//each of these 4 methods is more efficient than the previous...
//this method is the manual method where each state is setup peice by peice
private void DrawManual(DrawState state)
{
//manual render state
//First, take a copy of current render state..
DeviceRenderState currentState = state.RenderState;
//The DeviceRenderState structure stores common render state, it's bit-packed so it's small.
//The majority of render state is stored, with most commonly used xbox-supported state included.
//The entire structure is 16 bytes (the size of a Vector4)
//
//The DeviceRenderState structure stores four smaller structures:
//
// StencilTestState StencilTest; (8 bytes)
// AlphaBlendState AlphaBlend; (4 bytes)
// AlphaTestState AlphaTest; (2 bytes)
// DepthColourCullState DepthColourCull; (2 bytes)
//
//DepthColourCullState combines the three smaller states, Depth testing, Colour masking and FrustumCull mode
//
//When geometry is rendered, state.RenderState is compared to the current known device state
//This comparison is very fast. Any changes detected will be applied at render time.
//
//Because of this, changing state.RenderState is very fast and efficient, as actual render state
//on the GraphicsDevice doesn't change until the geometry is drawn. No logic is run when changing
//the value.
//
//In terms of efficiency, think of setting the DeviceRenderState as equivalent assigning integers.
//Here the alpha blend state is changed manually...
//reset the state to default (no blending)
state.RenderState.AlphaBlend = new AlphaBlendState(); //4 bytes assigned to zero, no heap allocations
//set blending...
state.RenderState.AlphaBlend.Enabled = true; //one bit is changed
state.RenderState.AlphaBlend.SourceBlend = Blend.SourceAlpha; //4 bits are changed
state.RenderState.AlphaBlend.DestinationBlend = Blend.InverseSourceAlpha; //4 bits are changed
//draw the sphere
DrawGeometry(state);
//set the previous state back
state.SetRenderState(ref currentState);
//Note:
//you cannot write:
//state.RenderState = currentState;
//you have to call 'SetRenderState()' instead.
}