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# Heightmap finding closest vertices

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2 replies to this topic

### #1ChobitsTheZero  Members

Posted 18 February 2017 - 09:53 AM

So I have rendered a terrain based on a heightmap. It's based on this tutorial that I followed - http://www.mbsoftworks.sk/index.php?page=tutorials&series=1&tutorial=8

Now I want to have my camera to be able to "walk" on the terrain. The getY() function gets the x and z coordinates of the camera, and I understand that with those I have to find the closest vertices of the terrain to decide which triangle the camera is over. The thing is i'm unsure of how to actually do that, I have looked for a lot of examples on google but haven't been able to find any concrete answers for it. Currently my code looks like this:

HM_SIZE_X and HM_SIZE_Y are both 6

float Terrain::getY(int x, int z)
{

//return
}

void Terrain::createTerrain()
{
glClearColor(0.0f, 0.0f, 0.0f, 1.0f);

// Setup heightmap

glGenVertexArrays(1, &uiVAOHeightmap); // Create one VAO
glGenBuffers(1, &uiVBOHeightmapData); // One VBO for data
glGenBuffers(1, &uiVBOIndices); // And finally one VBO for indices

glBindVertexArray(uiVAOHeightmap);
glBindBuffer(GL_ARRAY_BUFFER, uiVBOHeightmapData);

float fHeights[HM_SIZE_X*HM_SIZE_Y] =
{
10.0f, 10.0f, 10.0f, 10.0f, 10.0f, 10.0f,
5.0f, 5.0f,5.0f, 10.0f, 10.0f, 10.0f,
5.0f, 5.0f, 5.0f, 10.0f, 10.0f, 10.0f,
5.0f, 5.0f, 10.0f, 10.0f, 10.0f, 10.0f,
10.0f, 10.0f, 10.0f, 10.0f, 10.0f, 10.0f,
10.0f, 5.0f, 5.0f, 5.0f, 5.0f, 10.0f,
};

float fSizeX = 100.0f, fSizeZ = 100.0f;

for (int i = 0; i<HM_SIZE_X*HM_SIZE_Y;i++)
{
for (int j = 0; j < HM_SIZE_X*HM_SIZE_Y; j++)
{
float column = float(i%HM_SIZE_X), row = float(i / HM_SIZE_X);
vHeightmapData[i] = glm::vec3(
-fSizeX / 2 + fSizeX*column / float(HM_SIZE_X - 1), // X Coordinate
fHeights[i], // Y Coordinate (it's height)
-fSizeZ / 2 + fSizeZ*row / float(HM_SIZE_Y - 1) // Z Coordinate
);
}
}

glBufferData(GL_ARRAY_BUFFER, sizeof(glm::vec3)*HM_SIZE_X*HM_SIZE_Y, vHeightmapData, GL_STATIC_DRAW);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);

glGenBuffers(1, &uiVBOIndices);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, uiVBOIndices);
int iIndices[] =
{
0, 6, 1, 7, 2, 8, 3, 9, 4, 10, 5, 11, 36,
6, 12, 7, 13, 8, 14, 9, 15, 10, 16, 11, 17, 36,
12, 18, 13, 19, 14, 20, 15, 21, 16, 22, 17, 23, 36,
18, 24, 19, 25, 20, 26, 21, 27, 22, 28, 23, 29, 36,
24, 30, 25, 31, 26, 32, 27, 33, 28, 34, 29, 35
};
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(iIndices), iIndices, GL_STATIC_DRAW);
glEnable(GL_PRIMITIVE_RESTART);
glPrimitiveRestartIndex(HM_SIZE_X*HM_SIZE_Y);
}

### #2Norman Barrows  Members

Posted 18 February 2017 - 02:44 PM

You know where you vertices are.

You know the size of a quad.

You know where the camera is.

From there you can determine which quad the camera is in.   ( camera x - mesh x ) / quad size = quad x.   similar for z.

and from there you can determine which triangle of the quad the camera is in.

from that you can lerp down the two sides of the triangle, then lerp between those results to get the height of the triangle at the camera's location.

Norm Barrows

Rockland Software Productions

"Building PC games since 1989"

rocklandsoftware.net

PLAY CAVEMAN NOW!

http://rocklandsoftware.net/beta.php

### #3ChobitsTheZero  Members

Posted 20 February 2017 - 11:45 AM

You know where you vertices are.

You know the size of a quad.

You know where the camera is.

From there you can determine which quad the camera is in.   ( camera x - mesh x ) / quad size = quad x.   similar for z.

and from there you can determine which triangle of the quad the camera is in.

from that you can lerp down the two sides of the triangle, then lerp between those results to get the height of the triangle at the camera's location.

How would I determine which triangle of the quad the camera is in?

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