+ * Generate vertex indices for visualizing the normals.
+ */
+static GLfloat *verticesForNormalVisualization;
+static GLushort numNormalVertices = 0;
+static void fghGenerateNormalVisualization(GLfloat *vertices, GLfloat *normals, GLsizei numVertices,
+ GLushort *vertIdxs, GLsizei numParts, GLsizei numVertIdxsPerPart)
+{
+ GLushort i,j;
+ /* calc number of vertices to generate, allocate. TODO: FREE again after draw!
+ * two for each vertex in the input shape
+ */
+ if (!vertIdxs)
+ numNormalVertices = numVertices * 2;
+ else
+ numNormalVertices = numParts * numVertIdxsPerPart * 2;
+ verticesForNormalVisualization = malloc(numNormalVertices*3 * sizeof(GLfloat));
+
+ /* Now generate vertices for lines to draw the normals */
+ if (!vertIdxs)
+ {
+ for (i=0,j=0; i<numNormalVertices*3/2; i+=3, j+=6)
+ {
+ verticesForNormalVisualization[j+0] = vertices[i+0];
+ verticesForNormalVisualization[j+1] = vertices[i+1];
+ verticesForNormalVisualization[j+2] = vertices[i+2];
+ verticesForNormalVisualization[j+3] = vertices[i+0] + normals[i+0]/4.f;
+ verticesForNormalVisualization[j+4] = vertices[i+1] + normals[i+1]/4.f;
+ verticesForNormalVisualization[j+5] = vertices[i+2] + normals[i+2]/4.f;
+ }
+ }
+ else
+ {
+ for (i=0,j=0; i<numNormalVertices/2; i++, j+=6)
+ {
+ GLushort idx = vertIdxs[i]*3;
+ verticesForNormalVisualization[j+0] = vertices[idx+0];
+ verticesForNormalVisualization[j+1] = vertices[idx+1];
+ verticesForNormalVisualization[j+2] = vertices[idx+2];
+ verticesForNormalVisualization[j+3] = vertices[idx+0] + normals[idx+0]/4.f;
+ verticesForNormalVisualization[j+4] = vertices[idx+1] + normals[idx+1]/4.f;
+ verticesForNormalVisualization[j+5] = vertices[idx+2] + normals[idx+2]/4.f;
+ }
+ }
+}
+
+static void fghDrawNormalVisualization()
+{
+ GLfloat currentColor[4];
+ /* Setup draw color: (1,1,1)-shape's color */
+ glGetFloatv(GL_CURRENT_COLOR,currentColor);
+ glColor4f(1-currentColor[0],1-currentColor[1],1-currentColor[2],currentColor[3]);
+
+ glEnableClientState(GL_VERTEX_ARRAY);
+
+ glVertexPointer(3, GL_FLOAT, 0, verticesForNormalVisualization);
+ glDrawArrays(GL_LINES, 0, numNormalVertices);
+
+ glDisableClientState(GL_VERTEX_ARRAY);
+
+ /* Done, free memory, reset color */
+ free(verticesForNormalVisualization);
+ glColor4fv(currentColor);
+}
+
+/**