Understanding what values to expect in Fragment Shader for height of terrain

Hello all,

I’m generating a terrain through an array with the values for a gray scale image. So here I’m sure the range of values is from 0 to 255.

[java]public float[] convertBufferedImageToArray() {

int imageWidth = heightMap.getWidth();

int imageHeight = heightMap.getHeight();

float array[] = new float[imageWidth * imageHeight];

int[] dataBuffInt = heightMap.getRGB(0, 0, imageWidth, imageHeight, null, 0, imageWidth);

float average;

for (int i = 0; i < dataBuffInt.length; i++) {

average = (dataBuffInt >> 16) & 0xFF; // red

average += (dataBuffInt >> 8 ) & 0xFF ; // green

average += (dataBuffInt >> 0) & 0xFF; // blue

average = average / 3f;

array = average;


return array;


Then the terrain generation algorithm kicks in.

I’ve looked at the jME3 code. To me it seemed that the values stay the same, since I don’t provide scale factor at the constructor (=> it’s being multiplied by the unitary vector).

But there is probably a lot going on here that I have no idea of, so I have no idea what the range of values here might be.

Also I move the terrain and set the scale to one:

[java]terrain.setLocalTranslation(0, -300, 0);

terrain.setLocalScale(1f, 1f, 1f);[/java]

And finally we arrive at the shaders. In the Vertex Shader, I’m filling the gl_Position the usual way:

[java]void main(){

position = g_WorldMatrix * vec4(inPosition, 0.0);

vec4 pos = vec4(inPosition, 1.0);

gl_Position = g_WorldViewProjectionMatrix * pos;[/java]

In the Fragment Shader, I’m taking gl_Position.y as the height of things (example: how tall a mountain is) and doing my calculations as if this values still are from 0 to 255. I’m almost sure I can’t just assume that.

  • What are the transformations that I’m missing?
  • What is the range of values in the Fragment Shader?
  • Is the gl_Position.y the variable that I’m looking for for this?

inPosition.y is local height.

But there is probably a lot going on here that I have no idea of

Just run the app in debug mode. Terrain heights is a regular array, you can view it from there.

As far as I can see there is no transformation going on.

Btw is there anyway to do that in Eclipse?