glDrawElements has stopped working - c++

Question

I had glDrawElements working consistently, initially with a simple box and then with more complex shapes made up of a large amount of vertices. Then it simply stopped drawing the mesh. I have taken the code back to it's most basic, just drawing 2 triangles to make a 2D square. This also no longer works.
void createMesh(void) {
float vertices[12];
vertices[0] = -0.5; vertices[1] = -0.5; vertices[2] = 0.0; // Bottom left corner
vertices[3] = -0.5; vertices[4] = 0.5; vertices[5] = 0.0; // Top left corner
vertices[6] = 0.5; vertices[7] = 0.5; vertices[8] = 0.0; // Top Right corner
vertices[9] = 0.5; vertices[10] = -0.5; vertices[11] = 0.0; // Bottom right corner
short indices[] = { 0, 1, 2, 0, 2, 3};
glEnableClientState(GL_VERTEX_ARRAY); // Enable Vertex Arrays
glVertexPointer(3, GL_FLOAT, 0, vertices); // Set The Vertex Pointer To Our Vertex Data
glDrawElements(GL_TRIANGLES,6 , GL_UNSIGNED_SHORT, indices);
glDisableClientState(GL_VERTEX_ARRAY);
}
The more advanced code that used to work is shown below:
void createMesh(void) {
float vertices[(amountOfHorizontalScans * 480 * 3)];// Amount of vertices
//build the array of vertices from a matrix of data
int currentVertex = -1;
std::vector <std::vector<double>> currentPointCloudMatrix = distanceCalculator.getPointCloudMatrix();
double plotY = 0;
double plotX = 0;
for (int j = 0; j < currentPointCloudMatrix.size(); j++){
std::vector <double> singleDistancesVector = currentPointCloudMatrix.at(j);
for (int i = 0; i < singleDistancesVector.size(); i++){
if (singleDistancesVector.at(i) != 0){
vertices[++currentVertex] = plotX;
vertices[++currentVertex] = plotY;
vertices[++currentVertex] = singleDistancesVector.at(i);
}
plotX += 0.1;
}
plotX = 0;
plotY += 0.2; //increment y by 0.02
}
//Creating the array of indices, 480 is the amount of columns
int i = 0;
short indices2[(amountOfHorizontalScans * 480 * 3)];
for (int row = 0; row<amountOfHorizontalScans - 1; row++) {
if ((row & 1) == 0) { // even rows
for (int col = 0; col<480; col++) {
indices2[i++] = col + row * 480;
indices2[i++] = col + (row + 1) * 480;
}
}
else { // odd rows
for (int col = 480 - 1; col>0; col--) {
indices2[i++] = col + (row + 1) * 480;
indices2[i++] = col - 1 + +row * 480;
}
}
}
glEnableClientState(GL_VERTEX_ARRAY); // Enable Vertex Arrays
glVertexPointer(3, GL_FLOAT, 0, vertices); // Set The Vertex Pointer To Our Vertex Data
glDrawElements(GL_TRIANGLE_STRIP, (amountOfHorizontalScans * 480 * 3), GL_UNSIGNED_SHORT, indices2);
glDisableClientState(GL_VERTEX_ARRAY);
}
I am at a complete loss as to why it has stopped working as it was working perfectly for a good number of runs, then just completely stopped. I have debugged through and all the code is being reached, also the vertices and indices are populated with data. What could cause this to stop working?
EDIT:
So I am really quite confused now. I came back to this issue this morning, and everything worked fine again, as in the meshes would draw with no issues. After doing some tests and running the program a number of times it has simply stopped drawing meshes again!
Could this be something memory related? I am not 100% sure on how glDrawElements stores the data passed to it, so could it be that I have to clear something somewhere that I keep filling up with data?

Answer 1

You cannot allocate dynamically arrays in stack:
short indices2[(amountOfHorizontalScans * 480 * 3)];
In code:
short indices2[(amountOfHorizontalScans * 480 * 3)];
for (int row = 0; row<amountOfHorizontalScans - 1; row++) {
if ((row & 1) == 0) { // even rows
for (int col = 0; col<480; col++) {
indices2[i++] = col + row * 480;
indices2[i++] = col + (row + 1) * 480;
}
}
else { // odd rows
for (int col = 480 - 1; col>0; col--) {
indices2[i++] = col + (row + 1) * 480;
indices2[i++] = col - 1 + +row * 480;
}
}
}
Must be
short* indices2 = new short[(amountOfHorizontalScans * 480 * 3)];
than free allocated memory
delete [] indices2;
Triangle strip is pretty tricky mode did you try to work directly with GL_TRIANGLES.