Managed DirectX Tutorials: Part 7 - Using Heightmaps

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What Are Heightmaps and How To Read Them

In this (rather short) tutorial we will learn about heightmaps, and use them to add different height levels to our vertices to create realistic-looking terrain

What is a Heightmap?

A heightmap is a file used by game programmers to read height data.
In form, they are an image file, usually with as many pixels as the amount of vertices in the game world.
They only have greyscale colour. The program loads this heightmap into memory, and tests the colour value of each pixel. If it is pure white, (255), then the height of the vertex at that pixel location will be the highest (this is usually 255 scaled down by a factor), wheras if it is black it is at the lowest position.
The following is an example of a heightmap:

As you can see, it is greyscale, where the height will increase as the value does (ie whiter).

For simplicity, heightmaps are often saved in the .RAW file format.
This is an image format which just stores the pixel data, without any compression or anything else.

These can be opened in image editors such as Adobe Photoshop Elements, and work in a similar way to bmp.

How will we apply it to our terrain?

To apply a heightmap to our terrain, we will simply modify the SetGrid()
method we created in the last tutorial to accept a 2D array of points (which
we will apply to the Z-axis) and then create a new method to load the height data
into it.

 

public int[,] heightFromFile(string pFile, int WIDTH, int HEIGHT)
{ 
int[,] HeightData = new int[WIDTH, HEIGHT];
FileStream fs = new FileStream(pFile, FileMode.Open, FileAccess.Read);
BinaryReader r = new BinaryReader(fs);
int Currheight = new int();for (int i = 0; i < HEIGHT; i++)
for (int y = 0; y < WIDTH; y++)
{
Currheight = (int)(r.ReadByte()/2);
HeightData[WIDTH - 1 - y, HEIGHT - 1 - i] = Currheight;
}
r.Close();
return (HeightData);
}

The first four lines of this method are just setting it up.
FileStream opens a link between the program and a particular file (in this case the one passed through parameter pFile), and BinaryReader "attatches" itself to this stream so it can literally read the values of the heightmap.

We then loop through the file, reading the current byte value (ReadByte) and dividing it by two. This gives us a value out of 255, and then the division is simply to scale it down (we do not want our terrain to be able to be that high).
We then assign this value to the appropriate HeightData element.
Finally, we close the stream between the file and return the HeightData array, now full to the program.

Next, change the SetGrid() method so that it accepts a 2D int array called heightData, and replace the line:

CV[y, x].Z = 0;

with

CV[y, x].Z = heightData[y, x];

Finally, we can use the heightData member of the Form class in the previous sample, and load it using our new methods.
If everything went well, you will have heightmapped terrain when you run the sample :)
Next, we will learn to move around this terrain.

Feedback

I am always open for answering questions, whether through MSN (jamespraveen@aol.com), email (james@magclan.cwhnetworks.com) or through the message board attatched to this article.
If you have a problem with any of my samples / my topics in general please feel free to ask me.
Or you can post on my forums at http//www.just-code-it.net

History

26/05/06: Posted on CodeProject

Previous Articles

Part 1: Setting Up DirectX
Part 2: Initialising Direct3D
Part 3: Rendering Primitives
Part 4: The Transformation Pipeline
Part 7: Using Heightmaps