Make Ellipse by using DirectX 11 - game-engine

Question

if(shapeType == ELLIPSE)
{
Vertex* v = new Vertex[31];
v[0] = { 0.0f, 0.0f, 1.0f, 0.0f, 0.0f };
float theta;
for(int i = 1; i < 30; ++i)
{
theta = (MATH::TWO_PI * i) / static_cast<float>(30);
v[i] = { cos(theta * i), sin(theta * i), 1.0f, 0.0f, 0.0f };
}
HRESULT hr = this->vertexBuffer.Initialize(this->device, v,31);
if (FAILED(hr))
{
ErrorLogger::Log(hr, "Failed to create vertex buffer.");
return false;
}
DWORD* indices = new DWORD[90];
int indiceHelperNum1 = 1;
int indiceHelperNum2 = 2;
for(int i = 0; i < 87; i += 3)
{
indices[i] = 0;
indices[i + 1] = indiceHelperNum1;
indices[i + 2] = indiceHelperNum2;
indiceHelperNum1++;
indiceHelperNum2++;
}
indices[84] = 0;
indices[85] = 29;
indices[86] = 1;
hr = this->indexBuffer.Initialize(this->device, indices, 90);
if (FAILED(hr))
{
ErrorLogger::Log(hr, "Failed to create indices buffer.");
return false;
}
delete[] v;
delete[] indices;
}
This is my code and I think nothing is wrong in here except memory allocation. However, when I try this code, it doesn't work. I want to make a circle with radius one whose center is origin. I picked points by using vertex and I made triangles by using indices. Please tell me if something is wrong with my code.

Answer 1

There are a couple problems with this code.
The primary problem is in the following line
v[i] = { cos(theta * i), sin(theta * i), 1.0f, 0.0f, 0.0f };
There is no reason to multiply theta by i.
Once you resolve that issue, you should see something like this.
Notice the problem area outlined on the right side of the image.
In order to close the gap, the last 3 indices need to be modified.
Replace
indices[84] = 0;
indices[85] = 29;
indices[86] = 1;
with
indices[87] = 0;
indices[88] = 30;
indices[89] = 1;
One last thing, is your for loop to populate the vertices is not populating the last vertex at index 30. Adjust the for loops range like so
for (int i = 1; i < 31; ++i)
{
theta = (MATH::TWO_PI * i) / static_cast<float>(30);
v[i] = { cos(theta ), sin(theta ), 1.0f, 0.0f, 0.0f };
}
Finally, you should see something like this.