Figure 5: Example with multiple surfaces
Figure 5: Example with multiple surfaces
The following code sample shows how to build the list of indices required by subroutine XintView3DCreateMeshSurface in the case where the input vertices are stored in a regular grid.
int width; /* width of the grid */
int height; /* height of the grid */
XintVector3 *verts; /* grid data (size is width*height) */
int num_strips; /* Number of strips in quad mesh */
int **indices; /* Index lists */
int *num_indices; /* Number of indices per list */
int i, j, k, index;
...
/*
* Build list of indices to describe grid as quad strips
*/
num_strips = width - 1;
num_indices = (int *)malloc(num_strips * sizeof(int));
indices = (int **)malloc(num_strips * sizeof(int *));
for (i=0; i < num_strips; i++) {
num_indices[i] = height * 2;
indices[i] = (int *)malloc(num_indices[i] * sizeof(int));
}
/* loop over the strips */
for (k=0; k < (width - 1); k++) {
index = width * (k);
i = 0;
for (j=0; j < height; j++) {
indices[k][i] = width + index;
i++;
indices[k][i] = index;
i++;
index++;
}
}
The following diagram illustrates how each list of indices is built.
Figure 6: List of indices used to specify a quad strip
Function XintView3DCreateMeshSurface allows the user to specify a normal at each vertex on the surface. If the normals are not specified, they will be generated automatically. The normal at each vertex is generated by averaging the normals of each polygon that contains the vertex. A normal is a normalized vector, which is perpendicular to the surface and which points away from the surface. Normals are required to provide proper calculation of shading in the case where the surface has lighting turned on. Two convenience functions are provided to calculate normal vectors. Function XintGeomCalculateNormal takes as input three vertices and returns the corresponding normal vector. Function XintVectorNormalize3d takes as input a vector and returns a normalized vector.
The following figure demonstrates how the normals are calculated automatically.
Step 1: Calculation of normals at the center of each quadrilateral.
Step 2: Normal at a vertex is the average of four surrounding normals.
Figure 7: Normal calculation at a grid vertex
The following code sample, extracted from example file checknormal.c, illustrates how to use function XintView3DCreateNormalsForMesh.
Widget view3d;
XintView3DMaterial *material;
XintView3DObject *mesh, *normals;
...
/* material to display the normals */
color.single[0] = 0.0;
color.single[1] = 0.0;
color.single[2] = 1.0;
color.single[3] = 1.0;
material = XintView3DCreateMaterial(NULL, XintMATERIAL_SINGLE_COLOR,
&color, 0, NULL);
/* Create line object containing normals */
normals = XintView3DCreateNormalsForMesh(mesh, 5.0);
/* Add object to display */
XintView3DAddObjectAndMaterial (view3d, normals, material, NULL);
...
The output of this example is shown below.
Figure 8: Surface and its normal vectors
The following code sample, extracted from example grid4d.c, illustrates how to display grid surface and color it based on a fourth attribute. We use material type XintMATERIAL_COLOR_SCALE in this example.
Widget top_level, view3d;
XintView3DObject *surface;
XintView3DMaterial *material;
XintView3DMaterialColor scale_color;
XintView3DColorTable *color_table;
XintColor4 *colors;
XintVector3 *verts;
int ncolors;
XintReal *range, *data, *color_data;
float start_x, start_y, end_x, end_y;
float min_value, max_value;
float dx, dy;
int nx, ny;
int count;
int i, j;
...
/* Create a viewer */
view3d = XtVaCreateManagedWidget("Viewer", xintView3DWidgetClass, top_level,
XmNwidth, 400, XmNheight, 400, NULL);
/* Read a colormap file */
color_table = XintView3DReadColorTable(NULL, "contour.cmp");
if (!color_table)
XtError("Error reading colormap file contour.cmp");
/* Retrieve colors from the map */
colors = XintView3DColorTableData(color_table, &ncolors);
/*Read first grid used for surface */
data = ReadGrid("topology.grd", &nx, &ny, &start_x, &end_x,
&start_y, &end_y);
/* Build list of vertices */
verts = (XintVector3 *)malloc(nx * ny * sizeof(XintVector3));
dx = (end_x - start_x) / (nx - 1);
dy = (end_y - start_y) / (ny - 1);
count = 0;
for (j=0; j < ny; j++) {
for (i=0; i < nx; i++) {
verts[count][0] = start_x + (float) i * dx;
verts[count][1] = start_y + (float) j * dy;
verts[count][2] = data[count];
count++;
}
}
/* Read color attribute from another grid file*/
color_data = ReadGrid("attribute.grd", &nx, &ny,
&start_x, &end_x, &start_y, &end_y);
/* Find min and max */
min_value = color_data[0];
max_value = color_data[0];
for (i=1; i < nx*ny; i++) {
if (color_data[i] > max_value) max_value = color_data[i];
if (color_data[i] < min_value) min_value = color_data[i];
}
/* Setup range */
range = (XintReal *) XtMalloc(sizeof(XintReal) * (ncolors-1));
for (i=0; i < ncolors-1; i++)
range[i] = min_value + (float)i * (max_value - min_value) / (ncolors-1);
/* Create a color scale material */
scale_color.scale.orientation = `W';
scale_color.scale.range = range;
scale_color.scale.num_colors = ncolors;
scale_color.scale.colors = colors;
material = XintView3DCreateMaterial(NULL, XintMATERIAL_COLOR_SCALE,
&scale_color, 0, NULL);
/* Create uniform grid surface object */
surface = XintView3DCreateUniformGrid("grid", nx, ny, verts,
True, color_data, NULL,
False, NULL, NULL);
/* Free memory */
XintView3DColorTableFree(color_table);
XtFree((char *) range);
XtFree((char *) verts);
XtFree((char *) data);
XtFree((char *) color_data);
/* Add object to display */
XintView3DAddObject(view3d, surface, material, NULL);
...
The output of this example is shown below.
Figure 9: Surface colored based on a 4D attribute