protected override void Initialise()
{
camera = new Camera3D();
//create the draw target.
drawToScreen = new DrawTargetScreen(this, camera);
//clear to dark blue
drawToScreen.ClearBuffer.ClearColour = new Color(20, 20, 40);
//create the light collection
lights = new MaterialLightCollection();
//set a dark blue ambient colour
lights.AmbientLightColour = new Color(40, 40, 80).ToVector3();
//positions for two lights
Vector3[] lightPositions = new Vector3[]
{
new Vector3(0, 30, 2),
new Vector3(0, -30, 2)
};
//geometry for a light (shared for each light)
IDraw lightGeometry = null;
for (int i = 0; i < lightPositions.Length; i++)
{
float lightHalfFalloffDistance = 15;
Color lightColor = Color.LightYellow;
Color lightSpecularColour = Color.WhiteSmoke;
bool perPixel = i < 2; //first two lights are per-pixel
//interface to the light about to be created
IMaterialPointLight light = null;
//create the point light
light = lights.AddPointLight(perPixel, lightPositions[i], lightHalfFalloffDistance, lightColor, lightSpecularColour);
//adjust the lighting attenuation model, the constant defaults to 1, which prevents the light being brighter than 1.0 in the falloff equation
//set to 0.25, the light will get really bright in close (up to 4)
//(see light.QuadraticAttenuation remarks for an explanation of the falloff model)
light.ConstantAttenuation = 0.25f;
//create the light geometry (a sphere)
if (lightGeometry == null)
{
lightGeometry = new Xen.Ex.Geometry.Sphere(Vector3.One, 8, true, false, false);
}
//visually show the light with a light drawer
IDraw lightSourceDrawer = new LightSourceDrawer(lightPositions[i], lightGeometry, lightColor);
//add the light geometry to the screen
drawToScreen.Add(lightSourceDrawer);
}
//create the ground disk
GroundDisk ground = new GroundDisk(this.Content, lights, diskRadius);
//then add it to the screen
drawToScreen.Add(ground);
}
protected override void Initialise()
{
Resource.EnableResourceTracking();
camera = new Camera3D();
camera.Projection.FarClip = 300;
camera.Projection.NearClip = 10;
camera.Projection.FieldOfView *= 0.55f;
//create the draw target.
drawToScreen = new DrawTargetScreen(this, camera);
//no need to clear the colour buffer, as a special background will be drawn
drawToScreen.ClearBuffer.ClearColourEnabled = false;
//create the light collection first
lights = new MaterialLightCollection();
// In this example, the rendering order has been manually optimized to reduce the number of pixels drawn
//
// In xen, rendering is usually explicit. This means, when a call to Draw() is made, the draw order is
// respected, and internally the object will be drawn using the graphics API.
// Objects added to the screen will have Draw() called in the order they were added.
//
// However, the draw order can also cause performance problems.
// In general, it's best to draw front to back, this means draw the objects closest to the screen first.
//
// This way, the objects at the back will be drawing behind the objects already drawn.
// Modern video cards can quickly discard pixels if they are 'behind' what is already drawn.
// Without front-to-back, the objects at the front could be drawing *over* objects already drawn.
//
// This is known as overdraw, a case where an object is drawn, only to be 'overdrawn' later in the frame.
// Reducing overdraw can help performance, especially when complex shaders are used.
//
// In this example, the sample is usually vertex-limited (that is, the bottleneck is vertex processing)
// However, it can demonstrate how optimizing for overdraw can significantly reduce the number of pixels
// that are shaded.
//
// In debug builds, the DrawStatisticsDisplay class will show the number of pixels drawn in the frame.
//
// With overdraw optimized draw order, ~1,000,000 pixels are drawn per frame. Without, upto 2,100,000
// pixels are drawn per frame (usually ~1,800,000). (A 1280x720 display has 921,600 pixels)
//
// This means that without an overdraw optimized draw order, on average, each pixel is being drawn
// twice. With an optimized draw order, this number is closer to 1.1, which is very close to the
// optimal value of 1.0 (where each pixel is only drawn once).
