[gameprogrammer] Re: terrain geometry calculation problem

huzzah! congratulations that the code works now (:

On 10/18/06, Roger D Vargas <luo_hei@xxxxxxxx> wrote: 

The error was in the rendering code. Each line should have a 0, 1 and 2.
The last 3 have 1,1 and 2. Big stupid mistake I made.

Sami Näätänen escribió:
> On Tuesday 17 October 2006 18:12, Roger D Vargas wrote:
>> It is the same. Here is an screenshot of the problem:
>> http://www.granhotelstgo.cu/x/terrain.jpg
>
> As I said it will only draw the over the edge ones.
> You have also a face culling problem.
>
> When the array goes over the edge it will use the next rows first
> points.
>
> These are the vertex points in the grid
> a,b,c is the first triangle.
> The second triangle is b,c,d which it seams to draw on the screen.
>
> When correct shape is triangles e,f,g and f,g,h
> from vertices e,f,g,h.
>
>   0 1 2 3 4 5 6 7 8 9
>  0                  a
>  1b                 c
>  2d
>  3
>  4ef
>  5gh
>  6
>  7
>  8
>  9
> 10
>
> Try to exchange the drawing of vertex 1 and vertex 2 and see what it
> gives to you.
>
>> Sami Näätänen escribió:
>>> On Monday 16 October 2006 17:02, Roger D Vargas wrote:
>>>> Im trying to implement a basic terrain renderer following the one
>>>> explained in chapter 7 of Opengl game programming book. But the
>>>> result is a weird mesh far from looking like a terrain. Can
>>>> somebody see if Im missing something in the following code? Iti
>>>> copied from the book with very few modifications.
>>>>
>>>> I use this map for heights
>>>>
>>>> float hm[MAP_Z][MAP_X]={
>>>> {0,0,2.0,0,0,0,5.0,0,0,0},
>>>> {0,2.0,0,0,0,0,0,0,0,0},
>>>> {0,0,0,1.0,0,0,0,0,0,0},
>>>> {0,0,0,0,0,0,0,0,0,0},
>>>> {2,0,0,0,0,4.1,0,0,0,0},
>>>> {0,0,0,0,0,0,0,0,0,0},
>>>> {2,0,0,0,0,0,0,0,2.0,0},
>>>> {0,0,0,0,2.0,0,0,0,0,0},
>>>> {0,0,3.0,0,0,0,0,0,0,0},
>>>> {0,0,0,0,0,0,4.0,0,0,0}
>>>> };
>>>>
>>>> And here is the code to calculate the geometry
>>>>
>>>> void create_geometry()
>>>> {
>>>>   int z,x;
>>>>   for (z=0;z<MAP_Z;z++) {
>>>>    for (x=0;x<MAP_X;x++) {
>>>>       terrain[x][z][0]=x*ts;
>>>>       terrain[x][z][1]=hm[z][x];
>>>>       terrain[x][z][2]=z*ts;
>>>>    }//for x
>>>>   }//for z
>>>> }
>>>>
>>>> And this is the rendering code
>>>>
>>>> glBindTexture(GL_TEXTURE_2D,grass);
>>>> for (z=0;z<=9;z++) {
>>>>    glBegin(GL_TRIANGLE_STRIP);
>>>>    for (x=0;x<=9;x++) {
>>> The loops are going too far.
>>>
>>> 'vertex 1' will use x+1 as x index, which is 10 when the x is 9.
>>> So this will overflow the 0..9 index of the terrain array.
>>> Same happens to the z index in vertices 2 and 3 and to the x index
>>> in vertex 3.
>>>
>>>>     //vertex 0
>>>> glColor3f(terrain[x][z][0]/255.0,terrain[x][z][1]/255.0,terrain[x]
>>>> [z] [2]/255.0); glTexCoord2f(0.0,0.0);
>>>>
>>>> glVertex3f(terrain[x][z][0],terrain[x][z][1],terrain[x][z][2]);
>>>> //vertex 1
>>>> glColor3f(terrain[x+1][z][1]/255.0,terrain[x+1][z][1]/255.0,terrai
>>>> n[x +1][z][2]/255.0f); glTexCoord2f(1.0,0.0);
>>>>
>>>> glVertex3f(terrain[x+1][z][1],terrain[x+1][z][1],terrain[x+1][z][2
>>>> ]); //vertex 2
>>>> glColor3f(terrain[x][z+1][1]/255.0,terrain[x][z+1][1]/255.0,terrai
>>>> n[x ][z+1][2]/255.0); glTexCoord2f(0.0,1.0);
>>>>
>>>> glVertex3f(terrain[x][z+1][1],terrain[x][z+1][1],terrain[x][z+1][2
>>>> ]); //vertex 3
>>>> glColor3f(terrain[x+1][z+1][1]/255.0,terrain[x+1][z+1][1]/255.0,te
>>>> rra in[x+1][z+1][2]/255.0); glTexCoord2f(1.0,1.0);
>>>> glVertex3f(terrain[x+1][z+1][1],terrain[x+1][z+1][1],terrain[x+1][
>>>> z+1 ][2]);
>>>>
>>>>    }
>>>>    glEnd();
>>>>   }
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