private void RenderSphere(SphereElement sphere, float rotationSin, float rotationCos, float colorLerpProgress, Vector3 lightDir)
{
float fX = sphere.x * rotationSin - sphere.z * rotationCos;
float fY = sphere.y;
float fZ = sphere.screenZ;
fZ += 1.5f;
//Skip the sphere that's too close to camera frustum
if (fZ < 0.001f)
{
return;
}
//Weak perspective projection
float screenX = fX / fZ;
float screenY = fY / fZ;
float screenZ = fZ;
float screenRadius = sphere.r / fZ;
Vector3Byte sphereColor = Vector3Byte.Lerp(sphere.colorA, sphere.colorB, colorLerpProgress);
int centerY = (int)(screenY * _width / 2 + _width / 2);
int centerX = (int)(screenX * _width / 2 + _width / 2);
//For square 1024x1024 buffer - Rx == Ry
int R = (int)(screenRadius * _width / 2);
int Rsquared = R * R;
int minX = Math.Max(centerX - R * 2, 0);
int maxX = Math.Min(centerX + R * 2, _width - 1);
int minY = Math.Max(centerY - R * 2, 0);
int maxY = Math.Min(centerY + R * 2, _height - 1);
for (int x = minX; x <= maxX; ++x)
{
for (int y = minY; y <= maxY; ++y)
{
int dx = x - centerX;
int dy = y - centerY;
int dx2 = dx * dx;
int dy2 = dy * dy;
//Skip pixels which are not part of a circle
if (dx2 + dy2 > Rsquared)
{
continue;
}
if (screenZ < _zBuffer[x + y * _width])
{
//lock (_zBuffer)
{
//Writing a float to _zBuffer array is atomic, no danger of corruption
_zBuffer[x + y * _width] = screenZ;
}
// Phong shading
{
Vector3 vec_normal = new Vector3();
vec_normal.x = dx;
vec_normal.y = dy;
vec_normal.z = (float)Math.Sqrt(Rsquared - (dx2 + dy2));
vec_normal.Normalize();
float NdotL = lightDir.Dot(vec_normal);
if (NdotL > 0)
{
Vector3 vec_eye = new Vector3();
vec_eye.x = lightDir.x + screenX;
vec_eye.y = lightDir.y + screenY;
vec_eye.z = lightDir.z + 1.0f;
vec_eye.Normalize();
float NdotHV = vec_eye.Dot(vec_normal);
float specular = NdotHV * NdotHV * NdotHV * NdotHV * NdotHV * NdotHV * NdotHV * NdotHV * NdotHV; // shininess=9
float alpha = NdotL + specular;
alpha = Math.Min(alpha, 1.0f);
byte r = (byte)(sphereColor.x * alpha);
byte g = (byte)(sphereColor.y * alpha);
byte b = (byte)(sphereColor.z * alpha);
SetPixel(x, y, b, g, r);
}
else
{
//Unlit pixel
SetPixel(x, y, 0, 0, 0);
}
}
}
}
}
}
private int CompareSpheres(SphereElement s1, SphereElement s2)
{
return(Math.Sign(s2.screenZ - s1.screenZ));
}