//
// Note that the number of pixels reported by the DrawStatisticsDisplay is for the entire frame, including
// every render target. Some PCs may not support this value, and display -1.
//
// One last point....
// This sample is an extreme test of a GPU's ability to push triangles onto the screen (vertex/triangle rate).
// However, observation will show the number of triangles drawn is often over 3,300,000!
// Assuming half the triangles are back-face culled (an accurate approximation), this still means
// there are around 1,650,000 triangles that are visible at any time.
// (But remember, the vertex shader still runs for back facing triangles!)
//
// Assuming approximatly half of these triangles are depth occluded (very approximate), still
// results in a huge number of visible triangles.
// This all means that the average triangle is drawing a *very* small number of pixels, in this case,
// the average for the actors is probably *less than 1 pixel per triangle!*.
//
// Triangles averaging less than 1 pixel are known as subpixel triangles.
// For a number of reasons, subpixel triangles are very inefficent.
// For example, if a single pixel is drawn, due to the way a video card works, the pixel shader will always
// run in multiples of 4 pixels, so a single pixel triangle will still run the pixel shader 4 times.
//
// This makes this sample a perfect candidate for level of detail optimization, where a lower resolution
// model is used as an actor gets further away from the screen.
//
// The vertex shader is also very expensive, and for each triangle, it will be run upto 3 times.
// This means the vertex shader is quite possibly running more often than the pixel shader.
// This hypothesis can be confirmed; setting the lights to per-vertex, instead of per-pixel, results
// in a significantly *lower* frame rate!
//
//
//
bool optimizeForOverdraw = true;
//create a list of actors to added to the screen
List <Actor> actors = new List <Actor>(500);
//create 500 actors!
for (int i = 0; i < 500; i++)
{
Actor actor = new Actor(this.Content, this.UpdateManager, lights, diskRadius);
actors.Add(actor);
}
//create the lights, similar to Tutorial 14
lights.AmbientLightColour = new Vector3(0.45f, 0.45f, 0.5f);
Vector3[] lightPositions = new Vector3[]
{
new Vector3(0, 30, 12),
new Vector3(0, -30, 12)
};
//setup the two lights in the scene
IDraw lightGeometry = null;
IDraw lightPoleGeometry = null;
//create geometry to display the lights
List <IDraw> lightSourceGeometry = new List <IDraw>();
//setup the lights, and create the light globe geometry
for (int i = 0; i < lightPositions.Length; i++)
{
Vector3 colour = new Vector3(5, 5, 5);
IMaterialPointLight light = lights.AddPointLight(i < 2, lightPositions[i], 8, colour, colour);
light.ConstantAttenuation = 0.25f; // make the ligh falloff curve a lot sharper (brighter at the centre)
light.LinearAttenuation = 0;
light.QuadraticAttenuation = 0.075f; //approximate inverse distance in which the brightness of the light will halve
if (lightGeometry == null)
{
lightGeometry = new Xen.Ex.Geometry.Sphere(Vector3.One, 8, true, false, false);
lightPoleGeometry = new Xen.Ex.Geometry.Cube(new Vector3(0.4f, 0.4f, lightPositions[i].Z * 0.5f));
}
//visually show the light
//create the light sphere geometry from tutorial 14.
Vector3 position = lightPositions[i];
lightSourceGeometry.Add(new Tutorial_14.LightSourceDrawer(position, lightGeometry, Color.LightYellow));
position.Z *= 0.5f;
lightSourceGeometry.Add(new Tutorial_14.LightSourceDrawer(position, lightPoleGeometry, new Color(40, 40, 70)));
}
//create the ground plane, also from tutorial 14
Tutorial_14.GroundDisk ground = new Tutorial_14.GroundDisk(this.Content, lights, diskRadius);
//this is a special background element,
//it draws a gradient over the entire screen, fading from dark at the bottom to light at the top.
