DOH! Need help stapling texture to terrain map properly.

[Iceman]

Ok, I have found no really good explanation of how to properly calculate texture coordinates for this problem ... mebbe someone can help me out.

I have a variable size terrain whose dimensions as passed to glVertex3f are :

X Axis : -xMinT to xMaxT
Y Axis : -yMinT to yMaxT

(Note Z is up in this system)

So I want to staple the texture onto the terrain map with a 1:1 correspondence and rely on scaling the texture matrix to distort it at run time.

My last effort went like this ...

Compute the scaling functions ...

	// Compute function to map range [xMinT,xMaxT] onto [0,1]
	m_TexCoordSlope[0] = 1.0f/float(xMaxT-xMinT);
	m_TexCoordIntercept[0] = -float(xOffset)*m_TexCoordSlope[0];
 
	// Compute function to map range [yMinT,yMaxT] onto [0,1]
	m_TexCoordSlope[1] = 1.0f/float(yMaxT-yMinT);
	m_TexCoordIntercept[1] = -float(yOffset)*m_TexCoordSlope[1];

and my function to place a vertex and staple its texture coordinate ...

void TerrainRenderer: : placeVertex(float x, float y, float z)
{
	double z2 = z*m_ScaledElevationSlope+m_ScaledElevationIntercept;
	setHeightColor(z);
	glVertex3f(x,y,z2);
 
	float xt = m_TexCoordSlope[0]*x + m_TexCoordIntercept[0];
	float yt = m_TexCoordSlope[1]*y + m_TexCoordIntercept[1];
 
	glTexCoord2f(xt,yt);
}

The code that places the vertex is ...

glMatrixMode(GL_TEXTURE);
glPushMatrix();
glScalef(m_TexStretch[0],m_TexStretch[1],1);
glMatrixMode(GL_MODELVIEW);
 
// ...
 
placeVertex(terrainX, terrainY, terrainZ);
 
// ...
 
glMatrixMode(GL_TEXTURE);
glPopmatrix();
glMatrixMode(GL_MODEL_VIEW);
 
// ...

Well, I end up with a really nicely textured terrain but that texture is repeated over the terrain roughly 100 times in each direction when m_TexStretch[i] = 1. I want that case to result in the texture being stapled to the corners with a ONE TO ONE match of the texture to the terrain map.

Does anyone see what I am doing wrong? Or, are the better ways to do this?

Thanks in advance ...

Ice out


[This message has been edited by Iceman (edited 09-21-2002).]

[Iceman]

oops

[This message has been edited by Iceman (edited 09-21-2002).]

[Iceman]

oops

[This message has been edited by Iceman (edited 09-21-2002).]

[Iceman]

oops

[dorbie]

How about for each vertex:

s_tex = x_coord/terrain_x_size;
t_tex = 1.0-z_coord/terrain_z_size;

This assumes that the y axis points up.

There's no need for all the texture matrix stuff.