XBLIG-UK 2011Post Processing in XNA 4.0

By Charles Humphrey

2nd March 2011

What is Post Processing?

Wikipedia says:- “Post-processing is commonly used in 3D rendering,

especially for video games. Instead of rendering 3D objects directly to the display, the scene is first rendered to a buffer in the memory of the video card. Pixel shaders are then used to apply post-processing filters to the image buffer before displaying it to the screen. Post-processing allows effects to be used that require awareness of the entire image (since normally each 3D object is rendered in isolation).”

Post Processing Pipeline

Set Render Target

Render Scene

Resolve Render Target

Apply Pixel Shader

Render Result

PostProcessingManager

Holds a list of BasePostProcessingEffectDraw method

◦Receives the rendered scene and depth map as textures.

◦Loops through each BasePostProcessingEffect Call their Draw methods. Current scene is up dated after each

BasePostProcessingEffect.Draw call to be passed onto next BasePostProcessingEffect

◦Renders the final scene texture

BasePostProcessingEffect

Holds a list of BasePostProcessDraw Method

◦ Stores a copy of the original scene.◦ Loop through each BasePostProcess.◦ Set Half Pixel value.◦ Pass original scene texture (not all need it)◦ Set the BasePostProcess render target◦ Set the BasePostProcess back buffer (current scene)◦ Set the BasePostProcess depth buffer◦ Call the BasePostProcess Draw method◦ Resolve the BasePostProcess render target◦ Record the last scene rendered texture (used for next

BasePostProcess’s back buffer)

BasePostProcess

Holds an Effect for the required pixel shader

Renders the scene texture and applies the pixel shader

Post Process Samples

Depth of Field◦ Poison Disc Blur◦ Depth of Field

Bloom◦ Bright Pass◦ Gaussian Blur

Vertical Horizontal

◦ Bloom Haze

◦ Bump map Distort Radial Blur

◦ Radial Blur Ripple

◦ Ripple Fog

◦ Fog Sun

◦ Sun

Creating a Post Process

Write your pixel shader Derive from BasePostProcess

◦ public class Bloom : BasePostProcess

Override the Draw callpublic override void Draw(GameTime gameTime)

{ if (effect == null) { effect = Game.Content.Load<Effect>("Shaders/PostProcessing/Bloom"); effect.CurrentTechnique = effect.Techniques["BloomComposite"]; } effect.Parameters["SceneTex"].SetValue(orgBuffer); effect.Parameters["BloomIntensity"].SetValue(BloomIntensity); effect.Parameters["BloomSaturation"].SetValue(BloomSaturation); effect.Parameters["BaseIntensity"].SetValue(BaseIntensity); effect.Parameters["BaseSaturation"].SetValue(BaseSaturation);

// Set Params. base.Draw(gameTime); }

Creating a Post Process Effect

Derive from BasePostProcessingEffect◦ public class BloomEffect : BasePostProcessingEffect

Create the Post Process instances you needbp = new BrightPass(game, threshold);gbv = new GaussBlurV(game, blurAmount);gbh = new GaussBlurH(game, blurAmount);b = new Bloom(game, intensity, saturation, baseIntensity, baseSatration);

Add them to your list of BasePostProcess’sAddPostProcess(bp);AddPostProcess(gbv);AddPostProcess(gbh);AddPostProcess(b);

Use the new Post Process Effect

Create and instance of the Post Processing Manager

ppManager = new PostProcessingManager(this);

Create instance of your new effect bloom = new BloomEffect(this, 1.25f, 1f, 1f,

1f, .25f, 4f);

Add to the Post Processing Manager ppManager.AddEffect(bloom);

Questions?

Inspiration from…

Kyle Hayward aka Graphics RunnerBloghttp://graphicsrunner.blogspot.com

Post Processing Samplehttp://graphicsrunner.blogspot.com/2008/06/post-process-framework-sample.html