If I instantiate and position two separate quadrangles
Quadrangle q0;
q0.setPosition(glm::vec3(0, 0, 0));
Quadrangle q1;
q1.setPosition(glm::vec3(1, 1, 1));
I can draw them separately in separate draw calls with no problems.
I encounter problems if I try and draw them in the same draw call
glDrawElements(GL_TRIANGLES, m_numQuadrangles * 6, GL_UNSIGNED_SHORT, BUFFER_OFFSET(0));
A connecting triangle between the first and second quadrangle is drawn and the second quadrangle triangles are ignored completely.
My indices for each quadrangle are correct
int numIndices = 0;
for (int i = 0; i < maxQuadrangles; i++)
{
// CW Winding [0, 1, 2] [1, 3, 2]
m_indices[numIndices++] = 0 + i;
m_indices[numIndices++] = 1 + i;
m_indices[numIndices++] = 2 + i;
m_indices[numIndices++] = 1 + i;
m_indices[numIndices++] = 3 + i;
m_indices[numIndices++] = 2 + i;
}
m_numQuadrangles * 6 is the correct index count depending on the number of quadrangles.
The vertices are set correctly
std::array<VertexPositionTexture, 4> v = quadrangle.getVertices();
std::copy(v.begin(), v.end(), m_vertices.begin() + (m_numQuadrangles * 4));
...
glBindBuffer(GL_ARRAY_BUFFER, vbuffer);
glBufferData(GL_ARRAY_BUFFER, maxVertices * sizeof(VertexPositionTexture), &m_vertices[0], GL_DYNAMIC_DRAW);
How can I make sure the triangles making up each quadrangle are completely separate but only using one draw call?