2 dim float array not same as float[4][4]??

Started by HellRiZZer Nov 18, 2001 at 8:02 PM 1 replies 350+ views

Original Post

Nov 18, 2001 at 8:02 PM

I was recently trying to make a 2 dim array for use with glMap2f(OpenGL) and making all its values same as the array float[4][4][3]. E.g I made typedef float glVertex3fv[3]; Then, I do: glVertex3fv **Grid; Then I allocate 2 dim array as 4x4 Grid = new glVertex3fv*[4]; for (int i=0;i<4;i++) Grid = new glVertex3fv[4]; And here I just assign all values of float[4][4][3] to Grid[x][y][0,1,2]. When I go to glMap2f and pass it not as &float[0][0](starting array value), but as (float *)&Grid[0][0], it draws some buggy things, not the patch I had with float[4][4][3].. Why? Someone help please? Thanks.

Fruny

203

Fruny

Nov 19, 2001 at 12:53 AM

Ok... no, an array of arrays is not structurally equivalent to a 2D array (sorry if I pointed you in the wrong direction earlier).

float[4][4][3] is the same thing than float[48].

As others had said before, you will have to allocate it in one chunk and compute the indices yourself.

Fruny

203

Fruny

Nov 19, 2001 at 12:59 AM

Oh, and by the way, glVertex3fv is a function name.
You are calling for trouble to define it as a type.

try that way

  
#include <vector>

typedef struct
{
  float r, g, b;
} pixel_t;

typedef std::vector<pixel_t> grid_t;

.
.
.

grid_t Grid( rows * columns );

for( y = 0; y < rows; ++y ) // y outside to preserve locality of access

for( x = 0; x < columns; ++x )
{
  Grid[x + columns * y].r = ...
  Grid[x + columns * y].g = ...
  Grid[x + columns * y].b = ...
}

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