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problem with heightmapping


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#1 timothyjlaird   Members   -  Reputation: 404

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Posted 14 June 2012 - 08:32 PM

I am trying to do some heightmapping with XNA. Basically I'm making a grid of verticies and then linking them together with indicies to form triangles. I then read the red values from all the pixels in a JPG or PNG, divide by 255, multiply by a scale factor and then set each of the 'y' value in the verticies in the grid to that value...giving a rudimentary heightmap. My problem is that the geometry does not look quite right in the render. Also if there is a better way to generate terrain I would like to hear it...because I can't go beyond a 512x512 heightmap without exceeding XNA's max triangle count. I know terrain generation with heightmaps is an ancient problem...and I'm hoping there is a better way to do what I am trying to do. Any ideas on how to make this work better (at least from a geometry standpoint).


The code I use to generate the triangle grid and read the heightmap image:
private float[] getVertexYFromImage(Texture2D displacementmap, int scalefactor)
		{
			Color[] pixels = new Color[displacementmap.Width * displacementmap.Height];
			displacementmap.GetData<Color>(pixels);
			float[] vertexy = new float[pixels.Length];
			for (int cursor = 0; cursor < pixels.Length; cursor++)
			{
				//use red channel to get vert height (y)
				vertexy[cursor] = ((float)pixels[cursor].R / 255.0f) * scalefactor;
			}
			return vertexy;
		}
		private void getTerrainVertexIndexData(int size, int spread, out int[] indexData, out VertexPositionNormalTexture[] vertexData)
		{
			vertexData = new VertexPositionNormalTexture[size*size];
			indexData = new int[3 * (2 * (size - 1)) * (size - 1)];
			//get height data for verticies
			float[] vertexYData = getVertexYFromImage(displaceT2D, 32);
			//build grid of verts
			int xcounter = 0;
			int zcounter = 0;
			int x_vert = 0;
			float y_vert = 0;
			int z_vert = 0;
			float u = 0.0f;
			float v = 0.0f;
			for (int index = 0; index < vertexData.Length; index++)
			{
				y_vert = vertexYData[index];
				vertexData[index].Position = new Vector3(x_vert, y_vert, z_vert);
				vertexData[index].Normal = new Vector3(0.0f, 0.0f, 0.0f);
				vertexData[index].TextureCoordinate = new Vector2(u, v);
				if (xcounter < (size - 1))
				{
					x_vert = x_vert + spread;
					xcounter++;
				}
				else
				{
					x_vert = 0;
					xcounter = 0;
					z_vert = z_vert + spread;
					zcounter++;
				}
				u = (float)xcounter / (size - 1);
				v = (float)zcounter / (size - 1);
			}
			//build indixies to form triangles from verts
			int icounter = 0;
			int cursorx = 0;
			int skipcounter = size-1;
			for (int currentstrip = 0; currentstrip < (size - 1); currentstrip++)
			{
				for (int count = 0; count < (size - 1); count++)
				{
					indexData[icounter] = cursorx;
					indexData[icounter + 1] = cursorx + 1;
					indexData[icounter + 2] = cursorx + 1 + (size);
					icounter = icounter + 3;
					indexData[icounter] = cursorx;
					indexData[icounter + 1] = cursorx + 1 + size;
					indexData[icounter + 2] = cursorx + size;
					icounter = icounter + 3;
					cursorx++;
				}
				if (cursorx == skipcounter)
				{
					cursorx++;
					skipcounter = skipcounter + size;
				}
			}
			//calculate normals for smooth shading
			for(int counter=0; counter<indexData.Length / 3; counter++)
			{
				Vector3 firstvec = vertexData[indexData[counter * 3 + 1]].Position - vertexData[indexData[counter * 3]].Position;
				Vector3 secondvec = vertexData[indexData[counter * 3]].Position - vertexData[indexData[counter * 3 + 2]].Position;
				Vector3 normal = Vector3.Cross(firstvec, secondvec);
				normal.Normalize();
				vertexData[indexData[counter * 3]].Normal += normal;
				vertexData[indexData[counter * 3 + 1]].Normal += normal;
				vertexData[indexData[counter * 3 + 2]].Normal += normal;
			}
			for (int counter = 0; counter < vertexData.Length; counter++)
			{
				vertexData[counter].Normal.Normalize();
			}
		}

Thanks,
John

Attached Thumbnails

  • terrainss.jpg


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#2 Ashaman73   Crossbones+   -  Reputation: 7471

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Posted 15 June 2012 - 12:19 AM

JPG or PNG

For accurate data you need a lossless compression format, so avoid JPG and stick to lossless compressed PNG to avoid artifacts.

because I can't go beyond a 512x512 heightmap without exceeding XNA's max triangle count

Instead of creating your whole map at once, subdivide it in patches (i.e. 64x64) and create them on-the-fly once you get close to them.

#3 bwhiting   Members   -  Reputation: 753

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Posted 15 June 2012 - 10:14 AM

you could also generate your heightmap/noise in an application and store the heights across all the channels giving you much greater range of depth:

http://www.gamerendering.com/2008/09/25/packing-a-float-value-in-rgba/

I think that is derived from a post on this forum anyway, should help smooth out the results!

