How to read height map values to generate a terrain?

Question

I am trying to make a terrain using a height map image in OpenGL. As a experiment i use 4x4 pixel image. this is a zoomed screen shot. so you can see the pixels.

This is a part of my code.

ILubyte * image = ilGetData();

int bpp =  ilGetInteger(IL_IMAGE_BPP);
std::cout << "BPP = " << bpp << std::endl;

for (int z=0; z < terrainHeight; ++z)
{
    for (int x=0; x < terrainWidth; ++x)
    {
        pVertices[z*terrainWidth+x] = NxVec3(NxF32(x),
            NxF32(image[z*terrainWidth+x]*bpp), NxF32(z));
    }
}

for (int i=0; i < vertexCount; ++i)
{
    std::cout << "x = " << pVertices[i].x << "\t y = " 
            << pVertices[i].y << "\t z = " << pVertices[i].z << std::endl;
}

Then, i'm getting the following result.

I'm expecting the zero values(for y-coordinate) for (0,0), (1,1), (2,2) and (3,3). but the result is different. why i'm not getting the expected results ?

Answer 1

I think it should be image[(z*terrainWidth+x)*bpp] instead of image[z*terrainWidth+x]*bpp.