Color darkBlue = new Color(40, 40, 50);
Color lightBlue = new Color(100, 100, 110);
BackgroundGradient background = new BackgroundGradient(lightBlue, darkBlue);
if (optimizeForOverdraw == false)
{
//add all the objects in a naive order
//first add the background (fills the entire screen, draws to every pixel, but is very fast)
drawToScreen.Add(background);
//then add the ground plane (all the actors will appear on top of the ground plane, overdrawing it)
drawToScreen.Add(ground);
//then add the lights (which are on top of the ground, overdrawing it)
foreach (IDraw geometry in lightSourceGeometry)
{
drawToScreen.Add(geometry);
}
//then finally add the actors, in the order they were created
foreach (Actor actor in actors)
{
drawToScreen.Add(actor);
}
}
else
{
//or, add the objects in a order optimized for overdraw
#if !XBOX360
//first, add the actors. Because they are almost always closest to the screen
//however, use a depth sorter so the actors are sorted into a front to back draw order,
//this sorting is based on the centre point of the cull tests they perform.
Xen.Ex.Scene.DepthDrawSorter sorter = new Xen.Ex.Scene.DepthDrawSorter(Xen.Ex.Scene.DepthSortMode.FrontToBack);
//Remember, the objects placed in the sorter *must* perform a valid CullTest,
//if the CullTest simply returns true/false, no sorting will occur.
//(Note the Actor.CullTest method)
//to ease the CPU load, have the sorter only sort the actors every few frames...
sorter.SortDelayFrameCount = 5;
foreach (Actor actor in actors)
{
sorter.Add(actor); // add the actors to the sorter (not the screen)
}
//the sorter itself must be added to the screen!
drawToScreen.Add(sorter); // the sorter will then draw the actors in a sorted order
#else
//In this case (on the Xbox), because the application is heavily vertex limited
//and already heavily CPU stretched by the animation system, the cost of
//sorting the actors actually causes a larger performance hit on the CPU than
//the time saved on the GPU. This inballance causes a frame rate drop.
//
//However, the reason for this may be unexpected.
//The framerate drop is not caused by the overhead of sorting the actors.
//
//Any 3D API calls made are doubly expensive on the XBOX, so in order to
//maintain 20fps in this sample, the primary (rendering) thread must not
//block, or switch to task processing.
//If it does so, valuable rendering time is lost.
//
//When using a sorter, the actors are drawn in an order that is constantly changing.
//However, they always have Update() called in a consistent order.
//
//During Update() the actors animation controllers will spawn thread tasks to
//process their animation.
//
//These tasks are processed on the three spare xbox hardware threads, they are
//processed in the order they were added.
//Processing the animation usually completes before the rendering finishes.
//(the rendering is not delayed waiting for the animation to finish).
//
//However, when sorting the actors get drawn in an unpredictable order,
//this means the last actor added could be the first actor to draw,
//in such a case, the chances of it's animation processing having completed
//is *very* low. When this happens, the rendering thread has to switch to
//processing animations, delaying rendering.
//
//So, for the xbox, it's best just to draw in the update order.
foreach (Actor actor in actors)
{
drawToScreen.Add(actor);
}
#endif
//add the light source geometry, as they are usually below the actors, but above the ground
foreach (IDraw geometry in lightSourceGeometry)
{
drawToScreen.Add(geometry);
}
//then add the ground plane, which is usually below the actors and lights.
drawToScreen.Add(ground);
//finally, enable a special feature of ElementRect.
//This makes the element draw at the maximum possible Z distance
//(behind anything else that has been drawn)
background.DrawAtMaxZDepth = true;
//add it to the screen
drawToScreen.Add(background);
}
//finally,
//create the draw statistics display
stats = new Xen.Ex.Graphics2D.Statistics.DrawStatisticsDisplay(this.UpdateManager);
drawToScreen.Add(stats);
}