#4 timothyjlaird   Members   -  Reputation: 404

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Posted 15 June 2012 - 07:20 PM

I figured out how to magnfiy the problem. I just increased my red channel scale factor and this is what happened:

Posted Image

I found a vertex smoothing algorithm. I'll let you know how it works out...

http://www.nfostergames.com/Lessons/TerrainSmoothing.htm

#5 timothyjlaird   Members   -  Reputation: 404

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Posted 16 June 2012 - 08:57 PM

fixed...

Posted Image

and some of the code that I used (4 passes of it seems to be about right), in the rare chance anyone else runs into the same set of problems...

private float[] getSmoothedVertexData(float[] yvalues, int size)
	    {
		    for (int count = 0; count < yvalues.Length; count++)
		    {
			    float adjSum = 0.0f;
			    float adjAvg = 0.0f;
			    if (count == 0) //left bottom corner
			    {
				    adjSum = yvalues[1] + yvalues[size] + yvalues[size+1];
				    adjAvg = adjSum / 3.0f;
				    yvalues[count] = (yvalues[count] + adjAvg) / 2.0f;
			    }
			    else if(count == (size - 1)) //right bottom corner
			    {
				    adjSum = yvalues[size - 2] + yvalues[(size -2)+size] + yvalues[(size -1)+size];
				    adjAvg = adjSum / 3.0f;
				    yvalues[count] = (yvalues[count] + adjAvg) / 2.0f;
			    }
			    else if(count == (yvalues.Length - size)) //left top corner
			    {
				    adjSum = yvalues[(yvalues.Length - size) + 1] + yvalues[(yvalues.Length - size) - size] + yvalues[(yvalues.Length - size) - size + 1];
				    adjAvg = adjSum / 3.0f;
				    yvalues[count] = (yvalues[count] + adjAvg) / 2.0f;
			    }
			    else if(count == (yvalues.Length - 1)) //right top corner
			    {
				    adjSum = yvalues[(yvalues.Length - 2)] + yvalues[(yvalues.Length - 1) - size] + yvalues[(yvalues.Length - 1) - size - 1];
				    adjAvg = adjSum / 3.0f;
				    yvalues[count] = (yvalues[count] + adjAvg) / 2.0f;
			    }
			    else if (count > 0 && count < size) //bottom strip
			    {
				    adjSum = yvalues[count - 1] + yvalues[count + 1] + yvalues[count + size] + yvalues[count + size + 1] + yvalues[count + size - 1];
				    adjAvg = adjSum / 5.0f;
				    yvalues[count] = adjAvg;
			    }
			    else if (count > (yvalues.Length - size) && (count < (yvalues.Length - 1))) //top strip
			    {
				    adjSum = yvalues[count - 1] + yvalues[count + 1] + yvalues[count - size] + yvalues[count - size - 1] + yvalues[count - size + 1];
				    adjAvg = adjSum / 5.0f;
				    yvalues[count] = adjAvg;
			    }
			    else if ((count % size) == 0) //left strip
			    {
				    adjSum = yvalues[count + 1] + yvalues[count - size] + yvalues[count + size] + yvalues[count + size + 1] + yvalues[count - size + 1];
				    adjAvg = adjSum / 5.0f;
				    yvalues[count] = adjAvg;
			    }
			    else if ((count + 1) % size == 0) //right strip
			    {
				    adjSum = yvalues[count - 1] + yvalues[count - size] + yvalues[count + size] + yvalues[count - size - 1] + yvalues[count + size - 1];
				    adjAvg = adjSum / 5.0f;
				    yvalues[count] = adjAvg;
			    }
			    else
			    {
				    int[] adjacentVerts = getAdjacentVertPositions(count, size);
				    for (int index = 0; index < 8; index++)
				    {
					    adjSum = adjSum + yvalues[adjacentVerts[index]];
				    }
				    adjAvg = adjSum / 8.0f;
				    yvalues[count] = (yvalues[count] + adjAvg) / 2.0f;
			    }
		    }
		    return yvalues;
	    }
	    private int[] getAdjacentVertPositions(int arrayPos, int size)
	    {
		    int[] adjacentVertPositions = new int[8];
		    adjacentVertPositions[0] = arrayPos - 9;
		    adjacentVertPositions[1] = arrayPos - 8;
		    adjacentVertPositions[2] = arrayPos - 7;
		    adjacentVertPositions[3] = arrayPos + 1;
		    adjacentVertPositions[4] = arrayPos + 9;
		    adjacentVertPositions[5] = arrayPos + 8;
		    adjacentVertPositions[6] = arrayPos + 7;
		    adjacentVertPositions[7] = arrayPos - 1;
		    return adjacentVertPositions;
	    }


#6 skytiger   Members   -  Reputation: 258

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Posted 17 June 2012 - 12:57 PM

http://skytiger.wordpress.com/2010/11/28/xna-large-terrain/




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