C++ OpenGL Large Mesh is missing triangles - c++

Question

So I'm putting together a height map renderer that will do most of the work int he vertex shader, but first of course I generate a mesh to render, at the moment I'm playing around with upper limits of openGL and C++ to see how dense a mesh I can render (so I later have something to go by in terms of LoD mesh dividing)
ANYWAY! to cut to the issue;
the issue I noticed after testing a meshResolution of 32, 64 and at 128 I experienced runtime crashes, I stopped them by using the a self made class "indexFace" which holds 6 indices to lower the array length, problem is at 128 resolution only a 3rd of the mesh actually displays, I was wondering if there was a limit to how many indices openGL can render or hold using 1 set of BufferObjects or if its an issue with my handling of the C++ side of things.
I'm generating the mesh via the following:
void HeightMapMesh::GenerateMesh(GLfloat meshScale, GLushort meshResolution)
{
GLushort vertexCount = (meshResolution + 1) * (meshResolution + 1);
Vertex_Texture* vertexData = new Vertex_Texture[vertexCount];
GLushort indexCount = (meshResolution * meshResolution) * 6;
//indexFace holds 6 GLushort's in an attempt to overcome the array size limit
indexFace* indexData = new indexFace[meshResolution * meshResolution];
GLfloat scalar = meshScale / ((GLfloat)meshResolution);
GLfloat posX = 0;
GLfloat posY = 0;
for (int x = 0; x <= meshResolution; x++)
{
posX = ((GLfloat)x) * scalar;
for (int y = 0; y <= meshResolution; y++)
{
posY = ((GLfloat)y) * scalar;
vertexData[y + (x * (meshResolution + 1))] = Vertex_Texture(posX, posY, 0.0f, x, y);
}
}
GLint indexPosition;
GLint TL, TR, BL, BR;
for (int x = 0; x < meshResolution; x++)
{
for (int y = 0; y < meshResolution; y++)
{
indexPosition = (y + (x * (meshResolution)));
BL = y + (x * (meshResolution + 1));
TL = y + 1 + (x * (meshResolution + 1));
BR = y + ((x + 1) * (meshResolution + 1));
TR = y + 1 + ((x + 1) * (meshResolution + 1));
indexData[indexPosition] = indexFace(
BL, TR, TL,
BL, BR, TR
);
}
}
mesh.Fill(vertexData, vertexCount, (void *)indexData, indexCount, GL_STATIC_DRAW, GL_STATIC_DRAW);
delete [] vertexData;
delete [] indexData;
}
//This is for mesh.Fill()
void Fill(T* vertData, GLushort vertCount, void* indData, GLushort indCount, GLenum vertUsage, GLenum indUsage)
{
indexCount = indCount;
vertexCount = vertCount;
glBindBuffer(GL_ARRAY_BUFFER, vertexBufferObjectID);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBufferObjectID);
glBufferData(GL_ARRAY_BUFFER, sizeof(T) * vertexCount, vertData, vertUsage);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(GLushort) * indexCount, indData, indUsage);
}

Answer 1

its because you made your indices shorts.
For example this: GLushort indexCount = (meshResolution * meshResolution) * 6; is hitting USHRT_MAX at a value of 105 for meshResolution. (105*105*6 = 66150 > 65535)
Use ints as indices. So change your indices everywhere to unsigned ints and do the final draw call like this:
glDrawElements( GL_QUADS, indCount, GL_UNSIGNED_INT, indices); //do this
//glDrawElements( GL_QUADS, indCount, GL_UNSIGNED_SHORT, indices); //instead of this
//also GL_QUADS is deprecated but it seems your data is in that format so I left it that way
You could save a bunch of indices if you drew GL_TRIANGLE_STRIPs instead or better yet do tesselation on the GPU, since this is like the perfect use-case for it.